Does it move at a backward angle, or literally 7 inches vertical and then only the last two inches move back?
axle paths
- Thread starter _*sTiTcHeS*_
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another question. what would be the lightest out of the rearward axle pathed bikes?
and what does the axle path look like on the fsr bikes like an enduro or sx?
and what does the axle path look like on the fsr bikes like an enduro or sx?
Ah the golden years. Ohio and zedro actually discussing bikes.
it was a joke, surely you have noticed NSM's ability to talk endlessly about the Lahar.Ya, DW isn't qualified at all.Neither are any of the other fully fledged Mechanical Engineers on here.
Which looks like a great bike by the way.
vertical, haven't you been properly brainwashed yet???
Basically what affects traction and grip (suspension-wise) are a few things:
1. The ability of the wheel to stay on the ground. Obvious.
2. The change in normal force between ground and tyre. If this change is big or fast, you get less traction and more tendency to slip.
3. The "feel" delivered to the rider. This tends to come with firm setups that don't change much.
The problem is, numbers 1 and 3 involve a bit of a compromise - the most free-moving suspension will keep the wheel on the ground, but they also make the bike's geometry less stable and thus give less feel through to the rider. Notably, the slower (and thus less harshly) any changes occur, the more consistent the grip will be. The more rearwards the axle path, the longer time the wheel has to cover whatever vertical distance over a bump (in addition to being smoother and thus more stable to the rider), which means that the normal reaction force stays more consistent. This gives more traction (partly due to being more predictable).
In my opinion, the bike's stability is the number one priority for traction and cornering confidence. If the riding geometry is crap (or changes a lot during cornering, braking etc) then it's not going to be stable, and that will affect things a lot.
Although a Sunday uses dw-link, which pedals extremely well, the dw-link design's primary goal is traction. Pedaling efficiency just happens to go hand and hand with traction for a dw-link bike.
An overly rearward axle path causes the center of traction to vary excessively through the travel. There is no way for a rider to move his center of mass fast enough to compensate for the center of traction change during suspension movement, and therefore very rearward axle path bikes are deficient in cornering traction.
Dave
Please explain with a diagram how it maintains traction in bumps.
On a smooth corner,A rearward axle path provides a consisitent axle path,gradually increasing the chainstay,I'm yet to see someone loose rear traction from this.On a smooth corner,the rear suspension,wouldn't be used that much,so the chainstay extension would be minimal.
On a bumpy corner if the rear tyre had less weight on it due to it being say an inch further back,it's bump compliance will still give it better traction over a bike that's skipping over bumps.
this may sound stupid but can a rearward arch slow u down as it comes back foward as u are plowing through rocks? "a what goes up must come down"
Does your front wheel slow you down on the rebound stroke?Roughly the same angle wheel path.
did not think about it that way, ur right
could you explain what the center of traction means? is it the point in which the combination of front wheel traction and rear wheel traction combined act through? basically where you center of mass to be directly above to make use of the available traction from the two wheels most efficiently?
LOL I doubt it. I've been pointing this out and talking about this with Alex since before Ridemonkey existed..I sence a fight.
Ding.
Ding.
DW vs. BCD
What diagram specifically are you looking for? What diagram have you looked at before that helped you formulate any prior opinions on the subject?
Whether you have "seen" a bike lose traction, then realized the dynamics at work, then formed a hypothsis as to why the bike lost traction based on physics or not is irrelevant. The physics at work are defined by the world that we live in. My poitning them out here doesn't change them any more than newton qualifying gravity chaged the planetary forces at work that define it.
Based on your comment of how much suspension travel is used during cornering, I think that you would be very surprised after looking at data aquisition information from a properly set up DH bike.
What data are you using to surmise that a gradually increasing chainstay length necessarily is a defining factor in suspension compliance compared to other factors (such as compression damping, wheel rate, rider positioning, wheel diameter, bump location in relation the the wheel center)?
Lots to think about..
Exactly, you've got it. Its a point between the two contact patches and defined by the traction at each wheel. Typically this is also the yaw axis for the bike in a sliding situation, although lean angle can complicate things a little but not by enough to make a major difference. Center of mass location in relation to this center of traction determines how controlled of a slide a rider can maintain. Seeing as almost all cornering in any type of cycle requires some degree of sliding, and that at higher levels of cycling, maintaining a slide is the key to cornering quickly, a huge amount of importance is placed on keeping center of traction manageable in respect to the CM location.
I really don't think that there are more than a handful of people in the world who understand, care about or apply this type of information to cycle suspensions, and certainly nobody inthe bicycle industry other than myself.
