[Steve M]

Fixed for ya!


Edit- how about Biopace cogs rotated around 30* to give a larger chainforce that was in sync with the vertical increase in load. Is this "thinking out of the box" or just a brainfart!

haha, then you have variable chainline and thus variable anti-squat in the one gear... could work, could make people think you've lost the plot entirely

 

[TrueScotsman]

haha, then you have variable chainline and thus variable anti-squat in the one gear... could work, could make people think you've lost the plot entirely

There's a thin line between genius and insanity!

 

[no skid marks]

what i would really like to know is the ratio of rider who use flats on bikes with high PF to riders who ride clipped in on the same bikes, and vice versa. seems like if you are clipped in, then it will negate the feedback bouncing your feet of the pedals, and flats would work very well on bikes that have low pedal feedback forces.

Apart from Shimanno releasing the first Bio pace 90* out of whack, I couldn't see why it got so bashed. Did the mechs flap about.
I remember seeing at the Taipai show some spring loaded chainrings that apparently dissipated the power strokes.

 

[Sandwich]

Yep, absolutely correct. Different rider heights will slightly affect it, as will your tyre size and pressure, fork height, fork sag, fork sagged height, reach & stack of the cockpit setup, pedal thickness, frame size, head angle (yeah really), etc etc - riders move around a LOT on a bike too, so the best we'll ever get is "pretty close" really. You notice it too - even the bikes that are IMO the most efficient pedallers out there (DHR is probably it IMO) still move a bit. There just isn't any getting around certain aspects of bike performance - you are limited with just how efficient you can make it, and I believe there are bikes out there that have come pretty close to hitting the ceiling of realistic efficiency.

cool, that's the only point I was trying to make. 100% is quantifiable momentarily, but saying a bike has 100% anti-squat is unrealistic on the actual trail, unless the rider is height X has Y strength pedals only in Z gear at W sag and is on flat ground!

 

[TrueScotsman]

cool, that's the only point I was trying to make. 100% is quantifiable momentarily, but saying a bike has 100% anti-squat is unrealistic on the actual trail, unless the rider is height X has Y strength pedals only in Z gear at W sag and is on flat ground!

I see what you say, but just a wee correction- strength doesn't have much to do with it as the greater the acceleration force the greater the counter-acting chain force.

 

[fluider]

Yet another question.
How much does pedal feedback impact the internals of a gearbox? I mean some increased friction etc. Or are the internals highly immune and pass the pedal feedback to the pedals according to actual internal gear ratio?

 

[no skid marks]

Yet another question.
How much does pedal feedback impact the internals of a gearbox? I mean some increased friction etc. Or are the internals highly immune and pass the pedal feedback to the pedals according to actual internal gear ratio?

I can't think of any gearbox bike with any amount of chain growth worth mentioning. GT IT, Lahar Mk9, Zerode, BCD all have the final drive close to the high pivot, and as mentioned by Socket, don't BOB much so don't need much anti squat, and I think all the G-Box models have the pivot near output also.

 

[Steve M]

I can't think of any gearbox bike with any amount of chain growth worth mentioning. GT IT, Lahar Mk9, Zerode, BCD all have the final drive close to the high pivot, and as mentioned by Socket, don't BOB much so don't need much anti squat, and I think all the G-Box models have the pivot near output also.

Any bikes that pedal equally well with a given shock, will have roughly the same amounts of anti-squat. The reason they don't bob much is BECAUSE of the anti-squat characteristics. Higher pivot doesn't mean less anti squat, it means you need less chain extension to get the same amount of anti-squat.

 

[fluider]

If a bike has no chaingrowth does not mean it has no pedal-back. Imagine Lahar with swingarm cocentric with Speedhub sprocket and both Speedhub sprocket and rear wheel sprocket of the same size, then it will still have some amount of pedal-feedback. Lahar with the same size sprockets has pedal-feedback of up to 20° if I remember correctly.
With cocentric low(er) pivots you can get to negativ pedal-feedback. High pivots usually have positive values which can be nicely eliminated using an idler mounted on the swingarm...

Edit: this is why I like the idler idea. You can gain consistent AS curve and eliminate pedal-kickback on single-pivot linkage. Just how that damn AS is calculated in case of swingarm mounted idler ?

