[Honus]

Further to the "rider is sprung weight " debate:
On a conventional bike that has chain extension under compression where the rider is standing:
-the only part of the riders body at all rigidly connected to the bike is his feet and lower leg. As lashback through the pedal is the result of suspension actuation, this mass must be accelerated to activate the suspension.
Therefore the riders mass that is involved in the primary suspension system is unsprung not sprung weight!

OK- I can swing with that. The mass that is accelerated (rider's legs) is a result of pedal feedback. However, this is only a percentage of the rider's total weight and the degree to which the mass is accelerated is in direct correlation to chain growth. A similar mass acceleration happens in a URT design, except that the degree to which the mass is moved is a result of the pivot position- specifically in relation to the CG of the rider. Either way it does effectively add to the amount of unsprung weight but I wouldn't go so far as to say that the the rider's mass is entirely unsprung weight- the worst case scenario would be a forward pivot URT and the best case scenario conventional design would be one with minimal chain growth. A floating BB design would be somewhere in between....

So in a properly designed gearbox design the rider's mass is isolated from the suspension system, making the rider's mass entirely sprung weight so the suspension system is more effective. As always, the lower the unsprung weight the better the suspension system can function and ultimately improve grip.

And of course I would be interested in an "L-box." Who wouldn't....

 

[LaharDesign]

OK- I can swing with that. The mass that is accelerated (rider's legs) is a result of pedal feedback. However, this is only a percentage of the rider's total weight and the degree to which the mass is accelerated is in direct correlation to chain growth. A similar mass acceleration happens in a URT design, except that the degree to which the mass is moved is a result of the pivot position- specifically in relation to the CG of the rider. Either way it does effectively add to the amount of unsprung weight but I wouldn't go so far as to say that the the rider's mass is entirely unsprung weight- the worst case scenario would be a forward pivot URT and the best case scenario conventional design would be one with minimal chain growth. A floating BB design would be somewhere in between....

So in a properly designed gearbox design the rider's mass is isolated from the suspension system, making the rider's mass entirely sprung weight so the suspension system is more effective. As always, the lower the unsprung weight the better the suspension system can function and ultimately improve grip.

And of course I would be interested in an "L-box." Who wouldn't....

Good spotting. I was going to admit that if no-one bit.
a pivot or virtual pivot around the top of the chainring can move the pedal about 40% of suspension travel on quick bumps, so you could assume 40% of the mass of the lower legs as unsprung. Simular to standing on the swingarm 4/10 from the pivot to the axle.
Actually I'm not clear on whether the other 60% can be considered sprung. Anyone? It could in the swingarm analogy but its so long since I've seriously considered non-independant drive that I haven't pondered this in years.
Hondas running low pivot independant drive. They need an electric "Big Red" lockout button for this, but they wouldn't compromise their spr/unspr ratio by chain extension- or use an icky artificial stiction platform system.

 

[Whoops]

Hmm, what does this mean in practice? Is it also more than just the mass of the unsprung leg (or part thereof)? If the rider is exerting some force on the pedal that counts as 'mass' too.

So = dead weight of leg (shin/knee whatever, must get a hacksaw and find out) + force

That force could be muscular (ie above that required to hold the riders weight up... the dead weight), or accelerative (likey if the bike is compressing).

So let's say it's 40% of the leg mass. What's that? 10kg? Let's put a 3g accel in there - so roughly 10x9.81x3=300N-ish of instantaneous load. How much muscular force can a rider exert on one pedal (assuming disco slipper use)? A couple of hundred Newtons? Anyone got a good guess? My brain is a little hampered by the alcohol.

