Do you guys measure flex in a lab setting when designing bikes? Or perhaps more interestingly do batch testing for flexiness during production. I know from first...
Do you guys measure flex in a lab setting when designing bikes?
Or perhaps more interestingly do batch testing for flexiness during production. I know from first hand experience due to frame alignment and normal manufacturing variations some bikes wobble (not flexing I know) quite a bit when shaken from the BB or read wheel due to how the pivots and bearings all seat together and some are absolutely rock solid.
I know manufacturing tolerances is a different question but as designers do you consider this when designing compliance into a frame?
Companies often do measure flex in the lab. There are some simple standard fixtures for measuring head tube and bottom bracket stiffness that most companies use and some companies do batch test these. Companies can also make their own stiffness tests to dig into specially what they are interested in as well.
I've seen the wobble you speak of on some youtube videos. What bike in particular did you see this on? We can guess as to why its happening.
Can we get a side thread on what went into designing the horst flex stays at Cannondale? I have geeked out hard over anything I could...
Can we get a side thread on what went into designing the horst flex stays at Cannondale? I have geeked out hard over anything I could find online on those flex stays. Some site had images of steel plate bolted into aluminum stays.
This spring I built a frame that ditched two pivot point and relied on the seatsays to flex for both of them. Originally I envisioned it as flex horst but started running short on my build timeline and thew caution to the wind a decided to torture test the seatstays on a 160mm enduro frame. .
That would be cool but since I'm not at the company anymore I don't want to speak on their business. It's cool stuff though and it works well. Happy to give you a rundown of whys its rad though. Any specific questions about it?
I have a question about the stiffness and compliance on the bike as a whole system and is there anyone looking at this? For example: you...
I have a question about the stiffness and compliance on the bike as a whole system and is there anyone looking at this? For example: you talk about the tradeoffs in the RT but if paired with a rear certain wheel does that is overly stiff or compliant are you negating the effects in some regard. Or on the other end, an overly stiff front paired with a inverted fork might be better than a traditional fork. I guess to simplify it, if you were to design a bike just for your preferences would the stiffness of your preferred components play into how you tune your frame?
That's something that should be considered, but many companies probably don’t do much about it otherwise they would talk about it more. Components have gone through...
That's something that should be considered, but many companies probably don’t do much about it otherwise they would talk about it more. Components have gone through their own renaissance in terms of compliance, like bars and wheels, but you don’t often see them designed as a complete system. For the most part, it’s fine, so long as you don't have a component holding your bike back too much, but if you really wanted to fine-tune a bike, designing all the components to work together would be ideal. Most frame companies don’t make all the parts on the bike, so it’s hard to tackle this.
Maybe someday we’ll see a company that has in-house wheels and frames lean into this. It would be cool. You’re absolutely right with your examples, a stiff frame paired with a noodle wheel probably wouldn’t be ideal, or vice versa... I'm not sure. If you were to design a bike just to your preferences, the stiffness of your preferred components would definitely play a role.
One thing a race team can be strategic about is ensuring they have the components they like on the bike before iterating the frame. It would suck to develop a frame and then your wheel sponsor changes dramatically. Designing a frame around a wheelset that’s too stiff or too soft may not work well for the end consumer who might use a different set of wheels. Road bikes with their integrated cockpits are probably considering this stuff more than mountain bikes as they've been in the refinement stage longer. Great points and exactly the kind of ideas this article is meant to stir up.
I remember hearing a podcast with the guy from Enve about how they developed the new DH carbon rim with the Muc Off Commencal team. He mentioned at a certain point the team was changing the frame character so much that it was changing what they wanted it out of wheel.
Definitely a concept about developing an entire package to work together, this can go for consumer or production. Before I started testing parts and frames for ride quality, I would throw on parts that looked cool or color matched. This led me down a road where I had to rethink things because the bike started to handle so poorly.
Hey, I’m Ryan Burney. I’ve spent eight years as an engineer for full-suspension bikes, working on some fun projects, like developing the flex Horst link for...
Hey, I’m Ryan Burney. I’ve spent eight years as an engineer for full-suspension bikes, working on some fun projects, like developing the flex Horst link for the Cannondale Scalpel and being lead engineer for the latest GT Fury downhill bike. With over a decade of downhill racing under my belt (even made it to one World Cup—though I didn’t qualify so I stuck to engineering), I've had the pleasure of racing alongside the Vital crew, like Jason, Tanner, and Dak. Below is a photo of me, being slower than Dak. These days, I’m focused on my own projects, but I love the Vital community and wanted to jump into the good conversations happening here. Today, we’re diving into frame compliance and what it means for a bike's handling.
Please note that the following insights and conclusions are my own thoughts, observations, and opinions based on my experience riding bikes. Definitely could be wrong 😊.
What is Compliance?
So, what is compliance? It's essentially a fancier way of saying "reducing stiffness." Stiffness is how much something bends when you apply force to it. For a long time, the goal was to make bikes as stiff as possible. But after enough riders rattled their teeth out, we learned that it’s all about balance. Stiffness has its pros and cons, and the same goes for compliance.
Lately, many top downhill riders have been tuning their bikes to increase compliance. Why? To smooth out their ride. When you’re flying through rough terrain at speed, your ability to go faster can come down to how well you can see. If your eyeballs are bouncing around in your head like little mass dampers, you’re going to be forced to back down. Plus, your hands hurt, your body gets fatigued, and you generally just get beaten up.
Focusing on stiffness on bikes isn’t new; it’s been measured for a long time, especially on road bikes. Road bikes have been around long enough to truly refine their designs. Their simpler chassis allows for easier isolation of ride characteristics from design changes. Mountain bikes have only recently reached a point where most are considered really good. Thanks to refined suspension design and geometry, we can now chip away at the finer details like stiffness. It’s not that mountain bike companies weren’t aware of stiffness in the past, but they had larger issues to deal with, like frames rattling apart and bolts breaking. There was a lot to figure out before they could start making the rider more comfortable.
Stiffness and Its Impact
Stiffness matters. Certain stiffness traits affect control, efficiency, and comfort. There are standard tests for bottom bracket and head tube stiffness, which measure how much a frame flexes when forces are applied. Bottom bracket stiffness measurements show you how much your bottom bracket wags to a side when pedaling and gives you insight into the perceived pedal efficiency of a frame (that’s a whole other conversation—please feel free to ask about it in the comments). Head tube stiffness tells you how the bike may handle when given steering inputs and measures how much a frame twists given a certain force.
So, what makes for good stiffness? You need enough stiffness in key areas to ensure your bike performs its essential functions—like steering and pedaling—without making it so stiff that you’re lugging around excess frame material. Personally, I prefer bikes that go where I point them and don’t feel like a noodle when I’m mashing the pedals. I prefer an al dente frame stiffness. Where you have your stiffness on the frame makes a big difference to handling and adding compliance without a strategy can come to bite you.
The Importance of a Stiff Front Triangle
Let’s dig into why we want the front triangle to be stiff. The front triangle's stiffness is essential for maintaining steering precision. If the front triangle flexes too much, it can "wind up" under load. It can happen during hard braking to where your fork is wobbling fore and aft via the front triangle or high G berms where the fork can point over the one side of the bike. This twist in the front triangle affects the position of the front wheel, which directly impacts how the bike steers and your timing of front wheel placement. Unpredictability in the front end is something you want to avoid—when you’re going into a corner or tackling a rough section, you need to know that the front wheel is exactly where you expect it to be. Otherwise, you’ll lose trust in the bike and back down.
