[Pslide]

Is 100% antisquat really quantifiable, or is it more of a "qualitative" theoretical value? ... Certainly "100%" can't be 100% of the time.

To Pslide's point- if you're using chain torque to counteract pedaling forces, you're also counteracting suspension forces. So, wouldn't you lose some "suppleness" in the suspension when you're pedaling and therefore using chain force to firm up the rear end? ...

#1 is a very good question. With so many variables, it must be semi-arbitrary.

And #2 is a very good point. You are definitely right, but it depends on what the rider wants. How many people are pedaling through really rough sections? Perhaps not many, so maybe the trade off is worth it. I'd agree there is a upper limit, but the ideal amount of anti-squat is pretty rider subjective, and once again we see how many ways there are to skin a cat.

This trade-off is why Keith Scott is a very good designer. The Legend has lots of anti-squat at the sag point where you need it, but the chain stretch reduces as the suspension compresses, so you get the best of both worlds.

 

[fl1ppo]

I have always been skeptical about this anti squat stuff at dh bikes.
For me a simple neutral single pivot feels best overall.
All other bikes I've ridden until now had some characteristics in certain conditions, that I didn't like. But maybe those bikes just didn't have the perfect setup for me...

 

[TrueScotsman]

I have always been skeptical about this anti squat stuff at dh bikes.
For me a simple neutral single pivot feels best overall.

Could you enlighten us to what a simple neutral pivot is?

 

[TrueScotsman]

Is 100% antisquat really quantifiable, or is it more of a "qualitative" theoretical value? I mean, 100% is a great term to throw around, but the amount of chain torque required to achieve equal and not more or less mass-reactive force is going to change with rider positioning, bike positioning, suspension setup (soft or firm, if it's a position sensitive design it'll be at different positions of sag) as well as trail conditions and pedaling characteristics. Certainly "100%" can't be 100% of the time.

Quite right, 100% A-S is going to change as a rider moves around, etc. BUT, surely this is not a reason to not aim for 100% Anti-Squat but rather to analyse how the rider/bike moves around better to give an even more accurate model to aim for. I have often thought that a camera mounted to the side of a bike on a long pole would be very interesting to watch- the bike would remain static but you would be able to see how the COM moves around it.

 

[davec113]

Is 100% antisquat really quantifiable, or is it more of a "qualitative" theoretical value? I mean, 100% is a great term to throw around, but the amount of chain torque required to achieve equal and not more or less mass-reactive force is going to change with rider positioning, bike positioning, suspension setup (soft or firm, if it's a position sensitive design it'll be at different positions of sag) as well as trail conditions and pedaling characteristics. Certainly "100%" can't be 100% of the time.

Yes, it is quantifiable, but will have a lot of variables confusing the issue. Most bikes are designed to have anti-squat at the sag point to counteract pedaling forces, then less a/s as the sus progresses through its travel. My example of the Uzzi VPX is a bike that had a LOT of antisquat built into the sus design, it is/was a selling point of vpp because of it's increased traction and ability to reduce pedal bob when climbing. VPP2 is not nearly as extreme as the original vpp...

To Pslide's point- if you're using chain torque to counteract pedaling forces, you're also counteracting suspension forces. So, wouldn't you lose some "suppleness" in the suspension when you're pedaling and therefore using chain force to firm up the rear end? So yes, you won't be wasting energy against "bob", but you'll be wasting suspension capabilities. I think that's why, in theory, I think a bike with little or no anti-squat under non-climbing applications works well. That way the suspension is always working. It's then up to the rider to not mash pedals and activate the suspension.

The sus would work with less restriction but you'd have less traction and more pedal bob, the result would be a poor climbing bike, and a poor pedaling bike in general... the only way to have a neutral sus like that would be a pivot around the BB, and I think we all know that doesn't make for a good ride.

The other issue that affects climbing and pedal bob is how progressive the sus is... a more linear sus bobs a lot less than a progressive sus, which needs to rely more on a/s to not bob. A lot of trail bikes are moving to a sus with a very linear leverage rate curve which has it's tradeoffs vs. a more progressive design... I think it works well for a lot of trail conditions but not as well on jumps and bigger hits vs. a progressive sus.

DH bikes need anti squat to pedal efficiently, and are designed around a single front ring. This is part of why single pivot bikes pivot locations are all about the same these days... also, with that pivot location, after the 1st part of travel the axle stops moving backward so you don't have pedal feedback after about 50% travel.

 

[davec113]

For me a simple neutral single pivot feels best overall.

