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The Internet Was Wrong: Short Chainstays Suck*

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2/7/2019 12:53 PM

@Big Bird, can I see picture of your bike with super short CS and a the longest front you got? And can you give me an idea of how you like to ride it?

@Jeff/JFL: I'll tell you ahead of time that 50:50 is cruiser bike territory. Current examples of it include entry level 29er HTs in smaller sizes, on the compact end of the spectrum, and emtbs on the scaled up end of the spectrum. Enduro bikes are closer to 60:40 (more weight on the rear).

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2/7/2019 1:12 PM
Edited Date/Time: 2/7/2019 1:17 PM

ninjichor wrote:

@Big Bird, can I see picture of your bike with super short CS and a the longest front you got? And can you give me an idea of how you like to ride it?

@Jeff/JFL: I'll tell you ahead of time that 50:50 is cruiser bike territory. Current examples of it include entry level 29er HTs in smaller sizes, on the compact end of the spectrum, and emtbs on the scaled up end of the spectrum. Enduro bikes are closer to 60:40 (more weight on the rear).

https://dirtmountainbike.com/bike-reviews/homemade-bikes-big-bird.html

I didn't go quite as radical as some nowadays as I'd grown up on current L's, XL's, and it was a one shot deal. To pat myself on the back, it has a 62.5' HA and a 76' seat angle to make room for wheel travel. Both a bit ahead of their time.

And as to how I rode it. It was just my DH bike man. Fast and loose. High and low speed. Tech and flat out. For my 17 Questions, I'd say corner for the rest of my life instead of only air.

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2/7/2019 1:15 PM

HeatproofGenie wrote:

Great thread I'm definitely only looking at bikes with 443mm or greater CS for this seasons race bike. At 73" tall with an arm span of 75" I end up on longer bikes so I can have enough room and for stability but for sure when reach gets long it really undermines balance with 435ish CS bikes.

Another way to say it maybe is that the neutral zone is so small on an unbalanced bike so when reacting to terrain at speed it's really easy for that balance to get upset and then the rider has to react super quickly or lay on the brakes. As has been said that's fine if jibbing around but for a enduro race bike that is antithetical to the purpose.

Specialized Stumpjumper Evo is another candidate I think too. In S3 size, 475mm reach, 1252 WB, 443CS, 63.5 HA.

Was thinking of the L or XL Scott Ransom or L SB150 but both do not have the geo balance as nailed.

I rode a XL Spec Enduro 29 last year with 44mm offset fork and 50 mm stem and although it felt good at speed it did not have a big neutral zone and for sure my race results suffered as compared to two years ago on a short L SB5.5c. Trying to avoid investing a season on a bike that is compromised for racing.

The SB5.5 and SB6 have better numbers than either of the newer Yetis (130 & 150), as well as any bike released this year as far as I know.

Which is sad because Yeti used to be great about making balanced, neutral riding bikes. They've drunk the kool aid.

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2/7/2019 1:18 PM
Edited Date/Time: 2/7/2019 1:19 PM

ninjichor wrote:

@Big Bird, can I see picture of your bike with super short CS and a the longest front you got? And can you give me an idea of how you like to ride it?

@Jeff/JFL: I'll tell you ahead of time that 50:50 is cruiser bike territory. Current examples of it include entry level 29er HTs in smaller sizes, on the compact end of the spectrum, and emtbs on the scaled up end of the spectrum. Enduro bikes are closer to 60:40 (more weight on the rear).

I'm looking for bikes that sit close to the 1.7 FC:RC mark (or, a chainstay that is ~ 60% of the front-center). I haven't done the dual scale test to see what the weighting results are from that arrangement. I just know that bikes with that relationship have always felt faster in corners, predictable in chaos, and maneuverable with less body english than all the new, long front-end/short-cs bikes I have now.

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2/7/2019 1:23 PM
Edited Date/Time: 2/7/2019 1:31 PM

Big Bird wrote:

https://dirtmountainbike.com/bike-reviews/homemade-bikes-big-bird.html

I didn't go quite as radical as some nowadays as I'd grown up on current L's, XL's, and it was a one shot deal. To pat myself on the back, it has a 62.5' HA and a 76' seat angle to make room for wheel travel. Both a bit ahead of their time.

And as to how I rode it. It was just my DH bike man. Fast and loose. High and low speed. Tech and flat out. For my 17 Questions, I'd say corner for the rest of my life instead of only air.

I picture your DH bike being similar in CS and WB to Jerome Clementz's Jekyll (edit: med 27.5, which earned "bike of the year" recognition from pinkbike I believe). Differences include a slacker HA and shorter reach. You probably got more of an upright stance, compared to the tucked/aero one that racers use (vertical diamond config, rather than horizontal, if the shoulders, hip, feet, and hands were the 4 points).