DW you're talking a lot and saying not much in regard to the topic. Yes I am the uneducated layman using logic as I see it. Please explain to me,how a DW link bike has superior cornering compared to a high SP.
Please spell out exactly how small an amount of rear traction is lost due to a high pivot when cornering. This overlooks the minds learning and adapting. How many corners do you think it would take for a riders sub conscious to learn from experience and adapt to the minuscule movement of centre of traction,and counter act it if it was an issue?
This is the DH section,I still think the bump compliance benefits far outweigh any minute change in centred weight that the rider can counter act and that happens to a lesser extent due to forks on all bikes anyway.
So you're saying it's better to take the traction from the front for the rear on a DH bike?
Doesn't the lenght from centre also change when the bike is pointed down hill?Also making the rearward lengthening from centre ratio less?
What effect does it have on the Sundays traction making the riders legs and drivetrain part of the unsprung mass that has to be excellerated for the suspension to move?
Please spell out exactly how small an amount of rear traction is lost due to a high pivot when cornering. This overlooks the minds learning and adapting. How many corners do you think it would take for a riders sub conscious to learn from experience and adapt to the minuscule movement of centre of traction,and counter act it if it was an issue?
This is the DH section,I still think the bump compliance benefits far outweigh any minute change in centred weight that the rider can counter act and that happens to a lesser extent due to forks on all bikes anyway.
So you're saying it's better to take the traction from the front for the rear on a DH bike?
Doesn't the lenght from centre also change when the bike is pointed down hill?Also making the rearward lengthening from centre ratio less?
What effect does it have on the Sundays traction making the riders legs and drivetrain part of the unsprung mass that has to be excellerated for the suspension to move?
How about we do something a lot easier. Take your Sunday and your high pivot bike ALA Balfa BB7 out for a few runs and see how they feel. Make sure that all of the components and suspension are set up to perfectly complement your riding style, and that the bikes are appropriately sized so as to not taint your data.
What makes you think that the center of traction change between lower and really high pivot bikes is miniscule?
Your point about adaptation is exactly what I am talking about. Humans are incapable of moving fast enough to make adjustments to their CM movement to compensate for fast center of traction changes. The only way to give a rider that edge is to design a suspension that can work within that range where a human can react. From empirical testing we can quantify that range and use it as a baseline. The bottom line is that the more the CT changes, the more difficult the rider's task of maintaining traction.
I don't know about where you ride, but where I race, and on pretty much every racetrack (bikes, cars, whatever) I have ever seen, races are won in the corners and under braking. Anyone with skill and balls can straightline a rock garden at speed. Good riders pump and jump their way through.
While you were writing this I added more questions to my previous post.
By subconscious,I meant that the rider will know what to expect,therefore counteracting the actions as it happens without having to feel any loss in traction. I still believe we're arguing a trivial point here that really has very little effect.
It's DH,the bikes are aimed down,pushing the centre of traction forward. There's very few smooth flat corners,I'd dare say,none on most tracks. Bump compliance is not just about rock gardens but also brake bumps,ruts,and any other trail imperfection,no matter how small the high pivot will keep the wheel on the ground. Even when pedalling,it will keep the wheel suspended,unlike the Sunday.
TOTAL TRACTION,all the time Vs minuscule loss in rear traction on smooth predictable flat corners. Is that the equation?
Hopefully I can grab Aaron to comment,or BCD will chime in again.
yeah, you are correct. we both have our theories. we both have data to back them up. we both think our our better. nothing is going to change
minds.
things i like about high pivot:
matching 64 deg fork movement with a high pivot.
i like the feel of keeping moving back together.
low pivot always felt like they bucked me more when
going fast and into rock gardens hanging up fighting
my body weight pushing down rather than going where
it wants to. that is what the 2x4 was all about. just letting
the wheel run free in a zone. it would be fun to have mapped
out where it was actually going during a run.
You're starting to make a whole lot of unproven claims here...
can we pls now go a bit more in depth on how axle path effects traction? socket has already touched on it, but i am sure dw has a lot more to say.
so rear ward axle path is good for traction? but if it to rearward it effects the center of traction too much. so is the whole reason the dw link works well (besides the whole anti squat part) is because it starts off as a very rearward axle path then goes more vertical? so you have the traction you need, but its doesn't go on rear ward so that it doesn't effect the center of traction?
so rear ward axle path is good for traction? but if it to rearward it effects the center of traction too much. so is the whole reason the dw link works well (besides the whole anti squat part) is because it starts off as a very rearward axle path then goes more vertical? so you have the traction you need, but its doesn't go on rear ward so that it doesn't effect the center of traction?
i would like to see a sunday's axle path. could be figed but not divulged lightly i presume.
traction traction - tires, tires pressure, wheels size, quality of rear
damper and its setup and finally axle path.
