[TrumbullHucker]

pivots, shimz, and links

 

[Bikael Molton]

I was in Whistler for 6 days at the start of July, I feel like my buddy's 4 yo Totem was the only long travel single crown fork I saw on the trails.

 

[no skid marks]

wat

What I'm saying is pretty straight forward, a rearward axle path bike will make most people faster by the bottom of the hill. The pros outweigh the cons. You're not going to fall over the front wheel or skid out uncontrollably by the rear wheel moving backward an inch overall. Low pivot bike manufacturers neglect to mention a higher pivot will provide better square edge hit compliance and offer more stability. You can provide the best damping and leverage curve you want, it still won't give you as much square edge bump absorption and will have some compromises compared to a bike with more rearward axle path.

Lets not derail this thread anymore. Keep it on the Kona.
Is the Kona Pivot below a 34t chain rings chain line?

 

[Udi]

Doesn't take many runs for your subconscious to put your body weight further back to cater to any minute shift in COG.
Traction is best when the rear wheel is on the ground more, something more rearward axle path allows, with your theorizing, they also better front wheel traction.

You're missing the point, the key issue is large variations in mass distribution and thus normal forces, thus friction (traction) forces. In the case of DH racing in particular (as well as the increasing tendency towards steeper tracks), the last thing you want is forward shifts in COM under travel use. It literally means that as travel use increases, the rider is pitched in the direction of going over the bars.

"Better front wheel traction" is a far smaller concern given high normal forces at the front wheel in DH, and there is no need for "wheel base lengthening when bottomed out". Modern static WB lengths are huge these days anyway (~47" M, ~48" L) so if anything they should be capped.

The far greater concern, especially at or near the limits of traction, is increasing predictability. If you are maintaining a drift on a bike that has 60mm of axle path variation, when the rear wheel hits a bump, you are suddenly changing the friction force at the rear tire substantially - all while trying to maintain a drift.

I'm not saying this number needs to be 0mm either, but the point you miss is that as you increase this number, you make some things worse while you make some things better. If that wasn't the case, why don't we just build DH bikes with 100mm of rearwards travel?

As for subconscious compensation for instabilities, I think the goal of a frame designer should be to minimise this - because as per the example I gave, each time the rider has to compensate for a drop in predictability, the bike becomes more difficult to ride at the limit of traction. This means you either have to ride slower, or run a greater risk of crashing.

I do agree on the Stab however - great bike, and I think the pivot was in a pretty good place. For interest's sake, I think the GT I-drive concept was an interesting attempt at solving the rearward axle path / large COM change issue . Definitely left a lot to be desired in many other areas, but from a traction and mass distribution standpoint I think a design like this is superior to Zerode/Canfield/etc that ignore the issue and/or try to compensate with very short static CS lengths. Unfortunately a short static CS doesn't change the fact that the dynamic variation is very large - thus at any given time your feet (and thus largest percentage of vehicle mass) could be 16" or 18" from the rear wheel!

You're not going to fall over the front wheel or skid out uncontrollably by the rear wheel moving backward an inch overall.

Actually, if you're at the limit of traction or the limit of forward weight bias, this is exactly what is going to happen. Of course you can compensate for it - by going slower.

 

[blindboxx2334]

UdiJesus has spoken again.

 

[no skid marks]