The only way to have a neutral single pivot is to have the pivot concentric with the bottom bracket. One of my friends rides an old Lenz Pro Descender which has such a sus but it isn't the model of pedaling efficiency and certainly won't be as fast as a bike with a/s... also, the rear axle starts moving forward almost immediately with this design, which isn't optimal... single pivots with higher pivot locations have a rearward axle path for the 1st part of their travel before it reverses course and moves forward in the last part of its travel. I think it would feel a little weird to ride a bike that gets shorter as the sus cycles too.

 

[Pslide]

This is part of why single pivot bikes pivot locations are all about the same these days... also, with that pivot location, after the 1st part of travel the axle stops moving backward so you don't have pedal feedback after about 50% travel.

I agree with all of what you're saying but this. You should check it in linkage. Single pivots (around the chain line) have more chain stretch in the last part of travel than you would think. There will definitely still be some pedal feedback.

It's funny how we rehash all of these suspension design principles on a regular basis...

 

[Steve M]

that's what I thought...but I'm thinking if you were to compress the suspension with firm pressure on the pedals (but no actual rotation) on a bike with lots of chain pull, at zero speed, you would effectively get some rotation of the wheel. Again, if the pedals are locked and no speed.

Yeah like I said, a wheelie drop or something might generate that acceleration, but that's only because you're able to transfer vertical motion into horizontal motion. You can't already be moving horizontally, get accelerated vertically by a bump (which by definition also needs to have some horizontal/backwards component to it if the bump force is being applied to a wheel) and then have that magically accelerate you forwards, that'd be a perpetual motion machine

Is 100% antisquat really quantifiable, or is it more of a "qualitative" theoretical value? I mean, 100% is a great term to throw around, but the amount of chain torque required to achieve equal and not more or less mass-reactive force is going to change with rider positioning, bike positioning, suspension setup (soft or firm, if it's a position sensitive design it'll be at different positions of sag) as well as trail conditions and pedaling characteristics. Certainly "100%" can't be 100% of the time.

To Pslide's point- if you're using chain torque to counteract pedaling forces, you're also counteracting suspension forces. So, wouldn't you lose some "suppleness" in the suspension when you're pedaling and therefore using chain force to firm up the rear end? So yes, you won't be wasting energy against "bob", but you'll be wasting suspension capabilities. I think that's why, in theory, I think a bike with little or no anti-squat under non-climbing applications works well. That way the suspension is always working. It's then up to the rider to not mash pedals and activate the suspension.

100% anti-squat is entirely quantifiable. I gotta run right now but I'll explain exactly what anti-squat is, how it's relevant and how it affects the ride later tonight.

 

[fl1ppo]

Could you enlighten us to what a simple neutral single pivot is?

Actually, you got me. Now I am really confused with the term "anti-squat".
I thought with this it is meant, that the rear end extends unter pedaling, so that the downward mass transfer by the rider is balanced out.

But it seems like anti-squat is just a marketing word, and can stand for many different concepts.

I meant a single pivot were the pivot sits at the point where the chain touches the upper part of the chainring. So there is just a very small extension or compression on the rear end while pedaling.

The only way to have a neutral single pivot is to have the pivot concentric with the bottom bracket. One of my friends rides an old Lenz Pro Descender which has such a sus but it isn't the model of pedaling efficiency and certainly won't be as fast as a bike with a/s... also, the rear axle starts moving forward almost immediately with this design, which isn't optimal... single pivots with higher pivot locations have a rearward axle path for the 1st part of their travel before it reverses course and moves forward in the last part of its travel. I think it would feel a little weird to ride a bike that gets shorter as the sus cycles too.

Ah, I think I got it. 100% anti-squat seems to be what I have thought of being "neutral".
Having a pivot concentric with the bottom bracket, or a gear box bike with the pivot being concentric with the cog-wheel isn't neutral at all to me as those move the rear end massive while pedaling. But I guess, this is just a term-thing. How I hate confusing marketing...

 

[Wa-Aw]

Another benefit of chain torque counter acting suspension forces is keeping the BB steady or even raising the BB in times of pedalling. I notice this in my M9 vs past bikes which found ways to snag pedals on the ground despite having much higher BB heights. Also the M9 also seems to pedal a lot better and "higher" when it's in the linear positions vs the progressive ones.

 

[davec113]

I agree with all of what you're saying but this. You should check it in linkage. Single pivots (around the chain line) have more chain stretch in the last part of travel than you would think. There will definitely still be some pedal feedback.

It's funny how we rehash all of these suspension design principles on a regular basis...

Check out the 1st chart in this article and look at the axlepath in "main pivot 3". It has an inflection point approximately 50% of the way through travel...

Funny, the author of the article was in my Global Engineering class at CU, was finishing up his masters while working for Yeti... Hi Peter!

http://www.yeticycles.com/blog/?p=237

 

[davec113]

How I hate confusing marketing...

