Optimum anti-squat values

dw · Jan 20, 2009

TrueScotsman said:
Just a wee question for all suspension junkies;

What do you reckon the optimum anti-squat values for rear suspension are?
Obviously 100% anti-squat counteracts bobbing due to acceleration mass transfer, but what about mashing up and down on the pedals?- is it better to have a higher (>100%) anti-squat value to account for this? Or pedal mashing just rapid acceleration/deceleration?

Also, I have calculated my Center of Mass height to be around 1100mm- does this sound about right? (I'm 6'3")

Cheers for any help.

Yes if properly applied, anti-squat can counteract the mashing on the pedals, just like it can counteract aerodynamic load in other vehicles.

This is exactly what dw-link does, and the reason that I devised and patented dw-link's position sensitive anti-squat. More at www.dw-link.com, or search for posts by me. I've written about it on this very board probably 20 times in detail since 2001. The best explanation is actually in the dw-link patents, and they read like a textbook.

boogenman · Jan 20, 2009

ahhh I an answer from a suspension junkie and then a sales pitch! Classic!

jackalope · Jan 20, 2009

^^
Huh???

Rather than type a 4 page long explanation, he just gave a brief summary and said "look here" if you want a more in depth answer. I didn't see where he said a DW link is better than "X" or that you should buy a Pivot unless you're a D-bag.

CBJ · Jan 20, 2009

jackalope said:
^^
Huh???

Rather than type a 4 page long explanation, he just gave a brief summary and said "look here" if you want a more in depth answer. I ddin't see where he said a DW link is better than "X" or that you should buy a Pivot unless you're a D-bag.

Don't worry about him he is still angry that he bought his "fully active" suspension Trek Y-bike :biggrin:

Sandwich · Jan 20, 2009

I'm a firm believer in Zero pedal lockout or just a little. Too much and the bike rides like poo, and honestly any amount can make a bike turn into a hobby horse. I think the best riding designs are where the chain has no effect on the rear wheel.

Chain torque can help to firm up the suspension, and it could make the bike sprint faster, but you lose bump sensitivity and are susceptable to pedal feedback. IMO you should isolate all forces from the rear wheel to let it do it's job best.

This may not be the best choice for racing, where a bike that locks out to a degree isn't such a bad thing (for acceleration purposes).

dw · Jan 20, 2009

Sandwich said:
I'm a firm believer in Zero pedal lockout or just a little. Too much and the bike rides like poo, and honestly any amount can make a bike turn into a hobby horse. I think the best riding designs are where the chain has no effect on the rear wheel.

Chain torque can help to firm up the suspension, and it could make the bike sprint faster, but you lose bump sensitivity and are susceptable to pedal feedback. IMO you should isolate all forces from the rear wheel to let it do it's job best.

This may not be the best choice for racing, where a bike that locks out to a degree isn't such a bad thing (for acceleration purposes).

Please don't take this the wrong way, but believing in something and having it be true are two completely different things.

Mass transfer happens no matter what. It does not matter if you have zero anti squat, pro-squat, or anti-squat. When you accelerate forward, your mass transfers rearward and load on the rear wheel increases.

This is Newton's third law at work; Every action has an equal and opposite reaction.

Additionally, by default, if you are running a conventional drivetrain, and truly want your bike not to be "susceptible to pedal feedback" then you need some amount of anti squat. It's just the way things work out.

Anti-squat and the concept of squat in general can be difficult to grasp sometimes. As its core, squat is a suspension's reaction to mass transfer that happens during acceleration. Anti-squat is a term for a force that balances the suspension's reaction to mass transfer.

100% anti-squat is the exact amount that a suspension would need to develop to completely counteract the effects of mass transfer. One way to simplify this relationship is to think of it like an old style weight balance. More than 100% anti-squat would overbalance the suspension, and the suspension would extend under power. Less than 100% anti-squat would underbalance the suspension, and it would be allowed to compress under power. pro-squat (negative anti-squat) (and yes, some well advertised bikes actually feature this) not only allows the suspension to compress under power, it forcibly compresses the suspension while accelerating. Any amount of pro-squat is about the worst case scenario from an efficiency and traction standpoint.