Introducing Compliance Through the Rear Triangle
This is where the rear triangle comes into play. Since we want a stiff front triangle for precise handling, we can introduce compliance through the rear triangle to improve comfort and control. The rear triangle can flex in different ways to help the rear wheel move out of the way of impacts and obstacles without sacrificing too much control.
We’re talking about two directions of compliance from the rear triangle.
Roll: This is when the rear wheel rotates side to side about the chainstays (viewed from behind) as the wheel encounters angled obstacles. If the rear triangle is too stiff, these impacts can knock the wheel off line. Flex in this direction allows the wheel to track the ground better by reducing that "side-knock-off-line-effect" (fun term, right?), which improves grip and comfort through rough terrain. Most importantly, when the rear triangle and wheel roll side to side, the rear wheel stays straight, without changing the direction it's tracking on the ground.
Wag: This occurs when the rear triangle wags side to side, like a tail, when viewed from the top. This compliance also helps prevent the wheel from being knocked off line, especially on chunky, straight sections. However, too much wag can introduce a form of two-wheel steering in high-load corners. The rear wheel starts to steer independently of the front, and this happens more or less depending on how hard you load the bike. It can feel unpredictable, but hopefully, the wheel changes direction as expected when you come into that tight berm hotter than planned during your race run 🤞.
It’s crucial to find the right balance between roll and wag, as each affects the bike differently. Personal opinion incoming: Ideally, the rear triangle flexes via roll enough to allow the rear wheel to deflect impacts and avoids as much wag as possible, mitigating unpredictable steering. Too much flex in either roll or wag can leave you with you guessing where the rear wheel is as you lose your feeling of the ground through your feet. It’s smooth as heck but if you don’t know when your rear tire is on or off of certain obstacles you’re just guessing and eventually that will bite you and you’re going to have a bad time. Let’s look at a few bikes to help illustrate what we are talking about.
Example A: Amaury Pierron's Commencal Supreme
Amaury’s bike showcases both types of compliance—rear wheel roll and wag. The tiny chainstays flex significantly, effectively deflecting impacts. However, because the seat stay is stiffer and angled upward, the rear triangle allows both roll and wag. Imagine the wheel twisting about the seat stays when the rear triangle is loaded in a berm. This twisting both rolls and wags the wheel simultaneously when the frame allows the wheel to deflect from rocks. The roll is appreciated but the added wag introduces a degree of two-wheel steering, which complicates things. As discussed earlier, this wag makes the bike feel less consistent because the amount of two-wheel steering flex varies depending on how hard you hit a berm or corner. You’re left guessing how much the rear end will flex, which can lead to unpredictability, especially at high speeds. While Amaury’s bike performs well in rough terrain (and there’s no arguing its overall performance), this combination of roll and wag presents this challenge in high-G corners.
That said, these observations are hindsight reflections based on seeing where other teams are finding frame compliance. Amaury’s setup may not have as much of a compromise as I think it does. Who knows—it may be the next sliced bread. The chainstay is an okay place to introduce compliance just proceed with caution. I think there are better areas to introduce compliance with fewer compromises. Let’s take a look at another frame layout with a completely different approach to stiffness and compliance.
Example B: Loic Bruni’s Prototype Specialized
Let’s look at Loic’s bike. His setup takes a different approach, featuring very large chainstays and smaller seat stays that provide rear wheel roll without much wag. This design allows the rear wheel to still move out of the way and deflect impacts while minimizing wag during cornering. As a result, Loic benefits from rear triangle compliance—like increased comfort and traction over rough terrain—without sacrificing handling precision in corners, as there isn’t much wag to contend with. The race team also swaps out the seat stay linkage between bridged and bridgeless links to further tune compliance in this same direction. His bike should feel very consistent, enabling him to push harder through technical sections without worrying about unpredictable two-wheel steering. Additionally, the high bottom bracket stiffness (thanks to those chonky chainstays) prevents significant lateral flex while pedaling, ensuring high bottom bracket stiffness which equates to a part of the equation of high perceived pedal efficiency. This is excellent for a racer’s mental game.
Conclusion
In the end, achieving the right frame compliance is all about strategically balancing stiffness and flexibility in the areas that matter most. You want a stiff front triangle to ensure control and prevent twisting under big loads, while introducing carefully tuned compliance in the rear triangle enhances comfort and traction without sacrificing handling.
These examples highlight the pros and cons of different designs, though every frame layout brings its own unique advantages. Some frames allow for greater compliance tunability than others, and bike technology has made great strides in working towards the sweet spot between stiffness and compliance. Ultimately, the ideal mix will depend on the specific problems a design seeks to solve, as well as each rider’s strengths and preferences.
While compliance can smooth out your ride and keep you from being slowed down by the terrain, having too much in the wrong places can reduce control, leading to inconsistency and unpredictability. As bike designs keep pushing forward, achieving this balance will be what turns a good bike into a great one.
I'm stoked to hear what others are enjoying/disliking when it comes to frame stiffness and compliance. And I'm happy to answer any questions about the topic!
What kind of compliance do you think Dak's bike has?
Super interesting thread ! I am currently riding a custom made steel frame, superenduro/freeride type.
You thread comes just as I am considering frame flex on my own frame as I noticed some after riding it harder and harder.
Basically I noticed that my frame flexes on high side load situations, mostly high G berms. Initially I thought it was tire roll, pumped them up super hard and that didn't solve the issue. Which lead me to consider flex in my wheels. I went from soft alloy wheels to stiff carbon rims and that didn't change much to be fair. So last option is frame flex and I imagine mostly swingarm flex. I am considering replacing the rear triangle with a alu CNC one but should I try to improve wag or roll ? To me what I experience sounds more like roll since it feels exactly like rear tire roll but what's your take ?
Super interesting thread ! I am currently riding a custom made steel frame, superenduro/freeride type.You thread comes just as I am considering frame flex on my...
Super interesting thread ! I am currently riding a custom made steel frame, superenduro/freeride type.
You thread comes just as I am considering frame flex on my own frame as I noticed some after riding it harder and harder.
Basically I noticed that my frame flexes on high side load situations, mostly high G berms. Initially I thought it was tire roll, pumped them up super hard and that didn't solve the issue. Which lead me to consider flex in my wheels. I went from soft alloy wheels to stiff carbon rims and that didn't change much to be fair. So last option is frame flex and I imagine mostly swingarm flex. I am considering replacing the rear triangle with a alu CNC one but should I try to improve wag or roll ? To me what I experience sounds more like roll since it feels exactly like rear tire roll but what's your take ?
Great question! I would love to see a picture of your bike because custom builds are awesome. What suspension layout do you use? We can take a look and get you pointed in a good direction.
"Ideally, the rear triangle flexes via roll enough to allow the rear wheel to deflect impacts and avoids as much wag as possible, mitigating unpredictable steering."
Is this noticeable (in a good way) on single pivot bikes like Orange? Or maybe someone here rode a Chumba or Zonenschein DH bike and can remeber such feeling? Devinci Wilson and Rocky RMX also come to mind..
There is a wheel review on a prominent mtb website where the reviewer attempts to educate the reader about why different wheels have different compliance. He uses the example that a 2X laced wheel, a 3X laced wheel, and a 3X laced wheel detensioned a small amount will all have different compliance. The rationale offered is theoretical and to put it plainly, i don’t think it’s interesting whether or not it’s good theorizing or poor.
My question is what is the technical limitation in the way of building examples of these three wheels and measuring the compliance?
Does the rig not exist? Is it prohibitively expensive? Does the test protocol not exist? Are there competing protocols where the results of one would be protested by advocates for the alternative?
Can we get a side thread on what went into designing the horst flex stays at Cannondale? I have geeked out hard over anything I could...
