After watching the Rulezman video, I don't think he's suggesting that 30 km/h is the magic number where kickback disappears. He simply suggested that, with the...
After watching the Rulezman video, I don't think he's suggesting that 30 km/h is the magic number where kickback disappears. He simply suggested that, with the wheel spinning at "25-30 km/h" (which is a guess) there was no pedal kickback. So the magic number could be anywhere between 0 and 25 km/h according to his video.
I was not convinced by his video, because he moved the rear wheel through the suspension range so slowly when he was demonstrating there was no pedal kickback. A true, violent impact on a rock or root is more like putting your bike in a stand, spinning the wheel up to speed, and then hitting your tire with a sledgehammer uppercut as hard as you can. I don't know what the actual velocity is, but suspension moves very, very, very quickly during peak impacts, and they accelerate up to those speeds almost instantaneously.
A 5 m/s wheel speed input, which is reasonably fast, although not impossibly fast at all, 30 kph is right around where you wouldn’t experience kickback when in a 10t gear. 8 m/s is about as fast as you’ll ever see if I remember right. That would correspond to 49 kph. This is all using a typical leverage ratio at 50% travel for a 170 mm bike with a 65 mm stroke shock.
I’ve got something I’m working on right now that will have a massive range of leverage curves and axle paths. I’ll try and remember to share some data from that.
A 5 m/s wheel speed input, which is reasonably fast, although not impossibly fast at all, 30 kph is right around where you wouldn’t experience kickback...
A 5 m/s wheel speed input, which is reasonably fast, although not impossibly fast at all, 30 kph is right around where you wouldn’t experience kickback when in a 10t gear. 8 m/s is about as fast as you’ll ever see if I remember right. That would correspond to 49 kph. This is all using a typical leverage ratio at 50% travel for a 170 mm bike with a 65 mm stroke shock.
I’ve got something I’m working on right now that will have a massive range of leverage curves and axle paths. I’ll try and remember to share some data from that.
Thanks for the answer. To my earlier point, 30-49 km/h is real quick on a rough track with turns.
Dumb question: why would rear cog size matter for pedal kickback? Some people in this chat and the Rulezman video suggested that a smaller chainring would help you stay in a smaller rear cog, which would result in less kickback. To my thinking, it doesn't really matter what the size of the cogs is, only what the final drive ratio is. A crank would move just as much from a suspension compression if the bike was running a 36/17 ratio or a 28/13. The crank moves because the chainring moves, the chainring moves because the chain moves, and the final drive ratio determines how much the chain moves for a given rear axle rotation. Not saying I'm right, but that's my mental model. Tell me why I'm wrong.
Thanks for the answer. To my earlier point, 30-49 km/h is real quick on a rough track with turns.Dumb question: why would rear cog size matter...
Thanks for the answer. To my earlier point, 30-49 km/h is real quick on a rough track with turns.
Dumb question: why would rear cog size matter for pedal kickback? Some people in this chat and the Rulezman video suggested that a smaller chainring would help you stay in a smaller rear cog, which would result in less kickback. To my thinking, it doesn't really matter what the size of the cogs is, only what the final drive ratio is. A crank would move just as much from a suspension compression if the bike was running a 36/17 ratio or a 28/13. The crank moves because the chainring moves, the chainring moves because the chain moves, and the final drive ratio determines how much the chain moves for a given rear axle rotation. Not saying I'm right, but that's my mental model. Tell me why I'm wrong.
The size of the cog corresponds to how fast the chain length has to be growing in order for the freehub to “catch up” with the wheel speed. In a really low gear the chain has to be going super fast to spin the freehub fast enough. Not too different from how you’ll spin out if you drop it into gear 1 while going full speed. Whether or not to count the chainring is a whole other question. If you’re strong enough then you can pretty much say it’s rotationally fixed in which case its size doesn’t matter.
As for speed I completely agree. I can think of very few spots in local trails where I ever get going that fast.
After watching the Rulezman video, I don't think he's suggesting that 30 km/h is the magic number where kickback disappears. He simply suggested that, with the...
After watching the Rulezman video, I don't think he's suggesting that 30 km/h is the magic number where kickback disappears. He simply suggested that, with the wheel spinning at "25-30 km/h" (which is a guess) there was no pedal kickback. So the magic number could be anywhere between 0 and 25 km/h according to his video.
I was not convinced by his video, because he moved the rear wheel through the suspension range so slowly when he was demonstrating there was no pedal kickback. A true, violent impact on a rock or root is more like putting your bike in a stand, spinning the wheel up to speed, and then hitting your tire with a sledgehammer uppercut as hard as you can. I don't know what the actual velocity is, but suspension moves very, very, very quickly during peak impacts, and they accelerate up to those speeds almost instantaneously.
A 5 m/s wheel speed input, which is reasonably fast, although not impossibly fast at all, 30 kph is right around where you wouldn’t experience kickback...
A 5 m/s wheel speed input, which is reasonably fast, although not impossibly fast at all, 30 kph is right around where you wouldn’t experience kickback when in a 10t gear. 8 m/s is about as fast as you’ll ever see if I remember right. That would correspond to 49 kph. This is all using a typical leverage ratio at 50% travel for a 170 mm bike with a 65 mm stroke shock.
I’ve got something I’m working on right now that will have a massive range of leverage curves and axle paths. I’ll try and remember to share some data from that.
You wouldn’t experience pedal kickback*
*until you use your brakes right, when your wheel is rotating at as little as 0m/s?
*until you use your brakes right, when your wheel is rotating at as little as 0m/s?