On one side you have mass transfer loading up the suspension. On the other side, you have a balancing force. There are three approaches used in cycling suspensions today that one could take to balance (or not balance) out this mass transfer.

1) you could do nothing. The suspension would compress with every acceleration and subsequent mass transfer, and with every compression stroke and rebound stroke of the shock, you will lose energy. Your wheel rate rises as the suspension compresses, and your suspension is now stiffer with less compressive travel. Your suspension is at a disadvantage to absorb bumps. Traction decreases.

2) you could use a shock with a great deal extra low speed compression damping. The suspension would compress less than the first case with every acceleration and subsequent mass transfer, but still some, every time your shock compresses or rebounds you lose energy.

-a little bit of basic damper theory-

Keep in mind, that in order to support the mass that has transferred to the rear wheel under acceleration, the shock needs to develop force at the damper shaft. A damper develops force by pushing oil through a small orifice. As the oil in the damper is pushed at high pressure through the small orifice, the shearing force in the oil causes friction and energy is converted to heat and dissipated. The more resistance in the damper, the higher the shearing force, and the more energy is converted to heat and dissipated.

Here is the worst part. Now your suspension is unbalanced when you are cornering or not accelerating under power.

Think about it, your compression damping is raised to deal with the additional forces of mass transfer due to acceleration. When you are not accelerating, that mass transfer does not exit, and there is less force that the shock needs to deal with. Your shock is now overdamped when you are coasting. Most of your cornering happens when you are coasting, so effectively you have unbalanced your suspension for cornering. Traction decreases in all cases.

Note: Some people take this to mean that an ideal is absolutely zero low speed compression damping. This is not the case. Low speed compression damping is of paramount importance to a properly set up suspension, but like many things, too much is not good for you..

3) you could use anti-squat. This would allow the suspension to react to mass transfer only during acceleration. The closer a suspension is to operating at 100% anti-squat, the closer to being perfectly balanced the suspension is. The closer to balanced the suspension is, the MORE TRACTION the suspension has in all conditions.

In short, a position sensitive anti squat, with a higher level of anti-squat gives MORE TRACTION than any other approach, and especially more traction than approaches using less anti squat.

Hope this clears some things up.

jackalope · Jan 20, 2009

Criminy, that "sales pitch" sucked :biggrin:

Btw Dave, would a high forward single pivot be an example of a design with "pro-squat"? It sounds like it means the bike "inch worms" along when you're pedaling.

Sandwich · Jan 20, 2009

I guess I'm not up to speed on the concept of "squat" or "anti-squat" for that matter. I always thought it referred to chain torque/pedal lockout/feedback/etc.

On that topic though, can you explain what effect a rider moving forward on the bike while pedaling has? I mean, on a motorcycle or car squat is obvious. The acceleration pushes the wheel forward while the body of the car is still "sitting" there...inertia and all that jazz. On a bike, however, a rider can compensate for that, since most of the mass of the vehicle is the rider himself. How does anti-squat factor into such a situation? Do the dynamics change if a rider just stands vertically vs. leans forward?

When I learned how to sprint on a bike, and on a suspension bike in particular, I always learned to lean forward (attack position?). On a fully this has a particular value in taking your weight off the rear wheel and activating it less. I've never completely understood how that plays into the "anti-squat" characteristics on a suspension design.

Please note, I'm not trying to challenge you, just understand better.

Sandwich · Jan 20, 2009

I think "pro-squat" would be a bike like the old coves or arrows which had a BB mounted pivot. The chain is above and effectively pulls the wheel up when pedaling. I've had one and can attest to it's sucky nature.