Can we get a side thread on what went into designing the horst flex stays at Cannondale? I have geeked out hard over anything I could find online on those flex stays. Some site had images of steel plate bolted into aluminum stays.
This spring I built a frame that ditched two pivot point and relied on the seatsays to flex for both of them. Originally I envisioned it as flex horst but started running short on my build timeline and thew caution to the wind a decided to torture test the seatstays on a 160mm enduro frame. .
That would be cool but since I'm not at the company anymore I don't want to speak on their business. It's cool stuff though and it...
That would be cool but since I'm not at the company anymore I don't want to speak on their business. It's cool stuff though and it works well. Happy to give you a rundown of whys its rad though. Any specific questions about it?
Do you have photos of your bike? It sounds rad!
This has been the first flex stays frame I have built. Previously there have been three linkage driven single pivots and a classic single pivot. The rear end sits at neutral at 40% travel with the shock removed.
Super interesting thread ! I am currently riding a custom made steel frame, superenduro/freeride type.You thread comes just as I am considering frame flex on my...
Super interesting thread ! I am currently riding a custom made steel frame, superenduro/freeride type.
You thread comes just as I am considering frame flex on my own frame as I noticed some after riding it harder and harder.
Basically I noticed that my frame flexes on high side load situations, mostly high G berms. Initially I thought it was tire roll, pumped them up super hard and that didn't solve the issue. Which lead me to consider flex in my wheels. I went from soft alloy wheels to stiff carbon rims and that didn't change much to be fair. So last option is frame flex and I imagine mostly swingarm flex. I am considering replacing the rear triangle with a alu CNC one but should I try to improve wag or roll ? To me what I experience sounds more like roll since it feels exactly like rear tire roll but what's your take ?
I also ride a custom steel frame. Mine is single pivot with spherical bearings on the shock so the rear end is quite compliant.
I ride it on every type of riding.
It excels on off camber chunder and will hold a high line that other bikes won't. This matches the USD Dorado fork quite well.
G-out berms/ruts are it's weakness and I can feel the wag if I load up in the corner.
I find that the wag in corners becomes intuitive and you get to know the bike in consistent berms.
Harsh g out ruts that change lap to lap are a challenge or hitting something hard unexpected. That's the only big downside I see. The rear end is essentially a undamped spring that could buck you off if you are caught off guard.
Compliance like everything, is a compromise. Choose what suits the best. I think DH racer teams will eventually end up with different rear ends like they have different suspension setups for different courses, and of course different rider masses and styles. Moto GP has different rear ends for each track with left hand and right hand turn compliance baked in for the types of turns on the track.
Ideally I would want a bit less wag but still keep the roll compliance.
Great post, Ryan. Made me think about my bike, not to quantify its goodness but just to appreciate it. Seems like the ovalized chainstays would reduce wag...
Great post, Ryan. Made me think about my bike, not to quantify its goodness but just to appreciate it.
Seems like the ovalized chainstays would reduce wag but increase roll. Interesting!
Thank you! That Reeb is super cool. I would run that as a daily. That extra width definitely doesn't hurt!
They put some effort into achieving balanced compliance and it shows. Even though it is steel its no noodle; the triangular spindle in the rocker pivot makes it so both sides of the rocker move in unison, providing some stability to complement the steel flex. I run out of rear tire (trail casing) before I run out of rear end.
There is a wheel review on a prominent mtb website where the reviewer attempts to educate the reader about why different wheels have different compliance. He...
There is a wheel review on a prominent mtb website where the reviewer attempts to educate the reader about why different wheels have different compliance. He uses the example that a 2X laced wheel, a 3X laced wheel, and a 3X laced wheel detensioned a small amount will all have different compliance. The rationale offered is theoretical and to put it plainly, i don’t think it’s interesting whether or not it’s good theorizing or poor.
My question is what is the technical limitation in the way of building examples of these three wheels and measuring the compliance?
Does the rig not exist? Is it prohibitively expensive? Does the test protocol not exist? Are there competing protocols where the results of one would be protested by advocates for the alternative?
In this video by Enve, they show testing the wheels on a machine. Not sure if this is just a destruction test or gives them compliance/rigidity numbers.
But to your post, I totally believe that 2x and 3x have different compliance, along with spoke tension, spoke diameter, spoke count, and rim choice. The combination is endless. This also brings me full circle because trail testing depends on the dirt type, rider weight, and riding style, which could all push a wheel to a different extent. I don't think we could sit here and say "this combination" is best for everyone, but at least we are getting these conversations out in the open to make educated decisions on our parts before our next build or purchase.
Can we get a side thread on what went into designing the horst flex stays at Cannondale? I have geeked out hard over anything I could...
Can we get a side thread on what went into designing the horst flex stays at Cannondale? I have geeked out hard over anything I could find online on those flex stays. Some site had images of steel plate bolted into aluminum stays.
This spring I built a frame that ditched two pivot point and relied on the seatsays to flex for both of them. Originally I envisioned it as flex horst but started running short on my build timeline and thew caution to the wind a decided to torture test the seatstays on a 160mm enduro frame. .
That would be cool but since I'm not at the company anymore I don't want to speak on their business. It's cool stuff though and it...
That would be cool but since I'm not at the company anymore I don't want to speak on their business. It's cool stuff though and it works well. Happy to give you a rundown of whys its rad though. Any specific questions about it?
This has been the first flex stays frame I have built. Previously there have been three linkage driven single pivots and a classic single pivot. The...
This has been the first flex stays frame I have built. Previously there have been three linkage driven single pivots and a classic single pivot. The rear end sits at neutral at 40% travel with the shock removed.
I can definitely see why you think the rear end is compliant and maybe too much. Looks sick, though!
Super interesting thread ! I am currently riding a custom made steel frame, superenduro/freeride type.You thread comes just as I am considering frame flex on my...
Super interesting thread ! I am currently riding a custom made steel frame, superenduro/freeride type.
You thread comes just as I am considering frame flex on my own frame as I noticed some after riding it harder and harder.
Basically I noticed that my frame flexes on high side load situations, mostly high G berms. Initially I thought it was tire roll, pumped them up super hard and that didn't solve the issue. Which lead me to consider flex in my wheels. I went from soft alloy wheels to stiff carbon rims and that didn't change much to be fair. So last option is frame flex and I imagine mostly swingarm flex. I am considering replacing the rear triangle with a alu CNC one but should I try to improve wag or roll ? To me what I experience sounds more like roll since it feels exactly like rear tire roll but what's your take ?
I also ride a custom steel frame. Mine is single pivot with spherical bearings on the shock so the rear end is quite compliant. I ride it...
I also ride a custom steel frame. Mine is single pivot with spherical bearings on the shock so the rear end is quite compliant.
I ride it on every type of riding.
It excels on off camber chunder and will hold a high line that other bikes won't. This matches the USD Dorado fork quite well.
G-out berms/ruts are it's weakness and I can feel the wag if I load up in the corner.
I find that the wag in corners becomes intuitive and you get to know the bike in consistent berms.
Harsh g out ruts that change lap to lap are a challenge or hitting something hard unexpected. That's the only big downside I see. The rear end is essentially a undamped spring that could buck you off if you are caught off guard.
Compliance like everything, is a compromise. Choose what suits the best. I think DH racer teams will eventually end up with different rear ends like they have different suspension setups for different courses, and of course different rider masses and styles. Moto GP has different rear ends for each track with left hand and right hand turn compliance baked in for the types of turns on the track.
Ideally I would want a bit less wag but still keep the roll compliance.
Can you post a photo of your bike?
