Idea for compliance. Pivot bearings set in a polyurethane bushing. Different durometer bushings to tune the amount of flex.
I don’t think you need to go that far to have flex bushings, my steel frame and modified aluminum rear end from Trek session can give you that feeling. That’s just from using tubing that isn’t as rigid and me removing some of the seatstay and chainstay bridges.
My personal opinion is that brands just don’t need to make the bikes so rigid.
The idea of poly surrounded bearings sounds like a great experiment. If anyone here is planning to make a frame soon and wants to give this a try, keep us in the loop. I’d be happy to help out on the CAD front.
The easiest way to mock this up could be to start with an aluminum rear triangle that already has a lot of material around the bearing bores. We could machine out the bearing bore slightly to create more space and then find a smaller than stock bearing that fits the hardware, both buying us space to put stuff around the bearing. Using 3D printed rubber parts as the initial material would also make prototyping easy and cost effective.
@carlinojoevideo I agree. I think your approach will be the solution for most consumer products and even most race applications. Always fun to push it past the limit and learn what happens! *Inserting favorite graph*
Be very careful with poly mounted bearings. Don't just throw them in a poly sleeve and straight into the frame. That will eat the pivot bearing.
You'd need either a poly mounted tube to press the bearings in where the tube is strong enough to connect the two bearings so they move in unison, or a poly tube going through the bearings into which the pivot axle is inserted.
It would probably be easier to make a carbon chainstay that is the right amount and right direction of flexy vs. a poly mounted main pivot...
Be very careful with poly mounted bearings. Don't just throw them in a poly sleeve and straight into the frame. That will eat the pivot bearing. You'd...
Be very careful with poly mounted bearings. Don't just throw them in a poly sleeve and straight into the frame. That will eat the pivot bearing.
You'd need either a poly mounted tube to press the bearings in where the tube is strong enough to connect the two bearings so they move in unison, or a poly tube going through the bearings into which the pivot axle is inserted.
It would probably be easier to make a carbon chainstay that is the right amount and right direction of flexy vs. a poly mounted main pivot...
So your saying my options are, put skateboard wheels in my pivots, or stay drilling holes in my stays until it's flexy enough.
So your saying my options are, put skateboard wheels in my pivots, or stay drilling holes in my stays until it's flexy enough.
I like these ideas
haha, agreed that it doesn't sound very pro... if it's good enough for your cars suspension bushings it's probably ok for a bike. Who knows it may not work at all (good chance) but there's only one way to find out.
On a podcast with Dave Wiegal, he said the 3 holes in the Ironhorse Sunday link were hand drilled during test sessions to create more rider...
On a podcast with Dave Wiegal, he said the 3 holes in the Ironhorse Sunday link were hand drilled during test sessions to create more rider comfort.
I mean, look at that rear triangle, its looks ridiculously stiff. I'd want to drive over it with a truck just to develop some bearing play for comfort haha.
@Ryan_Burney I'm just about to upgrade from a pretty clapped out frame, i'll see if a friend is willing to help make some bushing inserts and do some test runs. Not sure if ill get around to it, but i'd like to try it.
It's a collet main pivot and rocker pivot, so if I get some PU mid durometer inserts machined I can't see why I cant just press in some lower OD bearings into them and mount everything up.
If i do, I might make a jig and fix the front triangle and suspend a weight of the rear axle before and after to measure frame deflection from the setup.
I found these photos of the Honda RN01 that I never noticed. Greg Minar mentioned on the, Making Up The Numbers podcast that when he went testing for Honda, the first frame they had was max stiffness. As the day went on they start drilling holes in the frame until it looked like Swiss cheese and he liked the ride feel. They went back and made the next frame to match that rigidity.
So I started looking up photos and noticed there was 2 versions, one with single backbone and one had double. Not sure which was first, but cool to hear that story.
I like the idea of having one end of the shock mount isolated on a polyurethane bushing to take up small vibration.
I don't think the poly bushing would work for a main pivot but maybe for the seatstay to a rocker link pivot it might add a tuneable flex that also isolated vibration.