For me it was a little confusing because anti-squat (which isn't a marketing term, it's a real engineering measurement that can be calculated...) means different things in the bike world than motorized. In a motor vehicle anti squat is calculated wrt the force of the tire on the ground, and will tell you how much the rear end of the vehicle will squat down under acceleration... in bikes a/s usually is the how the chain forces affect weight transfer, but the result is still a measurement of how much the rear end will squat.

From what you said, I also think by "neutral" you mean 100% anti-squat, so the pedaling forces cancel out bob, but don't actually try to extent the sus like vpp. I agree and I like this type of sus design, and it seems like most single pivots are converging around this setup.

 

[Sandwich]

Yeah like I said, a wheelie drop or something might generate that acceleration, but that's only because you're able to transfer vertical motion into horizontal motion. You can't already be moving horizontally, get accelerated vertically by a bump (which by definition also needs to have some horizontal/backwards component to it if the bump force is being applied to a wheel) and then have that magically accelerate you forwards, that'd be a perpetual motion machine



100% anti-squat is entirely quantifiable. I gotta run right now but I'll explain exactly what anti-squat is, how it's relevant and how it affects the ride later tonight.

Well, you wouldn't be able to start going 90 by hitting a few ripples in the trail, but you might be able to squirt out of a berm at just a bit faster instead of slowing down, or have the wheel rotate forward over a bump and be MOAR efficient instead of just absorbing it.

I'm not saying 100% AS isn't quantifiable at any one moment, but rather that quantifying it for a suspension design is far more convoluted as there are so many factors that go into both anti-squat and mass-transfer (squat) forces. If i'm wrong, I'll gladly shut up and get educated!

 

[Sandwich]

The sus would work with less restriction but you'd have less traction and more pedal bob, the result would be a poor climbing bike, and a poor pedaling bike in general... the only way to have a neutral sus like that would be a pivot around the BB, and I think we all know that doesn't make for a good ride.

Not necessarily. The brooklyn I had (which is and idler equipped bike) pedaled quite well. There should have been zero or negligible AS on that frame. The trick was the pivot location. Instead of the BB where all your weight is (the fulcrum point of the suspension) it was up higher, so your weight on the pedals was slightly offset. Think about standing on a teeter totter.

The other issue that affects climbing and pedal bob is how progressive the sus is... a more linear sus bobs a lot less than a progressive sus, which needs to rely more on a/s to not bob. A lot of trail bikes are moving to a sus with a very linear leverage rate curve which has it's tradeoffs vs. a more progressive design... I think it works well for a lot of trail conditions but not as well on jumps and bigger hits vs. a progressive sus.

Are you sure? I would think a progressive bike would react better since theoretically you are getting a higher damping rate and spring rate as you go into travel. So, every time you compress the suspension by pedaling, you have a natural rate increase against your fat ass on the pedals. If it were linear, it would move MOAR. In fact, I'm not sure linear rates are good unless you're dealing with a damper with it's own internal progression or platform system. It seems like most people want a degree of progression in the leverage rate to resist bottoming while still yielding a supple initial stroke. DW uses a dual rate curve, which I admittedly do not fully understand the benefit of, but I believe allows the suspension to react better post sag, pre bottom out. I wasn't aware of whether he used it for pedaling prowess though.

 

[davec113]

Not necessarily. The brooklyn I had (which is and idler equipped bike) pedaled quite well. There should have been zero or negligible AS on that frame. The trick was the pivot location. Instead of the BB where all your weight is (the fulcrum point of the suspension) it was up higher, so your weight on the pedals was slightly offset. Think about standing on a teeter totter.



Are you sure? I would think a progressive bike would react better since theoretically you are getting a higher damping rate and spring rate as you go into travel. So, every time you compress the suspension by pedaling, you have a natural rate increase against your fat ass on the pedals. If it were linear, it would move MOAR. In fact, I'm not sure linear rates are good unless you're dealing with a damper with it's own internal progression or platform system. It seems like most people want a degree of progression in the leverage rate to resist bottoming while still yielding a supple initial stroke. DW uses a dual rate curve, which I admittedly do not fully understand the benefit of, but I believe allows the suspension to react better post sag, pre bottom out. I wasn't aware of whether he used it for pedaling prowess though.

Your brooklyn's idler was probably positioned to provide some level of anti squat...

Bikes with a more progressive sus (w/o taking a/s into account) do seem to bob more because from the top of the sus has a higher leverage on the shock... so a 3:1 bike with a progressive sus might have a 4:1 rate at the top of the stroke and ramp up to 2:1 at bottom out while a linear bike always has a 3:1 leverage rate. This is just from personal experience... my '09 Remedy has a very linear sus... way too linear IMO but it does help with pedaling efficiency and plushness on small-medium hits, you just run out of sus on bigger hits, jumps and g-outs. DW link has a more progressive sus than a lot of others at the moment... some people think it has more of a "dead" feel to it vs. other bikes with a linear sus but I definitely prefer a more progressive feel as I'm sure most dh riders do.