This was my project last winter with Adam Prosise (Formally from REEB )
Steel front end, stock Trek aluminum rear end with some compliance mods. Also matched with Dorado Pro. I'll some data that can show the rear lateral accelerations and torsional movement.
I can definitely see why you think the rear end is compliant and maybe too much. Looks sick, though!
I didn't find it to have too much. If anything I'd look to try and get a wee bit more wag out of it to balance the roll. This frame I wasn't getting any tire rub on the inner cs's from wag. Previous frames I have had wear marks on the cs's.
In the next iteration I will built it with a removeable cs's bridge. I can then play with bridge configurations to see what that does.
How do you like the steel front end on the session? Did you ride it with stock front end? I think the session is damn near perfect from a suspension kinematics perspective and I imagine the steel front end improves that. I may need to source a rear end to follow your path.
I know Adam. He made some bits for my bike too. Rad guy.
My bike from The Freedom Machine. We tried to keep the rear as stiff as we could while avoiding belt etc on this bike. We made the pivot very stiff and brace up to shock mount very stiff. Next iteration will have more wag stiffness.
I didn't find it to have too much. If anything I'd look to try and get a wee bit more wag out of it to balance...
I didn't find it to have too much. If anything I'd look to try and get a wee bit more wag out of it to balance the roll. This frame I wasn't getting any tire rub on the inner cs's from wag. Previous frames I have had wear marks on the cs's.
In the next iteration I will built it with a removeable cs's bridge. I can then play with bridge configurations to see what that does.
That would be sick with the adjustable bridges. I did some testing on the Commencal V5 with them and it made a pretty big change in berms and G-outs.
Could you share what CS and SS tubing you used on the rear?
How do you like the steel front end on the session? Did you ride it with stock front end? I think the session is damn near...
How do you like the steel front end on the session? Did you ride it with stock front end? I think the session is damn near perfect from a suspension kinematics perspective and I imagine the steel front end improves that. I may need to source a rear end to follow your path.
I know Adam. He made some bits for my bike too. Rad guy.
My bike from The Freedom Machine. We tried to keep the rear as stiff as we could while avoiding belt etc on this bike. We made the pivot very stiff and brace up to shock mount very stiff. Next iteration will have more wag stiffness.
That looks rad! The front end and BB area look great, looks like an awesome job keeping that bb area from swaying. I could definitely understand that rear end being great in some areas but then moving too much in others. But like you said, it's all give in take. Personally, I'd rather have a soft compliant ride with maybe 1 or 2 areas that are "too soft", than an entire trail that is rigid and rattling my body.
I'm working on a steel DH gearbox frame with @VesselBikeProject now.
Yes I rode the Trek before, It was a much more comfortable ride with this front end. The Session is such a good base platform, as you mentioned, but I did remove some material from the CS and SS bridge to make it more compliant rear. I think I had to match some of the softer front end.
How do you like the steel front end on the session? Did you ride it with stock front end? I think the session is damn near...
How do you like the steel front end on the session? Did you ride it with stock front end? I think the session is damn near perfect from a suspension kinematics perspective and I imagine the steel front end improves that. I may need to source a rear end to follow your path.
I know Adam. He made some bits for my bike too. Rad guy.
My bike from The Freedom Machine. We tried to keep the rear as stiff as we could while avoiding belt etc on this bike. We made the pivot very stiff and brace up to shock mount very stiff. Next iteration will have more wag stiffness.
That looks rad! The front end and BB area look great, looks like an awesome job keeping that bb area from swaying. I could definitely understand...
That looks rad! The front end and BB area look great, looks like an awesome job keeping that bb area from swaying. I could definitely understand that rear end being great in some areas but then moving too much in others. But like you said, it's all give in take. Personally, I'd rather have a soft compliant ride with maybe 1 or 2 areas that are "too soft", than an entire trail that is rigid and rattling my body.
I'm working on a steel DH gearbox frame with @VesselBikeProject now.
Yes I rode the Trek before, It was a much more comfortable ride with this front end. The Session is such a good base platform, as you mentioned, but I did remove some material from the CS and SS bridge to make it more compliant rear. I think I had to match some of the softer front end.
Yes it is all give/take. Exactly like suspension setup.
This bike (The Homer) gets pedalled as an Enduro bike, Whistler laps and then Prevost shuttle laps.
For enduro and Whistler laps, I think the compliance is perfect. It eats rough and softens the harsh Whistler laps. Even with the firm suspension setup I run.
Prevost is another beast though. It's perfect 85% of the time but there's some hefty hits and corners on that hill. And hitting those fast, you want to be fully comfortable that you know how the bike will handle. Those scenarios are like racing, so I can see the downside of too much compliance too.
Rear end length, wheel size and tire size has a huge effect on rear end compliance too. Mine has 25mm CS range and it's noticeably softer in long setting. Bigger tires give a similar feel too with tire roll.
Vessel bikes stuff is rad too. I like his plate pull links to decouple shock side loading.
Gearboxes are the future and the belt is a game changer too. Low mass, no chain effect on your feet etc. And the cassette weight off the rear wheel is hugely noticable.
I'm currently schemeing a DH linkage driven bike with belt. Either SS or gearbox. Stiff front end, slighter stiffer rear end than The Homer.
"Ideally, the rear triangle flexes via roll enough to allow the rear wheel to deflect impacts and avoids as much wag as possible, mitigating unpredictable steering."Is...
"Ideally, the rear triangle flexes via roll enough to allow the rear wheel to deflect impacts and avoids as much wag as possible, mitigating unpredictable steering."
Is this noticeable (in a good way) on single pivot bikes like Orange? Or maybe someone here rode a Chumba or Zonenschein DH bike and can remeber such feeling? Devinci Wilson and Rocky RMX also come to mind..
Just looking at the Orange, it seems like it mostly rolls, but the shock helps resist that. Since the shock is bolted to the flexing rear triangle, it acts like part of the frame, kind of like a strut on a car. This does put extra side load on the shock, but modern shocks are built tough and can probably handle it without issue. As long as the shock can take it, it’s not a bad thing.
I’d say the Orange probably rolls more, but there’s a bit of wag too because the shock is part of the structure. If the shock wasn’t there or had a spherical bushing, I’d guess it would have mostly roll!
In this video by Enve, they show testing the wheels on a machine. Not sure if this is just a destruction test or gives them compliance/rigidity...
In this video by Enve, they show testing the wheels on a machine. Not sure if this is just a destruction test or gives them compliance/rigidity numbers.
But to your post, I totally believe that 2x and 3x have different compliance, along with spoke tension, spoke diameter, spoke count, and rim choice. The combination is endless. This also brings me full circle because trail testing depends on the dirt type, rider weight, and riding style, which could all push a wheel to a different extent. I don't think we could sit here and say "this combination" is best for everyone, but at least we are getting these conversations out in the open to make educated decisions on our parts before our next build or purchase.
It looks like an impact machine but it does seem as though Enve does measure displacement during impact somehow as they claim improved radial deflection during riding to improve comfort. It's cool stuff! Honestly I think those are the coolest wheels on the market right now. Someday I'll save up enough!
That would be cool but since I'm not at the company anymore I don't want to speak on their business. It's cool stuff though and it...
That would be cool but since I'm not at the company anymore I don't want to speak on their business. It's cool stuff though and it works well. Happy to give you a rundown of whys its rad though. Any specific questions about it?
This has been the first flex stays frame I have built. Previously there have been three linkage driven single pivots and a classic single pivot. The...
This has been the first flex stays frame I have built. Previously there have been three linkage driven single pivots and a classic single pivot. The rear end sits at neutral at 40% travel with the shock removed.
I can definitely see why you think the rear end is compliant and maybe too much. Looks sick, though!