I think "too much" anti squat would be something like the old Sunn bikes with a way-high pivot but no pulley to compensate. That's when you get a lot of bobbing or pedal feedback.

I was under the impression that some manufacturers use that to fix bad riding styles, like the VPP for example. It uses chain torque to balance a riders weight. If the rider can pedal cleanly, then he shouldn't have too much effect on the suspension.

monkeyfcuker · Jan 20, 2009

love reading stuff like that, gimme more :imstupid:

ohio · Jan 20, 2009

Highly recommend reading Tony Foale's Motorcycle Handling and Chassis Design. Very straightforward definition of braking and acceleration effects.

Hougham · Jan 20, 2009

I still really like the old Mert Lawwill design. The patent is a great read if your interested.

C4dev · Jan 20, 2009

dw said:
3) you could use anti-squat. This would allow the suspension to react to mass transfer only during acceleration. The closer a suspension is to operating at 100% anti-squat, the closer to being perfectly balanced the suspension is. The closer to balanced the suspension is, the MORE TRACTION the suspension has in all conditions.

My understanding was that most texts on vehicle dynamics only refer to anti-squat with no reference to the vibration of the engine used to drive the acceleration: in your definition of anti-squat do you include all inputs contributing to the suspension including input from the chain? This is the only way that I can see the moving mass of a pedaling rider being neutralized through suspension geometry - unless I'm missing something?

Cheers

djamgils · Jan 20, 2009

I think you would have pro squat when your IC is below ground level or behind the rear axle.
I had a rough sketch of the squat of my socom but I cant find it anymore. But when close to bottoming (160mm compression and further) you would get 0% anti squat and even a little amount of pro squat and thus compress the bike even more. But it depends on what gear you are in and it was done based on prints out of linkage so highly inacurate.

ohio · Jan 20, 2009

C4dev said:
This is the only way that I can see the moving mass of a pedaling rider being neutralized through suspension geometry - unless I'm missing something?

Oh snap! Bikes totally need counter-balancers

dw · Jan 20, 2009

Hi C4, I'm not sure that I understand your question totally, can you rephrase it a little more clearly?

dw · Jan 20, 2009

Sandwich said:
I guess I'm not up to speed on the concept of "squat" or "anti-squat" for that matter. I always thought it referred to chain torque/pedal lockout/feedback/etc.

On that topic though, can you explain what effect a rider moving forward on the bike while pedaling has? I mean, on a motorcycle or car squat is obvious. The acceleration pushes the wheel forward while the body of the car is still "sitting" there...inertia and all that jazz. On a bike, however, a rider can compensate for that, since most of the mass of the vehicle is the rider himself. How does anti-squat factor into such a situation? Do the dynamics change if a rider just stands vertically vs. leans forward?

When I learned how to sprint on a bike, and on a suspension bike in particular, I always learned to lean forward (attack position?). On a fully this has a particular value in taking your weight off the rear wheel and activating it less. I've never completely understood how that plays into the "anti-squat" characteristics on a suspension design.

Please note, I'm not trying to challenge you, just understand better.

If you move forward, you increase anti-squat, because the amount of anti squat is dependant on the location of the rider and bike's combined center of mass. With a lot of the older style low single pivots (low amt. of A.S.) the technique you describe can (to a point) help acceleration response by increasing anti-squat amount. It's the same thing that happens when you get on the nose of the saddle when granny gear XC seated climbing.

I love when physics applies directly to increasing performance!

ChrisKring · Jan 20, 2009

C4dev said:
My understanding was that most texts on vehicle dynamics only refer to anti-squat with no reference to the vibration of the engine used to drive the acceleration: in your definition of anti-squat do you include all inputs contributing to the suspension including input from the chain? This is the only way that I can see the moving mass of a pedaling rider being neutralized through suspension geometry - unless I'm missing something?