I personally like that upright positioning. Seems more mtb, like you'd see in Vital's G-out photos, as opposed to the tucked aero position where people get their shoulders low and behind the bars.

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2/7/2019 1:45 PM
Edited Date/Time: 2/7/2019 1:55 PM

JLF1200 wrote:

I'm looking for bikes that sit close to the 1.7 FC:RC mark (or, a chainstay that is ~ 60% of the front-center). I haven't done the dual scale test to see what the weighting results are from that arrangement. I just know that bikes with that relationship have always felt faster in corners, predictable in chaos, and maneuverable with less body english than all the new, long front-end/short-cs bikes I have now.

That math scales absolutely horrendously. No wonder you are so prejudiced about long wheelbase bikes. I suggest another method.

May I suggest one that uses a fixed # to determine how forward the center point between the axles is in front of the BB? It scales decently, but doesn't account for suspension compression affecting the CS/WB:

(WB/2) - horizontal CS length

For this to work, you need to determine your target #. The larger the #, the more forward/aggro you are on the bike. The smaller the #, the more rearward/defensive you are on the bike. Modern bikes are increasing this number, by lengthening the front (forward geo), and also moving the seated position forward with longer reach and steeper STA.

I suggest you find a bike that you feel is dialed, out-of-the-saddle, and find its #. I found that 140-150mm FS bikes around 175-185mm were pretty nice, for someone of my height. I found that a 130mm HT around 155-165mm felt pretty nice. I imagine a Pole/Geometron-like bike, with even slacker front, more travel, and steeper STA, would maybe feel dialed with an even higher # (180-195?).

The issue with this formula is that it basically highlights the whole fixed CS length across sizes fiasco.

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2/7/2019 1:57 PM

ninjichor wrote:

I picture your DH bike being similar in CS and WB to Jerome Clementz's Jekyll (edit: med 27.5, which earned "bike of the year" recognition from pinkbike I believe). Differences include a slacker HA and shorter reach. You probably got more of an upright stance, compared to the tucked/aero one that racers use (vertical diamond config, rather than horizontal, if the shoulders, hip, feet, and hands were the 4 points).

I personally like that upright positioning. Seems more mtb, like you'd see in Vital's G-out photos, as opposed to the tucked aero position where people get their shoulders low and behind the bars.

I've actually thought recently of building the frame into more of a trail bike. A LONG dropper could get me to good pedaling geometry with the 76' SA, but I wouldn't trust any long travel fork to work with it's 1 1/8" head tube.

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2/7/2019 2:02 PM

JLF1200 wrote:

The SB5.5 and SB6 have better numbers than either of the newer Yetis (130 & 150), as well as any bike released this year as far as I know.

Which is sad because Yeti used to be great about making balanced, neutral riding bikes. They've drunk the kool aid.

While I agree that "balance" is important, I disagree that Yeti's old geometry was superior.

If we look at only balance, then a child's bike could have perfect balance, but seated climbing would be impossible and the rider would have to make rapid and frequent weight shifts to avoid going over the front or looping out. Balance and length are both important.

A short bike may have more potential for performance, but the skill and agility required from the rider may reach a point that's unrealistic. A longer bike - both front-centre and rear-centre - is less demanding of the rider. My last two bikes have been very long, with reaches over 500 mm and wheelbases closing in on 1300 mm for a 6' tall rider. As expected, climbing is easier and descending is so much more relaxed; the unexpected corollary is that some formerly exciting and/or sketchy sections of trail became a lot less involving.

The experience continues to evolve, though. With every new development that makes things easier - suspension, disc brakes, tire compounds, dropper posts, geometry - our riding adapts. Even the trails we choose to ride may evolve. I've learned to ride with a more forward stance and make "bigger" movements when I need to shift my weight - and to ride faster, thanks to the larger margin of error afforded to my mediocre skills. Longer chainstays could improve things further, but giving up front-centre length - especially reach - to restore balance isn't the right solution for me.

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2/7/2019 2:15 PM

ninjichor wrote:

That math scales absolutely horrendously. No wonder you are so prejudiced about long wheelbase bikes. I suggest another method.

May I suggest one that uses a fixed # to determine how forward the center point between the axles is in front of the BB? It scales decently, but doesn't account for suspension compression affecting the CS/WB:

(WB/2) - horizontal CS length

For this to work, you need to determine your target #. The larger the #, the more forward/aggro you are on the bike. The smaller the #, the more rearward/defensive you are on the bike. Modern bikes are increasing this number, by lengthening the front (forward geo), and also moving the seated position forward with longer reach and steeper STA.