 

[Pslide]

Check out the 1st chart in this article and look at the axlepath in "main pivot 3". It has an inflection point approximately 50% of the way through travel...

The axle may be moving forward once it goes beyond the inflection point, but the chainstay length is still growing relative to the BB.

Your buddy is a lucky dude!

 

[P.T.W]

Seems to me that to discuss this subject properly a lot of you guys need to decide whether you are talking about Anti squat in the traditional sense, or chain induced pedal feed back/chain pull? As they are two different things that are usually closely related, but can be "tuned" separately at the design phase of the frame. I could tell you but i think it will take DW or Socket to explain it fully or you could just teach yourself and use your old friend Google

P.S Seems to me that Sandwich original post is about using high amounts of chain pull to aid in pumping the bike. Am i right Sandwich?

 

[Steve M]

Part 1: What Anti-squat actually is:

Ok here we go... Anti-squat is a measurable performance characteristic. That doesn't mean that "more is better", it's simply a way to measure the BALANCE of forces that are acting to either compress or extend the suspension. When a vehicle accelerates forwards, because the centre of mass is above ground level, you get a rearwards load shift (more weight on the rear wheel). The technical reason for this is that the line of force that is accelerating you (the horizontal traction force at the tyre), isn't acting directly through your centre of mass, so it's trying to rotate you backwards, thus loading up the rear tyre. This is what causes the suspension to compress, and the fact that pedalling loads are far from constant (can vary from full load to almost zero every cycle) means that you get an uneven, sinusoidal acceleration rather than a smooth, near-constant acceleration like an engine can deliver. This means that your weight is constantly shifting backwards and forwards, loading and unloading your rear wheel, hence causing the bob.

100% anti-squat is defined as all acceleration-related forces in the vehicle, cancelling each other out, such that the forwards acceleration of the bike does not extend or compress the suspension. Your body mass moving up and down when you pedal is not considered a "forwards acceleration" force, and unfortunately the sinusoidal vertical acceleration of your body due to the pedalling motion is somewhat out of phase with the sinusoidal horizontal acceleration of the bike, so there isn't any easy way to simply alter the amount of anti-squat (from 100%) to totally eliminate bobbing.

The defining points on the anti-squat curve are basically 0% and 100%. 0% anti-squat refers to a situation where the acceleration forces within the bike (chain force and driving force at the axle) don't offer any extension or compression force to the suspension. That is to say, that if you considered all the forces acting on the rear suspension as you pedal, they would all cancel out exactly EXCEPT the vertical loading/unloading caused by your uneven acceleration. 100% anti-squat is where they all cancel out INCLUDING the vertical loading/unloading caused by your uneven acceleration, in other words, the acceleration-related forces acting to extend the suspension are equal to 100% of the vertical-load-shift forces acting to compress (squat) the suspension - hence the term "anti-squat". 0% means that that there aren't any chain/drive forces acting to counteract the increased load on the rear wheel during acceleration, and below 0% anti-squat (negative anti-squat or positive pro-squat) is where the chain/drive forces actually help the increased vertical load to compress the suspension. Above 100% anti-squat means that the amount of force acting to extend the suspension, is more than 100% of the magnitude of the rearwards load shift that is trying to compress the suspension, so the net effect is actually extension.

Anti-squat characteristics are determined by both the chain force (which is pulling backwards on the front triangle through the BB or the idler) and the driving force on the axle. The driving force (or "impulsion force" as Cossalter refers to it) is the vector sum of the chain force (pulling the wheel forwards) and the tractive force at the tyre. This means that you can achieve a very high driving force at the axle, and get an appropriate degree of anti-squat out of it, without chain extension (at least at one instant in the travel) if your pivot is sufficiently high. This is why Brooklyns, Lahars, Supercos, most likely Zerodes etc all pedal quite well despite having far smaller amounts of chain extension (and therefore pedal kickback) than conventional-chainline bikes that pedal equally well. If you went to the other extreme, you could build a bike (though you'd never want to) that had a super low pivot below the BB, an altered chainline to get it way down below the BB, still use geometry that gave you 100% anti-squat, and get an unbelievably bad amount of pedal kickback out of it. In other words, anti-squat does NOT refer to how much chain extension a bike has - there is a relationship between the two, but more of one does not necessarily mean more of the other.

Hopefully this clears a few things up regarding the technical definitions.

 

[Steve M]

Part 2: How it's relevant to how a bike rides.