How much chain lash could occur? over what time?


edit to ask - hang on, what was the original question for this thread? traction? Sorry. some tyres grip well, some not so well. usually ALL tyres work better in dry conditions on smooth (but not too smooth), flat surfaces. the suspension is the to make the ride comfortable and cushion my haemaroids.

edit # 2 to add bibliographic references - "Race Car Engineering & Mechanics" by Paul van Valkensomething. and anything by Carroll Smith ("Engineer to win" etc). Both a bit dated now and looking at 4 wheels (bad) not 2 wheels (good) - but still worth a read - even if just from a race prep point of view.

edit #3 to appologise to any orwell fans. I meant 4 wheels good, 2 wheels bad. Long live the revolution!

 

[Steve M]

Cheers whoops

Further to the "rider is sprung weight " debate:
On a conventional bike that has chain extension under compression where the rider is standing:
-the only part of the riders body at all rigidly connected to the bike is his feet and lower leg. As lashback through the pedal is the result of suspension actuation, this mass must be accelerated to activate the suspension.
Therefore the riders mass that is involved in the primary suspension system is unsprung not sprung weight!

This is, of course, only if the rate of chain extension is great enough to exceed the potential chain slack of the wheel's rotational speed (when coasting - obviously irrelevant when pedalling).

By the way, a pivot height around the top of the chainring will NOT produce 40% of the wheel's travel as pedal kickback. By my calculations, it would be about 16.5% which, for the record is about 0.8" total pedal movement if you bottom out an 8" travel bike fully, from the sag point (assuming about 37.5% sag), and that's only if the rear wheel is NOT rotating at all relative to the cassette (eg you're pedalling or at a standstill). Once the wheel rotation speed picks up (assuming coasting) this number decreases greatly, especially as shaft speed is directly linked to wheel speed for a given bump. In other words, standard bike industry marketing hyperbole

 

[Honus]

I'm going to have to go with Socket on this one- I haven't crunched the numbers but just quickly thinking about it there's no way it's going to be as high as 40%- the chain growth under load just isn't that great given pivot placement at the top of the chainring.

Ultimately, the best design for all around DH performance (and by that I mean not having the chain influence suspension one way or the other) is to have the chain force parallel to the swingarm, which is different from zero chain growth. This can be argued against of course if you specifically wanted to generate a squat/anti-squat force. In motorcycle design they shift the positions of swingarm pivot and engine output sprocket to achieve a desired result- as in pro-squat, anti-squat, etc. Even if a bicycle had only one chainring and one rear sprocket it still becomes difficult to completely model a system- it's like having a motorcycle that has a huge poorly balanced parallel twin engine with a constantly moving CG. And on a bicycle the ratio between rider/bike mass is so much greater, further complicating things....

Which is why we have platform valving- it has more to do with abrubt weight transfer than it does with chain torque reaction. So we're getting off topic but ultimately it does all affect traction....

 

[dhkid]

This is, of course, only if the rate of chain extension is great enough to exceed the potential chain slack of the wheel's rotational speed (when coasting - obviously irrelevant when pedalling).

yea, i was just gonna say that. the speed of the cassette, or freehub will have to be the same as the wheel, aka the hub engaging. so it would depend on how fast you hit a bump and how much travel you use..

keep the disicusion going guys... great stuff!!

 

[Whoops]

... to have the chain force parallel to the swingarm, ...

You mean parallel to an imaginary line between the (swingarm/instantaneous) pivot and the axle, right?

btw - sorry for my previous post. Came home a little boozed. Kids, don't drink and surf!

 

[dhkid]

edit, drunken sillyness

 

[Honus]

You mean parallel to an imaginary line between the (swingarm/instantaneous) pivot and the axle, right?

Yep- sorry, I should have been more specific.

 

[RimJobbed]

i am confused on how some bikes grip amazingly and some not so... (rear traction.)

does this apply to when the rear tire skips in a drift too??

discuss, are my assumptions valid?

This reminds me of couffee taulk with Linda Richmond. Please talk amongst yourselves, I'll give you a topic, RideMonkey neither rides nor is a monkey.. discuss

 

[Steve M]

Ultimately, the best design for all around DH performance (and by that I mean not having the chain influence suspension one way or the other) is to have the chain force parallel to the swingarm, which is different from zero chain growth.