I suggest you find a bike that you feel is dialed, out-of-the-saddle, and find its #. I found that 140-150mm FS bikes around 175-185mm were pretty nice, for someone of my height. I found that a 130mm HT around 155-165mm felt pretty nice. I imagine a Pole/Geometron-like bike, with even slacker front, more travel, and steeper STA, would maybe feel dialed with an even higher # (180-195?).

The issue with this formula is that it basically highlights the whole fixed CS length across sizes fiasco.

That's an interesting equation. Plugging some numbers in from different bikes I've ridden

'18 Enduro 29 XL189.5

Commencal Meta Power XL 177

Spec EVO S3 183

L Norco Range 29 175.5

L Yeti SB5.5C 160.5

As I stated above the large SB5.5 I had awhile ago was probably my fastest race bike I've been on and it has the lowest number. It did get a bit squirrelly at high speed though (1195 WB!)

So in a sense by dividing the WB you are arriving at the midpoint of the bike, then subtracting CS gives a somewhat arbitrary number that starts to gain some meaning after applying it to lots of bikes one has ridden.

I think that if it somehow incorporated HA it would have more meaning.

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2/7/2019 2:25 PM

ninjichor wrote:

@Big Bird, can I see picture of your bike with super short CS and a the longest front you got? And can you give me an idea of how you like to ride it?

@Jeff/JFL: I'll tell you ahead of time that 50:50 is cruiser bike territory. Current examples of it include entry level 29er HTs in smaller sizes, on the compact end of the spectrum, and emtbs on the scaled up end of the spectrum. Enduro bikes are closer to 60:40 (more weight on the rear).

This hasn't proven true for me at all on scales. There is actually a video from awhile back where Greg M and Marshy were dialing in his race bike with (gasp) really long CSs to try and get the bike to "handle right". He noted a 45/55 weight distribution being optimal, at least for Fort Bill, which is obviously not nearly as steep. I still want to aim for something north of 45%, at least with the method I'm using to measure. I rarely go over the bars. I often lose the front wheel. I often have to move my entire body forward to keep ample weight on the front tire. This is exhausting, especially when I'm trying to support all 200lbs of my weight on my front end with my hands.

50/50 may be cruiser bike territory/entry level bike territory, but there are a lot of things not accounted for there such as absolute length and head tube angle. Which is going to change things immenely.

Really, I need to try a lot of this before I can go a lot further, and let my subjective findings backed by objectivity (timing) and then we can worry about somehow explaining all this objectively. Right now all I've got is a theory, but not a ton of testing around it to prove it.

As far as what will my CSs look like? Ideally they'll be of the swiss cheese variety so I can play with a number of positions. It'll be a pain to get my brake mount to work, but I have a dirt bike inspired method.

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2/7/2019 2:32 PM

ninjichor wrote:

That math scales absolutely horrendously. No wonder you are so prejudiced about long wheelbase bikes. I suggest another method.

May I suggest one that uses a fixed # to determine how forward the center point between the axles is in front of the BB? It scales decently, but doesn't account for suspension compression affecting the CS/WB:

(WB/2) - horizontal CS length

For this to work, you need to determine your target #. The larger the #, the more forward/aggro you are on the bike. The smaller the #, the more rearward/defensive you are on the bike. Modern bikes are increasing this number, by lengthening the front (forward geo), and also moving the seated position forward with longer reach and steeper STA.

I suggest you find a bike that you feel is dialed, out-of-the-saddle, and find its #. I found that 140-150mm FS bikes around 175-185mm were pretty nice, for someone of my height. I found that a 130mm HT around 155-165mm felt pretty nice. I imagine a Pole/Geometron-like bike, with even slacker front, more travel, and steeper STA, would maybe feel dialed with an even higher # (180-195?).

The issue with this formula is that it basically highlights the whole fixed CS length across sizes fiasco.

I have given you some wrong impressions about my preferences.

No, I would *prefer* a very long bike with modern angles and lengthy reach. Just *not* at the expense of imbalance between front and rear. I would almost rather race on an older style geo (like the SB5.5) than a new style (like a Transition) simply because I know, from experience, that my riding becomes increasingly out of control as I fatigue on a bike like that.

The FC:RC ratio might scale poorly, I have no idea. I've only been looking for bikes that fit me, and I ride a medium, which means the common chainstay lengths are only a wee bit shorter than I would like them to be, whereas you guys are dealing with much more extreme imbalances on XL frames.

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2/7/2019 2:33 PM

@HeatproofGenie Thanks for trying it out. To me, it only helps determine how far my hips are "forced" behind the BB. I hate the strain of the "toiletbowl hover" position. I wanted more of a boxer's/fighter's position, hence I've been happy seeing the number increase.

