"Acceleration" over bumps
- Thread starter Viv92
- Start date
No, it just may feel like it because most bikes slow down so significantly when going through a rock garden, when hopping on something like a Lahar or a BMW with all very rearward travel, you slow down a lot less.
The difference is a heck of a lot less than you might think. People seem to think that somehow a super high single pivot is some sort of magical thing that is going to help your suspension absorb bumps some incredible amount better. It's just not true. When you actually calculate forces in the suspension, most current suspensions are so close to each other that the difference is less than a couple percent. Most riders forget that the wheel is part of your suspension system. Your wheel is in essence a big lever that manipulates your swingarm. The wheel acts somewhat like a cam, and the action of your wheel levering your suspension over a bump really makes the reality of how suspensions absorb bumps a lot different than most riders envision suspensions functioning. Leverage rate, shock setup, and anti-squat all have huge impacts on suspension performance as compared to how rearward or not your axle path is.
Sure, as long as your freewheel is not overrunning, which is commonly the case (like 99.9% of the time) when you are on a descent.
A person on a bike can speed up by pumping over bumps, but the question you posed is with regard to the slight movement of the chain due to "chain stretch" during compression of the rear suspension, right?
My buddy has asked me this question a few times, and I don't see it.
A bike won't speed up as a result of hitting a bump. There is no new energy being added to the equation. Any force on the chain is indirectly a result of the kinetic energy the bike and rider already have. The impact can only impede forward movement.
Assuming the best case scenario:
-The cranks are fixed
-The suspension design makes for lots of chain stretch
-The bike is in a very high gear
-Backlash is negligible
The result of this is the suspension being prevented from compressing.
This is all moot though. The effect is so minimal that during normal riding the freewheel is always overrunning. Here's a good way to see how small the effect is. Take a bike with lots of chain stretch to a parking lot and, from a dead stop, try to move yourself just by holding the cranks still and compressing the suspension.
My buddy has asked me this question a few times, and I don't see it.
A bike won't speed up as a result of hitting a bump. There is no new energy being added to the equation. Any force on the chain is indirectly a result of the kinetic energy the bike and rider already have. The impact can only impede forward movement.
Assuming the best case scenario:
-The cranks are fixed
-The suspension design makes for lots of chain stretch
-The bike is in a very high gear
-Backlash is negligible
The result of this is the suspension being prevented from compressing.
This is all moot though. The effect is so minimal that during normal riding the freewheel is always overrunning. Here's a good way to see how small the effect is. Take a bike with lots of chain stretch to a parking lot and, from a dead stop, try to move yourself just by holding the cranks still and compressing the suspension.
it might not be a big difference on paper, but it is certainly tangible on the bike, yes. pretty neat, the relative 'lack of hanging up' does feel like acceleration through the big square edged hooky stuff.
I've spent a lot of time years ago comparing a BB7 vs an FSR bike, timed, with data aquisition, and regardless of what you "think" you are feeling, the difference is negligible.
Just like people feel like they are faster on a 500CC 2 stroke MX bike, then compare their times to their 125 and find out they lapped slower on the big bike. In many, MANY cases, perception is not reality. This is why we have stopwatches and data acquisition to analyze suspension.
dw, that mention of the rear wheel being both a lever and a cam is helpful for me to understand suspension dynamics. thanks for that. and thanks also for stating the point that perception often doesn't match reality, that's a point I try to make with people in many subjects of discussion. people often perceive what they want to perceive. this is why pharma tests run placebos.
Still if you feel the bike rides faster and it makes you more comfortable/confident with the bike the placebo may make you go faster
true. seat of the pants 'faster' does not always equate to significant time savings. just a perceptual observation for what it's worth. if you've got good geometry & properly tuned dampers, suspension platform probably doesn't make a huge difference (though it's amusing to squabble about); the guy on the bike is obviously the biggest factor.
DW-
When you performed the instrumented testing did you include the rider in your measurements or did you only instrument the bikes? It would be interesting to compare the movement of the rider on various bikes but I would expect it to be difficult to filter the signal appropriately. Little differences in feel make big differences in confidence on a bike, probably more so at the experienced amatuer level than the pro level.
When you performed the instrumented testing did you include the rider in your measurements or did you only instrument the bikes? It would be interesting to compare the movement of the rider on various bikes but I would expect it to be difficult to filter the signal appropriately. Little differences in feel make big differences in confidence on a bike, probably more so at the experienced amatuer level than the pro level.
Hmm ineresting, how was this data aquistion carried out?
I find that I can hardly ride through some parts of a local track on a certain FSR bike compered to a rearward/hi pivot bike, having to slow down due to a bike not holding it's line(it's the bikes fault to mine:biggrin
does "feel" a lot slower to me, maybe I'm missing something?there's lots of other things to go on about but yeah that is all for now.
It does "feel" faster. If post-enlightenment European philosophy has taught us anything it is that perception and reality can at times be disconnected. The proprioceptive responses of our central nervous system are highly advanced, but not in any sort of way that reliably notices changes in velocity.