@earleb Dang that's a cool ride and cool idea too! Well done. Here are a few places you could buy back some stiffness: 1) seat stay bridge 2) increase the chain stay bridge length 3) add bracing to the swingarm here 4) and if you're really going for it, add a swing link like the older fury. Hope that helps!
Here is some data from riding my steel Trek in Southern California.
Approx 2 minute run in Laguna.
The rear axle showed 67% more lateral accelerations than the bb. (Negative is to riders left and positive is to riders right.)
The rear axle showed that it twisted torsionally 35% more than the lower frame/bb.
What does all this mean? Hahha, nothing really until I gather more data on the same trail, in the same conditions. But I’m starting to gather a baseline with a few frames. The problem is dirt conditions and trail style play a big load(literally) on what the data will look like.
Here is some data from riding my steel Trek in Southern California.Approx 2 minute run in Laguna.The rear axle showed 67% more lateral accelerations than the...
Here is some data from riding my steel Trek in Southern California.
Approx 2 minute run in Laguna.
The rear axle showed 67% more lateral accelerations than the bb. (Negative is to riders left and positive is to riders right.)
The rear axle showed that it twisted torsionally 35% more than the lower frame/bb.
What does all this mean? Hahha, nothing really until I gather more data on the same trail, in the same conditions. But I’m starting to gather a baseline with a few frames. The problem is dirt conditions and trail style play a big load(literally) on what the data will look like.
Rad stuff. Can I guess the trail: Telonics? I don't know of any other DH trails there that have any G's besides a little bit on Silver Surfer. Great data! Any chance you have a full rundown of your setup? I think this is the perfect thread to show off your hard work on on the topic!
Before conducting the tests, based on observations like material, tube section size, bridges, and key features at pinch points (such as chain stay yokes), do you think you could have accurately predicted which data set would correspond to each frame? It's a fun question to consider!
Also what beer did you get at Laguna Beer co after? :D
Here is some data from riding my steel Trek in Southern California.Approx 2 minute run in Laguna.The rear axle showed 67% more lateral accelerations than the...
Here is some data from riding my steel Trek in Southern California.
Approx 2 minute run in Laguna.
The rear axle showed 67% more lateral accelerations than the bb. (Negative is to riders left and positive is to riders right.)
The rear axle showed that it twisted torsionally 35% more than the lower frame/bb.
What does all this mean? Hahha, nothing really until I gather more data on the same trail, in the same conditions. But I’m starting to gather a baseline with a few frames. The problem is dirt conditions and trail style play a big load(literally) on what the data will look like.
Rad stuff. Can I guess the trail: Telonics? I don't know of any other DH trails there that have any G's besides a little bit on...
Rad stuff. Can I guess the trail: Telonics? I don't know of any other DH trails there that have any G's besides a little bit on Silver Surfer. Great data! Any chance you have a full rundown of your setup? I think this is the perfect thread to show off your hard work on on the topic!
Before conducting the tests, based on observations like material, tube section size, bridges, and key features at pinch points (such as chain stay yokes), do you think you could have accurately predicted which data set would correspond to each frame? It's a fun question to consider!
Also what beer did you get at Laguna Beer co after? :D
Yeah the above trail was Teleonics from the upper dirt road before the "ski jump" to the parking lot.
Bike set up: Steel front end(modeled after 23' Trek Session), stock aluminum rear end, Ochain, Dorado fork, DT 471 front rim 1.6 spokes, Crank bros DH carbon rear rim 1.5 spokes, CounterShox mounted on fork 800g and behind BB 600g, Conti Kryp tires 24/26psi.
I only got a few runs in this day, then had a little get-off that stopped my riding for the day. So I didn't really test anything here, just trying to get some more baselines and data for conditions and trails. I used the SynBike data system that has fork and shock linear pot for suspension data and a 6-axis IMU mounted to the front and rear axle, bars and bb. These IMU record 2000 times per second their position in space in all axis and gyro.
Observations are interesting from the data I have recorded. I have done testing with this kit on 2 different bikes and 3 locations. Sometimes the stiffer bike or rear end actually has more lateral accelerations because the rear wheel is losing grip, and chattering and those catch/release moments are creating spikes in the data. Below you can see the yellow line(rear axle) chattering. The red line bb actually looks fairly stable. From 30.4-30.6 seconds, you can see the rear axle skip 6 times and that's about in the same time it takes to blink an eye.
Photo Below: The softer bike, might actually move less at the axle laterally because of more grip, but then torsionally the % change will be higher. Red line is BB and yellow is rear axle. You can see the bb isn't very stable torsionally
Data is cool and now I have a baseline on this trail, but unless we are doing back-to-back on the same day and same trail, same rider, same air pressure, ect, it's kind of just fun data to have. I hope at this point next year, I have a bigger data set with 10-20 bikes (my goal), then I can really draw some conclusions!
There is a wheel review on a prominent mtb website where the reviewer attempts to educate the reader about why different wheels have different compliance. He...
There is a wheel review on a prominent mtb website where the reviewer attempts to educate the reader about why different wheels have different compliance. He uses the example that a 2X laced wheel, a 3X laced wheel, and a 3X laced wheel detensioned a small amount will all have different compliance. The rationale offered is theoretical and to put it plainly, i don’t think it’s interesting whether or not it’s good theorizing or poor.
My question is what is the technical limitation in the way of building examples of these three wheels and measuring the compliance?
Does the rig not exist? Is it prohibitively expensive? Does the test protocol not exist? Are there competing protocols where the results of one would be protested by advocates for the alternative?
Henry at PB, and many others, including very good friends of mine who are bike mechanics/wheelbuilders, all seem to think that increasing spoke tension will increase the stiffness of a wheel, and vice versa. They all rely on some sort of "feel" related justification, and post hoc rationalization of why they think the tension is leading to what they think they are feeling.
I am still unconvinced. I am not sure if you have ever seen it, but Damon Rinard (who has been a lead engineer at many bike companies) designed a rig back in the 90s to test the theory. His article and results are archived on the Sheldon Brown website. Yobst Brant, the guru of wheelbuilding and author of "The Bicycle Wheel" is in agreement on the validity of these tests as far as I know. Here are links to the Rinard paper and data:
1. The Rinard tests were measuring lateral stiffness, so I suppose it is possible that lateral stiffness and radial stiffness are affected differently by spoke tension, however I find that to be unlikely.
2. As far as I know, while he compared equivalent builds with a few different spoke lacing configurations, I don't think he ever tested 1 vs 2 vs 3 cross. Three cross spoke patterns are more tangent to the hub flange, so they generally would be superior in terms of tortional loads (pedaling and braking) not that it really matters, but by virtue of their longer path to the rim they have a very slightly inferior lateral bracing angle, so that would be one reason for different flex characteristics. Henry's explanation for different crossings having different stiffnesses seemed to derive from the 3 cross being more tolerant of lower tension, so his theory was ultimately tension derived, not related to the wheel geometry.
3. Just to clarify, under loads so severe that some of the spokes go completely slack, the wheel momentarily becomes massively more flexible and weaker, both laterally and radially. Then, assuming you haven't flexed it too far and exceeded it's elastic limit, it should snap back and regain its normal strength and stiffness. Everyone is in agreement that a complete lack of tension will allow a wheel to flex more, however those de-tensioning/re-tensioning events are terrible for wheel longevity, and it is normally the goal of a wheel builder to spec the parts and build to a sufficient tension that you completely avoid those events. That is both because you run the risk of exceeding the elastic limit of the wheels, and because in the long term those massive unload/load cycles will fatigue the spoke heads/nipples/hub flanges/and spoke holes in the rim, eventually leading to fatigue failures/cracking.