It basically is the distance between the BB to this line:Photo

The problem is that the seated position also needs to be balanced according to the center point. This is why I'm opting to go as far as making the seated position the same as the standing position, in terms of "hip distance behind the BB", to get my desired standing position.

See here how a saddle needed to be slammed forward to balance out the seated position:
Photo

This Starling Murmur was named "easily top 2 favorite trail bikes" by Paul Aston of PB.

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2/7/2019 3:05 PM

jeff.brines wrote:

This hasn't proven true for me at all on scales. There is actually a video from awhile back where Greg M and Marshy were dialing in his race bike with (gasp) really long CSs to try and get the bike to "handle right". He noted a 45/55 weight distribution being optimal, at least for Fort Bill, which is obviously not nearly as steep. I still want to aim for something north of 45%, at least with the method I'm using to measure. I rarely go over the bars. I often lose the front wheel. I often have to move my entire body forward to keep ample weight on the front tire. This is exhausting, especially when I'm trying to support all 200lbs of my weight on my front end with my hands.

50/50 may be cruiser bike territory/entry level bike territory, but there are a lot of things not accounted for there such as absolute length and head tube angle. Which is going to change things immenely.

Really, I need to try a lot of this before I can go a lot further, and let my subjective findings backed by objectivity (timing) and then we can worry about somehow explaining all this objectively. Right now all I've got is a theory, but not a ton of testing around it to prove it.

As far as what will my CSs look like? Ideally they'll be of the swiss cheese variety so I can play with a number of positions. It'll be a pain to get my brake mount to work, but I have a dirt bike inspired method.

Doh, lost my reply when I tried to edit:

Measured my own bike with a casual standing position and it was 55:45 with more weight on the rear. If I sit down, it's 68:32. That's not the same standing position I use on the trail--I find that I plow and corner with a much more rearward stance, with my hips further behind the BB than my casual standing position.

Basically recorded the weights, added them up, then divided the rear by the sum to get the %, and confirmed with the front, even though I know I can subtract that from 100. What and how are you and Minnaar measuring?

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2/7/2019 5:31 PM

ninjichor wrote:

Doh, lost my reply when I tried to edit:

Measured my own bike with a casual standing position and it was 55:45 with more weight on the rear. If I sit down, it's 68:32. That's not the same standing position I use on the trail--I find that I plow and corner with a much more rearward stance, with my hips further behind the BB than my casual standing position.

Basically recorded the weights, added them up, then divided the rear by the sum to get the %, and confirmed with the front, even though I know I can subtract that from 100. What and how are you and Minnaar measuring?

Exactly. The lab / garage / shop / pit measurement is a poor analogy to riding. Differences include:

- Stance: neutral, turning, impact
- Slope of the trail
- Use of brakes
- Suspension compression
- Tire traction balance
- Rider strength, especially in the shoulders

Next, exactly what aspects of the ride are we trying to optimize? Any bike - from a cyclocross racer to a tandem - will feel fine when cruising on smooth, flat trails, so weight distribution isn't an end unto itself. Maybe someone's priorities are 50% on traction through loose, flat turns, since balance makes a huge difference there; 20% on slow, steep descents; 20% on fast, rough descents; and 10% on not looping out while climbing. That's a lot more than can be addressed by standing on a bike in your garage with a bathroom scale under each wheel.

Weight distribution and chainstay length are related - in varying degrees - to these handling behaviours, but weight distribution or some formula pertaining to front-centre and rear-centre lengths isn't a universal key to unlocking performance potential.

I'm glad we now have options for geometries that didn't exist a few years ago. Steep seat tube angles and long reaches suit me, but I can see how other riders wouldn't like it. Prioritization of handling on super steep terrain, a fondness for rear wheel carves, and enjoying quick manuals would favour long fronts and short rears. A preference for monster trucking through dusty, fast, wide open trails would favour long fronts and long rears. Vive le choice.

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2/7/2019 5:42 PM

"Prioritization of handling on super steep terrain, a fondness for rear wheel carves, and enjoying quick manuals would favour long fronts and short rears. A preference for monster trucking through dusty, fast, wide open trails would favour long fronts and long rears."

I think the claim "short chainstays suck" is intentionally hyperbolic. What actually sucks is the lack of options for bikes suited for the second use case you mention.

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2/7/2019 5:53 PM

Would it not be cool if such a casual standing position were the position you plowed and cornered in, if you could design geo to be balanced around it? Of course, you'd want to get your CoG lower, but the idea of not having to strain yourself to give proper weight to the wheel that needs it for traction, instead already being in that position more naturally?