As soon as you lock up all bets are off course. To be honest I’ve never really ridden anything where I found pedal kickback to be annoying beyond when the wheel is locked up. Even going back to back with and without chain. There’s a part of me that actually kind of likes being able to use chain tension to keep it a little higher. Let the cranks rotate backwards a little on landing and the impact is lessened using more travel. Keep feet entirely flat and push through it for more efficiency.
As soon as you lock up all bets are off course. To be honest I’ve never really ridden anything where I found pedal kickback to be...
As soon as you lock up all bets are off course. To be honest I’ve never really ridden anything where I found pedal kickback to be annoying beyond when the wheel is locked up. Even going back to back with and without chain. There’s a part of me that actually kind of likes being able to use chain tension to keep it a little higher. Let the cranks rotate backwards a little on landing and the impact is lessened using more travel. Keep feet entirely flat and push through it for more efficiency.
I feel that heavy braking is the largest contributor/least discussed for pedal kick. The situation where you might be locking up the rear brake but still using a good amount of travel is the exact situation where you’d really want your suspension performing at its best
The size of the cog corresponds to how fast the chain length has to be growing in order for the freehub to “catch up” with the...
The size of the cog corresponds to how fast the chain length has to be growing in order for the freehub to “catch up” with the wheel speed. In a really low gear the chain has to be going super fast to spin the freehub fast enough. Not too different from how you’ll spin out if you drop it into gear 1 while going full speed. Whether or not to count the chainring is a whole other question. If you’re strong enough then you can pretty much say it’s rotationally fixed in which case its size doesn’t matter.
As for speed I completely agree. I can think of very few spots in local trails where I ever get going that fast.
Despite your description I still couldn't see it, so I drew it with values. Three hypothetical chainring/cog combos, two with the same 3:1 final drive ratio but different sized rear cogs, and two drivetrains with the same size rear cogs but different final drive ratios (3:1 vs. 1:1). I'm not an engineer so I'm happy to be wrong, but I came to the opposite conclusion, and it looks like, in terms of pedal kickback, a bigger rear cog is better for the same gear ratio. Please chime in and point out if my values, arrows, or math are wrong.
The arrows represent where chain growth is happening and the direction of forces occurring in the drivetrain. It looks a little weird at first, because horizontal chain velocity is the value I kept constant across all three models. I kept horizontal chain velocity the same because (roughly speaking) that's the direction where acceleration happens in a harsh suspension compression as the rear axle moves away from the BB. It also looks weird because I drew it on MS Paint. I didn't calculate the real value for "x" because I didn't care, but you could if you wanted to. You'd have to measure the diameters of different cog and chainring sizes. Here are my takeaways:
1. The blue drivetrain (big rear cog, high gear ratio) will only experience pedal kickback at lower speeds relative to the other two. If your rear suspension compresses and your rear axle moves away from the BB at a velocity of "x" meters per second, the blue drivetrain will experience pedal kickback at all trail speeds where the rear wheel is spinning at 90 rpm or lower (roughly 8 mph with a 29" rear wheel). By contrast, the red drivetrain with the same gear ratio would experience pedal kickback at speeds up to 24 mph (rear wheel spinning at 270 rpm or less). The blue drivetrain won't have pedal kickback in the 8-24 mph range, which is preferred.
2. However, at a speed of 24 mph or less, the red drivetrain (small rear cog, high gear ratio) will produce less pedal kickback at the crank than the green drivetrain given the same suspension compression. At similar trail speeds (rear hub rotational velocity) and impacts, the green drivetrain will accelerate the cranks more (a velocity of 270 rpm vs. 90 rpm for the red drivetrain), which results in more radians of rotation at the crank for the same radians of rotation at the freehub.
Despite your description I still couldn't see it, so I drew it with values. Three hypothetical chainring/cog combos, two with the same 3:1 final drive ratio...
Despite your description I still couldn't see it, so I drew it with values. Three hypothetical chainring/cog combos, two with the same 3:1 final drive ratio but different sized rear cogs, and two drivetrains with the same size rear cogs but different final drive ratios (3:1 vs. 1:1). I'm not an engineer so I'm happy to be wrong, but I came to the opposite conclusion, and it looks like, in terms of pedal kickback, a bigger rear cog is better for the same gear ratio. Please chime in and point out if my values, arrows, or math are wrong.
The arrows represent where chain growth is happening and the direction of forces occurring in the drivetrain. It looks a little weird at first, because horizontal chain velocity is the value I kept constant across all three models. I kept horizontal chain velocity the same because (roughly speaking) that's the direction where acceleration happens in a harsh suspension compression as the rear axle moves away from the BB. It also looks weird because I drew it on MS Paint. I didn't calculate the real value for "x" because I didn't care, but you could if you wanted to. You'd have to measure the diameters of different cog and chainring sizes. Here are my takeaways:
1. The blue drivetrain (big rear cog, high gear ratio) will only experience pedal kickback at lower speeds relative to the other two. If your rear suspension compresses and your rear axle moves away from the BB at a velocity of "x" meters per second, the blue drivetrain will experience pedal kickback at all trail speeds where the rear wheel is spinning at 90 rpm or lower (roughly 8 mph with a 29" rear wheel). By contrast, the red drivetrain with the same gear ratio would experience pedal kickback at speeds up to 24 mph (rear wheel spinning at 270 rpm or less). The blue drivetrain won't have pedal kickback in the 8-24 mph range, which is preferred.
2. However, at a speed of 24 mph or less, the red drivetrain (small rear cog, high gear ratio) will produce less pedal kickback at the crank than the green drivetrain given the same suspension compression. At similar trail speeds (rear hub rotational velocity) and impacts, the green drivetrain will accelerate the cranks more (a velocity of 270 rpm vs. 90 rpm for the red drivetrain), which results in more radians of rotation at the crank for the same radians of rotation at the freehub.