If the chain is parallel to the swingarm then there will be no "chain growth" in the sense that you will never tension/slacken the chain by moving the suspension even though the BB-to-axle distance changes (and conversely, as you say, the chain itself will not have any input to the suspension) but in my opinion it is more useful to have a small amount of chain-induced extension force (ie chain-component of anti-squat) than it is to totally eliminate the possibility of ANY amount of pedal feedback. I know LaharDesign disagrees on this point (believing that it is more important to be able to pedal through the rough at any cost), but my own experience is that if it's that rough, you can't pedal efficiently anyway and sometimes you're simply better off being smooth and coasting than trying to crank hard over choppy ground.

 

[Honus]

If the chain is parallel to the swingarm then there will be no "chain growth" in the sense that you will never tension/slacken the chain by moving the suspension even though the BB-to-axle distance changes (and conversely, as you say, the chain itself will not have any input to the suspension) but in my opinion it is more useful to have a small amount of chain-induced extension force (ie chain-component of anti-squat) than it is to totally eliminate the possibility of ANY amount of pedal feedback. I know LaharDesign disagrees on this point (believing that it is more important to be able to pedal through the rough at any cost), but my own experience is that if it's that rough, you can't pedal efficiently anyway and sometimes you're simply better off being smooth and coasting than trying to crank hard over choppy ground.

There are definitely mixed feelings on the subject of chain-induced extension force. If it's a small amount I really don't see it as that big a problem- it's not an absolutely optimal situation but a large percentage of riders will probably never feel it and if it makes the design of the bike more effective in another area then I think it's fine. There are plenty of successful bike designs out there that have it to a small degree.

With the chain being parallel to the swingarm there won't be any chain growth BUT conversely it is possible to not have chain growth and and still not have the chain force parallel to the swingarm. Many bikes that pivot around the BB shell have this issue- the original Rotec bikes come to mind.

 

[Steve M]

There are definitely mixed feelings on the subject of chain-induced extension force. If it's a small amount I really don't see it as that big a problem- it's not an absolutely optimal situation but a large percentage of riders will probably never feel it and if it makes the design of the bike more effective in another area then I think it's fine. There are plenty of successful bike designs out there that have it to a small degree.

With the chain being parallel to the swingarm there won't be any chain growth BUT conversely it is possible to not have chain growth and and still not have the chain force parallel to the swingarm. Many bikes that pivot around the BB shell have this issue- the original Rotec bikes come to mind.

A large percentage (I'd say ~100%) of riders will most certainly feel the difference between a bike with 0% anti-squat (ie no chain- or tractive-force-induced response to acceleration, only weight shift) and a bike that uses that small amount of chain extension to generate ~100% anti-squat. If I've misinterpreted that, and you actually meant that most riders won't feel a small amount of (theoretical) feedback, then yes I agree. There can be a certain amount of chain pull before it will be sufficient to overcome the speed of the spinning wheel, and then another small amount before it becomes noticeable to the rider. Subtract the amount required to overcome the speed of the wheel, and you've got the maximum amount of chain pull (I use the term "pull" separate to the term "growth" intentionally btw, I'll get to that in a sec) that you can "ideally" have.

I propose that we use the term "chain growth" as referring to the change in distance from axle to BB (or centre of drive sprocket for a jackshaft/idler setup), and "chain pull" as the radial (axial to the chain) distance that the chain is actually pulled by suspension compression. These are obviously not the same; if you imagine that you had a BB-centric pivot like a Rotec with a 38t on the front and a 19t on the back, no matter what happened there'd never be any chain growth because the BB-axle distance is constant. However, if you imagine rotating the swingarm around the BB in complete circles, the amount of chain unwound from the front chainring would be 38 links (well 19 links if you're gonna be technical, 38 half-links) per revolution, yet the amount wound onto the rear sprocket would only be 19 half links (9.5 full links), so clearly slack would generate in the chain. Therefore, a BB-centric bike with positive gearing will actually have negative chain pull, yet zero chain growth. Since chain pull (not chain growth) is a direct component of the extensive force on the axle (used to counter the rider/bike weight shift to the rear wheel under acceleration), one can summarise that chain pull is directly related to the pedalling efficiency of a bike (though it is not the ONLY thing... tractive force is the other component, whole 'nuther story I don't have time for now).