When you hear about pro's running really low tension for a more compliant ride, I think they're just experiencing much more frequent de-tensioning events. You can see it clearly if you watch slow-mo videos of them getting rowdy and really loading the wheels, where you can see spokes going loose and then snapping back straight. That may be desirable in a pro-racing environment, where they are getting new wheels built for every race, but for most of us wondering about compliance for our daily drivers, and trying to get decent longevity out of the wheels, it probably isn't a good match. For compliance and longevity, I think a better match is to use a thinner/more elastic spoke, which can allow for the rim to flex more without going totally slack, while keeping the tension high enough to avoid de-tensioning events. Another alternative, I suppose, if you wanted to mess around with low spoke tension like the pros, durability be damned, is to just buy really cheap wheels and consider them to be disposable.
Yeah the above trail was Teleonics from the upper dirt road before the "ski jump" to the parking lot. Bike set up: Steel front end(modeled after 23'...
Yeah the above trail was Teleonics from the upper dirt road before the "ski jump" to the parking lot.
Bike set up: Steel front end(modeled after 23' Trek Session), stock aluminum rear end, Ochain, Dorado fork, DT 471 front rim 1.6 spokes, Crank bros DH carbon rear rim 1.5 spokes, CounterShox mounted on fork 800g and behind BB 600g, Conti Kryp tires 24/26psi.
I only got a few runs in this day, then had a little get-off that stopped my riding for the day. So I didn't really test anything here, just trying to get some more baselines and data for conditions and trails. I used the SynBike data system that has fork and shock linear pot for suspension data and a 6-axis IMU mounted to the front and rear axle, bars and bb. These IMU record 2000 times per second their position in space in all axis and gyro.
Observations are interesting from the data I have recorded. I have done testing with this kit on 2 different bikes and 3 locations. Sometimes the stiffer bike or rear end actually has more lateral accelerations because the rear wheel is losing grip, and chattering and those catch/release moments are creating spikes in the data. Below you can see the yellow line(rear axle) chattering. The red line bb actually looks fairly stable. From 30.4-30.6 seconds, you can see the rear axle skip 6 times and that's about in the same time it takes to blink an eye.
Photo Below: The softer bike, might actually move less at the axle laterally because of more grip, but then torsionally the % change will be higher. Red line is BB and yellow is rear axle. You can see the bb isn't very stable torsionally
Data is cool and now I have a baseline on this trail, but unless we are doing back-to-back on the same day and same trail, same rider, same air pressure, ect, it's kind of just fun data to have. I hope at this point next year, I have a bigger data set with 10-20 bikes (my goal), then I can really draw some conclusions!
So Rad Joe, very well done. Please keep us in the loop on this!
Henry at PB, and many others, including very good friends of mine who are bike mechanics/wheelbuilders, all seem to think that increasing spoke tension will increase...
Henry at PB, and many others, including very good friends of mine who are bike mechanics/wheelbuilders, all seem to think that increasing spoke tension will increase the stiffness of a wheel, and vice versa. They all rely on some sort of "feel" related justification, and post hoc rationalization of why they think the tension is leading to what they think they are feeling.
I am still unconvinced. I am not sure if you have ever seen it, but Damon Rinard (who has been a lead engineer at many bike companies) designed a rig back in the 90s to test the theory. His article and results are archived on the Sheldon Brown website. Yobst Brant, the guru of wheelbuilding and author of "The Bicycle Wheel" is in agreement on the validity of these tests as far as I know. Here are links to the Rinard paper and data:
1. The Rinard tests were measuring lateral stiffness, so I suppose it is possible that lateral stiffness and radial stiffness are affected differently by spoke tension, however I find that to be unlikely.
2. As far as I know, while he compared equivalent builds with a few different spoke lacing configurations, I don't think he ever tested 1 vs 2 vs 3 cross. Three cross spoke patterns are more tangent to the hub flange, so they generally would be superior in terms of tortional loads (pedaling and braking) not that it really matters, but by virtue of their longer path to the rim they have a very slightly inferior lateral bracing angle, so that would be one reason for different flex characteristics. Henry's explanation for different crossings having different stiffnesses seemed to derive from the 3 cross being more tolerant of lower tension, so his theory was ultimately tension derived, not related to the wheel geometry.
3. Just to clarify, under loads so severe that some of the spokes go completely slack, the wheel momentarily becomes massively more flexible and weaker, both laterally and radially. Then, assuming you haven't flexed it too far and exceeded it's elastic limit, it should snap back and regain its normal strength and stiffness. Everyone is in agreement that a complete lack of tension will allow a wheel to flex more, however those de-tensioning/re-tensioning events are terrible for wheel longevity, and it is normally the goal of a wheel builder to spec the parts and build to a sufficient tension that you completely avoid those events. That is both because you run the risk of exceeding the elastic limit of the wheels, and because in the long term those massive unload/load cycles will fatigue the spoke heads/nipples/hub flanges/and spoke holes in the rim, eventually leading to fatigue failures/cracking.
When you hear about pro's running really low tension for a more compliant ride, I think they're just experiencing much more frequent de-tensioning events. You can see it clearly if you watch slow-mo videos of them getting rowdy and really loading the wheels, where you can see spokes going loose and then snapping back straight. That may be desirable in a pro-racing environment, where they are getting new wheels built for every race, but for most of us wondering about compliance for our daily drivers, and trying to get decent longevity out of the wheels, it probably isn't a good match. For compliance and longevity, I think a better match is to use a thinner/more elastic spoke, which can allow for the rim to flex more without going totally slack, while keeping the tension high enough to avoid de-tensioning events. Another alternative, I suppose, if you wanted to mess around with low spoke tension like the pros, durability be damned, is to just buy really cheap wheels and consider them to be disposable.
Great points. To add on, when you are running low spoke tension, you see the spokes lose tension above the contact patch. On a large side impact, this is where wheels can fold because the spokes don’t “catch” the rim when regaining tension as it takes off to the side. If the rim moves enough and has already begun to deform, your rim can fold in half or taco. You can get away with this more on carbon rims since they are more stout, but as soon as an aluminum wheel starts to yield and warp or bend to the side, and the spokes don’t catch it, the rim folds. That’s a bad time. Good way to get hurt.
Remember this photo? It’s a good reminder not to let spoke tension get too low. Also, please correct me if this isn’t right. That’s my understanding, and I don’t think this issue gets brought up enough but its good for people to know as it can be dangerous.
This sounds cheezy so bear with me but I just wanted to say thank you for the great conversations here so far. I’ve already learned some new things and it’s got me pumped. If even one person learns something new from this, then this whole article was worth the effort. With discussions like this, we can spark great ideas and figure out how to make bikes better for everyone, faster. There are so many smart people here and I don’t see any reason why we can’t collaborate to figure out the next big steps for mountain biking progress. 🤘
And to those just watching the conversation and have a question that they don't want to ask publicly, please feel free to reach out directly. I definitely don't know everything or much for that matter but am happy to try and help answer.
Companies often do measure flex in the lab. There are some simple standard fixtures for measuring head tube and bottom bracket stiffness that most companies use and some companies do batch test these. Companies can also make their own stiffness tests to dig into specially what they are interested in as well.
I've seen the wobble you speak of on some youtube videos. What bike in particular did you see this on? We can guess as to why its happening.
That would be cool but since I'm not at the company anymore I don't want to speak on their business. It's cool stuff though and it works well. Happy to give you a rundown of whys its rad though. Any specific questions about it?
Do you have photos of your bike? It sounds rad!