 

[Steve M]

cool, that's the only point I was trying to make. 100% is quantifiable momentarily, but saying a bike has 100% anti-squat is unrealistic on the actual trail, unless the rider is height X has Y strength pedals only in Z gear at W sag and is on flat ground!

Yeah but the cumulative variation of anti-squat due to all that stuff (except for gradient of the ground) is probably less than 10%, whereas the variation in anti-squat characteristics between bikes can be over 300%! Compare say a Lenz to an old Karpiel, and you go from like 30% pro-squat to about 300% anti-squat in a fairly standard DH gear! Yet neither of them is completely unrideable - a couple of percent difference in anti-squat isn't an enormous difference.

 

[no skid marks]

Any bikes that pedal equally well with a given shock, will have roughly the same amounts of anti-squat. The reason they don't bob much is BECAUSE of the anti-squat characteristics. Higher pivot doesn't mean less anti squat, it means you need less chain extension to get the same amount of anti-squat.

LOL, sorry, meant they don't need extra designed into it. There's also two freehubs to counter any chain growth.

 

[Steve M]

If a bike has no chaingrowth does not mean it has no pedal-back. Imagine Lahar with swingarm cocentric with Speedhub sprocket and both Speedhub sprocket and rear wheel sprocket of the same size, then it will still have some amount of pedal-feedback. Lahar with the same size sprockets has pedal-feedback of up to 20° if I remember correctly.
With cocentric low(er) pivots you can get to negativ pedal-feedback. High pivots usually have positive values which can be nicely eliminated using an idler mounted on the swingarm...

Edit: this is why I like the idler idea. You can gain consistent AS curve and eliminate pedal-kickback on single-pivot linkage. Just how that damn AS is calculated in case of swingarm mounted idler ?

Hey? Concentric swingarm pivot/drive sprocket, and drive/rear sprockets of the same size = no chain extension or pedal feedback at all.

 

[Steve M]

LOL, sorry, meant they don't need extra designed into it. There's also two freehubs to counter any chain growth.

There isn't any "extra" anti-squat required on any bike. You're confusing anti-squat with chain extension... re-read the explanations of what anti-squat is.

 

[no skid marks]

If a bike has no chaingrowth does not mean it has no pedal-back. Imagine Lahar with swingarm cocentric with Speedhub sprocket and both Speedhub sprocket and rear wheel sprocket of the same size, then it will still have some amount of pedal-feedback. Lahar with the same size sprockets has pedal-feedback of up to 20° if I remember correctly.
With cocentric low(er) pivots you can get to negativ pedal-feedback. High pivots usually have positive values which can be nicely eliminated using an idler mounted on the swingarm...

Edit: this is why I like the idler idea. You can gain consistent AS curve and eliminate pedal-kickback on single-pivot linkage. Just how that damn AS is calculated in case of swingarm mounted idler ?

Not sure where you get 20* from, but even if it was true, would you notice it? I never noticed any pedal feedback on my Lahar, or Zerode.

 

[no skid marks]

There isn't any "extra" anti-squat required on any bike. You're confusing anti-squat with chain extension... re-read the explanations of what anti-squat is.

I just got in, takes the brain a bit to warm to 100% anti-fault. Even with an idle mind, I don't think I ever reach peak anti-fault. I think I'm a few links short.
so don't need much chain growth induced anti squat then then.

 

[fluider]

This is a pedal-kickback plot of linkage very similiar to Lahar/Zerode but with sprockets of the same size! It's a pedal-kickback that comes from secondary chain through gearbox (Speedhub, so IGR is included in calculation) onto gearbox input sprocket. 40°, quite a lot, isn't it? You probably wouldn't like to bottom out with 1st gear in and hear how internals are eating each other in your Alfine/Speedhub .
The 2nd picture is pedal-kickback on primary chain that rider can feel, because a primary chain gearing is considered.

Primary pedal-kickback (at gearbox):

Secondary pedal-kickback (at crankset, felt by rider):

 

[Steve M]

This is a pedal-kickback plot of linkage very similiar to Lahar/Zerode but with sprockets of the same size! It's a pedal-kickback that comes from secondary chain through gearbox (Speedhub, so IGR is included in calculation) onto gearbox input sprocket. 40°, quite a lot, isn't it? You probably wouldn't like to bottom out with 1st gear in and hear how internals are eating each other in your Alfine/Speedhub .
The 2nd picture is pedal-kickback on primary chain that rider can feel, because a primary chain gearing is considered.