3. I need to find an alternative to MS Paint.
Am I way off base or does that check out?
The key is that in a likelihood of experiencing kickback. The smaller the tooth count, the faster the shock can compress before you experience any kickback. The way to look at it is “if the chain gets pulled at some speed v, how fast does the freehub rotate and is that faster than the hub?” The smaller the tooth count, the faster the freehub spins for that given speed. How much exactly your cranks get rotated by an instance of kickback is a massive guess because in reality neither ends are fixed.
Despite your description I still couldn't see it, so I drew it with values. Three hypothetical chainring/cog combos, two with the same 3:1 final drive ratio...
Despite your description I still couldn't see it, so I drew it with values. Three hypothetical chainring/cog combos, two with the same 3:1 final drive ratio but different sized rear cogs, and two drivetrains with the same size rear cogs but different final drive ratios (3:1 vs. 1:1). I'm not an engineer so I'm happy to be wrong, but I came to the opposite conclusion, and it looks like, in terms of pedal kickback, a bigger rear cog is better for the same gear ratio. Please chime in and point out if my values, arrows, or math are wrong.
The arrows represent where chain growth is happening and the direction of forces occurring in the drivetrain. It looks a little weird at first, because horizontal chain velocity is the value I kept constant across all three models. I kept horizontal chain velocity the same because (roughly speaking) that's the direction where acceleration happens in a harsh suspension compression as the rear axle moves away from the BB. It also looks weird because I drew it on MS Paint. I didn't calculate the real value for "x" because I didn't care, but you could if you wanted to. You'd have to measure the diameters of different cog and chainring sizes. Here are my takeaways:
1. The blue drivetrain (big rear cog, high gear ratio) will only experience pedal kickback at lower speeds relative to the other two. If your rear suspension compresses and your rear axle moves away from the BB at a velocity of "x" meters per second, the blue drivetrain will experience pedal kickback at all trail speeds where the rear wheel is spinning at 90 rpm or lower (roughly 8 mph with a 29" rear wheel). By contrast, the red drivetrain with the same gear ratio would experience pedal kickback at speeds up to 24 mph (rear wheel spinning at 270 rpm or less). The blue drivetrain won't have pedal kickback in the 8-24 mph range, which is preferred.
2. However, at a speed of 24 mph or less, the red drivetrain (small rear cog, high gear ratio) will produce less pedal kickback at the crank than the green drivetrain given the same suspension compression. At similar trail speeds (rear hub rotational velocity) and impacts, the green drivetrain will accelerate the cranks more (a velocity of 270 rpm vs. 90 rpm for the red drivetrain), which results in more radians of rotation at the crank for the same radians of rotation at the freehub.
3. I need to find an alternative to MS Paint.
Am I way off base or does that check out?
Smaller cog equals worse for pedal kickback in the sense that it is more likely. So making everything bigger is helpful. I think that aligns with what you wrote. To be clear, to me low gear on the cassette equals high tooth count.
The key is that in a likelihood of experiencing kickback. The smaller the tooth count, the faster the shock can compress before you experience any kickback...
The key is that in a likelihood of experiencing kickback. The smaller the tooth count, the faster the shock can compress before you experience any kickback. The way to look at it is “if the chain gets pulled at some speed v, how fast does the freehub rotate and is that faster than the hub?” The smaller the tooth count, the faster the freehub spins for that given speed. How much exactly your cranks get rotated by an instance of kickback is a massive guess because in reality neither ends are fixed.
[EDIT: after your latest post it sounds like we're in agreement] "The smaller the tooth count, the faster the freehub spins for that given speed." But if the freehub spins faster than the hub, it will engage the hub, creating kickback, right?
Smaller tooth count ==> faster freehub spin ==> catches up with hub
Larger tooth count ==> slower freehub spin ==> doesn't catch up with hub
There isn’t a magic number at which it disappears. It depends on how fast your suspension is getting compressed relative to how fast you are going...
There isn’t a magic number at which it disappears. It depends on how fast your suspension is getting compressed relative to how fast you are going and what gear you are in. If your suspension were to compress infinitely fast you would need to be going infinitely fast to not have any feedback from the chain. So while it’s most apparent when going slow, it really can happen at any speed.
You are correct, reading more about it mine was an oversimplification. Still, if pk is just a function of gearing, frame design, wheel speed, and wheel vertical acceleration (is it?) we could still calculate what speed you need to be going to not feel pedal kickback while the suspension is moving at a certain speed. In theory, with data acquisition you could even calculate the % of time you spend while being susceptible to pk during a full run. That'd be interesting to see.
Edit: sorry I somehow missed a lot of posts discussing this.
Another cool product I'm curious about. A couple years ago I would have thought it was hokey and unnecessary, but now after testing some of the...
Another cool product I'm curious about. A couple years ago I would have thought it was hokey and unnecessary, but now after testing some of the new pedal kickback devices I'm drinking the Koolaid. Here's a thought to add to the discussion: adjustable lower pulley position to remove as much lower chain growth as possible. Idlers go a long way towards addressing chain growth, but only on the top of the drivetrain. I was having a sidebar chat with Erwan Ghesquiere (fellow nerd on this forum) about lower pulley position, because he's messing around with a moveable lower pulley and was able to find a location that yields negative chain growth. Pretty cool! If you combine a pedal kickback device (like Ochain, Rimpact, Sidekick Hub, or idler) with a strategically-placed lower pulley, you would (in theory) be able to remove nearly all suspension-induced chain movement. Adjustability of the lower pulley location is key because its optimal position is dependent on pivot locations and will be different for every bike. I'm curious if there will be a chainguide in the near future with independently adjustable upper and lower guide components, so you can adjust the top for chain retention and adjust the bottom for chain growth.