I like the idea of having one end of the shock mount isolated on a polyurethane bushing to take up small vibration.
I don't think the poly bushing would work for a main pivot but maybe for the seatstay to a rocker link pivot it might add a tuneable flex that also isolated vibration.
I like this idea on the top or bottom shock mount. I don’t really see a negative to it.
17% isn't much but compared to most single pivot on the market that have 0 to 5% of progression this is a lot lol. As an enduro...
17% isn't much but compared to most single pivot on the market that have 0 to 5% of progression this is a lot lol.
As an enduro bike I wouldn't change anything on it really.
As a DH bike I would use some slightly shorter chainstays (460 or 465mm) to help a little in the very steep stuff and add a little rear end stiffness (the whole point of this thread) as it is a bit lacking sometimes in high G scenarios. Other than that it is very capable as it is. If I was to use it as pur DH I would use an Ochain, double crown, DH transmission etc.
I might do a dedicated DH frame in the near future which is why I participated to this thread. If I can identify where my lack of stiffness comes from it could be addressed for the DH frame. The frame would be mid-pivot, fixed, non concentric idler, similar geometry, travel, progression and AR characteristics. The concept is pretty much ready in Linkage but I haven't pulled the trigger yet as I am considering other options.
Right now, it looks like your main loss of stiffness is coming from the seat stays not being supported by anything other than the shock. The...
Right now, it looks like your main loss of stiffness is coming from the seat stays not being supported by anything other than the shock. The shock is essentially acting as a structural member of your bike, taking on twisting forces in corners. The biggest improvement would likely come from adding a small swing link to connect the seat stays to the front triangle. Your shock will thank you for it 😅.
From there, you could increase rear triangle rigidity by adding a seat stay bridge. If you want to take it even further, you could beef up the chain stay bridge or the bridge on the rear triangle in front of the seat tube. You asked about the downside? It might change the ride feel you currently like. And if you make the rear triangle too rigid compared to the front triangle, you could shift the flexing to the front triangle in high-G corners, potentially causing handling issues.
If you like the way your bike feels now but want just a bit more stiffness, I’d prioritize adding both a removable seat stay bridge and a small swing link. This setup would let you experiment with both independently. A swing link could introduce a little wag and reduce roll stiffness, but if you keep it light, it tiny/flexible minimize those effects.
One quick test you can try: sit on the rear wheel, grab your seat and swing you hips side to side on the wheel. Boom, you've created a test machine out of a human. Watch how things move and see what’s flexing the most. This can give you a better idea of whether a swing link would help.
I had a Gery Fisher full suspension bike way back in ~2010, don't remember the model but it was 100mm travel front and rear. The seat stays were carbon which I thought was cool, but they had no bracing between them. On climbs where I would start to pedal hard the chain would skip on the cassette. I would go through the cable tension settings after a ride and everything looked great on the stand. Would be interesting to see if it was the BB or the rear triangle torsionally twisting screwing with the chain alignment.
I like the idea of having one end of the shock mount isolated on a polyurethane bushing to take up small vibration.
I don't think the poly bushing would work for a main pivot but maybe for the seatstay to a rocker link pivot it might add a tuneable flex that also isolated vibration.
Developed for a frame designed for trunnion mount shocks. 1 step forward, 2 steps back.
I grew up riding dirt bikes and never really felt comfortable with MTBs. This thread brings up a lot of what I was feeling. I had a hard tail, and I would occasionally catch a hidden stump or square edge and that thing would throw me over the bars. I moved to full suspension and had the flexing issue with the Gery Fisher, then had a specialized camber pro 26inch wheel. It felt pretty good, but still seemed to be a bit too ridged and unforgiving in some instances. Last year I picked up a polygon colossus N8e and feel the most comfortable I've ever been on a bicycle. I'm not sure if it's the extra weight of the emtb, the 6 bar linkage, or the 160mm of travel but to me it feels like a great balance of compliance and responsive rigidity. So far it's never done anything unexpected, it's very stable while also plenty responsive. What are your thoughts on this design?