Edit: not that I don't think you understand this stuff... just for clarity's sake, because your statements were a bit ambiguous.

 

[Honus]

A large percentage (I'd say ~100%) of riders will most certainly feel the difference between a bike with 0% anti-squat (ie no chain- or tractive-force-induced response to acceleration, only weight shift) and a bike that uses that small amount of chain extension to generate ~100% anti-squat. If I've misinterpreted that, and you actually meant that most riders won't feel a small amount of (theoretical) feedback, then yes I agree. There can be a certain amount of chain pull before it will be sufficient to overcome the speed of the spinning wheel, and then another small amount before it becomes noticeable to the rider. Subtract the amount required to overcome the speed of the wheel, and you've got the maximum amount of chain pull (I use the term "pull" separate to the term "growth" intentionally btw, I'll get to that in a sec) that you can "ideally" have.

I propose that we use the term "chain growth" as referring to the change in distance from axle to BB (or centre of drive sprocket for a jackshaft/idler setup), and "chain pull" as the radial (axial to the chain) distance that the chain is actually pulled by suspension compression. These are obviously not the same; if you imagine that you had a BB-centric pivot like a Rotec with a 38t on the front and a 19t on the back, no matter what happened there'd never be any chain growth because the BB-axle distance is constant. However, if you imagine rotating the swingarm around the BB in complete circles, the amount of chain unwound from the front chainring would be 38 links (well 19 links if you're gonna be technical, 38 half-links) per revolution, yet the amount wound onto the rear sprocket would only be 19 half links (9.5 full links), so clearly slack would generate in the chain. Therefore, a BB-centric bike with positive gearing will actually have negative chain pull, yet zero chain growth. Since chain pull (not chain growth) is a direct component of the extensive force on the axle (used to counter the rider/bike weight shift to the rear wheel under acceleration), one can summarise that chain pull is directly related to the pedalling efficiency of a bike (though it is not the ONLY thing... tractive force is the other component, whole 'nuther story I don't have time for now).

Edit: not that I don't think you understand this stuff... just for clarity's sake, because your statements were a bit ambiguous.

Yes, you are absolutely correct and I concur on your use of terminology. I do have a tendency to over simplify in my explanations. I shall endeavour to describe with a greater degree of clarity in the future - I was going to go into an identical explanation of a BB-centric design but I had to put my older son to bed- kids come before bike talk!

And yes I did mean that most riders probably wouldn't feel the small amount of feedback....

 

[LaharDesign]

over 8 inches travel a pivot at the top of the chainring gives 40mm extension of the distance bb to axle.

 

[LaharDesign]

hmmm...
If positive chaingrowth means that you have to split the riders weight between say 30% unsprung and 70% sprung when standing...
Does it follow that negative chain growth means that the split may be -30% unsprung and 130% sprung mass?

 

[mech]

Grip is mostly determined by damping in combination with the wheelrate. Kicking of the bike has for 95% to do with compression damping not rebound. Your compression damping (Low speed)needs to be quite soft at the inital stage (about 35-40% with the sag set at 25-30%) this will provide mechanical grip, grip is also affected by tire choice and pressure. Problem with bikes is the better the grip the worse the pedaling wil be. Then you want to get your compression damping as stiff as possible in a progressive build-up. Spring rate is also of great effect for grip, the softer the spring the more grip, but also more kicking will happen. Most kicking occurs when you have the compression damping in combination with the spring to soft. The bike will ride to deep in the stroke and can't handle highspeed impacts, this causes kicking.
As for rebound you want the rebound damping as fast as possible until the bike start to feel bouncy, like when you hit a rock at a slower speed you feel the bike pushes you backwards and slows you down.