I’m on board with this idea. I rode my Kavenz VHP last season with no lower guide pulley. The high pivot is great for reducing pedal...
I’m on board with this idea. I rode my Kavenz VHP last season with no lower guide pulley. The high pivot is great for reducing pedal kickback, but after tearing a derailleur off and riding a chainless lap at Whistler, the rear end without a doubt worked more freely, which I chalked up to having no chain or derailleur. This season Kavenz made a dedicated lower idler guide, the first thing I noticed was how when cycling the suspension the derailleur moved backward instead of being pulled forward. After riding it for the majority of this season, I’m convinced it allows the rear end to move more freely, while also reducing chain slap/noise.
Saddly some events didn't allow me to do all the testing I wanted to do this weekend, keep in mind that I also had to ride with a different shock since mine blew up last week.
- Lower chain guide: basically the same as Dolface, quieter and you can visually see your derailleur moving much less when cycling your suspension (I don't have an upper pulley). Now for the noise reduction it often misslead you to think the bike is also smoother, and I didn't have a chance to test a lower pulley position that wouldn't reduce lower chain growth but would still keep the chain more stable.
- AS to PK to dynamic behaviour: I wanted to test my frame with a 38t ring instead of 30t (gear ration held constant, so 17t vs 13t cogs) to see if reduced AS values impact the bike dynamic behaviour (pumping, jumping) and if I could tell the difference with reducing my PK from 8° to 3.6°. I can confirm that AS has no business in how well your bike will pump and jump, and that an AS value of ~50% at SAG is horrendous to get the bike up to speed when needed. As for the PK reduction it is hard to tell as I didn't get a chance to move back to the 30t ring to compare. Since I had to borrow a shock for the weekend I can't compare with my 2 years of experience on that frame.
Another thing I would consider to explain why chain/derailleur less runs make suspension feel better is unsprung weight. I'd be curious to see how a run would feel with no chain/derailleur but the equivalent weight strapped to the rear axle, tight or slightly loose to mimic the chain moving around.
Another cool product I'm curious about. A couple years ago I would have thought it was hokey and unnecessary, but now after testing some of the...
Another cool product I'm curious about. A couple years ago I would have thought it was hokey and unnecessary, but now after testing some of the new pedal kickback devices I'm drinking the Koolaid. Here's a thought to add to the discussion: adjustable lower pulley position to remove as much lower chain growth as possible. Idlers go a long way towards addressing chain growth, but only on the top of the drivetrain. I was having a sidebar chat with Erwan Ghesquiere (fellow nerd on this forum) about lower pulley position, because he's messing around with a moveable lower pulley and was able to find a location that yields negative chain growth. Pretty cool! If you combine a pedal kickback device (like Ochain, Rimpact, Sidekick Hub, or idler) with a strategically-placed lower pulley, you would (in theory) be able to remove nearly all suspension-induced chain movement. Adjustability of the lower pulley location is key because its optimal position is dependent on pivot locations and will be different for every bike. I'm curious if there will be a chainguide in the near future with independently adjustable upper and lower guide components, so you can adjust the top for chain retention and adjust the bottom for chain growth.
I’m on board with this idea. I rode my Kavenz VHP last season with no lower guide pulley. The high pivot is great for reducing pedal...
I’m on board with this idea. I rode my Kavenz VHP last season with no lower guide pulley. The high pivot is great for reducing pedal kickback, but after tearing a derailleur off and riding a chainless lap at Whistler, the rear end without a doubt worked more freely, which I chalked up to having no chain or derailleur. This season Kavenz made a dedicated lower idler guide, the first thing I noticed was how when cycling the suspension the derailleur moved backward instead of being pulled forward. After riding it for the majority of this season, I’m convinced it allows the rear end to move more freely, while also reducing chain slap/noise.
Saddly some events didn't allow me to do all the testing I wanted to do this weekend, keep in mind that I also had to ride...
Saddly some events didn't allow me to do all the testing I wanted to do this weekend, keep in mind that I also had to ride with a different shock since mine blew up last week.
- Lower chain guide: basically the same as Dolface, quieter and you can visually see your derailleur moving much less when cycling your suspension (I don't have an upper pulley). Now for the noise reduction it often misslead you to think the bike is also smoother, and I didn't have a chance to test a lower pulley position that wouldn't reduce lower chain growth but would still keep the chain more stable.
- AS to PK to dynamic behaviour: I wanted to test my frame with a 38t ring instead of 30t (gear ration held constant, so 17t vs 13t cogs) to see if reduced AS values impact the bike dynamic behaviour (pumping, jumping) and if I could tell the difference with reducing my PK from 8° to 3.6°. I can confirm that AS has no business in how well your bike will pump and jump, and that an AS value of ~50% at SAG is horrendous to get the bike up to speed when needed. As for the PK reduction it is hard to tell as I didn't get a chance to move back to the 30t ring to compare. Since I had to borrow a shock for the weekend I can't compare with my 2 years of experience on that frame.
Another thing I would consider to explain why chain/derailleur less runs make suspension feel better is unsprung weight. I'd be curious to see how a run would feel with no chain/derailleur but the equivalent weight strapped to the rear axle, tight or slightly loose to mimic the chain moving around.
The key is that in a likelihood of experiencing kickback. The smaller the tooth count, the faster the shock can compress before you experience any kickback...