I wouldn't say it's doing weird things here, but it does look weird. It's "just" flexing. But it does look a bit hectic. It's a perfect illustration...
I wouldn't say it's doing weird things here, but it does look weird. It's "just" flexing. But it does look a bit hectic.
It's a perfect illustration as to why frame compliance and wheel flex is important.
The way I think about it is this (could be totally wrong), he's pushed aggressively hard into the corner, the front is tracking perfectly as it has an axle to pivot on (the fork) and thus flex isn't really an issue up front.
The rear wheel of a bike/motorbike will always understeer in a corner, which is an issue in berms, as it means the rear wheel always takes a lower line in a berm with less support (if the bike is only angled and the front wheel not turned there won't be understeer fyi, it's the act of the front wheel being turned creates understeer). He pushes into the corner to generate grip and speed and starts to exceed to limit of grip on the rear and it will slide up the berm until it can grip enough to stop sliding (a schralp as we say). On the more angled part of the berm the tyre gets more support (grip) and stops sliding, but the sideways moment of the slide has to go somewhere now, the tyre stops moving but the force hasn't gone, so we see the frame (imagine it from the axles perspective) continue to move past the contact point of the tyre from this momentum. Now we have a few options, either the rear triangle flexes to absorb this, or the spokes do. Both are good, as it means the tyre can stay happily stuck to berm, the issue is if when this flex occurs, since it's a spring, on corner exit when the load is gone, it violently whips back and forces the tyre to ping to the riders right-hand side and lose grip.
Imagine the counterfactual, if the frame and wheel don't flex here, his sideways momentum will continue to drag the rear tyre up the berm, even though the tyre has enough grip now. Because the energy has to go somewhere. If it's not absorbed by the spokes and rim and rear triangle it will be translated into the tyre and cause a slide. You probably won't crash, but you will schralp harder and destabilize the front of the bike by pivoting so much and probably have to counter steer the front tyre to account for now large amounts of oversteer, which is slower, and harder.
It's this harmony between wheel flex and frame flex that makes a nice tracking bike, some rear triangle flex allows a more skateboard like approach to cornering where the rear can track closer to the front tyre path. A few high end cars have rear wheel steering to achieve this.
It goes to far when you get crabbing however, particularly from g-outs the rear triangle can want to move sideways and kinda spear you off trail.
How to engineer this all? Well that's for Ryan to figure out haha. I know a bit about wheel building though to help it.
A bit late to the party. This one is a though provoke for sure, looking at what the wheels do theoretically you need completely different things flex wise from the front and the rear...
As for rear wheel steer on cars, it's mostly counter steer under way 50 to 80 kph, costeer above that and no steer when things go sideways. It is to add agility at low speeds (because cars are getting bigger) and stability at higher speeds.
I mean, look at that rear triangle, its looks ridiculously stiff. I'd want to drive over it with a truck just to develop some bearing play...
I mean, look at that rear triangle, its looks ridiculously stiff. I'd want to drive over it with a truck just to develop some bearing play for comfort haha.
@Ryan_Burney I'm just about to upgrade from a pretty clapped out frame, i'll see if a friend is willing to help make some bushing inserts and do some test runs. Not sure if ill get around to it, but i'd like to try it.
It's a collet main pivot and rocker pivot, so if I get some PU mid durometer inserts machined I can't see why I cant just press in some lower OD bearings into them and mount everything up.
If i do, I might make a jig and fix the front triangle and suspend a weight of the rear axle before and after to measure frame deflection from the setup.
That sounds rad! Please keep us updated, and if you run into any challenges, don’t hesitate to reach out. I’m sure I speak for everyone when I say we’d be happy to help troubleshoot and lend a hand!
I grew up riding dirt bikes and never really felt comfortable with MTBs. This thread brings up a lot of what I was feeling. I had...