 

[dhkid]

If the chain is parallel to the swingarm then there will be no "chain growth" in the sense that you will never tension/slacken the chain by moving the suspension even though the BB-to-axle distance changes (and conversely, as you say, the chain itself will not have any input to the suspension) but in my opinion it is more useful to have a small amount of chain-induced extension force (ie chain-component of anti-squat) than it is to totally eliminate the possibility of ANY amount of pedal feedback. I know LaharDesign disagrees on this point (believing that it is more important to be able to pedal through the rough at any cost), but my own experience is that if it's that rough, you can't pedal efficiently anyway and sometimes you're simply better off being smooth and coasting than trying to crank hard over choppy ground.

umm, i am a bit confused by the 'chain is parellel to the swingarm' statement... wouldn't the chain slacken under compression? and tug under rebound. there still would be "chain growth" right?

lahardesign, i do not follow what you saying anymore.. :huh:

 

[Honus]

umm, i am a bit confused by the 'chain is parellel to the swingarm' statement... wouldn't the chain slacken under compression? and tug under rebound. there still would be "chain growth" right?

What we should really be saying is chain force..... Imagine a swingarm where the drive sprocket (chainring) is concentric to the swingarm pivot. Now imagine that the drive sprocket (chainring) and the drive sprocket at the rear wheel are the exact same size. In this case the chain would always run directly parallel to the swingarm and wouldn't influence suspension action.

Given the same situation, if the drive sprocket (chainring) is larger than the rear sprocket then the suspension would tend to compress under a pedaling load- the chain force wants to pull the rear wheel up. If the drive sprocket (chainring) is smaller than the rear sprocket then the suspension would tend to extend under a pedaling load. In either case there is no chain growth. This is why single swingarm bikes like the Rotec that had the swingarm pivoting around the BB shell pedaled poorly.

Make sense?

 

[Honus]

hmmm...
If positive chaingrowth means that you have to split the riders weight between say 30% unsprung and 70% sprung when standing...
Does it follow that negative chain growth means that the split may be -30% unsprung and 130% sprung mass?

Hmmm.... well I don't think you can have more than 100% of the rider's mass as sprung. I don't really think it's possible to divide the rider's mass percentages, at least with any degree of accuracy.

 

[Honus]

Grip is mostly determined by damping in combination with the wheelrate. Kicking of the bike has for 95% to do with compression damping not rebound. Your compression damping (Low speed)needs to be quite soft at the inital stage (about 35-40% with the sag set at 25-30%) this will provide mechanical grip, grip is also affected by tire choice and pressure. Problem with bikes is the better the grip the worse the pedaling wil be. Then you want to get your compression damping as stiff as possible in a progressive build-up. Spring rate is also of great effect for grip, the softer the spring the more grip, but also more kicking will happen. Most kicking occurs when you have the compression damping in combination with the spring to soft. The bike will ride to deep in the stroke and can't handle highspeed impacts, this causes kicking.
As for rebound you want the rebound damping as fast as possible until the bike start to feel bouncy, like when you hit a rock at a slower speed you feel the bike pushes you backwards and slows you down.

Given that everyone has more or less the same damper technology (unless you're a pro running double top secret stuff) a damper wouldn't determine why one bike had more grip than another- which I believe was the original question. Dialing in a damper to work with a given bike design and rider preference plays a tremendous role here of course. What I mean to say is that dampers do play a large part in how much grip is generated but they are far from the only thing to consider.

But since we're on the topic of damping.....
All suspension settings are a compromise between having as much compliance as possible and having as much chassis stability as possible. Rebound damping unloads the tire whenever the suspension has an extension velocity, resulting in reduced grip on the downhill side of a bump- too much rebound damping and the tire loses grip. Too little rebound and the suspension extends too rapidly, causing loss of grip and chassis instability.