4 i believe to be more important than axle path. we are splitting hairs
here IMO. wheel path IMO from using both high and low matters more
for large hits. not slowing you down as much, causing flats and displacing your bike making you squerlly sketch into a tree.
of course something like the right tire choice and tire pressure might make a much bigger difference at the end of the day. i am just interested right now on how one element of the whole system works, hopefully one day trying to understand how the whole system works together.
of course something like the right tire choice and tire pressure might make a much bigger difference at the end of the day. i am just interested right now on how one element of the whole system works, hopefully on day trying to understand how the whole system works together one day.
yeah, but you will never know.
you will only have your own conclusions.
something scrawled on a cocktail napkin after a couple mojitos should do the trick. it cleared up everything about brake jack.
back on topic, I got less flat tires with the Sunday than with other, low-pivot frames... take that for what you will, but it was pretty noticeable.
Your drinking partner mustn't have noticed the "floater"in his drink,and that's why he was talking $hitsomething scrawled on a cocktail napkin after a couple mojitos should do the trick. it cleared up everything about brake jack.
Maybe a cute woman can bring me a cheap shot.
We're not talking about cornering traction on smooth flat corners, we're talking about cornering traction PERIOD. Smooth and flat, off camber with rocks, all the same. If it makes anyone feel better, a Sunday has a rearward axle path through 45% of its travel, more than a 303 does if I'm not mistaken.
Keep in mind with the discussion of "rearward axle path" that you have a big lever that all bumps act on your suspension through (your wheel). That wheel generates huge amounts of leverage, and changes the direction of the bump force as you roll over an obstacle. The axle path tangent could be 45 degrees forwards and this lever would still have no problem compressing the suspension. The axle center is just a pivot point in a larger link system which includes your suspension and your wheel. For most kinematic layouts which will fit a bicycle, friction in the suspension, and wheel damping rate both have a larger effect on bump compliance (within limits of course) than axle path. Its just not a major issue for bump compliance, although some marketing would like you to think it is. I guess it appeals to the same intuition that makes people imagine that a vertical axle path would somehow eliminate suspension reaction to acceleration forces.
This stuff is not simple. There is a huge amount of time and thinking that goes into understanding, and ultimately being able to use this information to develop or analyze a suspension. You seem like you have interest in learning more. You should think of picking up Tony Foale's book for starters, then start doing math and writing programs on your own.
floater in a Mojito?! gack! not sure how that one would workYour drinking partner mustn't have noticed the "floater"in his drink,and that's why he was talking $hit
Maybe a cute woman can bring me a cheap shot.
I agree with you, especially in racing downhill. However, this thread left me with a few questions in regards to the dw-link. If downhill races are won with traction and cornering opposed to straightlining square-edged hits (due to the nature of the tracks), and the dw-link was designed around this widely known fact, then how does it work outside of DH racing? For example technical xc riding, where there are more flat straightaways with roots and rocks, opposed to winding turns where carrying speed is crucial. Does the relatively veritcal axelpath of a dw-link then become a disadvantage over something more rearward (such as a vpp)?
dw-link wasn't designed specifically for downhill. Actually it was first used on shorter travel trail bikes. Each dw-link design is tuned for its intended riding purpose. DH bikes used DH tuned parameters, XC bikes are XC tuned and so on. With the wide range of leverage rate curves that can be designed into the system, along with its anti-squat and braking squat stability, pretty much any desired suspension "feel" that one would want can be engineered.
Dw-link's axle path is anything but vertical. It is less vertical than almost every bike on the market outside of the VPP bikes. The more bumps, the better the suspension performs.
dw-link = Traction through bumps, on or off the power, cornering or straightaway, with as little rider interaction as possible.
I guess this is related to what I was saying about stability and slow input changes to the rider... I haven't got numbers to back me up so I can't *prove* that bump absorption/wheel tracking is more or less important than the centre of traction. Actually something I'd wondered about for quite a while, should investigate more.
You can guarantee what other people DON'T know? hahaha... I have a lot of respect for your knowledge mate, but that was flat out arrogant. The fact that a handful of people on this forum alone, several of whom don't even work in the bike industry let alone make a living out of thinking about this stuff, are thinking about it MIGHT be enough to suggest otherwise. I'm not claiming to have a "complete" understanding of anything at all, but really dude...
BTW, claiming the Sunday to have a "rearwards" axle path is IMO a bit misleading... sure everything is either rearwards or forwards except for that one instant where it's vertical, but when it's between like 3-0° away it's not exactly comparable to a high-pivot bike.