I grew up riding dirt bikes and never really felt comfortable with MTBs. This thread brings up a lot of what I was feeling. I had a hard tail, and I would occasionally catch a hidden stump or square edge and that thing would throw me over the bars. I moved to full suspension and had the flexing issue with the Gery Fisher, then had a specialized camber pro 26inch wheel. It felt pretty good, but still seemed to be a bit too ridged and unforgiving in some instances. Last year I picked up a polygon colossus N8e and feel the most comfortable I've ever been on a bicycle. I'm not sure if it's the extra weight of the emtb, the 6 bar linkage, or the 160mm of travel but to me it feels like a great balance of compliance and responsive rigidity. So far it's never done anything unexpected, it's very stable while also plenty responsive. What are your thoughts on this design?
The extra weight of the e bike definitely helps with stability and improves the unsprung mass ratio. I’m not surprised that bike feels comfortable and its cool to hear how stoked you are on it. The acute angle between the seat stays and chain stays of the rear triangle would allow for a decent amount of compliance, so that makes sense that it would be comfortable. Six-bar bikes are interesting. It’s cool how they manage to isolate kinematic variables a bit more compared to a four-bar design. That extra effort to squeeze out every bit of performance is always fun to see, and it’s great when it noticeably pays off for the rider.
I mean, look at that rear triangle, its looks ridiculously stiff. I'd want to drive over it with a truck just to develop some bearing play...
I mean, look at that rear triangle, its looks ridiculously stiff. I'd want to drive over it with a truck just to develop some bearing play for comfort haha.
@Ryan_Burney I'm just about to upgrade from a pretty clapped out frame, i'll see if a friend is willing to help make some bushing inserts and do some test runs. Not sure if ill get around to it, but i'd like to try it.
It's a collet main pivot and rocker pivot, so if I get some PU mid durometer inserts machined I can't see why I cant just press in some lower OD bearings into them and mount everything up.
If i do, I might make a jig and fix the front triangle and suspend a weight of the rear axle before and after to measure frame deflection from the setup.
That sounds rad! Please keep us updated, and if you run into any challenges, don’t hesitate to reach out. I’m sure I speak for everyone when...
That sounds rad! Please keep us updated, and if you run into any challenges, don’t hesitate to reach out. I’m sure I speak for everyone when I say we’d be happy to help troubleshoot and lend a hand!
Unfortunately this won't be happening, as the donor frame is dead haha. Maybe if I can find another donor frame from someone to destroy to test I'll look at doing it, but my old frame cracked so I won't be able to modify it safely.
I saw this on pink bike this morning, it's obviously a joke/gag bike, but from what little riding we saw, it really does highlight some interesting characteristics of front triangle flex. Worth a watch for sure.
Unfortunately this won't be happening, as the donor frame is dead haha. Maybe if I can find another donor frame from someone to destroy to test...
Unfortunately this won't be happening, as the donor frame is dead haha. Maybe if I can find another donor frame from someone to destroy to test I'll look at doing it, but my old frame cracked so I won't be able to modify it safely.
I saw this on pink bike this morning, it's obviously a joke/gag bike, but from what little riding we saw, it really does highlight some interesting characteristics of front triangle flex. Worth a watch for sure.
May it RIP in peace 🙏 No worries! Was thinking about how to do this on my bike as well though bike season is now over as I just got my first ski day in (warning: humble brag). I have 17mm aluminum axles for the main pivot and link pivot of my trail bike. I could replace them with a steel bolt that's ~10mm in diameter and 3d print some TPU bushings to take up the space between the parts and that would be a fairly quick way to try this idea on. It'll probably fall apart quickly but should last a few runs. Could just do a few back to backs to see if the idea is worth exploring further. Again, cant ride rn but if anyone else wants to play around with this send it. Happy to held with CAD/2D. It'll be fun for the new year. Excuse the lack of replies recently, I've been working on a future thing for in a few weeks that relates to this.
Has anyone tried oval tubing for front end? Wondering if it can give some extra compliance but make lateral stiffness? Commencal has been on the rectangle tubing and it’s a great ride feel!
Bringing this back to the top.Has anyone tried oval tubing for front end? Wondering if it can give some extra compliance but make lateral stiffness? Commencal...
Bringing this back to the top.