The key is that in a likelihood of experiencing kickback. The smaller the tooth count, the faster the shock can compress before you experience any kickback. The way to look at it is “if the chain gets pulled at some speed v, how fast does the freehub rotate and is that faster than the hub?” The smaller the tooth count, the faster the freehub spins for that given speed. How much exactly your cranks get rotated by an instance of kickback is a massive guess because in reality neither ends are fixed.
[EDIT: after your latest post it sounds like we're in agreement] "The smaller the tooth count, the faster the freehub spins for that given speed." But...
[EDIT: after your latest post it sounds like we're in agreement] "The smaller the tooth count, the faster the freehub spins for that given speed." But if the freehub spins faster than the hub, it will engage the hub, creating kickback, right?
Smaller tooth count ==> faster freehub spin ==> catches up with hub
Larger tooth count ==> slower freehub spin ==> doesn't catch up with hub
On a side note; It's been really interesting observing your journey into the topic of pedal kickback unfold from the sidelines. From denying its existence to doing unbiased real-world testing and making an actual effort to understand the physics behind the phenomenon is a transition that requies a commendably open mind.
I’m on board with this idea. I rode my Kavenz VHP last season with no lower guide pulley. The high pivot is great for reducing pedal...
I’m on board with this idea. I rode my Kavenz VHP last season with no lower guide pulley. The high pivot is great for reducing pedal kickback, but after tearing a derailleur off and riding a chainless lap at Whistler, the rear end without a doubt worked more freely, which I chalked up to having no chain or derailleur. This season Kavenz made a dedicated lower idler guide, the first thing I noticed was how when cycling the suspension the derailleur moved backward instead of being pulled forward. After riding it for the majority of this season, I’m convinced it allows the rear end to move more freely, while also reducing chain slap/noise.
Saddly some events didn't allow me to do all the testing I wanted to do this weekend, keep in mind that I also had to ride...
Saddly some events didn't allow me to do all the testing I wanted to do this weekend, keep in mind that I also had to ride with a different shock since mine blew up last week.
- Lower chain guide: basically the same as Dolface, quieter and you can visually see your derailleur moving much less when cycling your suspension (I don't have an upper pulley). Now for the noise reduction it often misslead you to think the bike is also smoother, and I didn't have a chance to test a lower pulley position that wouldn't reduce lower chain growth but would still keep the chain more stable.
- AS to PK to dynamic behaviour: I wanted to test my frame with a 38t ring instead of 30t (gear ration held constant, so 17t vs 13t cogs) to see if reduced AS values impact the bike dynamic behaviour (pumping, jumping) and if I could tell the difference with reducing my PK from 8° to 3.6°. I can confirm that AS has no business in how well your bike will pump and jump, and that an AS value of ~50% at SAG is horrendous to get the bike up to speed when needed. As for the PK reduction it is hard to tell as I didn't get a chance to move back to the 30t ring to compare. Since I had to borrow a shock for the weekend I can't compare with my 2 years of experience on that frame.
Another thing I would consider to explain why chain/derailleur less runs make suspension feel better is unsprung weight. I'd be curious to see how a run would feel with no chain/derailleur but the equivalent weight strapped to the rear axle, tight or slightly loose to mimic the chain moving around.
ahah good point. I guess I learned about sag before learning how to speak english and never questioned the use of the term, which is actually just an english word.
I’m on board with this idea. I rode my Kavenz VHP last season with no lower guide pulley. The high pivot is great for reducing pedal...
I’m on board with this idea. I rode my Kavenz VHP last season with no lower guide pulley. The high pivot is great for reducing pedal kickback, but after tearing a derailleur off and riding a chainless lap at Whistler, the rear end without a doubt worked more freely, which I chalked up to having no chain or derailleur. This season Kavenz made a dedicated lower idler guide, the first thing I noticed was how when cycling the suspension the derailleur moved backward instead of being pulled forward. After riding it for the majority of this season, I’m convinced it allows the rear end to move more freely, while also reducing chain slap/noise.
Saddly some events didn't allow me to do all the testing I wanted to do this weekend, keep in mind that I also had to ride...
Saddly some events didn't allow me to do all the testing I wanted to do this weekend, keep in mind that I also had to ride with a different shock since mine blew up last week.
- Lower chain guide: basically the same as Dolface, quieter and you can visually see your derailleur moving much less when cycling your suspension (I don't have an upper pulley). Now for the noise reduction it often misslead you to think the bike is also smoother, and I didn't have a chance to test a lower pulley position that wouldn't reduce lower chain growth but would still keep the chain more stable.
- AS to PK to dynamic behaviour: I wanted to test my frame with a 38t ring instead of 30t (gear ration held constant, so 17t vs 13t cogs) to see if reduced AS values impact the bike dynamic behaviour (pumping, jumping) and if I could tell the difference with reducing my PK from 8° to 3.6°. I can confirm that AS has no business in how well your bike will pump and jump, and that an AS value of ~50% at SAG is horrendous to get the bike up to speed when needed. As for the PK reduction it is hard to tell as I didn't get a chance to move back to the 30t ring to compare. Since I had to borrow a shock for the weekend I can't compare with my 2 years of experience on that frame.
Another thing I would consider to explain why chain/derailleur less runs make suspension feel better is unsprung weight. I'd be curious to see how a run would feel with no chain/derailleur but the equivalent weight strapped to the rear axle, tight or slightly loose to mimic the chain moving around.
On a side note; It's been really interesting observing your journey into the topic of pedal kickback unfold from the sidelines. From denying its existence to...
On a side note; It's been really interesting observing your journey into the topic of pedal kickback unfold from the sidelines. From denying its existence to doing unbiased real-world testing and making an actual effort to understand the physics behind the phenomenon is a transition that requies a commendably open mind.