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2/7/2019 6:03 PM
Edited Date/Time: 2/7/2019 6:05 PM

ninjichor wrote:

Would it not be cool if such a casual standing position were the position you plowed and cornered in, if you could design geo to be balanced around it? Of course, you'd want to get your CoG lower, but the idea of not having to strain yourself to give proper weight to the wheel that needs it for traction, instead already being in that position more naturally?

This has been recognized in other sports-- that you use quite a bit of mental energy propping yourself up in extreme stances that vary greatly from a "neutral athletic position." The team physiologists starting arguing about it a lot in pro road racing about 5-7 years ago. And the trade off between fighting with a defensive guard vs. naturally/hands down has been known in boxing forever.

I watch a lot of racing footage, and it has always struck me that the epic champions of gravity riding are almost boring to watch, in terms of how consistently neutral and balanced they are on their bikes (what their bikes are doing is not boring, however).

Steve points this out in his video, citing Sam Hill's uncanny stance on his bike while he's slashing turns and taking incredibly risky, off camber lines. But I see that in Minnaar, Gwin, and Loic as well. Their bodies are just locked in, they rarely leave that position. Not super leaned, never ape-hanging, like they're not working. I think it's an ideal to strive for in general.

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2/7/2019 6:34 PM

JLF1200 wrote:

"Prioritization of handling on super steep terrain, a fondness for rear wheel carves, and enjoying quick manuals would favour long fronts and short rears. A preference for monster trucking through dusty, fast, wide open trails would favour long fronts and long rears."

I think the claim "short chainstays suck" is intentionally hyperbolic. What actually sucks is the lack of options for bikes suited for the second use case you mention.

Yeah, that's fair. Progress is always made in a stepwise manner. We saw the need for long front-centres and steeper seat tube angles, so those were updated. The effect on weight distribution wasn't fully anticipated and we're making progress there, too.

Those who remember the early days of rear suspension on 29ers may recall chainstays initially being very long as designers were reluctant to overhaul the kinematics of their rear suspension designs, instead grafting a longer rear end onto a barely-changed front. At the time, wheelbase was a primary design parameter, so head angles and, sometimes, reaches were tightened to compensate for the long chainstays. My favourite example is the Giant Trance X 29, which may have had the most forward weight bias of the last quarter century.

Photo

Designs have rebounded and rear-centres shortened while front-centres lengthened. Perhaps things went a little too far, but rear-centres have been growing a little over the past few years. Not as fast as front-centres, but we'll get there.

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2/7/2019 6:36 PM
Edited Date/Time: 2/7/2019 7:05 PM

JLF1200 wrote:

"Prioritization of handling on super steep terrain, a fondness for rear wheel carves, and enjoying quick manuals would favour long fronts and short rears. A preference for monster trucking through dusty, fast, wide open trails would favour long fronts and long rears."

I think the claim "short chainstays suck" is intentionally hyperbolic. What actually sucks is the lack of options for bikes suited for the second use case you mention.

That's exactly my point. The whole "short chainstays suck" is a blanket crapshoot statement in terms of general body proportions/general preferences variance. Coming from a dirt jumping background, I like to steer my bikes from the hip, not follow whatever the front wheel does. Just pretend you have a laser pointer in your bellybutton and point the bike wherever it goes.

Plus the whole "I'm unable to do anything at warp speed unless my chainstays are 460mm or longer" argument conspires against a playful bike. Just try to manual those monstrosities with 500mm+ reach and 460mm+ chainstays, they'll give you a very stable/steamrolling bike, but also one unable to be thrown around/jumped as easily, unless your last name is Olajewon or Sasquatch.

Also, I believe you cannot leave the whole suspension system outside of the equation. A single pivot like my Orbea Rallon -or a Trek Remedy- will react differently to body input when compared to any dual-parallel/horst-link setup, and to a VPP-like system.

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2/7/2019 10:04 PM

“Coming from a dirt jumping background, I like to steer my bikes from the hip, not follow whatever the front wheel does. Just pretend you have a laser pointer in your bellybutton and point the bike wherever it goes. ”

Steering from the hips is more easily achieved when the front wheel isn’t pushing from lack of weighting. I’m not sure you understand why people hate short chainstays.

The guy who wrote the blogpost I linked to earlier titled “425mm Chainstays Still Suck” was a pro DH rider with a very long dirt jumping background. And his position on it is shared by the fastest local DH/enduro racer near me, also pro for many years, also with a long dirt jumping background.

“I’ll extend an olive branch here, and concede that 425mm chainstays can be fun in certain circumstances, like if you’re building a dirt jump bike, or you’re 5’4″, or you suck at riding, or some combination of the three. But if you’re riding somewhere above walking pace, and are at or above global average height, and we’re talking about a full suspension for trail riding, 425 chainstays suck.”