As mentioned above, suspended bikes bob when you pedal them, we all know this and we all hate the inefficiency of it, so we want to minimise that. Anti-squat is not a single figure like a steerer tube diameter, nor is it 12 different single figures like steerer tube diameters, but it's a number that changes continuously as the bike cycles through its travel. That basically means that it's best viewed as a curve on a graph, so you can understand how much you have and how it's changing vs travel. With conventional-chainline bikes, more anti-squat typically does mean more chain extension, so you only want as much as you need and only where you actually need it.

Generally speaking, the most refined designs with conventional chainlines will use a fairly constant amount of anti-squat around the sag region, and have it drop off fairly sharply after 50% travel to manage chain extension and reduce pedal kickback, however the high-pivot/low-chain-extension bikes generally don't need to do anything too fancy like that simply because the chain extension is low enough anyway.

Where you win and where you lose - gearing. Chainline is obviously decided by your gearing, and this massively affects the anti-squat characteristics, so you'll never have an "ideal" anti-squat profile across all your gears in every situation you ever find. When well set-up so that the kind of gear you'd usually push on flat ground nets you 100% anti-squat (this involves careful consideration by the designer of the frame), lower gears will generate higher amounts of extension forces, which is fairly lucky in that climbing steep hills also loads up the rear wheel harder with each pedal stroke (shorter effective wheelbase, higher CoM relative to direction of gravity) and thus requires higher extension forces in order to 100% balance the forces trying to compress the suspension. The reverse occurs when descending - you need less force to balance out the rearwards load shift, which is delivered by the higher gears you typically find yourself in when pedalling down a hill instead of up. Obviously, the ratios are never going to line up perfectly with the gradient you're riding on, but a good designer will keep them as close as possible.

 

[I.van]

Socket,

With regard to chainline and anti-squat, is the force 'vector' from the rear axle to the top of the front chainring, or is it from the top of the rear cog to the top of the front chainring. Or is it the magnitude of the force (torque) applied through the chain that matters and not the direction of the force so much?

 

[TrueScotsman]

Part 1: What Anti-squat actually is:

Ok here we go... Anti-squat is a measurable performance characteristic. That doesn't mean that "more is better", it's simply a way to measure the BALANCE of forces that are acting to either compress or extend the suspension. When a vehicle accelerates forwards, because the centre of mass is above ground level, you get a rearwards load shift (more weight on the rear wheel). The technical reason for this is that the line of force that is accelerating you (the horizontal traction force at the tyre), isn't acting directly through your centre of mass, so it's trying to rotate you backwards, thus loading up the rear tyre. This is what causes the suspension to compress, and the fact that pedalling loads are far from constant (can vary from full load to almost zero every cycle) means that you get an uneven, sinusoidal acceleration rather than a smooth, near-constant acceleration like an engine can deliver. This means that your weight is constantly shifting backwards and forwards, loading and unloading your rear wheel, hence causing the bob.

100% anti-squat is defined as all acceleration-related forces in the vehicle, cancelling each other out, such that the forwards acceleration of the bike does not extend or compress the suspension. Your body mass moving up and down when you pedal is not considered a "forwards acceleration" force, and unfortunately the sinusoidal vertical acceleration of your body due to the pedalling motion is somewhat out of phase with the sinusoidal horizontal acceleration of the bike, so there isn't any easy way to simply alter the amount of anti-squat (from 100%) to totally eliminate bobbing.The defining points on the anti-squat curve are basically 0% and 100%. 0% anti-squat refers to a situation where the acceleration forces within the bike (chain force and driving force at the axle) don't offer any extension or compression force to the suspension. That is to say, that if you considered all the forces acting on the rear suspension as you pedal, they would all cancel out exactly EXCEPT the vertical loading/unloading caused by your uneven acceleration. 100% anti-squat is where they all cancel out INCLUDING the vertical loading/unloading caused by your uneven acceleration, in other words, the acceleration-related forces acting to extend the suspension are equal to 100% of the vertical-load-shift forces acting to compress (squat) the suspension - hence the term "anti-squat". 0% means that that there aren't any chain/drive forces acting to counteract the increased load on the rear wheel during acceleration, and below 0% anti-squat (negative anti-squat or positive pro-squat) is where the chain/drive forces actually help the increased vertical load to compress the suspension. Above 100% anti-squat means that the amount of force acting to extend the suspension, is more than 100% of the magnitude of the rearwards load shift that is trying to compress the suspension, so the net effect is actually extension.