I remember hearing a podcast with the guy from Enve about how they developed the new DH carbon rim with the Muc Off Commencal team. He mentioned at a certain point the team was changing the frame character so much that it was changing what they wanted it out of wheel.
Definitely a concept about developing an entire package to work together, this can go for consumer or production. Before I started testing parts and frames for ride quality, I would throw on parts that looked cool or color matched. This led me down a road where I had to rethink things because the bike started to handle so poorly.
Fantastic reading!
Super interesting thread ! I am currently riding a custom made steel frame, superenduro/freeride type.
You thread comes just as I am considering frame flex on my own frame as I noticed some after riding it harder and harder.
Basically I noticed that my frame flexes on high side load situations, mostly high G berms. Initially I thought it was tire roll, pumped them up super hard and that didn't solve the issue. Which lead me to consider flex in my wheels. I went from soft alloy wheels to stiff carbon rims and that didn't change much to be fair. So last option is frame flex and I imagine mostly swingarm flex. I am considering replacing the rear triangle with a alu CNC one but should I try to improve wag or roll ? To me what I experience sounds more like roll since it feels exactly like rear tire roll but what's your take ?
Great question! I would love to see a picture of your bike because custom builds are awesome. What suspension layout do you use? We can take a look and get you pointed in a good direction.
"Ideally, the rear triangle flexes via roll enough to allow the rear wheel to deflect impacts and avoids as much wag as possible, mitigating unpredictable steering."
Is this noticeable (in a good way) on single pivot bikes like Orange? Or maybe someone here rode a Chumba or Zonenschein DH bike and can remeber such feeling? Devinci Wilson and Rocky RMX also come to mind..
There is a wheel review on a prominent mtb website where the reviewer attempts to educate the reader about why different wheels have different compliance. He uses the example that a 2X laced wheel, a 3X laced wheel, and a 3X laced wheel detensioned a small amount will all have different compliance. The rationale offered is theoretical and to put it plainly, i don’t think it’s interesting whether or not it’s good theorizing or poor.
My question is what is the technical limitation in the way of building examples of these three wheels and measuring the compliance?
Does the rig not exist? Is it prohibitively expensive? Does the test protocol not exist? Are there competing protocols where the results of one would be protested by advocates for the alternative?
This has been the first flex stays frame I have built. Previously there have been three linkage driven single pivots and a classic single pivot. The rear end sits at neutral at 40% travel with the shock removed.
I also ride a custom steel frame. Mine is single pivot with spherical bearings on the shock so the rear end is quite compliant.
I ride it on every type of riding.
It excels on off camber chunder and will hold a high line that other bikes won't. This matches the USD Dorado fork quite well.
G-out berms/ruts are it's weakness and I can feel the wag if I load up in the corner.
I find that the wag in corners becomes intuitive and you get to know the bike in consistent berms.
Harsh g out ruts that change lap to lap are a challenge or hitting something hard unexpected. That's the only big downside I see. The rear end is essentially a undamped spring that could buck you off if you are caught off guard.
Compliance like everything, is a compromise. Choose what suits the best. I think DH racer teams will eventually end up with different rear ends like they have different suspension setups for different courses, and of course different rider masses and styles. Moto GP has different rear ends for each track with left hand and right hand turn compliance baked in for the types of turns on the track.
Ideally I would want a bit less wag but still keep the roll compliance.
They put some effort into achieving balanced compliance and it shows. Even though it is steel its no noodle; the triangular spindle in the rocker pivot makes it so both sides of the rocker move in unison, providing some stability to complement the steel flex. I run out of rear tire (trail casing) before I run out of rear end.
In this video by Enve, they show testing the wheels on a machine. Not sure if this is just a destruction test or gives them compliance/rigidity numbers.
But to your post, I totally believe that 2x and 3x have different compliance, along with spoke tension, spoke diameter, spoke count, and rim choice. The combination is endless. This also brings me full circle because trail testing depends on the dirt type, rider weight, and riding style, which could all push a wheel to a different extent. I don't think we could sit here and say "this combination" is best for everyone, but at least we are getting these conversations out in the open to make educated decisions on our parts before our next build or purchase.
I can definitely see why you think the rear end is compliant and maybe too much. Looks sick, though!
Can you post a photo of your bike?
This was my project last winter with Adam Prosise (Formally from REEB )
Steel front end, stock Trek aluminum rear end with some compliance mods. Also matched with Dorado Pro. I'll some data that can show the rear lateral accelerations and torsional movement.
I didn't find it to have too much. If anything I'd look to try and get a wee bit more wag out of it to balance the roll. This frame I wasn't getting any tire rub on the inner cs's from wag. Previous frames I have had wear marks on the cs's.
In the next iteration I will built it with a removeable cs's bridge. I can then play with bridge configurations to see what that does.
How do you like the steel front end on the session? Did you ride it with stock front end? I think the session is damn near perfect from a suspension kinematics perspective and I imagine the steel front end improves that. I may need to source a rear end to follow your path.
I know Adam. He made some bits for my bike too. Rad guy.
My bike from The Freedom Machine. We tried to keep the rear as stiff as we could while avoiding belt etc on this bike. We made the pivot very stiff and brace up to shock mount very stiff. Next iteration will have more wag stiffness.
That would be sick with the adjustable bridges. I did some testing on the Commencal V5 with them and it made a pretty big change in berms and G-outs.
Could you share what CS and SS tubing you used on the rear?
That looks rad! The front end and BB area look great, looks like an awesome job keeping that bb area from swaying. I could definitely understand that rear end being great in some areas but then moving too much in others. But like you said, it's all give in take. Personally, I'd rather have a soft compliant ride with maybe 1 or 2 areas that are "too soft", than an entire trail that is rigid and rattling my body.
I'm working on a steel DH gearbox frame with @VesselBikeProject now.
Yes I rode the Trek before, It was a much more comfortable ride with this front end. The Session is such a good base platform, as you mentioned, but I did remove some material from the CS and SS bridge to make it more compliant rear. I think I had to match some of the softer front end.
Yes it is all give/take. Exactly like suspension setup.
This bike (The Homer) gets pedalled as an Enduro bike, Whistler laps and then Prevost shuttle laps.
For enduro and Whistler laps, I think the compliance is perfect. It eats rough and softens the harsh Whistler laps. Even with the firm suspension setup I run.
Prevost is another beast though. It's perfect 85% of the time but there's some hefty hits and corners on that hill. And hitting those fast, you want to be fully comfortable that you know how the bike will handle. Those scenarios are like racing, so I can see the downside of too much compliance too.
Rear end length, wheel size and tire size has a huge effect on rear end compliance too. Mine has 25mm CS range and it's noticeably softer in long setting. Bigger tires give a similar feel too with tire roll.
Vessel bikes stuff is rad too. I like his plate pull links to decouple shock side loading.
Gearboxes are the future and the belt is a game changer too. Low mass, no chain effect on your feet etc. And the cassette weight off the rear wheel is hugely noticable.
I'm currently schemeing a DH linkage driven bike with belt. Either SS or gearbox. Stiff front end, slighter stiffer rear end than The Homer.
Just looking at the Orange, it seems like it mostly rolls, but the shock helps resist that. Since the shock is bolted to the flexing rear triangle, it acts like part of the frame, kind of like a strut on a car. This does put extra side load on the shock, but modern shocks are built tough and can probably handle it without issue. As long as the shock can take it, it’s not a bad thing.
I’d say the Orange probably rolls more, but there’s a bit of wag too because the shock is part of the structure. If the shock wasn’t there or had a spherical bushing, I’d guess it would have mostly roll!