Primary pedal-kickback (at gearbox):

Secondary pedal-kickback (at crankset, felt by rider):

Sorry to say but I'm pretty sure there's something wrong with your calculations or measurements, there is no way you're getting 40 degrees worth of rotation on the secondary drive output sprocket with the same size sprockets front and rear, with a pivot/hub layout like the Zerode and Lahar use.

 

[TrueScotsman]

Hey? Concentric swingarm pivot/drive sprocket, and drive/rear sprockets of the same size = no chain extension or pedal feedback at all.

Are you sure? You wouldn't get any chain extension (distance from centre to centre of sprockets) but you would get pedal feedback (angular displacement relative to front triangle) depending on front suspension travel - you would get around 25* at zero front travel depending on gearing.

 

[xy9ine]

Sorry to say but I'm pretty sure there's something wrong with your calculations or measurements, there is no way you're getting 40 degrees worth of rotation on the secondary drive output sprocket with the same size sprockets front and rear, with a pivot/hub layout like the Zerode and Lahar use.

yer. no idea how the graphs are arrived at, but i can't discern pedal feedback. there should be observable rearward crank rotation when the suspension cycles?

 

[Steve M]

Are you sure? You wouldn't get any chain extension (distance from centre to centre of sprockets) but you would get pedal feedback (angular displacement relative to front triangle) depending on front suspension travel - you would get around 25* at zero front travel depending on gearing.

How are you calculating that one? Concentric pivot/front sprocket + same size sprockets front and rear = no true chain extension (ie actual pulling of the chain), because the chain unwraps from the top of the front sprocket at the same rate it wraps around the top of the rear sprocket. It's the equivalent of a parallelogram linkage, there is no rotation of one link (in this case the links are the sprockets) relative to the one opposite...

 

[fluider]

Chain extension is just one part of pedal-kickback. Angular displacement may become bigger factor in case of hich pivots.
How Linkage calculates pedal-kickback:
http://www.bikechecker.com/download/PedalKickbackCalculation.pdf

Socket, xy9ine: my graphs are based on Linkage method of calculating pedal-kickback. I have no opportunity to try it on my own, I really would like to. Perhapds xy9ine you can shift the 1st gear in and try some smaller drop on the street.

 

[fluider]

How are you calculating that one? Concentric pivot/front sprocket + same size sprockets front and rear = no true chain extension (ie actual pulling of the chain), because the chain unwraps from the top of the front sprocket at the same rate it wraps around the top of the rear sprocket. It's the equivalent of a parallelogram linkage, there is no rotation of one link (in this case the links are the sprockets) relative to the one opposite...

But then you have a rear wheel which in case of high-pivot is forced to spin back a lot (rearward axlepath) which pulls back the chain from front sprocket.

 

[Sandwich]

Yeah but the cumulative variation of anti-squat due to all that stuff (except for gradient of the ground) is probably less than 10%, whereas the variation in anti-squat characteristics between bikes can be over 300%! Compare say a Lenz to an old Karpiel, and you go from like 30% pro-squat to about 300% anti-squat in a fairly standard DH gear! Yet neither of them is completely unrideable - a couple of percent difference in anti-squat isn't an enormous difference.

Interesting...I would have thought it would be way more/different.

Question for you though...if a Lenz/BB concentric bike has pro-squat, and then a brooklyn/pivot concentric bike has some level of anti-squat, then isn't that solely related to chainring size? and doesn't that fall within the <10% as described before? I'm confused....

In the real world, I know my arrow dss-3 was the worst pedaling bike I've owned, and the Racelink was among the best.

 

[no skid marks]

Chain extension is just one part of pedal-kickback. Angular displacement may become bigger factor in case of hich pivots.
How Linkage calculates pedal-kickback:
http://www.bikechecker.com/download/PedalKickbackCalculation.pdf

Socket, xy9ine: my graphs are based on Linkage method of calculating pedal-kickback. I have no opportunity to try it on my own, I really would like to. Perhapds xy9ine you can shift the 1st gear in and try some smaller drop on the street.

That linkage calc is with a big chainring isn't it.
I'm riding a Zerode, and I've ridden a Lahar, there's sweet F A noticeable kick back, you can go on trying to fault either bike with some messed up rational, but the Zerode is fricken sick, pedals really well, and eats bumps better than anything else IMO. Every bikes a compromise to some extent. Zerodes the best balance for me.