Cheers

The only engines (powering a vehicle) that I can think of that oscillate at the same frequency as a bicycle would be a steam locomotive and a desiel cargo ship.

Anyway, you are onto the reason why bicycle suspension is not exactly the same as motorcycle suspension. That said, I agree with DW in that most racers turn while coasting. Most also are not mashing the pedals through rock gardens.

Maybe you could talk DW into writing a suspension design book after he is done with bikes.

JCL · Jan 20, 2009

Is it fair to say that in general anti-squat is far more relevant to non DH bikes.

I'm personally more concerned with braking performance and leverage rate. If I we're interested in XC I'm sure it would be different. In saying that I also think the best climbing bike in pure traction terms that I've ridden (I haven't ridden a DW XC bike) was an FSR. The compression of the suspension under load sort of attenuates the uneven power delivery of pedaling motion. A kind of crude version of traction control if you will.

Udi · Jan 20, 2009

Something like dw-link will truly shine on a trailbike, but I think it's still pretty beneficial on a DH bike.

Pedalling stints on a DH bike are short and generally very crude (regardless of how well you think you pedal). I know that given today's pedal-eating courses and low-bb bikes, there is precious little time to get in a few strokes... making efficiency that much more critical. You want as much of your energy to be converted into forward momentum as possible.

MorewoodKid · Jan 21, 2009

dw said:
Here is the worst part. Now your suspension is unbalanced when you are cornering or not accelerating under power.

Think about it, your compression damping is raised to deal with the additional forces of mass transfer due to acceleration. When you are not accelerating, that mass transfer does not exit...

...you could use anti-squat. This would allow the suspension to react to mass transfer only during acceleration...

Now it all makes sense:

Sam Hill, [that Australian downhiller?] benefited from DW suspension because he is ALWAYS accelerating, due to his constant acceleration his vehicle requires large amounts of anti squat to counter-balance his rearward mass transfer.

I on the other hand am ALWAYS decelerating, hence I require pro-squat in large amounts to counter-balance my forward mass transfer

Can anyone make some bike suggestions? Wish list as follows:

must not look flexy
must be available in root-beer
must possess large amounts of pro squat

:huh:

djamgils · Jan 21, 2009

dw said:
If you move forward, you increase anti-squat, because the amount of anti squat is dependant on the location of the rider and bike's combined center of mass. With a lot of the older style low single pivots (low amt. of A.S.) the technique you describe can (to a point) help acceleration response by increasing anti-squat amount. It's the same thing that happens when you get on the nose of the saddle when granny gear XC seated climbing.

I love when physics applies directly to increasing performance!

I read your patents and the chapter on squat in the Foale book. But I feel like I am missing some important parts here.

According to foale and how I understand it 100% anti squat is where the line from your rear contact patch trough your IC crosses the point where the line parallel to gravity and trough the front contact patch coincides with the line perpendicular to gravity trough your center of mass. hmm difficult sentence.
So according to that definition the longitudinal positioning of the mass doesnt matter. Or am I missing something here?
I dont have the book with me right now but some side notes that I remember is that the height of the CoG is taken the same as the wheelbase and positioned in the middle of the wheelbase in longitudinal direction.

fluider · Jan 21, 2009

djamgils said:
I read your patents and the chapter on squat in the Foale book. But I feel like I am missing some important parts here.

According to foale and how I understand it 100% anti squat is where the line from your rear contact patch trough your IC crosses the point where the line parallel to gravity and trough the front contact patch coincides with the line perpendicular to gravity trough your center of mass. hmm difficult sentence.
So according to that definition the longitudinal positioning of the mass doesnt matter. Or am I missing something here?
I dont have the book with me right now but some side notes that I remember is that the height of the CoG is taken the same as the wheelbase and positioned in the middle of the wheelbase in longitudinal direction.