Has anyone tried oval tubing for front end? Wondering if it can give some extra compliance but make lateral stiffness? Commencal has been on the rectangle tubing and it’s a great ride feel!
Great question! You can totally do that. Road bikes have been doing this for a minute. You can see the tubes change shape to make bending happen in specific areas more than others. It's a great way to add compliance to the frame only where you want it, so you maintain precise handling and good pedal efficiency. They've done this on both carbon and aluminum road frames. Check out this link for more details.
Do you have any projects in the works where you might use this?
With carbon why not just adapt the layup along the tube?
You can absolutely adjust stiffness through layup, and companies do it all the time, but the gains are marginal. Tube stiffness is still primarily determined by the cross-section of the tube. While layup can influence the bending properties of a tube, there are limits to what it can achieve. Beyond a certain point, you either end up with a tube that is very strong in one direction and weak in another, or it becomes too thick and heavy. MTB tubes aren't that large so you can quickly get too heavy by adding just another layer of directional carbon which means you only have a few ways to layup a tube. Layup is excellent for fine-tuning, but if you're relying solely on it to solve stiffness issues, you're gonna have a bad time.
Bringing this back to the top.Has anyone tried oval tubing for front end? Wondering if it can give some extra compliance but make lateral stiffness? Commencal...
Bringing this back to the top.
Has anyone tried oval tubing for front end? Wondering if it can give some extra compliance but make lateral stiffness? Commencal has been on the rectangle tubing and it’s a great ride feel!
Great question! You can totally do that. Road bikes have been doing this for a minute. You can see the tubes change shape to make bending...
Great question! You can totally do that. Road bikes have been doing this for a minute. You can see the tubes change shape to make bending happen in specific areas more than others. It's a great way to add compliance to the frame only where you want it, so you maintain precise handling and good pedal efficiency. They've done this on both carbon and aluminum road frames. Check out this link for more details.
Do you have any projects in the works where you might use this?
I’m interested in trying some oval tubing for a steel bike so it can be stiffer laterally. I just can’t find any with the wall thickness that is thin enough.
Bringing this back to the top.Has anyone tried oval tubing for front end? Wondering if it can give some extra compliance but make lateral stiffness? Commencal...
Bringing this back to the top.
Has anyone tried oval tubing for front end? Wondering if it can give some extra compliance but make lateral stiffness? Commencal has been on the rectangle tubing and it’s a great ride feel!
Great question! You can totally do that. Road bikes have been doing this for a minute. You can see the tubes change shape to make bending...
Great question! You can totally do that. Road bikes have been doing this for a minute. You can see the tubes change shape to make bending happen in specific areas more than others. It's a great way to add compliance to the frame only where you want it, so you maintain precise handling and good pedal efficiency. They've done this on both carbon and aluminum road frames. Check out this link for more details.
Do you have any projects in the works where you might use this?
I’m interested in trying some oval tubing for a steel bike so it can be stiffer laterally. I just can’t find any with the wall thickness...
I’m interested in trying some oval tubing for a steel bike so it can be stiffer laterally. I just can’t find any with the wall thickness that is thin enough.
If you can find the tubes you can always change the geometry of the frame, smaller front triangle, larger head tube brace etc.
It's also worth mentioning that steels most desirable trait is its compliance, stiff steel( large diameter)is too heavy which is why we use aluminum, or carbon for even stiffer triangles.
You can absolutely adjust stiffness through layup, and companies do it all the time, but the gains are marginal. Tube stiffness is still primarily determined by...
You can absolutely adjust stiffness through layup, and companies do it all the time, but the gains are marginal. Tube stiffness is still primarily determined by the cross-section of the tube. While layup can influence the bending properties of a tube, there are limits to what it can achieve. Beyond a certain point, you either end up with a tube that is very strong in one direction and weak in another, or it becomes too thick and heavy. MTB tubes aren't that large so you can quickly get too heavy by adding just another layer of directional carbon which means you only have a few ways to layup a tube. Layup is excellent for fine-tuning, but if you're relying solely on it to solve stiffness issues, you're gonna have a bad time.