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2/7/2019 11:37 PM

And that's right for them to uphold, as it's what works for them. But wielding that argument blindly doesn't make it an universal solution. They are surely a lot -and I mean A LOT- faster than me, but I'm not racing anyone, not even Stravadorkius.

Like I wrote above, I still think you cannot leave the suspension system out of the equation. It ultimately dictates how your own mass fluctuates over the bike, and since we are talking about mere millimeters of variation in front/rear center ratios, it certainly affects the outcome in a significant way.

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2/8/2019 5:58 AM

Sigh.

Before anyone comments further PLEASE watch the Vorsprung video. If you don't spend the 10 minutes there we'll basically be debating the color of the sky, or similar.

I did put a * on the title for a reason. Short chainstays do suck. But only on longer bikes that are intended for racing.

If you are looking for the best dirt jump, 4x, BMX, park bike, road bike, townie bike, fixed gear bike this may not apply.

I'm 100% after the best handling bike for those that prefer a longer reach **when standing**. This is my goal. This is why I started this thread. I'm not worried about seated weight distribution, how hard a bike is to manual, how easy I can cutty etc. Moreover, I've ridden bikes with 18" chainstays and am positive I can do all those things. Just takes a little practice. I want this thing to allow me to stay right in the middle of the bike, using my legs (not my hands) to drive the bike all the while keeping weight on the front tire.

Vorprung articulated it with more math than I have, they confirmed my hypothesis 100%. I'll start playing with this, and I'll see if it makes me faster, allows me to ride with less fatigue and makes bike riding more fun. I'm betting it does.

The further I get into moto and the longer I keep riding bikes I realize "moto had it right all along" (almost started another thread with that title). From suspension to weight distribution to how durable shit is. In this case, moto allows the rider to vary their "chainstays" (rear center) with a horizontal dropout. I know, they do this for chain tension, but it is a handling thing as well. I'd love it if mountain bike manufacturers (even just one or two) brought back adjustable chainstay length. Sure your travel changes too, and your damper may need more air in it - whatever. You can get your bike to handle just how you want.

More to my point, motorcycle engineers have spent decades getting the weight distribution *just* right for the best handling. Go geek out on some moto sites and you'll see those guys are making changes in the mms and even your intermediate riders notice a difference (as opposed to CMs on a mountain bike). I know, we're talking a machine that weighs as much as the rider (or more) but the point I'm getting at is distribution between the front and back tire is HUGE.

I found it interesting I can ride a 250 two stroke for a lot longer with no arm pump compared to descending on my mountain bike. The reason is I'm in the middle of the bike. I'm riding with my legs. I don't have to consciously hold my body up with my arms to keep weight on the front tire. Funny enough, a lot of my shorter friends on more balanced size medium bikes get to ride their mountain bike this way. (again, watch the video)

To those suggesting suspension, braking, angle of the ground etc play into this, OF COURSE it does. That's a no brainer. This is why I said real time data acquisition would be the best way to figure all this out, but that isn't happening.

Before we start playing with all those other variables, you first have to get your static weight distribution close to "ideal". What is this number? Verdict is still out!

I feel a lot of riders are tuning suspension, tire pressure, stem length & bar height to try and "tune around" the elephant in the room. I know I have. I'm trying like hell to get weight on the front tire without requiring my entire body to shift an uncomfortable amount forward.

...oh and if you want some proof (in the racing form) when Greg Minnaar started growing his rear center he started winning again. He even looked quieter on the bike.

I know this will work.

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2/8/2019 6:09 AM

Great to see this thread back in action!

I would like to throw something else into it.
Wow does the option of a non telescopic fork change this discussion?
A 29" linkage fork with, lets say 60mm offset but 40mm OS when in SAG and 28mm OS at 70% of its travel (max.163mm) I will try it (hopefully this year) but would love to hear your thoughts about it.

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2/8/2019 6:50 AM

Thomsen wrote:

Great to see this thread back in action!

I would like to throw something else into it.
Wow does the option of a non telescopic fork change this discussion?
A 29" linkage fork with, lets say 60mm offset but 40mm OS when in SAG and 28mm OS at 70% of its travel (max.163mm) I will try it (hopefully this year) but would love to hear your thoughts about it.

It would change things for sure.

However, I'd lump that into the "lets worry about it later" category. Mostly because I don't see linkage forks being the bestest thing ever like many are expecting.

...again, at this point, I just look at moto and go "what did they do"? If mountain bike is headed that direction, I expect it to stick. If its running a different direction, I don't bet on it wink

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2/8/2019 7:21 AM

Man I just look at what my hero is doing on his bike and copy that shit. So much less maths to nerd on though with forum fast numbers and lines to extrapolate

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2/8/2019 8:17 AM

Splayleg wrote:

Man I just look at what my hero is doing on his bike and copy that shit. So much less maths to nerd on though with forum fast numbers and lines to extrapolate

Haha

If it were only that easy.