Thanks! It's been a fun journey. Bikes are cool, and I really appreciate having a place to discuss this stuff with so many knowledgeable people. The amount of mechanical engineers and industry workers in this forum makes it a pretty lively forum.
The size of the cog corresponds to how fast the chain length has to be growing in order for the freehub to “catch up” with the...
The size of the cog corresponds to how fast the chain length has to be growing in order for the freehub to “catch up” with the wheel speed. In a really low gear the chain has to be going super fast to spin the freehub fast enough. Not too different from how you’ll spin out if you drop it into gear 1 while going full speed. Whether or not to count the chainring is a whole other question. If you’re strong enough then you can pretty much say it’s rotationally fixed in which case its size doesn’t matter.
As for speed I completely agree. I can think of very few spots in local trails where I ever get going that fast.
Despite your description I still couldn't see it, so I drew it with values. Three hypothetical chainring/cog combos, two with the same 3:1 final drive ratio...
Despite your description I still couldn't see it, so I drew it with values. Three hypothetical chainring/cog combos, two with the same 3:1 final drive ratio but different sized rear cogs, and two drivetrains with the same size rear cogs but different final drive ratios (3:1 vs. 1:1). I'm not an engineer so I'm happy to be wrong, but I came to the opposite conclusion, and it looks like, in terms of pedal kickback, a bigger rear cog is better for the same gear ratio. Please chime in and point out if my values, arrows, or math are wrong.
The arrows represent where chain growth is happening and the direction of forces occurring in the drivetrain. It looks a little weird at first, because horizontal chain velocity is the value I kept constant across all three models. I kept horizontal chain velocity the same because (roughly speaking) that's the direction where acceleration happens in a harsh suspension compression as the rear axle moves away from the BB. It also looks weird because I drew it on MS Paint. I didn't calculate the real value for "x" because I didn't care, but you could if you wanted to. You'd have to measure the diameters of different cog and chainring sizes. Here are my takeaways:
1. The blue drivetrain (big rear cog, high gear ratio) will only experience pedal kickback at lower speeds relative to the other two. If your rear suspension compresses and your rear axle moves away from the BB at a velocity of "x" meters per second, the blue drivetrain will experience pedal kickback at all trail speeds where the rear wheel is spinning at 90 rpm or lower (roughly 8 mph with a 29" rear wheel). By contrast, the red drivetrain with the same gear ratio would experience pedal kickback at speeds up to 24 mph (rear wheel spinning at 270 rpm or less). The blue drivetrain won't have pedal kickback in the 8-24 mph range, which is preferred.
2. However, at a speed of 24 mph or less, the red drivetrain (small rear cog, high gear ratio) will produce less pedal kickback at the crank than the green drivetrain given the same suspension compression. At similar trail speeds (rear hub rotational velocity) and impacts, the green drivetrain will accelerate the cranks more (a velocity of 270 rpm vs. 90 rpm for the red drivetrain), which results in more radians of rotation at the crank for the same radians of rotation at the freehub.
As soon as you lock up all bets are off course. To be honest I’ve never really ridden anything where I found pedal kickback to be...
As soon as you lock up all bets are off course. To be honest I’ve never really ridden anything where I found pedal kickback to be annoying beyond when the wheel is locked up. Even going back to back with and without chain. There’s a part of me that actually kind of likes being able to use chain tension to keep it a little higher. Let the cranks rotate backwards a little on landing and the impact is lessened using more travel. Keep feet entirely flat and push through it for more efficiency.
I feel that heavy braking is the largest contributor/least discussed for pedal kick. The situation where you might be locking up the rear brake but still...
I feel that heavy braking is the largest contributor/least discussed for pedal kick. The situation where you might be locking up the rear brake but still using a good amount of travel is the exact situation where you’d really want your suspension performing at its best
@Blake_Motley Agreed, steep chunky stuff is really the only place I notice it.
I asked ChatGPT what Sesame Seed was talking about and to be okay with being brutally honest and distasteful if it wants. Enjoy:This comment seems to...
I asked ChatGPT what Sesame Seed was talking about and to be okay with being brutally honest and distasteful if it wants. Enjoy:
This comment seems to be a convoluted attempt at drawing parallels between professional bike racing and motorsports, particularly Formula 1, but it’s a jumbled mess of loose associations and misplaced terminology. Let’s break it down brutally:
1. Chain Drive Skepticism: The commenter kicks off with skepticism about recent changes to bike racing due to “chain drive,” but gives no real details or context for what exactly they are skeptical about. It feels like they are grasping at straws, trying to sound knowledgeable while being vague about their actual critique.
2. Motility and Suspension Nonsense: They throw in the term “motility” from motorsports, trying to sound profound by equating it with bike suspension and the manipulation of gravity. This is a bizarre, over-complicated analogy that tries to link the biological term with bike mechanics in a way that doesn’t really make sense or add anything to the argument. It feels like an attempt to sound smart, but ends up being pretentious and confusing.
3. Useless F1 Comparison: The person rambles about how there is no connection between downhill (DH) biking and Formula 1, but goes on to compare them anyway, just to say there’s no point in comparing them. They even mention they’ve never heard anyone call a Formula 1 car “the DH Bicycle of Motorsport”—which is, unsurprisingly, irrelevant because no one in their right mind would make that comparison in the first place. It’s a strawman argument that detracts from any valid point they might have tried to make.
4. Cost Cap Irrelevance: They seem to miss the mark entirely on the concept of cost caps. In motorsport, cost caps are imposed to level the playing field between teams with different budgets. But how this is relevant to UCI or professional biking is left unclear. They seem to want UCI to enforce stricter part regulations, but don’t explain why or how this would improve the sport.