I read DWLink patent 3 times past November. IMO, you're not correct with the "anti-squat construction". In the image below, which I took from the original patent file (excuse me DW for that), you can clearly see how squat force line is constructed.
1) Rear-axle and IC defines driving force line
2) Driving force line intersects with chainf force line, call this point "P"
3) Line from rear-tyre-contact-patch through the intersection point P is the squat force line
4) Height of the point of intersection of squat force line and sqaut layout line (as DW calls it) nr. 11 on the picture, relative to the CoG height (100% anti-squat) defines the actual amount of anti-squat.

CoG height = Wheel Base is just a rough estimate in case of bicycles for ease of calculations and I do belive that moving the top of your body forward will slitly lower the CoG.

djamgils · Jan 21, 2009

Fluider, I now realize I described the way to determine anti rise. I am aware that for anti squat you also need to take the chain forces into concideration.
But what I wanted to know is how and why the forward movement of mass changes your anti squat/anti rise value. I think you can move the CoG forward without lowering it because you are in a position where your arms and legs arent fully extended.

But your picture already shows that the longitudinal position of the CoG doesnt matter for the amount of ant-rise.

dw · Jan 21, 2009

TrueScotsman said:
Right, i have read and understood the DW-link patent ( the anti-squat curves show a percentage of the initial anti-squat value, but what is this value)

Ohio- I do have Tony Foales book (bought it in about 2002) so I understand the concept of Anti-Squat. What a fantastic book it is- highly recommended!

To get back to the initial question, What amount of anti-squat is preferable in the pedalling range of travel (ie; 100%, 130%, etc.)?

Also as the dw-link patent states, the COG height of bike and rider is close to 100% of the wheelbase, so my calculation of 1100mm COG height must be in the ballpark, but how close?

The figures in the patent are for illustrative purposes only, not based on any real model.

dw · Jan 21, 2009

Udi said:
Something like dw-link will truly shine on a trailbike, but I think it's still pretty beneficial on a DH bike.

Pedalling stints on a DH bike are short and generally very crude (regardless of how well you think you pedal). I know that given today's pedal-eating courses and low-bb bikes, there is precious little time to get in a few strokes... making efficiency that much more critical. You want as much of your energy to be converted into forward momentum as possible.

Here's a little cut and paste from above with some minor tweaks that explains one of the the benefits for DH chassis. Attaining leverage rates that other linkage axle path suspension systems simply can't is another great advantage not discussed in this piece.

In order to support the mass that has transferred to the rear wheel under acceleration, the shock needs to develop force at the damper shaft. When you are not accelerating, your damper is still valved with additional spring and or compression damping to control the chassis during acceleration.

So in other words, when you are not accelerating your suspension is unbalanced (oversprung / overdamped) when you are cornering or not accelerating under power.

Think about it, your compression damping is raised to deal with the additional forces of mass transfer due to acceleration. When you are not accelerating, that mass transfer does not exit, and there is less force that the shock needs to deal with. Your shock is now overdamped when you are coasting. Most of your cornering happens when you are coasting, so effectively you have unbalanced your suspension for cornering. Traction decreases in all cases.

dw · Jan 21, 2009

fluider said:
I read DWLink patent 3 times past November. IMO, you're not correct with the "anti-squat construction". In the image below, which I took from the original patent file (excuse me DW for that), you can clearly see how squat force line is constructed.
1) Rear-axle and IC defines driving force line
2) Driving force line intersects with chainf force line, call this point "P"
3) Line from rear-tyre-contact-patch through the intersection point P is the squat force line
4) Height of the point of intersection of squat force line and sqaut layout line (as DW calls it) nr. 11 on the picture, relative to the CoG height (100% anti-squat) defines the actual amount of anti-squat.

CoG height = Wheel Base is just a rough estimate in case of bicycles for ease of calculations and I do belive that moving the top of your body forward will slitly lower the CoG.