Anti-squat characteristics are determined by both the chain force (which is pulling backwards on the front triangle through the BB or the idler) and the driving force on the axle. The driving force (or "impulsion force" as Cossalter refers to it) is the vector sum of the chain force (pulling the wheel forwards) and the tractive force at the tyre. This means that you can achieve a very high driving force at the axle, and get an appropriate degree of anti-squat out of it, without chain extension (at least at one instant in the travel) if your pivot is sufficiently high. This is why Brooklyns, Lahars, Supercos, most likely Zerodes etc all pedal quite well despite having far smaller amounts of chain extension (and therefore pedal kickback) than conventional-chainline bikes that pedal equally well. If you went to the other extreme, you could build a bike (though you'd never want to) that had a super low pivot below the BB, an altered chainline to get it way down below the BB, still use geometry that gave you 100% anti-squat, and get an unbelievably bad amount of pedal kickback out of it. In other words, anti-squat does NOT refer to how much chain extension a bike has - there is a relationship between the two, but more of one does not necessarily mean more of the other.

Hopefully this clears a few things up regarding the technical definitions.

Wow, +rep Socket! You have a way of explaining things that is both educational and interesting.

Green highlighted part- hadn't considered this before- cheers for the education.

Orange highlighted part- is this (graphically) because the line of the chainline/swingarm is closer to parallel with the 100% A-S force line? Sorry, my brain generally works better with pictures!!!

 

[Steve M]

Socket,

With regard to chainline and anti-squat, is the force 'vector' from the rear axle to the top of the front chainring, or is it from the top of the rear cog to the top of the front chainring. Or is it the magnitude of the force (torque) applied through the chain that matters and not the direction of the force so much?

The force vector is exactly as the line of the chain goes, so tangent to the rear cog to tangent to the front cog. The magnitude actually doesn't matter much at all, because all the forces involved (chain force, tractive force, driving force, rearwards load shift due to acceleration) are proportional for any given gear, so in other words, if you push twice as hard on the pedals, you get twice the rearwards load shift, but you also get twice as much force counteracting it. If there is a net force left over (ie the extension force isn't exactly equal to the compressive force) then there will be a net extension or compression of the suspension that is obviously going to be somewhat proportional to the chain force (and hence how hard you're pedalling), but the closer you get to 100% anti-squat, the closer you get to zero net compressive or extensive force, which means you can pedal twice as hard with exactly the same reaction because 2 x 0 = 0.

 

[Steve M]

Wow, +rep Socket! You have a way of explaining things that is both educational and interesting.

Green highlighted part- hadn't considered this before- cheers for the education.

Orange highlighted part- is this (graphically) because the line of the chainline/swingarm is closer to parallel with the 100% A-S force line? Sorry, my brain generally works better with pictures!!!

Ah kind of - chainline being closer to parallel with the swingarm means closer to zero chain extension. This is why you sometimes feel a lot of pedal feedback when climbing in the granny ring on certain bikes, that you don't notice when climbing in the middle ring. The fact that it's closer to 100% AS is incidental really.

 

[fluider]

This is where gearboxes like Speedhub or GBoxx take huge advantage over conventional derailuer shi(f)ters. With typical derailuer drivetrain there is wide variation of chainline direction which leads to quite different AS characteristics throughout the entire gear range. However, gearbox provides you a gear shifting mechanism that does not effect the AS characteristic.

Haven't I already said I hate derailuers ?

 

[Steve M]

This is where gearboxes like Speedhub or GBoxx take huge advantage over conventional derailuer shi(f)ters. With typical derailuer drivetrain there is wide variation of chainline direction which leads to quite different AS characteristics throughout the entire gear range. However, gearbox provides you a gear shifting mechanism that does not effect the AS characteristic.

Haven't I already said I hate derailuers ?

Yeah but as I mentioned before, you win some, you lose some - having a single chainline also ignores the fact that you need different amounts of extension force to generate the same amount of anti-squat for different gradients. Fine if you're only ever pedalling on the same gradient (on a DH bike, I'd agree close enough is more or less good enough) but it's one of a few reasons why it's less suited for XC/AM stuff, besides the weight/driveline efficiency issues.

 

[monkeyfcuker]

I've really enjoyed this topic, thanks to all the contributers! Awesome last few posts Socket! I can't +rep you from my phone, but I'll get round to it.

 

[Steve M]

All this and not one "socket needs a girlfriend" tag?

 

[no skid marks]

I did chat with Orange about that idler setup. Apparently they ran an idler on some of their 224's, but they couldn't prove it worked or didn't - they even did chainless runs and got some fast times doing that as well.

They also tried forward pivot, low pivot, high pivot etc etc and best DH frame they made was the 224 evo

Did they try an idler on a 222? They should, that'd be their best bike yet IMO.
Speaking of the 222, it rode like a dog due to the pedal kickback. I don't care if super strong Peaty won on it, he'd probably have been faster still if it had an idler.

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.

Even with clips, it still feels like you've got less suspension as you're feeling the pedal kick back in your feet

So IMO no, pedal feedback is irrelevant for 99.9% of coasting situations.

I'm pretty sure from memory ever 222 I rode felt like a hardtail in the rocks. But I was probably breaking??