5. Ship of Theseus Tangent: They throw in some pseudo-philosophical garbage about the “Ship of Theseus” to imply that the constant upgrading of parts in biking removes any claim to originality. This is an overblown and irrelevant philosophical detour that doesn’t help their argument—whatever it even is at this point.
6. Mass Dampers and Renault’s Aero Advantage: They attempt to end on a high note by throwing in technical jargon about “mass dampers,” likening them to a decade-old strategy used by Renault in F1 to reduce tire rebound. The implication here is that people relying on mass dampers in biking are compensating for poor skills. But this comparison feels forced and unclear, as the two sports have very different engineering challenges.
In conclusion, the comment is an incoherent mess. The author tries to blend unrelated concepts from motorsport and biking to sound insightful, but instead they come across as someone with surface-level knowledge throwing around technical terms to mask the lack of a coherent point. It’s a hodgepodge of overreaching analogies and poorly articulated frustration that ultimately says very little.
I just hope one day we as a community will stop trying to compare DH or any form of bike racing to motorsports. Now if you'll...
I just hope one day we as a community will stop trying to compare DH or any form of bike racing to motorsports. Now if you'll excuse me, I'm going to go and try to figure out how to make high pivot moto suspension for ultimate enduro prowess.
I'll just use a jack shaft and an extra chain with 1 to 1 cogs. Easy easy.
A 5 m/s wheel speed input, which is reasonably fast, although not impossibly fast at all, 30 kph is right around where you wouldn’t experience kickback when in a 10t gear. 8 m/s is about as fast as you’ll ever see if I remember right. That would correspond to 49 kph. This is all using a typical leverage ratio at 50% travel for a 170 mm bike with a 65 mm stroke shock.
I’ve got something I’m working on right now that will have a massive range of leverage curves and axle paths. I’ll try and remember to share some data from that.
Thanks for the answer. To my earlier point, 30-49 km/h is real quick on a rough track with turns.
Dumb question: why would rear cog size matter for pedal kickback? Some people in this chat and the Rulezman video suggested that a smaller chainring would help you stay in a smaller rear cog, which would result in less kickback. To my thinking, it doesn't really matter what the size of the cogs is, only what the final drive ratio is. A crank would move just as much from a suspension compression if the bike was running a 36/17 ratio or a 28/13. The crank moves because the chainring moves, the chainring moves because the chain moves, and the final drive ratio determines how much the chain moves for a given rear axle rotation. Not saying I'm right, but that's my mental model. Tell me why I'm wrong.
The size of the cog corresponds to how fast the chain length has to be growing in order for the freehub to “catch up” with the wheel speed. In a really low gear the chain has to be going super fast to spin the freehub fast enough. Not too different from how you’ll spin out if you drop it into gear 1 while going full speed. Whether or not to count the chainring is a whole other question. If you’re strong enough then you can pretty much say it’s rotationally fixed in which case its size doesn’t matter.
As for speed I completely agree. I can think of very few spots in local trails where I ever get going that fast.
You wouldn’t experience pedal kickback*
*until you use your brakes right, when your wheel is rotating at as little as 0m/s?
As soon as you lock up all bets are off course. To be honest I’ve never really ridden anything where I found pedal kickback to be annoying beyond when the wheel is locked up. Even going back to back with and without chain. There’s a part of me that actually kind of likes being able to use chain tension to keep it a little higher. Let the cranks rotate backwards a little on landing and the impact is lessened using more travel. Keep feet entirely flat and push through it for more efficiency.
I feel that heavy braking is the largest contributor/least discussed for pedal kick. The situation where you might be locking up the rear brake but still using a good amount of travel is the exact situation where you’d really want your suspension performing at its best
Despite your description I still couldn't see it, so I drew it with values. Three hypothetical chainring/cog combos, two with the same 3:1 final drive ratio but different sized rear cogs, and two drivetrains with the same size rear cogs but different final drive ratios (3:1 vs. 1:1). I'm not an engineer so I'm happy to be wrong, but I came to the opposite conclusion, and it looks like, in terms of pedal kickback, a bigger rear cog is better for the same gear ratio. Please chime in and point out if my values, arrows, or math are wrong.
The arrows represent where chain growth is happening and the direction of forces occurring in the drivetrain. It looks a little weird at first, because horizontal chain velocity is the value I kept constant across all three models. I kept horizontal chain velocity the same because (roughly speaking) that's the direction where acceleration happens in a harsh suspension compression as the rear axle moves away from the BB. It also looks weird because I drew it on MS Paint. I didn't calculate the real value for "x" because I didn't care, but you could if you wanted to. You'd have to measure the diameters of different cog and chainring sizes. Here are my takeaways:
1. The blue drivetrain (big rear cog, high gear ratio) will only experience pedal kickback at lower speeds relative to the other two. If your rear suspension compresses and your rear axle moves away from the BB at a velocity of "x" meters per second, the blue drivetrain will experience pedal kickback at all trail speeds where the rear wheel is spinning at 90 rpm or lower (roughly 8 mph with a 29" rear wheel). By contrast, the red drivetrain with the same gear ratio would experience pedal kickback at speeds up to 24 mph (rear wheel spinning at 270 rpm or less). The blue drivetrain won't have pedal kickback in the 8-24 mph range, which is preferred.
2. However, at a speed of 24 mph or less, the red drivetrain (small rear cog, high gear ratio) will produce less pedal kickback at the crank than the green drivetrain given the same suspension compression. At similar trail speeds (rear hub rotational velocity) and impacts, the green drivetrain will accelerate the cranks more (a velocity of 270 rpm vs. 90 rpm for the red drivetrain), which results in more radians of rotation at the crank for the same radians of rotation at the freehub.