You're missing the pointNo I feel you're exaggerating a point and missing other more important points., the key issue is largeIt isn't large. variations in mass distribution and thus normal forces, thus friction (traction) forces. In the case of DH racing in particular (as well as the increasing tendency towards steeper tracks), the last thing you want is forward shifts in COM under travel use.Exactly, so not having the rear wheel get deflected upwards over a bump(steeper, the more bumps generally) is quite critical. It literally means that as travel use increases, the rider is pitched in the direction of going over the bars. Hitting a bump will lift the back wheel on a low pivot bike, or absorb it on a high pivot bike. Add this to a cornering situation and I know what I think is least likely to cause a loss of traction or OTB crash.
"Better front wheel traction" is a far smaller concern given high normal forces at the front wheel in DHSo there's plenty of room to move the riders weight back with negligible effect on front traction., and there is no need for"wheel base lengthening when bottomed out"Nonsense, a more stable bike when bottomed is beneficial, you don't need a short wheel base when bottoming out.. Modern static WB lengths are huge these days anyway (~47" M, ~48" L) so if anything they should be capped.Talking on the minutely trivial scale of things as you are, The lessening stability of a low pivot bike is still felt and has effects.
The far greater concern, especially at or near the limits of traction, is increasing predictabilityAgain, bike not bucking the back wheel up unsettling geo and COM, makes for a more predictable ride.. If you are maintaining a drift on a bike that has 60mm of axle path variation, when the rear wheel hits a bump, you are suddenly changing the friction force at the rear tire substantiallyNot by 60mm - all while trying to maintain a drift. and so is the wheel skipping into the air on a low pivot bike. A bump will lengthen the rear more on a high pivot bike, but the tyre will be on the ground more while hitting bumps. While using the brakes without a floater, you can set up the suspension and traction quite well on a Zerode and feel the rear tyre. I know my long wheelbase ute feels very predictable to drift compared to a short wheel based car. On a scale of relativity, you aren't maintaining a drift at the limit of traction on bumpy ground very often anyway.
I'm not saying this number needs to be 0mm either, but the point you miss is that as you increase this number, you make some things worse while you make some things betterEverything is a balance of compromise, a rearward axle path on a DH bike will result in faster times for most. This is the goal no?. If that wasn't the case, why don't we just build DH bikes with 100mm of rearwards travel?Wheelbase consistency would be the main reason. As well as everything else you're saying, but in moderation.
As for subconscious compensation for instabilities, I think the goal of a frame designer should be to minimise this Your brain works out where to put your weight on any bike. The only difference is changing from one bike to another, but your brain has to adjust to other equally important differences with any two bikes anyway. Keep it in perspective, it's a tiny difference.- because as per the example I gave, each time the rider has to compensate for a drop in predictability, the bike becomes more difficult to ride at the limit of traction. There is no drop in predictability, and there is far more confidence offered by predictability in rock gardens, of drops and jumps etc.This means you either have to ride slower, or run a greater risk of crashing.Not at all, quite the opposite. Most people gain far more confidence after one run on a Zerode.
I do agree on the Stab however - great bike, and I think the pivot was in a pretty good place. For interest's sake, I think the GT I-drive concept was an interesting attempt at solving the rearward axle path / large COM change issueHow so compared to any other rearward axle path bike? . Definitely left a lot to be desired in many other areasYes shame they didn't update their geo to suit current trends as their design was a few years old at least by the time of release., but from a traction and mass distribution standpoint I think a design like this is superior to Zerode/Canfield/etc that ignore the issue and/or try to compensate with very short static CS lengths. Unfortunately a short static CS doesn't change the fact that the dynamic variation is very large - thus at any given time your feet (and thus largest percentage of vehicle mass) could be 16" or 18" from the rear wheel!Canfield and Zerode have quite different chain stay lengths. Neither jump 2" spontaneously. It's quite obvious as you've just hit a big rock or whatever, and you know to get weight back.
A touch more finesse with the rear brake on off camber corners, is a small price to pay for the added confidence and speed achieved everywhere else on a DH track.
Actually, if you're at the limit of traction or the limit of forward weight bias, this is exactly what is going to happen. Of course you can compensate for it - by going slower.You will be less likely to go OTB as the back end isn't getting airborne as easy off bumps. If you're already at the limit of going OTBs, the rear wheel getting airborne on a low pivot bike is going to send you over easier.

Rearward axle path will provide more confidence and higher speeds for most, you have mentioned a small generally easily compensated for negative point, that is easily outweighed by the many benefits.
The points you make may have validity UDI, there relevance is misguided though.

 

[Sandwich]

What I'm saying is pretty straight forward,

yeah, and I disagree with almost every part of it, and almost all of it is counter to current, cutting edge suspension design for bikes. There are almost no high pivot bikes on the podium on the world cup circuit.

You use the analogy of drifting a truck vs. a small car...that's the point that Udi is saying, picture starting a drift in a small car, then having the wheelbase extend to the point that you were driving a truck by the end of the turn. Things are going to get uncontrollable.