Photo

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2/8/2019 8:32 AM
Edited Date/Time: 2/8/2019 8:33 AM

He's on a medium bike so 435mm reach and 435 mm CS. On 27.5 wheels.

I bet that bike is pretty balanced whistling

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2/8/2019 9:29 AM

HeatproofGenie wrote:

He's on a medium bike so 435mm reach and 435 mm CS. On 27.5 wheels.

I bet that bike is pretty balanced whistling

Yes, so much so that the Vorpsrung video calls his bike (and riding style) out specifically. I know people like to point out that Sam is a freak, but that is painfully obvious and doesn't actually negate the point. He's constantly riding off camber lines that aren't even lines at all, and he's doing it with body positioning that looks about like me riding to the corner store for beer on my townie.

Is that because of his long stays? No, of course not. It's the reverse causal relationship: that bike was developed under him. The long stays are there because Sam wanted it so. And that, I think, is no coincidence.

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2/8/2019 3:06 PM
Edited Date/Time: 2/8/2019 3:16 PM

@jeff.brines If Vorsprung confirmed your hypothesis 100%, why aren't you confident enough to put money down on it yourself and get a bike based off of it? What do you need from us, if not to be contrary or double check? I've already pretty said Steve's math is bunk, since the ratio for a mid-wheelbase bike can't be used to judge short wheelbase bikes or longer wheelbase bikes without questioning, lacking the ability to scale. Also, the conclusions he makes in that video are very questionable. The way Leo responded to him in the comments was quite telling that Steve's not accounting for many variables, jumping to such conclusions. The only real thing I agreed with out of that entire video is that making CS proportional to the WB, to tune the fore-aft balance, was important.

If you're after speed and handling out of the saddle, there's far more to worry about than fore-aft balance, especially if you want to get closer to world cup elite level. Being caught up in CS to FC is akin to being caught up in anti-squat and anti-rise. Do you even know how good your understanding is? Attempt to design your own FS bike and put reason behind all your decisions. BikeCAD and bikechecker are good places to start.

Elite WC pros know there's perfect form for specific bikes. The know how it should feel, in order to compete at the highest level, and train/practice to improve consistency. They're highly reluctant to change bikes, since they feel the training the did to *adapt to the bike* would possibly not cross over to the new bike, requiring new adaptation, and they weren't willing to take that compromise on the track if it wouldn't pay off in a consistently better result. In cases where they did switch to a new bike, perhaps it felt more natural to them, and the adaptation period was more about finding the nuances of the bike, of where it created opportunities and what trade-offs were made, to get the most out of it and cover for its shortcomings.

The disagreements, contradictions, and exceptions in this thread should not be ignored. With perfect knowledge, all of these perspectives should be explainable without contradiction, if they weren't pure BS made in defense, but honest. Is the SB55 better or not, compared to the SB150/130? I could investigate the perspectives, that the SB55 in question is ridden by a tall rider and the CS-WB relationship (to simplify from saying RC:FC ratio), resulted in a fore-aft balance that they preferred over the XL SB150, which they may think needs a longer CS. Those that think the SB150 is better, might be thinking all the other bits are improved except for CS-WB proportions, unless that rider is short and can ride the size Med.

I like the idea of having adjustable CS length. I question, what's the downsides of a sliding dropout for an "enduro" bike? Another source for creaks? Would be a win-win if bike brands did this, rather than keep CS length constant across the size range, since it would reduce the need for multiple jigs/molds for different length rear triangles, and we get adjustability for personal preference, on top of longer CS for taller riders and shorter CS for shorter riders for the same bike model.


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2/8/2019 3:23 PM
Edited Date/Time: 2/8/2019 3:27 PM

ninjichor wrote:

@jeff.brines If Vorsprung confirmed your hypothesis 100%, why aren't you confident enough to put money down on it yourself and get a bike based off of it? What do you need from us, if not to be contrary or double check? I've already pretty said Steve's math is bunk, since the ratio for a mid-wheelbase bike can't be used to judge short wheelbase bikes or longer wheelbase bikes without questioning, lacking the ability to scale. Also, the conclusions he makes in that video are very questionable. The way Leo responded to him in the comments was quite telling that Steve's not accounting for many variables, jumping to such conclusions. The only real thing I agreed with out of that entire video is that making CS proportional to the WB, to tune the fore-aft balance, was important.

If you're after speed and handling out of the saddle, there's far more to worry about than fore-aft balance, especially if you want to get closer to world cup elite level. Being caught up in CS to FC is akin to being caught up in anti-squat and anti-rise. Do you even know how good your understanding is? Attempt to design your own FS bike and put reason behind all your decisions. BikeCAD and bikechecker are good places to start.