Agree on shape being primary factor (second moment of area usually being width x height cubed for vertical bending).
Strongly disagree on layup effects being marginal though. I know for a fact layup can influence the stiffness to the tune of 5x from the same mould. Granted, what I'm talking about is making things softer, not stiffer, which is a different problem altogether as making a small diameter tube into a rod by filling it in still won't get you to the point that taking a larger diameter tube would stiffness wise, but still. Layup can have an immense factor. It's also not just unidirectional plies that can be used in the layup, which opens up a whole other set of variables.
Ewh road bike but the other Framework (the canadian one) does a great job explaining how different layup and tube shape affect stiffness in different plane and post regularly on instagram his process:
Agree on shape being primary factor (second moment of area usually being width x height cubed for vertical bending). Strongly disagree on layup effects being marginal though...
Agree on shape being primary factor (second moment of area usually being width x height cubed for vertical bending).
Strongly disagree on layup effects being marginal though. I know for a fact layup can influence the stiffness to the tune of 5x from the same mould. Granted, what I'm talking about is making things softer, not stiffer, which is a different problem altogether as making a small diameter tube into a rod by filling it in still won't get you to the point that taking a larger diameter tube would stiffness wise, but still. Layup can have an immense factor. It's also not just unidirectional plies that can be used in the layup, which opens up a whole other set of variables.
Great points! I agree, but much of that range won't be usable while still meeting your goals for strength, weight, price, and stiffness. Within the practical limits of bike frame manufacturing, there are many adjustments you can make to the layup. However, you're unlikely to achieve drastic changes in stiffness while meeting those requirements, that's why you end up having to mainly rely on tube section.
Woven plies are interesting but often heavy, and high tech fibers are appealing but typically too expensive to produce a competitively priced frame. It's not that you can't adjust these factors, it’s that you still need to tune them in a way that results in a bike that sells and keeps the business running. Great discussion!
Idea for compliance. Pivot bearings set in a polyurethane bushing. Different durometer bushings to tune the amount of flex.
I don’t think you need to go that far to have flex bushings, my steel frame and modified aluminum rear end from Trek session can give you that feeling. That’s just from using tubing that isn’t as rigid and me removing some of the seatstay and chainstay bridges.
My personal opinion is that brands just don’t need to make the bikes so rigid.
The idea of poly surrounded bearings sounds like a great experiment. If anyone here is planning to make a frame soon and wants to give this a try, keep us in the loop. I’d be happy to help out on the CAD front.
The easiest way to mock this up could be to start with an aluminum rear triangle that already has a lot of material around the bearing bores. We could machine out the bearing bore slightly to create more space and then find a smaller than stock bearing that fits the hardware, both buying us space to put stuff around the bearing. Using 3D printed rubber parts as the initial material would also make prototyping easy and cost effective.
@carlinojoevideo I agree. I think your approach will be the solution for most consumer products and even most race applications. Always fun to push it past the limit and learn what happens! *Inserting favorite graph*
Be very careful with poly mounted bearings. Don't just throw them in a poly sleeve and straight into the frame. That will eat the pivot bearing.
You'd need either a poly mounted tube to press the bearings in where the tube is strong enough to connect the two bearings so they move in unison, or a poly tube going through the bearings into which the pivot axle is inserted.
It would probably be easier to make a carbon chainstay that is the right amount and right direction of flexy vs. a poly mounted main pivot...
So your saying my options are, put skateboard wheels in my pivots, or stay drilling holes in my stays until it's flexy enough.
I like these ideas
haha, agreed that it doesn't sound very pro... if it's good enough for your cars suspension bushings it's probably ok for a bike. Who knows it may not work at all (good chance) but there's only one way to find out.
Wouldn't it be funny if all we had to do to smooth out our mtb ride was to add rubber bushings to your shock bolts and a few suspension pivots 😅
On a podcast with Dave Wiegal, he said the 3 holes in the Ironhorse Sunday link were hand drilled during test sessions to create more rider comfort.
I mean, look at that rear triangle, its looks ridiculously stiff. I'd want to drive over it with a truck just to develop some bearing play for comfort haha.