As for people being faster...yeah sure, joe hucksalot is going to really pin it through the rock garden, but at the highest level it very clearly doesn't matter. Having a good handling bike is far more critical, and finding the right compromise between pedaling characteristics, handling, and bump absorption is key. Hell, the top two racers are on what is effectively a low pivot bike, there's a mid-single pivot, and a low pivot URT up there too. That's why I think this bike would be better with a higher pivot, but I question whether it needs to be sky high either.

 

[Samoto]

You use the analogy of drifting a truck vs. a small car...that's the point that Udi is saying, picture starting a drift in a small car, then having the wheelbase extend to the point that you were driving a truck by the end of the turn. Things are going to get uncontrollable.

That part I understood and I re-read Udi's post. It makes sense. It is not hard to understand that by changing wheelbase, it loses traction.

As rider, I want to see consistency whether smooth drift or going through rockgarden, at least i know how much the bike can turn so I predict a fast enter and exit the turn. With extended wheelbase, it is confusing and adds more variations. Subconscious compensation? BS. There are many things to deal in riding FAST (at WC level). Give decent and predictable linkage then sort out the rest like shock parameters (absorption, traction).

Cars are not that hard to drive because their wheels are not moving forth and back

 

[no skid marks]

yeah, and I disagree with almost every part of it, and almost all of it is counter to current, cutting edge suspension design for bikes. There are almost no high pivot bikes on the podium on the world cup circuit.The World Cup circuit is hardly a fair judge as ALL top riders are sponsored. Zerodes have done well for where they are, same with Canfield at Red Bull Rampage. Relatively speaking though, lots of smaller class riders unsponsored riders are doing better on high pivot bikes.

You use the analogy of drifting a truck vs. a small carIt was a bit of a joke...that's the point that Udi is saying, picture starting a drift in a small car, then having the wheelbase extend to the point that you were driving a truck by the end of the turn. Things are going to get uncontrollable.
You'd actually have more feel and control, but it is virtually irrelevant to bikes.
As for people being faster...yeah sure, joe hucksalot is going to really pin it through the rock garden, but at the highest level it very clearly doesn't matter. Who here is at the highest level? Are we talking about bikes for .00001% of riders or the other 99+%? Having a good handling bike is far more criticalHigh Pivot bikes are good handling bikes. UDI is focusing on 1% of the time where there's a minute possible negative., and finding the right compromise between pedaling characteristics, handling, and bump absorption is key. Hell, the top two racers are on what is effectively a low pivot bike, there's a mid-single pivot, and a low pivot URT up there too. That's why I think this bike would be better with a higher pivot, but I question whether it needs to be sky high either.

That part I understood and I re-read Udi's post. It makes sense. It is not hard to understand that by changing wheelbase, it loses traction. Yes in theory, but in practice it doesn't just flick a switch and gain 2" all at once.

As rider, I want to see consistency whether smooth drift or going through rockgarden, at least i know how much the bike can turn so I predict a fast enterHigh pivot will absorb stutter bumps etc better. and exit the turnHigh pivot will power out of turn.. With extended wheelbase, it is confusing and adds more variations.It adds stability. That's pretty predictable. Subconscious compensation? BS. There are many things to deal in riding FAST (at WC level). Give decent and predictable linkage then sort out the rest like shock parameters (absorption, traction).

Cars are not that hard to drive because their wheels are not moving forth and back

My point is just about the scale of relativity. There are not many off camber corners, if they have bumps the wheel of a high pivot bike will be on the ground more, and it's other benefits will more than make up for any possible time lost in a few off camber corners. Most riders won't handle a bike skipping over everything instead of the suspension absorbing it. World cup riders are at a different level in this regard. That's not to say they'd not benefit from a higher pivot point.
I see lots of low/mid pivot bikes aren't even being used with the correct size chain ring they're designed around. I'm not sure how much effect this would have on anti squat, but there'd be some.
There's pros and cons to everything, it's best to keep them in correct scale of relevance when discussing them.
Watch what's happening to WC riders back wheels, then tell me less bouncing or being slowed by obstacles wouldn't benefit them more than a possible difference in feel on off camber corners. Gwin may have not even flatted with more rearward axle path protecting his tyre.