Elite WC pros know there's perfect form for specific bikes. The know how it should feel, in order to compete at the highest level, and train/practice to improve consistency. They're highly reluctant to change bikes, since they feel the training the did to *adapt to the bike* would possibly not cross over to the new bike, requiring new adaptation, and they weren't willing to take that compromise on the track if it wouldn't pay off in a consistently better result. In cases where they did switch to a new bike, perhaps it felt more natural to them, and the adaptation period was more about finding the nuances of the bike, of where it created opportunities and what trade-offs were made, to get the most out of it and cover for its shortcomings.

The disagreements, contradictions, and exceptions in this thread should not be ignored. With perfect knowledge, all of these perspectives should be explainable without contradiction, if they weren't pure BS made in defense, but honest. Is the SB55 better or not, compared to the SB150/130? I could investigate the perspectives, that the SB55 in question is ridden by a tall rider and the CS-WB relationship (to simplify from saying RC:FC ratio), resulted in a fore-aft balance that they preferred over the XL SB150, which they may think needs a longer CS. Those that think the SB150 is better, might be thinking all the other bits are improved except for CS-WB proportions, unless that rider is short and can ride the size Med.

I like the idea of having adjustable CS length. I question, what's the downsides of a sliding dropout for an "enduro" bike? Another source for creaks? Would be a win-win if bike brands did this, rather than keep CS length constant across the size range, since it would reduce the need for multiple jigs/molds for different length rear triangles, and we get adjustability for personal preference, on top of longer CS for taller riders and shorter CS for shorter riders for the same bike model.


1) I posted this thread years ago. Way before that video came out as a way to say "hey, this is what I'm finding".

2) I literally can't buy a bike that has the proportions I want. I already noted my solution (build my own seatstay).

3) I was chiming in here because I found that video to be very helpful, and someone else did resurrect this thread.

4) I'm in a unique position that I have tested a lot of bikes. I also ride more than most. Not saying that as some form of dick waving, but rather to suggest I get to really suss bikes out beyond the point of a few rides. This is what started me down the path of "longer reach needs longer chainstays".

5) Nowhere did I say I was going to design my own FS bike. I was asking for bike designers to make their chainstays in proportion to reach. So far as I know, no brand is utilizing data acquisition across a size run to see how leaving rear center static effects the bike. Cause it does...

6) You are assuming a lot more about the way a bicycle manufacturer works than I think you should. There are guys who are super talented and could literally ride a washing machine with wheels. Then there are guys that can tell 1mm of reach change (Greg). As I indicated elsewhere, a LOT of what I've typed here started with my realization that Greg's awesome season on a V10 was with 18.3 (?) inch chainstays. Yeah. He was one of the only guys that had his rear center grow in proportion to his front center. Guess what? It looks like he never moves on the bike. Yeah, he's one of the best ever, but I'd like to suggest getting your bike setup right is a big deal - which is the point of this thread.

7) Not sure what you are getting at with the whole Yeti thing. The only real way to know if this works is to have the same bike, same rider, same suspension, same everything and vary the rear end length. See what lap times do.

8) Adjustable CSs would be possible but the big issue is changing the leverage rate on the damper. This is why companies are reluctant. That, and it creates more complexity than they want to deal with it. But if they could show it works, and if some company could built a bike fit system around it (and other variables) It'd 100% be something companies start doing simply because a bike that fits you better is a bike you'll ride better.

9) (Okay so this should have been #1) - aren't you also contradicting yourself with respect to the whole vorrsprung thing? His over arching point is proportions matter. The math is'nt "bunk". Of course it could be more comprehensive, but even in this simple form it works to articulate a theory (that you yourself acknowledged!) There are two videos, and one explains a lot of why longer wheel bases have a positive effect on the rider.

I made my point. I believe it. I want rear center to be proportional to front center and I'd like to objectively figure out what this means.

I'm doing so in part to ask the industry to pay attention to this stuff, partially to ask what others have found, partially to ask what's out there that I might have missed and partially to say "fuck it I'm going to make my own iteration of this".

We've spent so long focusing on suspension, carbon this or that, giant wheels or small wheels all the while ignoring exactly how a rider interacts with both wheels in a standing position. Its been guess work. I've seen 100x the math into how a new suspension design works, and next to none around how a geometry will effect a rider with real numbers. This is what I'd like to see changed and this is what I'm trying to do.

Saying "the pros (either engineers or rider know best so stop trying" is silly. There are plenty of guys like me who have done this for awhile (longer than I haven't) and happily contribute where they see a place to do so. This is me doing that.


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