Compression damping also does this because when the suspension resists compression, the sprung mass (rider and frame) has a greater upward velocity on the uphill side of the bump. Too much compression damping and the tire loses contact with the ground at the crest of the bump. It's always a balance ....

As a general rule, the response to large bumps is controlled by high speed damping (meaning high damper piston velocity) while the overall attitude of the bike (chassis stability) is controlled by low speed damping (meaning low damper piston velocity.) So, bump inputs are at high velocities and rider inputs are at low velocities. So if your bike design is able to minimise rider inputs due to chain/weight transfer forces (braking/accelerating) then you have greater overall chassis stability. What platform dampers try to do is discriminate between rider inputs and bump inputs to give better levels of chassis control.

When designing a bike, you also have to take into account the amount of mechanical friction in the suspension sytem. This is known as Coulomb damping. Coulomb damping is independent of velocity and is digressive at low velocities. A bike design with multiple pivots will inherently have more of this than a simple three pivot swingarm bike. Detail design (bearing systems, etc.) is very important here and can greatly affect damping.

 

[Steve M]

over 8 inches travel a pivot at the top of the chainring gives 40mm extension of the distance bb to axle.

Which as you know means approximately f**k all unless you specify gearing. If your gearing was high enough you could STILL have negative chainpull even with that increase in BB-axle distance. Stop pulling out irrelevant figures.

hmmm...
If positive chaingrowth means that you have to split the riders weight between say 30% unsprung and 70% sprung when standing...
Does it follow that negative chain growth means that the split may be -30% unsprung and 130% sprung mass?

Again, assuming we're talking whilst pedalling here, because coasting as we have seen is not affected unless the chainpull is sufficient to overcome the wheel's speed... If you had so much negative chain growth that your foot actually DROPPED when you hit a bump, and I mean dropped relative to the ground not the bike frame, then yes you could effectively have negative unsprung mass. A notable side effect would be that your bike would tend to bob like crazy because every time you pedalled, you'd compress the suspension a loooong way.

 

[Steve M]

umm, i am a bit confused by the 'chain is parellel to the swingarm' statement... wouldn't the chain slacken under compression? and tug under rebound. there still would be "chain growth" right?

lahardesign, i do not follow what you saying anymore.. :huh:

If the chain is parallel to the swingarm (ie the chainline being parallel to an imaginary line drawn between the pivot and the axle), then there will be no component of the axle's motion that is parallel to the chainline. In other words, the only movement of the chain will be to rotate it, not to pull on it.

 

[Whoops]

over 8 inches travel a pivot at the top of the chainring gives 40mm extension of the distance bb to axle.

So - just measured mine (whoooor)

Axle to BB dimension

uncompressed length = 545mm
compressed length = 585mm

all dimensions approximate (using a builders tape measure).

 

[Steve M]

Yeah VERY approximate I'd say... unless you really do have 21.5" static chainstays. Don't spose you actually meant 445 and 485mm?

 

[dhkid]

If the chain is parallel to the swingarm (ie the chainline being parallel to an imaginary line drawn between the pivot and the axle), then there will be no component of the axle's motion that is parallel to the chainline. In other words, the only movement of the chain will be to rotate it, not to pull on it.

i get that, but are you talking about an instant in the bikes travel? coz the only way this can happen is when a consentric pivot about the bb. or are you thinking about a single pivot that is designed so that in its travel when traction is most important it was designed so there the chain will have the least amount of effect on it within that region of travel?

 

[Whoops]

Yeah VERY approximate I'd say... unless you really do have 21.5" static chainstays. Don't spose you actually meant 445 and 485mm?

Yep. my bad. the 40mm was right though.

 

[Steve M]

i get that, but are you talking about an instant in the bikes travel? coz the only way this can happen is when a consentric pivot about the bb. or are you thinking about a single pivot that is designed so that in its travel when traction is most important it was designed so there the chain will have the least amount of effect on it within that region of travel?