You can think what you want, but I have been working with one of the largest and most successful motorcycle companies in the world to apply a motorcycle suspension similar to dw-link to racing platforms, and engineers from this company straight up told me that they are not working with this data, yet they understand it has a huge impact on performance. Like I said, think what you want, I'm calling it like I see it. If the motorcycles I'm working on start winning world championships etc.. then we'll see.
BTW, where other than from me have you read about Center of Traction and dynamics of mass transfer and CT movement, and how they relate to cornering traction? I have only talked with one other person ever who understood it. I'd love to talk with more.
Keep reading. I think I gave a travel measurement where it ceases to be rearward. Rearwardness is not a requirement, it just happens to be a result for some geometries and link layouts.
Hate to wade into your head butting contest, but DW - you should try to speak with some of the F1 boys. This stuff (MoI, turn moments etc) is common parlance for them. Sorry, I don't have any up to date contacts, but perhaps some of the superbike teams (circuit racing) might also be good to talk with as well.
Oh hell yeah, F1, I have no doubt. The guys that I am working with ARE Superbike guys and work with Moto GP also.
to see the wheelpath on a sunday it can be done through the analysis of a four-bar coupler curve. one needs the dimensions off of a sunday and without writing out the position vectors for the 4bars and doing some lagrangian/hamiltonian math to get a system of equations that can be solved w/ some custom code, you can just plug them in here http://www.softintegration.com/chhtml/toolkit/mechanism/fourbar/fourbarCouplerCurve.html
(you can work in meters or feet, so convert your measurements accordingly)
r1 is your ground link so use the distance between the the pivots on the seat-tube (~8.75")
r2 is the distance between the center of pivots on upper link (~4.5")
r3 is the dist. between upper and lower link pivots (on the rear triangle ~ 10.5")
r4 is the length of the lower link between pivots (~4")
rp is the length of the pseudo seat-stay on the rear triangle (15 7/8")
i set theta to 0 and beta to 60 degrees (i took the measurements with a tape measure and guessed beta for the sake of time... you could measure that with a protractor and get close enough and fine tune the other numbers)
point "p" is the axle and its trajectory is what is plotted in the 2d plane of the coupler curve. here is what it looks like for my numbers:
on the curve you see multiple solutions for some points. this is because the program allows the fourbar system to rotate more than a system would that is constrained by a shock. and you also see over a foot of travel... you'd see less if the program would allow constraints on angles and then we could dial in 8". however, the important part of the curve is between the black lines. this gives the bike about .6 ft of travel (0.66 ft = 8") and the rearward travel is small about 0.03 ft or 0.36" *. (the way i oriented the linkage the x dimension is the vertical direction and y is horizontal or fore/aft.)
*btw, i chose the top of the curve almost arbitrarily, one could do a little thinking about the boundary conditions and slide the 8" width to the right spot to get a proper representation of the axle path for a sunday. the good news is we have something to look at and anyone can fine tune it as they wish.
here is an animation of what is getting plotted, although it is a different 4bar system. (it too allows full rotation unlike a real suspension linkage that would just oscillate back and forth.)
(you can work in meters or feet, so convert your measurements accordingly)
r1 is your ground link so use the distance between the the pivots on the seat-tube (~8.75")
r2 is the distance between the center of pivots on upper link (~4.5")
r3 is the dist. between upper and lower link pivots (on the rear triangle ~ 10.5")
r4 is the length of the lower link between pivots (~4")
rp is the length of the pseudo seat-stay on the rear triangle (15 7/8")
i set theta to 0 and beta to 60 degrees (i took the measurements with a tape measure and guessed beta for the sake of time... you could measure that with a protractor and get close enough and fine tune the other numbers)
point "p" is the axle and its trajectory is what is plotted in the 2d plane of the coupler curve. here is what it looks like for my numbers:
on the curve you see multiple solutions for some points. this is because the program allows the fourbar system to rotate more than a system would that is constrained by a shock. and you also see over a foot of travel... you'd see less if the program would allow constraints on angles and then we could dial in 8". however, the important part of the curve is between the black lines. this gives the bike about .6 ft of travel (0.66 ft = 8") and the rearward travel is small about 0.03 ft or 0.36" *. (the way i oriented the linkage the x dimension is the vertical direction and y is horizontal or fore/aft.)
*btw, i chose the top of the curve almost arbitrarily, one could do a little thinking about the boundary conditions and slide the 8" width to the right spot to get a proper representation of the axle path for a sunday. the good news is we have something to look at and anyone can fine tune it as they wish.
here is an animation of what is getting plotted, although it is a different 4bar system. (it too allows full rotation unlike a real suspension linkage that would just oscillate back and forth.)