 

[TrueScotsman]

How are you calculating that one? Concentric pivot/front sprocket + same size sprockets front and rear = no true chain extension (ie actual pulling of the chain), because the chain unwraps from the top of the front sprocket at the same rate it wraps around the top of the rear sprocket. It's the equivalent of a parallelogram linkage, there is no rotation of one link (in this case the links are the sprockets) relative to the one opposite...

Socket- this assumes the same rate of front wheel travel as rear travel. The tyre contact point changes if you only have rear wheel travel.

no skid marks- I don't think any one is "trying to fault" either bike, but rather discussing the technical merits of different systems.

 

[Steve M]

But then you have a rear wheel which in case of high-pivot is forced to spin back a lot (rearward axlepath) which pulls back the chain from front sprocket.

I think that's a misleading characteristic shown by linkage due to the change in wheelbase when the bike is static, because the reference point is the front triangle rather than actual wheel speed as per actual riding. It isn't allowing for the fact that the front wheel will accelerate forwards faster (given that it's unbraked and unpowered) than the rear wheel will slow down under pedalling power.

Interesting...I would have thought it would be way more/different.

Question for you though...if a Lenz/BB concentric bike has pro-squat, and then a brooklyn/pivot concentric bike has some level of anti-squat, then isn't that solely related to chainring size? and doesn't that fall within the <10% as described before? I'm confused....

In the real world, I know my arrow dss-3 was the worst pedaling bike I've owned, and the Racelink was among the best.

The "10%" figure I totally made up before (yes it's an estimation) was referring to all the cockpit/bike geo/rider size alterations that affect the amount of anti-squat. The difference in anti-squat between different gearings can be very large.

However, while you are correct that the different gearing plays a considerable role, a large part of the reason your Brooklyn pedaled a lot better than your Arrow was simply the much higher pivot. The chain force on the Brooklyn is having very little effect on the suspension and its component in what I previously referred to as the "driving force" at the axle can be more or less ignored, but the actual tractive force component (ie force equal to the tractive force at the tyre, but applied through the axle) is acting horizontally but significantly (maybe 7-8 inches or so?) below the pivot. This vertical distance means that you now have a moment arm (lever) that the force at the axle can use to try to extend the suspension, in order to balance the rearwards load shift that's trying to compress the suspension.

For future reference - the actual height of the pivot isn't relevant, but the angle between the swingarm line (axle to pivot) and the ground is. This is a fairly unique case though, because most bikes don't have pivot-centric drive sprockets of a size very similar to the mid-range of most cassettes, and even as you change gears on that bike you'll find that it pedals differently. I never used to be a huge fan of the design, but after thinking the principles through a bit more as well as actually riding a Superco, I'm pretty sold on the jackshaft setup being quite a good system in a lot of ways. Sure it has its detractions as well as its benefits but overall it does work pretty well.

 

[Sandwich]

However, while you are correct that the different gearing plays a considerable role, a large part of the reason your Brooklyn pedaled a lot better than your Arrow was simply the much higher pivot. The chain force on the Brooklyn is having very little effect on the suspension and its component in what I previously referred to as the "driving force" at the axle can be more or less ignored, but the actual tractive force component (ie force equal to the tractive force at the tyre, but applied through the axle) is acting horizontally but significantly (maybe 7-8 inches or so?) below the pivot. This vertical distance means that you now have a moment arm (lever) that the force at the axle can use to try to extend the suspension, in order to balance the rearwards load shift that's trying to compress the suspension.

cool. This is something that seems like is never or rarely discussed...the effect of the"swingarm line" on pedaling characteristics has a huge effect IMO. Thanks for the explanation- I knew the results but didn't know why. Yay science!

 

[fluider]

Since English is not my native language I cannot understand all semantics and feelings behind it, most of the time I'm happy I understand the content, so I just keep reading without the feel of some personal arguments if there are any .

 

[Steve M]

Since English is not my native language I cannot understand all semantics and feelings behind it, most of the time I'm happy I understand the content, so I just keep reading without the feel of some personal arguments if there are any .

Nah this thread has been good, there are no personal disagreements going on. You are doing EXTREMELY well to have a discussion this technical in your 2nd language, it's hard enough for me to find the right words sometimes and this is my first language!

 

[TrueScotsman]

Okay, i had to go and make a picture (as I said my brain works graphically!) to show how pedal feedback CAN occur with a concentric pivot and same size sprockets.