At any point or region yeah. You could fairly easily design a linkage (well, if you only had a single chainline, ie gearbox bike) that moved the CC in such a way that the chainline and swingarm line were always kept parallel however. The only time that could happen with a concentric pivot is if you had a 1:1 gear ratio (which would require a gearbox, unless you happen to be on a trials bike or something).

 

[LaharDesign]

.. If you had so much negative chain growth that your foot actually DROPPED when you hit a bump, and I mean dropped relative to the ground not the bike frame, then yes you could effectively have negative unsprung mass. A notable side effect would be that your bike would tend to bob like crazy because every time you pedalled, you'd compress the suspension a loooong way.

Not neccesariry so grasshopper.
neutral inertial pitch behaviour is with a pivot ~200mm above the bb and close to the wheel. with sag ~40% and zero chain extension at 50% travel the m9 is mostly in negative extension in even small bumps. Guys like Nico V rated my highest 25cm ovr bb pivot bike as the most promising design with even more negative chain extension.
The possibility of infinite sprung/unsprung mass ratio is an intriguing scenario for high pivot bikes under pedalling. (or other vehicles with counter leveraged masses to achieve the same effect)

 

[Steve M]

Not neccesariry so grasshopper.
neutral inertial pitch behaviour is with a pivot ~200mm above the bb and close to the wheel. with sag ~40% and zero chain extension at 50% travel the m9 is mostly in negative extension in even small bumps. Guys like Nico V rated my highest 25cm ovr bb pivot bike as the most promising design with even more negative chain extension.
The possibility of infinite sprung/unsprung mass ratio is an intriguing scenario for high pivot bikes under pedalling. (or other vehicles with counter leveraged masses to achieve the same effect)

Yes, it is necessarily so. If your foot/lower leg moves in the same direction as the bump force then its inertia will resist the force, regardless of all else (since F = ma, if a is positive then so must be F). If it moves in the opposite direction then you could say that A is negative and thus so is the force required to accelerate it. Having negative feedback may decrease the effective unsprung mass but it will not create an actual negative effective unsprung mass until such time as your foot actually drops whilst pedalling, when you hit a bump. That requires that the amplitude of the movement transmitted to the frame be lower than the negative feedback.

Edit: this is based on your theory of "more travel at the pedal" which of course assumes you are weighting the front pedal heavily at the time of the impact, and ignores the possibility that your cranks are at 12 and 6 instead of 3 and 9, in which case the effect obviously shifts to fore/aft motion. If the force you're applying through your legs is still sufficient to accelerate at a great enough rate that the chain never slackens then you can still decrease the effective unsprung mass... however personally I think it's just a wank. I can pedal my low-pivot, positive feedback bike over 6" high bumps easily enough, but regardless of whether I'm pedalling or not, it's simply a rough ride, and when I'm pedalling I can't smooth things out like I can when I'm coasting.

 

[LaharDesign]

Yes, it is necessarily soreferring to "wallowing under pedalling" I was. If your foot/lower leg moves in the same direction as the bump force then its inertia will resist the force, regardless of all else (since F = ma, if a is positive then so must be F). If it moves in the opposite direction then you could say that A is negative and thus so is the force required to accelerate it. Having negative feedback may decrease the effective unsprung mass but it will not create an actual negative effective unsprung mass until such time as your foot actually drops whilst pedalling, when you hit a bump.better than kicking up when you hit a bump is That requires that the amplitude of the movement transmitted to the frame be lower than the negative feedback.

Edit: this is based on your theory of "more travel at the pedal" which of course assumes you are weighting the front pedal heavily at the time of the impact,in a power stand I am and ignores the possibility that your cranks are at 12 and 6 instead of 3 and 9, in which case the effect obviously shifts to fore/aft motion.fully sprung mass % I think Personally I think it's just a wank.

ngahngahferrousPonyfan

 

[Steve M]

haha I was editing while you were posting... re-read.