I have a Rune and this is the biggest negative of the frame. There is way too much anti-squat in a 22t chainring. When trying to stand up and pedal up a steep climb, I top-out the shock with every pedal stroke. sitting and spinning is ok though until it gets super steep.

Get a Hammershmidt. Isn't the term for this inchworming? Or was that just some marketing crap?

This trade-off is why Keith Scott is a very good designer. The Legend has lots of anti-squat at the sag point where you need it, but the chain stretch reduces as the suspension compresses, so you get the best of both worlds.

Um, isn't that what the Sunday does that DW designed? Is that the ultimate flattery from Scott to DW?

sus would work with less restriction but you'd have less traction and more pedal bob, the result would be a poor climbing bike, and a poor pedaling bike in general... the only way to have a neutral sus like that would be a pivot around the BB, and I think we all know that doesn't make for a good ride.

Or a pivot located Idler or gearbox output with same size sprockets etc.

Having a pivot concentric with the bottom bracket, or a gear box bike with the pivot being concentric with the cog-wheel isn't neutral at all to me as those move the rear end massive while pedaling. But I guess, this is just a term-thing. How I hate confusing marketing...

A concentric pivot isn't neutral if the sprockets aren't the same size. a 38 tooth front ring, and anything less on the back will have pro squat.

Not necessarily. The brooklyn I had (which is and idler equipped bike) pedaled quite well. There should have been zero or negligible AS on that frame. The trick was the pivot location. Instead of the BB where all your weight is (the fulcrum point of the suspension) it was up higher, so your weight on the pedals was slightly offset. Think about standing on a teeter totter.

Nope, it's due to the "Jack-Shaft" sprocket size, being closer to the rear cassettes sprocket sizes.

Chainline is obviously decided by your gearing, and this massively affects the anti-squat characteristics, so you'll never have an "ideal" anti-squat profile across all your gears in every situation you ever find.

Unless you have a gearbox and rear hub(or chainring if gearbox is rear hub)with the correct sized sprockets.

Wow, +rep Socket! You have a way of explaining things that is both educational and interesting.

For sure, He's getting heaps better at layman language. I only had to look up one word this time. and there were no "moments" mentioned. +2

 

[Pslide]

Interesting, thanks Socket. I guess I didn't realize that 100% anti-squat should counter all forces even when mashing on the pedals in a standing sprint.

So back to one of our original questions, is 100% anti-squat at the sag point all you'd ever need on a DH bike? The holy grail?

On a trail bike, I can see where over 100% can be beneficial to get a traction improvement for steep climbs, but this naturally occurs when you drop to granny ring anyway.

So is 100% at the sag point the ideal?

 

[daisycutter]

Zzzzzzzzzzzzzzzzz

 

[fluider]

Yeah but as I mentioned before, you win some, you lose some - having a single chainline also ignores the fact that you need different amounts of extension force to generate the same amount of anti-squat for different gradients. Fine if you're only ever pedalling on the same gradient (on a DH bike, I'd agree close enough is more or less good enough) but it's one of a few reasons why it's less suited for XC/AM stuff, besides the weight/driveline efficiency issues.

Fair point ! So bike needs more anti-squat for uphill pedalling due to 'with slope parallel' component of gravitational acceleration that adds to my own acceleration. Right ?

 

[Steve M]

Interesting, thanks Socket. I guess I didn't realize that 100% anti-squat should counter all forces even when mashing on the pedals in a standing sprint.

So back to one of our original questions, is 100% anti-squat at the sag point all you'd ever need on a DH bike? The holy grail?

On a trail bike, I can see where over 100% can be beneficial to get a traction improvement for steep climbs, but this naturally occurs when you drop to granny ring anyway.

So is 100% at the sag point the ideal?

Like I said, it can only really counter the forces generated by the forwards acceleration. The vertical acceleration of your body mass is in my estimation about 30 degrees out of phase with the forwards acceleration. 90 degrees out of phase would be worst possible, as in, your peak vertical acceleration would be at the time where horizontal acceleration is zero and vice versa, and 0 degrees out of phase (ie in phase) would mean you could potentially use anti-squat to entirely counteract your body mass induced movement of the suspension because all the vertical loading and unloading of the rear wheel would be happening at the same time.

In reality I suspect that the "optimum" value to minimise bob would be slightly higher than 100%, such that it accounted for the maximum vertical increase in load including those caused by both horizontal and vertical accelerations. Think of overlaying two slightly out of phase sin waves of different amplitudes, adding them together to get the sum total, picking the highest point and equating your extension force to that... and then I reckon you'd probably find the number you're looking for. Depending on the actual value of the phase shift, and the proportional values of body mass vertical acceleration force vs horizontal acceleration force, you could probably get it pretty close to "ideal". Graph below (totally arbitrary numbers, scale means nothing, proportions might be wrong by as much as 10 million percent as well).