@Ryan_Burney I'm just about to upgrade from a pretty clapped out frame, i'll see if a friend is willing to help make some bushing inserts and do some test runs. Not sure if ill get around to it, but i'd like to try it.
It's a collet main pivot and rocker pivot, so if I get some PU mid durometer inserts machined I can't see why I cant just press in some lower OD bearings into them and mount everything up.
If i do, I might make a jig and fix the front triangle and suspend a weight of the rear axle before and after to measure frame deflection from the setup.
I found these photos of the Honda RN01 that I never noticed. Greg Minar mentioned on the, Making Up The Numbers podcast that when he went testing for Honda, the first frame they had was max stiffness. As the day went on they start drilling holes in the frame until it looked like Swiss cheese and he liked the ride feel. They went back and made the next frame to match that rigidity.
So I started looking up photos and noticed there was 2 versions, one with single backbone and one had double. Not sure which was first, but cool to hear that story.
The bearing in a poly bush exists and has I think patented for bikes.
https://www.instagram.com/p/Ccu0xQCM9dG/?igsh=Y3V4b3AxMjk3NWUw
Same guys that developed the stem with isolation bushings.
https://www.instagram.com/p/CiffPjpsIbR/?igsh=cDR1ZDZkcnB5aXhp
I like the idea of having one end of the shock mount isolated on a polyurethane bushing to take up small vibration.
I don't think the poly bushing would work for a main pivot but maybe for the seatstay to a rocker link pivot it might add a tuneable flex that also isolated vibration.
I like this idea on the top or bottom shock mount. I don’t really see a negative to it.
I had a Gery Fisher full suspension bike way back in ~2010, don't remember the model but it was 100mm travel front and rear. The seat stays were carbon which I thought was cool, but they had no bracing between them. On climbs where I would start to pedal hard the chain would skip on the cassette. I would go through the cable tension settings after a ride and everything looked great on the stand. Would be interesting to see if it was the BB or the rear triangle torsionally twisting screwing with the chain alignment.
Developed for a frame designed for trunnion mount shocks. 1 step forward, 2 steps back.
I grew up riding dirt bikes and never really felt comfortable with MTBs. This thread brings up a lot of what I was feeling. I had a hard tail, and I would occasionally catch a hidden stump or square edge and that thing would throw me over the bars. I moved to full suspension and had the flexing issue with the Gery Fisher, then had a specialized camber pro 26inch wheel. It felt pretty good, but still seemed to be a bit too ridged and unforgiving in some instances. Last year I picked up a polygon colossus N8e and feel the most comfortable I've ever been on a bicycle. I'm not sure if it's the extra weight of the emtb, the 6 bar linkage, or the 160mm of travel but to me it feels like a great balance of compliance and responsive rigidity. So far it's never done anything unexpected, it's very stable while also plenty responsive. What are your thoughts on this design?
A bit late to the party. This one is a though provoke for sure, looking at what the wheels do theoretically you need completely different things flex wise from the front and the rear...
As for rear wheel steer on cars, it's mostly counter steer under way 50 to 80 kph, costeer above that and no steer when things go sideways. It is to add agility at low speeds (because cars are getting bigger) and stability at higher speeds.
That sounds rad! Please keep us updated, and if you run into any challenges, don’t hesitate to reach out. I’m sure I speak for everyone when I say we’d be happy to help troubleshoot and lend a hand!
The extra weight of the e bike definitely helps with stability and improves the unsprung mass ratio. I’m not surprised that bike feels comfortable and its cool to hear how stoked you are on it. The acute angle between the seat stays and chain stays of the rear triangle would allow for a decent amount of compliance, so that makes sense that it would be comfortable. Six-bar bikes are interesting. It’s cool how they manage to isolate kinematic variables a bit more compared to a four-bar design. That extra effort to squeeze out every bit of performance is always fun to see, and it’s great when it noticeably pays off for the rider.
Unfortunately this won't be happening, as the donor frame is dead haha. Maybe if I can find another donor frame from someone to destroy to test I'll look at doing it, but my old frame cracked so I won't be able to modify it safely.