 

[Whoops]

So when will active suspension be trialled? (a la Williams F1)

I can't see 'fully active' (ie driving the linkages) suspension due to weight penalties, but I can imagine active valving on dampers and (if air sprung) perhaps active chamber dimensions (to alter 'spring' rates).

Perhaps Honda could do it and get some more patents?

 

[LaharDesign]

So when will active suspension be trialled? (a la Williams F1)

I can't see 'fully active' (ie driving the linkages) suspension due to weight penalties, but I can imagine active valving on dampers and (if air sprung) perhaps active chamber dimensions (to alter 'spring' rates).

Perhaps Honda could do it and get some more patents?

Quick lets talk about it and get our priors in!
Socket you nerd I was going to qualify my comment about 12 and 6 oclock cranks with comment on how pedal force may overcome inertial force or not dependant on frequency but you beat me too it.
sockets issues with more sag when you point things uphill would be eliminated with active pressure adjustments. saw a german bike with that stuff in a mag about 10 years ago. you pitched it forward or back and reset the attitude with a button. Bulky and klutzy but thats just the detail.

 

[Honus]

So when will active suspension be trialled? (a la Williams F1)

I can't see 'fully active' (ie driving the linkages) suspension due to weight penalties, but I can imagine active valving on dampers and (if air sprung) perhaps active chamber dimensions (to alter 'spring' rates).

Perhaps Honda could do it and get some more patents?

As if bikes aren't expensive/complex enough as it is.....

Have they even used active suspension in motocross yet? I know it's been used in GP bikes....

 

[Whoops]

So instead of sensors reading the ground ahead... perhaps an interim system might 'just' use a pot on the forks to feed data for controlling the rear.

Add inputs from the brake levers, and maybe a strain gauge on the cranks...

Easy.

Mr Honda, pm me and I'll send my CV and renumeration requirements immediately.

Edit to say: we can put the flux capacitor under the seat tower.

 

[Honus]

So instead of sensors reading the ground ahead... perhaps an interim system might 'just' use a pot on the forks to feed data for controlling the rear.

Add inputs from the brake levers, and maybe a strain gauge on the cranks...

Easy.

Mr Honda, pm me and I'll send my CV and renumeration requirements immediately.

Edit to say: we can put the flux capacitor under the seat tower.

I know a guy that's a data acquisition engineer for one of the top CART teams- I'm sure he could hook something up. Now trying to take that and effectively control damper valving using a solenoid or ERM fluid and software- that's something else. Didn't Noleen make an electronic brain shock several years ago that kind of adjusted itself? I know Cannondale played around with some electronic valving control on their team DH bikes in the Fulcrum era.... If I remember correctly everyone hated this stuff.

And using a flux capacitor would be cheating- no bending of the space time continuum to finsh first.

 

[LaharDesign]

I can't see on the fly attitude control should add more than a couple of bucks. Given that both forks and rear shocks have air pressure spring boosting commonly all you need is systems designed to have simular pressure at a good pitch attitude on flat ground. And some hose connecting them both to a push button valve on the bar.

As for terrain sensors and active control, why not add quantum computing to instantly evaluate all possible outcomes and pick the best.
our brains probably already do that though.

 

[Honus]

I can't see on the fly attitude control should add more than a couple of bucks. Given that both forks and rear shocks have air pressure spring boosting commonly all you need is systems designed to have simular pressure at a good pitch attitude on flat ground. And some hose connecting them both to a push button valve on the bar.

As for terrain sensors and active control, why not add quantum computing to instantly evaluate all possible outcomes and pick the best.
our brains probably already do that though.

All you need to do is get a super MRI scan of Vouilloz's brain to model your computer......

 

[LaharDesign]

All you need to do is get a super MRI scan of Vouilloz's brain to model your computer......

I've always thought the super reaction speed and 3D processing abilities of the common houseflys brain to hold enormous promise as a downhill pilot.
Australian flys are particularly tenacious, chasing you along a trail as fast as you can pedal.