At zero suspension travel the rear cog/chain contact point is a1. With rear travel only the cog/chain contact point has moved to b1. However, the point on the sprocket that was a1 has now moved to a2. This would cause an anti-clockwise rotation of the front cog (and therefore pedals).

Or am I wrong?

EDIT- I may be wrong- because the chain "unwraps" itself more than point a1 moves anti-clockwise. Therefore, you would actually get negative chainpull/pedal feedback.
Oh, I don't know anymore- I need a beer!

 

[fluider]

One must know that pedal-kickback curve in Linkage graphs is calculated with front suspension in ZERO travel, as TrueScotsman mentioned. But you can watch the "Wheel rot." value at small yellow rectangle that changes depending on both rear and front travel.
If you open Zerode model from web lib, and move rear and front suspension together you'll see that rear wheel induced rotation goes up to 15°.
Or I dodn't get what Socket meant. I need to go out tonight .

 

[TrueScotsman]

Okay, I now reckon that I was wrong with my first drawing/theory- If the pivot is concentric and the sprockets are the same size you do in fact get negative pedal feedback (at zero front suspension travel).

Note that angle X* (chain unwrap) is greater than angle y*.

What make this more interesting is that if the chain is taut (no tensioner) it is the under-run of the chain that is in tension. What does this do to affect chain forces on the suspension? Bearing in mind that this negative pedal-feedback can happen whilst coasting.

Any thoughts?

 

[Steve M]

I think the key thing to remember here is that pedal feedback is typically defined as relative to the front triangle (which is what the rider is attached to, so the best frame of reference IMO). The rearwards rotation of the front triangle isn't a relevant factor IMO.

 

[Vrock]

Linkage do both calculations. Relative to the front triangle and relative to the ground. But the graph only shows the rotation relative to the ground. Anyway, You can play with the frame by hand and read the two calculations... Turn off horizontal mode, bottom out the suspension and see what happens.

In a Superco Silencer for example, the Graph says 11º of pedal Kickback, but relative to the main triangle it's just 0.7º, and that's nothing.

 

[TrueScotsman]

But in the above sketches the front triangle is static, no?

(I will have to get onto Cad instead of relying on Paint doodles!)

 

[Vrock]

Yep, when you turn off the horizontal mode the the front triangle is static.

 

[TrueScotsman]

Sorry Vrock i was meaning my sketches/doodles.

Time for another sketch!

Help me to understand, is this right?:
angle a -angle b = anti-clockwise rotation of rear sprocket.
angle x = clockwise "wrapping" of chain around rear sprocket.
therefore, in this case; (a-b)+(-x)= chain "pull"/pedal kickback.
In this instance the answer is negative, therefore the under-run of the chain will be under tension.

No?

 

[no skid marks]

Sorry Vrock i was meaning my sketches/doodles.

Time for another sketch!

Help me to understand, is this right?:
angle a -angle b = anti-clockwise rotation of rear sprocket.
angle x = clockwise "wrapping" of chain around rear sprocket.
therefore, in this case; (a-b)+(-x)= chain "pull"/pedal kickback.
In this instance the answer is negative, therefore the under-run of the chain will be under tension.

No?

I only just got up, so I'm not playing. I will say that both Lahar and Zerode have tensioner underneath, so no pedal kickback if what you're saying is true. and the rear free hub would absorb that reverse chain pul wouldn't it?

 

[TrueScotsman]

I only just got up, so I'm not playing. I will say that both Lahar and Zerode have tensioner underneath, so no pedal kickback if what you're saying is true. and the rear free hub would absorb that reverse chain pul wouldn't it?

Ha ha- I know what you mean- it's not yet 6.00am here in the UK and here I am posting about bloody pedal feedback!

right- I was so absorbed in the theory of it I forgot about the freehub! D'oh

Am I still right with the equation though?

 

[fluider]

Freehub: It spins freely only in forward direction, however pedal-kickback (well its positive values because positive values are those 'kicking' crankarm back) goes rearward so standard freehub can't help you here. Standard freewheel or fixie is part of a problem.
But ... what if we made a reversed freewheel, where it would spin like fixie in forward direction (which should be no problemo in gearbox design where gearbox has its own freewheel) and in rearward direction it would isolate wheel backward rotation from sprocket rotation thus wouldn't be pulling the chain back from front chainring ?