3. I need to find an alternative to MS Paint.
Am I way off base or does that check out?
The key is that in a likelihood of experiencing kickback. The smaller the tooth count, the faster the shock can compress before you experience any kickback. The way to look at it is “if the chain gets pulled at some speed v, how fast does the freehub rotate and is that faster than the hub?” The smaller the tooth count, the faster the freehub spins for that given speed. How much exactly your cranks get rotated by an instance of kickback is a massive guess because in reality neither ends are fixed.
Smaller cog equals worse for pedal kickback in the sense that it is more likely. So making everything bigger is helpful. I think that aligns with what you wrote. To be clear, to me low gear on the cassette equals high tooth count.
[EDIT: after your latest post it sounds like we're in agreement] "The smaller the tooth count, the faster the freehub spins for that given speed." But if the freehub spins faster than the hub, it will engage the hub, creating kickback, right?
Smaller tooth count ==> faster freehub spin ==> catches up with hub
Larger tooth count ==> slower freehub spin ==> doesn't catch up with hub
You are correct, reading more about it mine was an oversimplification. Still, if pk is just a function of gearing, frame design, wheel speed, and wheel vertical acceleration (is it?) we could still calculate what speed you need to be going to not feel pedal kickback while the suspension is moving at a certain speed. In theory, with data acquisition you could even calculate the % of time you spend while being susceptible to pk during a full run. That'd be interesting to see.
Edit: sorry I somehow missed a lot of posts discussing this.
Saddly some events didn't allow me to do all the testing I wanted to do this weekend, keep in mind that I also had to ride with a different shock since mine blew up last week.
- Lower chain guide: basically the same as Dolface, quieter and you can visually see your derailleur moving much less when cycling your suspension (I don't have an upper pulley). Now for the noise reduction it often misslead you to think the bike is also smoother, and I didn't have a chance to test a lower pulley position that wouldn't reduce lower chain growth but would still keep the chain more stable.
- AS to PK to dynamic behaviour: I wanted to test my frame with a 38t ring instead of 30t (gear ration held constant, so 17t vs 13t cogs) to see if reduced AS values impact the bike dynamic behaviour (pumping, jumping) and if I could tell the difference with reducing my PK from 8° to 3.6°. I can confirm that AS has no business in how well your bike will pump and jump, and that an AS value of ~50% at SAG is horrendous to get the bike up to speed when needed. As for the PK reduction it is hard to tell as I didn't get a chance to move back to the 30t ring to compare. Since I had to borrow a shock for the weekend I can't compare with my 2 years of experience on that frame.
Another thing I would consider to explain why chain/derailleur less runs make suspension feel better is unsprung weight. I'd be curious to see how a run would feel with no chain/derailleur but the equivalent weight strapped to the rear axle, tight or slightly loose to mimic the chain moving around.
What is SAG an abbreviation of?
On a side note; It's been really interesting observing your journey into the topic of pedal kickback unfold from the sidelines. From denying its existence to doing unbiased real-world testing and making an actual effort to understand the physics behind the phenomenon is a transition that requies a commendably open mind.
ahah good point. I guess I learned about sag before learning how to speak english and never questioned the use of the term, which is actually just an english word.
50% SAG = 50% Screen Actors Guild. Duh. You should know that, you're in BH
Thanks! It's been a fun journey. Bikes are cool, and I really appreciate having a place to discuss this stuff with so many knowledgeable people. The amount of mechanical engineers and industry workers in this forum makes it a pretty lively forum.
@Blake_Motley Agreed, steep chunky stuff is really the only place I notice it.
I'll just use a jack shaft and an extra chain with 1 to 1 cogs. Easy easy.
taking all recent discussion into account, I'm thinking this with an ochain will be my next ride.
And an e13 Sidekick hub for safety purposes.
Their rear suspension design must be horrible to warrant such a design to combat pedal kickback. Cant blame the owner. 1000 iq design.
Back to tech rumors!
An interesting drivetrain on the KTMs!
Looks like it’s wireless and the derailleur seems very close to the rear triangle…
Eleven speed linkglide too
Edit: Here's one that isn't blurred out, not that you see very much more.
Edit x2: oh...
This one is TRP E.A.S.I. A12 as pictured thiugh
There's also this in the regular bike catalog.
The text which has had a filter applied, when copied, spits out this:
R.DERAILL. Shimano XTR Di2 M9250-12 GS shadow+
SHIFTLEV. Shimano XTR Di2 M9250
CRANKSET Shimano XTR M9200-12 Carbon 32T
BOTTOM BR. Shimano MT900 pressfit PA29 MTB
SPROCKET Shimano XTR M9200-12 / 9-45
CHAIN Shimano M9100-12
So that's Shimano's first(?) carbon cranks confirmed?
And the brake name is in full view, the new protos we've seen aren't saint? M9220 seems it would be the 4 piston variant.
Sorry Shimano, but there's more:
Shimano Deore XT Di2 M8250-12 GS shadow+
Shimano Deore XT Di2 M8250
Shimano Deore XT M8200-12 30T
Shimano MT800 pressfit MTB
Shimano Deore XT M8200-12 / 9-45
Shimano M8100-12
And M8200 brakes. So at least XTR and XT will be moving to the new lever shape?
Still 12s, Carbon cranks (at least in xtr trim), and they don't look like direct mount derailleurs.
9-45t seems like an odd choice, arent 10t sprockets inefficient enough already?
The source of the pics?
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