I saw this on pink bike this morning, it's obviously a joke/gag bike, but from what little riding we saw, it really does highlight some interesting characteristics of front triangle flex. Worth a watch for sure.
May it RIP in peace 🙏 No worries! Was thinking about how to do this on my bike as well though bike season is now over as I just got my first ski day in (warning: humble brag). I have 17mm aluminum axles for the main pivot and link pivot of my trail bike. I could replace them with a steel bolt that's ~10mm in diameter and 3d print some TPU bushings to take up the space between the parts and that would be a fairly quick way to try this idea on. It'll probably fall apart quickly but should last a few runs. Could just do a few back to backs to see if the idea is worth exploring further. Again, cant ride rn but if anyone else wants to play around with this send it. Happy to held with CAD/2D. It'll be fun for the new year. Excuse the lack of replies recently, I've been working on a future thing for in a few weeks that relates to this.
Bringing this back to the top.
Has anyone tried oval tubing for front end? Wondering if it can give some extra compliance but make lateral stiffness? Commencal has been on the rectangle tubing and it’s a great ride feel!
Great question! You can totally do that. Road bikes have been doing this for a minute. You can see the tubes change shape to make bending happen in specific areas more than others. It's a great way to add compliance to the frame only where you want it, so you maintain precise handling and good pedal efficiency. They've done this on both carbon and aluminum road frames. Check out this link for more details.
Do you have any projects in the works where you might use this?
With carbon why not just adapt the layup along the tube?
You can absolutely adjust stiffness through layup, and companies do it all the time, but the gains are marginal. Tube stiffness is still primarily determined by the cross-section of the tube. While layup can influence the bending properties of a tube, there are limits to what it can achieve. Beyond a certain point, you either end up with a tube that is very strong in one direction and weak in another, or it becomes too thick and heavy. MTB tubes aren't that large so you can quickly get too heavy by adding just another layer of directional carbon which means you only have a few ways to layup a tube. Layup is excellent for fine-tuning, but if you're relying solely on it to solve stiffness issues, you're gonna have a bad time.
I’m interested in trying some oval tubing for a steel bike so it can be stiffer laterally. I just can’t find any with the wall thickness that is thin enough.
Ti Cycles sells an ovalized 1.75x.035 tandem tube that might work for ya. https://www.ticycles.com/ticycletubes/main-tube-ovalized-4130-tandem-bottom-tube-steel
If you can find the tubes you can always change the geometry of the frame, smaller front triangle, larger head tube brace etc.
It's also worth mentioning that steels most desirable trait is its compliance, stiff steel( large diameter)is too heavy which is why we use aluminum, or carbon for even stiffer triangles.
Agree on shape being primary factor (second moment of area usually being width x height cubed for vertical bending).
Strongly disagree on layup effects being marginal though. I know for a fact layup can influence the stiffness to the tune of 5x from the same mould. Granted, what I'm talking about is making things softer, not stiffer, which is a different problem altogether as making a small diameter tube into a rod by filling it in still won't get you to the point that taking a larger diameter tube would stiffness wise, but still. Layup can have an immense factor. It's also not just unidirectional plies that can be used in the layup, which opens up a whole other set of variables.
Ewh road bike but the other Framework (the canadian one) does a great job explaining how different layup and tube shape affect stiffness in different plane and post regularly on instagram his process:
https://www.instagram.com/frameworkbikes/
It helps that he also wind his own tubes not using prepreg.
Great points! I agree, but much of that range won't be usable while still meeting your goals for strength, weight, price, and stiffness. Within the practical limits of bike frame manufacturing, there are many adjustments you can make to the layup. However, you're unlikely to achieve drastic changes in stiffness while meeting those requirements, that's why you end up having to mainly rely on tube section.
Woven plies are interesting but often heavy, and high tech fibers are appealing but typically too expensive to produce a competitively priced frame. It's not that you can't adjust these factors, it’s that you still need to tune them in a way that results in a bike that sells and keeps the business running. Great discussion!
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