It looks like an impact machine but it does seem as though Enve does measure displacement during impact somehow as they claim improved radial deflection during riding to improve comfort. It's cool stuff! Honestly I think those are the coolest wheels on the market right now. Someday I'll save up enough!
@earleb Dang that's a cool ride and cool idea too! Well done. Here are a few places you could buy back some stiffness: 1) seat stay bridge 2) increase the chain stay bridge length 3) add bracing to the swingarm here 4) and if you're really going for it, add a swing link like the older fury. Hope that helps!
@Roryb @carlinojoevideo @earleb you guys are freaking rad. Great work on your bikes! Hell yeah.
Here is some data from riding my steel Trek in Southern California.
Approx 2 minute run in Laguna.
The rear axle showed 67% more lateral accelerations than the bb. (Negative is to riders left and positive is to riders right.)
The rear axle showed that it twisted torsionally 35% more than the lower frame/bb.
What does all this mean? Hahha, nothing really until I gather more data on the same trail, in the same conditions. But I’m starting to gather a baseline with a few frames. The problem is dirt conditions and trail style play a big load(literally) on what the data will look like.
Rad stuff. Can I guess the trail: Telonics? I don't know of any other DH trails there that have any G's besides a little bit on Silver Surfer. Great data! Any chance you have a full rundown of your setup? I think this is the perfect thread to show off your hard work on on the topic!
Before conducting the tests, based on observations like material, tube section size, bridges, and key features at pinch points (such as chain stay yokes), do you think you could have accurately predicted which data set would correspond to each frame? It's a fun question to consider!
Also what beer did you get at Laguna Beer co after? :D
Yeah the above trail was Teleonics from the upper dirt road before the "ski jump" to the parking lot.
Bike set up: Steel front end(modeled after 23' Trek Session), stock aluminum rear end, Ochain, Dorado fork, DT 471 front rim 1.6 spokes, Crank bros DH carbon rear rim 1.5 spokes, CounterShox mounted on fork 800g and behind BB 600g, Conti Kryp tires 24/26psi.
I only got a few runs in this day, then had a little get-off that stopped my riding for the day. So I didn't really test anything here, just trying to get some more baselines and data for conditions and trails. I used the SynBike data system that has fork and shock linear pot for suspension data and a 6-axis IMU mounted to the front and rear axle, bars and bb. These IMU record 2000 times per second their position in space in all axis and gyro.
Observations are interesting from the data I have recorded. I have done testing with this kit on 2 different bikes and 3 locations. Sometimes the stiffer bike or rear end actually has more lateral accelerations because the rear wheel is losing grip, and chattering and those catch/release moments are creating spikes in the data. Below you can see the yellow line(rear axle) chattering. The red line bb actually looks fairly stable. From 30.4-30.6 seconds, you can see the rear axle skip 6 times and that's about in the same time it takes to blink an eye.
Photo Below: The softer bike, might actually move less at the axle laterally because of more grip, but then torsionally the % change will be higher. Red line is BB and yellow is rear axle. You can see the bb isn't very stable torsionally
Data is cool and now I have a baseline on this trail, but unless we are doing back-to-back on the same day and same trail, same rider, same air pressure, ect, it's kind of just fun data to have. I hope at this point next year, I have a bigger data set with 10-20 bikes (my goal), then I can really draw some conclusions!
Henry at PB, and many others, including very good friends of mine who are bike mechanics/wheelbuilders, all seem to think that increasing spoke tension will increase the stiffness of a wheel, and vice versa. They all rely on some sort of "feel" related justification, and post hoc rationalization of why they think the tension is leading to what they think they are feeling.
I am still unconvinced. I am not sure if you have ever seen it, but Damon Rinard (who has been a lead engineer at many bike companies) designed a rig back in the 90s to test the theory. His article and results are archived on the Sheldon Brown website. Yobst Brant, the guru of wheelbuilding and author of "The Bicycle Wheel" is in agreement on the validity of these tests as far as I know. Here are links to the Rinard paper and data:
https://www.sheldonbrown.com/rinard/wheel_index.html
https://www.sheldonbrown.com/rinard/wheel/data.htm
A few disclaimers from me though:
1. The Rinard tests were measuring lateral stiffness, so I suppose it is possible that lateral stiffness and radial stiffness are affected differently by spoke tension, however I find that to be unlikely.
2. As far as I know, while he compared equivalent builds with a few different spoke lacing configurations, I don't think he ever tested 1 vs 2 vs 3 cross. Three cross spoke patterns are more tangent to the hub flange, so they generally would be superior in terms of tortional loads (pedaling and braking) not that it really matters, but by virtue of their longer path to the rim they have a very slightly inferior lateral bracing angle, so that would be one reason for different flex characteristics. Henry's explanation for different crossings having different stiffnesses seemed to derive from the 3 cross being more tolerant of lower tension, so his theory was ultimately tension derived, not related to the wheel geometry.
3. Just to clarify, under loads so severe that some of the spokes go completely slack, the wheel momentarily becomes massively more flexible and weaker, both laterally and radially. Then, assuming you haven't flexed it too far and exceeded it's elastic limit, it should snap back and regain its normal strength and stiffness. Everyone is in agreement that a complete lack of tension will allow a wheel to flex more, however those de-tensioning/re-tensioning events are terrible for wheel longevity, and it is normally the goal of a wheel builder to spec the parts and build to a sufficient tension that you completely avoid those events. That is both because you run the risk of exceeding the elastic limit of the wheels, and because in the long term those massive unload/load cycles will fatigue the spoke heads/nipples/hub flanges/and spoke holes in the rim, eventually leading to fatigue failures/cracking.
When you hear about pro's running really low tension for a more compliant ride, I think they're just experiencing much more frequent de-tensioning events. You can see it clearly if you watch slow-mo videos of them getting rowdy and really loading the wheels, where you can see spokes going loose and then snapping back straight. That may be desirable in a pro-racing environment, where they are getting new wheels built for every race, but for most of us wondering about compliance for our daily drivers, and trying to get decent longevity out of the wheels, it probably isn't a good match. For compliance and longevity, I think a better match is to use a thinner/more elastic spoke, which can allow for the rim to flex more without going totally slack, while keeping the tension high enough to avoid de-tensioning events. Another alternative, I suppose, if you wanted to mess around with low spoke tension like the pros, durability be damned, is to just buy really cheap wheels and consider them to be disposable.
So Rad Joe, very well done. Please keep us in the loop on this!
Great points. To add on, when you are running low spoke tension, you see the spokes lose tension above the contact patch. On a large side impact, this is where wheels can fold because the spokes don’t “catch” the rim when regaining tension as it takes off to the side. If the rim moves enough and has already begun to deform, your rim can fold in half or taco. You can get away with this more on carbon rims since they are more stout, but as soon as an aluminum wheel starts to yield and warp or bend to the side, and the spokes don’t catch it, the rim folds. That’s a bad time. Good way to get hurt.
Remember this photo? It’s a good reminder not to let spoke tension get too low. Also, please correct me if this isn’t right. That’s my understanding, and I don’t think this issue gets brought up enough but its good for people to know as it can be dangerous.
This sounds cheezy so bear with me but I just wanted to say thank you for the great conversations here so far. I’ve already learned some new things and it’s got me pumped. If even one person learns something new from this, then this whole article was worth the effort. With discussions like this, we can spark great ideas and figure out how to make bikes better for everyone, faster. There are so many smart people here and I don’t see any reason why we can’t collaborate to figure out the next big steps for mountain biking progress. 🤘
And to those just watching the conversation and have a question that they don't want to ask publicly, please feel free to reach out directly. I definitely don't know everything or much for that matter but am happy to try and help answer.
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