Favorite post in days.
yeah, for sure! that's more important in the long run for getting faster -- being confident, being comfortable. I'd eat any placebo that helped me relax and feel more confident when things get hairy!Still if you feel the bike rides faster and it makes you more comfortable/confident with the bike the placebo may make you go faster
I try not to eat anything too hairy
What are the opinions on the canfield jedi not slowing down with the 2.5 inches of rearward travel, scientifically it "Shouldn't" slow down nearly as much and (at least to me) it feels as if it doesn't slow down at all, but im very curios about the science behind it.
I don't think a super high pivot does much, but an axle path that is lightly rearward vectored for most of it's path (lapierre dh920) will have more ease at transfering the potential energy of the bike+rider to the shock than to the bump. It may not be much, but it is definitly noticeble to me in both feel (which is by far the most important to me) as well as speed.
I've ridden a Demo 9 that has quite a forward path past sag and my cove is definitely faster over a long downhill rock garden one one of our regular runs.
dilzy, one of the things I think of when I read that statement is, "isn't he really saying that he's faster on the Cove?"
I don't see how the bike is faster, I don't know how it can be, unless you can let the Demo and Cove ghost-ride from the same start position and same start speed.
am I making sense? I'm saying it sounds like you are more comfortable in the rocks on the Cove, and that means you're faster in the rocks on the Cove.
Wow, total topic shift. Anyone with thoughts on the dynamics of thread derailment?
If I run lots of LSC and not much HSC I feel like my bike is faster through the rough stuff. If I run lots of HSC and not much LSC my bike feels like it hangs up more in the rough.
Yeah I see what your saying, It's a bit of a dodge test, but I remember following a mate on that demo going down at the same speed not pedalling and I caught right up to him by the end. He said he didn't use any brakes.
to get some proper results from a test like this you would need identical bike builds ( so weight and suspension performance would be the same. the same distance between ground and handlebars, ground vs pedals so that the weight distribution is the same ) geometry, tire pressures , suspension set up, riders (same weight, riding style, skill level). they would have to be riding exactly the same line, and even than differences in weight shifts/distributions over obstacles or in the corners would mess it up... all in all... nearly impossible.
I disagree, the vestibular apparatus of the inner ear allow us to balance by accurately measuring changes in the direction of the acceleration due to gravity. In addition, any change in velocity is an acceleration which results in forces tangible to the entire body. While I concede that a person's sense of time is not accurate enough to judge the speed of an entire race run, it is possible that for small sections of terrain a rider may accurately deduce, if given a direct comparison, the faster of two velocipedes.
I thought any acceleration in rough stuff was dew to rider input. The bike has very little to do with this. At the end of the day, they all are doing almost the same thing as DW said. It is all in rider feed back, to the bike. That feed back may be greatly be influenced by the feel that a rider gets from the bike. Hence why the debates rage, over why one bike feels faster. Over another for one person, on a style on terrain and setup. We all play by the same rules. We just read them differently.
Just to make sure that my point isn't taken out of context, let me reiterate the important parts.
There are other factors in a suspension design (wheel diameter, wheel rate/ leverage rate, shock setup) that have a much larger effect on a suspension's ability to absorb bumps than the rearwardness of your suspension travel. You could have the most rearward axle path in the world, but if your suspension isn't engineered to work properly with your damper, then it's not going to matter. This doesn't even get into the fact that too rearward of an axle path is detrimental to cornering. I've written a lot about this in detail in the past on this board, I'm sure someone could dig it up if they were interested.
There are other factors in a suspension design (wheel diameter, wheel rate/ leverage rate, shock setup) that have a much larger effect on a suspension's ability to absorb bumps than the rearwardness of your suspension travel. You could have the most rearward axle path in the world, but if your suspension isn't engineered to work properly with your damper, then it's not going to matter. This doesn't even get into the fact that too rearward of an axle path is detrimental to cornering. I've written a lot about this in detail in the past on this board, I'm sure someone could dig it up if they were interested.
you use your mouth prettier than a $20 whore
I realise you've done the DAQ work and that, and to some degree and in some cases I agree with what you're saying - but particularly as angles of incidence get higher (ie larger square bumps) the difference becomes more pronounced (from my empirical experience, not actual measurements). The wheel acts as another bar of the suspension, yes, but any force components that are perpendicular to the direction of the bike's movement (ie horizontal) will act to decelerate the bike, which is that hanging up sensation you get. If the horizontal impulse is reduced (by having the wheel able to decelerate in the horizontal axis without taking the whole bike with it) then it is irrefutable that the bike will slow down less. As the bump gets closer and closer to the critical angle, the difference becomes more and more pronounced. If I get time I'll draw up a simulation of it - theoretical I know, but I honestly believe there is merit to fairly rearwards axle paths (wheel rate etc all being equal) in terms of straight-line bump absorption.
I think that we are making the same point. I'm not saying that rearwardness of axle path is completely insignificant, I'm just stating that mathematics and data acquisition show that other suspension factors are incredibly more significant when it comes strictly to effectively absorbing bumps.
Isn't there also a factor of having the wheel "push" down the backside of bumps? In which case a suspension design with initial rearward AP to forward is actually faster with a good rider on there?
Seems like too much rearward would result in not pushing down the backside, and instead slapping the next hit.
That's one bump. How does it all change when hitting multiple bumps really fast?
That's where your shock setup has vastly more effect. The extra forward momentum of a wheel swinging back into place on a high-pivot would be nearly immeasurable.