 

[Steve M]

Fair point ! So bike needs more anti-squat for uphill pedalling due to 'with slope parallel' component of gravitational acceleration that adds to my own acceleration. Right ?

Well gravitational acceleration itself is constant, meaning constant force too, so that won't increase the transient (changing) load at the rear tyre when you accelerate. However, your centre of mass is up higher relative to the contact patch of the tyre, and your wheelbase shortens, which both affect how much additional vertical load is transferred to the back wheel when you accelerate.

Obviously, the same amount of load comes off the front wheel too, which everyone is familiar with, because whenever you climb something steep, your front wheel wants to pop up all the time. Think of it this way - if it's easier to pull a wheelie, that must mean that your weight is able to transfer backwards more easily, which in turn means you'll need more force to balance that out.

 

[TrueScotsman]

Zzzzzzzzzzzzzzzzz

Funny- your opinion means as much to me!

 

[Pslide]

Zzzzzzzzzzzzzzzzz

Dude, even you can benefit from this thread. Just read it before you go to bed rather than in the morning.

 

[Sandwich]

OK, I'll probably end up reading that several times until I grasp everything you wrote, but am I correct in thinking that squat values will change with differences in elevation/slope and rider positioning, and antisquat values change with gearing and pedal forces/torque? I'm just trying to wrap my head around it.

 

[Pslide]

Like I said, it can only really counter the forces generated by the forwards acceleration...

In reality I suspect that the "optimum" value to minimise bob would be slightly higher than 100%, such that it accounted for the maximum vertical increase in load including those caused by both horizontal and vertical accelerations. Think of overlaying two slightly out of phase sin waves of different amplitudes, adding them together to get the sum total, picking the highest point and equating your extension force to that... and then I reckon you'd probably find the number you're looking for. Depending on the actual value of the phase shift, and the proportional values of body mass vertical acceleration force vs horizontal acceleration force, you could probably get it pretty close to "ideal". Graph below (totally arbitrary numbers, scale means nothing, proportions might be wrong by as much as 10 million percent as well).

OK, I guess I misunderstood your original statement. I thought anti-squat cancelled out both the weight transfer and the vertical motion, but actually it does not consider the vertical motion.

So your adding the curves in your graph would be the right thing to do to get the ideal amount of anti-squat.

So really, to find the ideal amount of anti-squat, we'd need to know the magnitude of the vertical force generated in a standing sprint. I wonder if bike companies have actually measured this?

 

[Pslide]

Um, isn't that what the Sunday does that DW designed? Is that the ultimate flattery from Scott to DW?

Oh, don't get me wrong, DW is a good designer too. I just don't like to feed his ego.

 

[Steve M]

OK, I'll probably end up reading that several times until I grasp everything you wrote, but am I correct in thinking that squat values will change with differences in elevation/slope and rider positioning, and antisquat values change with gearing and pedal forces/torque? I'm just trying to wrap my head around it.

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.

OK, I guess I misunderstood your original statement. I thought anti-squat cancelled out both the weight transfer and the vertical motion, but actually it does not consider the vertical motion.

So your adding the curves in your graph would be the right thing to do to get the ideal amount of anti-squat.

So really, to find the ideal amount of anti-squat, we'd need to know the magnitude of the vertical force generated in a standing sprint. I wonder if bike companies have actually measured this?

Yeah, anti-squat is a term that's come from the automotive industry, and accounts only for the vehicle's mass and geometry, and the way that affects it under acceleration. The term doesn't get quite so much press in terms of motor vehicle dynamics because the priorities they have for their suspension are significantly different from ours - cars don't bob under power, for starters! For bike design, I think it's one of the most important characteristics to consider (possible exception being DH bikes where really, they CAN pedal like crap and still be amazingly fun to ride - 2003 Bighit anyone?), right up there with shock rate and steering geometry. Everyone these days is paying more attention, whether they use the same nomenclature or prioritise things in the same way as I tend to or not.

BTW Weagle has claimed he's measured all this, in the past (btw these are not new ideas of my own, DW has mentioned this stuff years ago). As for exactly what he measured and how he quantified it, whether it was accurate or whatever, is anyone's guess, but he does manage to make bikes pedal pretty damn well so if he hasn't measured it, he's done a pretty good job of calculating/estimating it. There is always room for improvement however, it's entirely possible that tomorrow someone (probably from NZ) will have a bright idea that makes it entirely possible to improve some of the existing compromises that have to be made.

 

[TrueScotsman]

There is always room for improvement however, it's entirely possible that tomorrow someone (probably from Scotland) will have a bright idea that makes it entirely possible to improve some of the existing compromises that have to be made.

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!