Your graph here is still missing a couple of parts, unless the CG is exactly 50% between the front and rear wheel, this graph won't be accurate. You need to find the 200% anti-squat force line and the direction of gravity to determine where 100% anti squat is.

dw · Jan 21, 2009

TrueScotsman said:
Ain't gonna get a real figure from ya, am I!:biggrin:

Oh well, worth a try! thanks anyway dw (or F1moto as I remember you- been a while since I posted on this interweb-type thingy)

Hey, I've gotten you this far, bust out the slide rule!

F1moto back on MTBR and talking a LOT of suspension. Wow, yeah, that was a long time ago! Good to see you back!

fluider · Jan 21, 2009

Dave, there is a similitude in Slovakia for situations when someone is trying to get information from another person who is not very helpful to say that info.
It goes like from the furry rug.

ridefast · Jan 21, 2009

you kids want to get into a real squat discussion?

head on over to : http://www.pirate4x4.com/forum and try looking up anti-squat (you may need to search through google...the search function may be for members only)

talk about wrapping your head around a difficult subject...

Steve M · Jan 22, 2009

dw said:
Yes if properly applied, anti-squat can counteract the mashing on the pedals, just like it can counteract aerodynamic load in other vehicles.

I don't agree with that 100% - "mashing" on the pedals, as well as generating oscillatory power output, also tends to create vertical motion of the rider/bike's CoM. Unless the maxima/minima of the vertical accelerations involved were in phase with the chain tension maxima/minima (which I think they'd be somewhere near 90deg out of phase since max chain tension would be at about 9/3 o'clock pedal position, whereas max vertical acceleration of the rider's mass would be at closer to 6/12 o'clock) then the vertical motion alone of the rider would move the bike up and down in response, in addition to varying your anti-squat amounts. I don't think an ideal geometric solution exists for this - biopace sounds good in theory but screws up other things, like constant chainline/anti-squat anyway. Aerodynamic load can certainly be countered, being a force that changes at typically low frequencies.

C4dev said:
My understanding was that most texts on vehicle dynamics only refer to anti-squat with no reference to the vibration of the engine used to drive the acceleration: in your definition of anti-squat do you include all inputs contributing to the suspension including input from the chain? This is the only way that I can see the moving mass of a pedaling rider being neutralized through suspension geometry - unless I'm missing something?

Cheers

Cars and motorbikes typically use anti-squat (as well as anti-rise, anti-roll etc) to control geometry and dynamic normal wheel loads. For example, if you had a car with a roll centre at the same height as the CoM, you'd get instantaneous weight transfer to the outside wheels when you began to turn the car - it'd stay nice and level but it'd suck in the sense that you'd have poor turn-in grip and hence the car would be prone to understeering when you turned in hard. Motorbikes can use anti-squat to instantaneously transfer vertical load (as opposed to waiting for the suspension to compress) to the rear tyre under hard acceleration, giving you maximum traction as soon as you crack the throttle. The reason for this is that the power output comes very consistently - it can be effectively considered constant because the frequency of the engine's torque pulses is WAY higher than the natural frequency of the suspension, and the amplitude of the torque pulses is tiny compared to the mean torque output value. With MTBs however, the amplitude can be seriously nearly 100% of the mean torque output (in actual fact it could possibly even be more, if you pedaled in a square deliberately). Unfortunately bicycles are typically pedalled at between 60 and 120rpm, which translates to 2-4Hz (two power pulses per revolution of the cranks). This is the same region as the natural frequency of a DH bike, so the transmissibility of the vibration through the suspension is very high.

TrueScotsman said:
Right, i have read and understood the DW-link patent ( the anti-squat curves show a percentage of the initial anti-squat value, but what is this value)

Ohio- I do have Tony Foales book (bought it in about 2002) so I understand the concept of Anti-Squat. What a fantastic book it is- highly recommended!

To get back to the initial question, What amount of anti-squat is preferable in the pedalling range of travel (ie; 100%, 130%, etc.)?

Also as the dw-link patent states, the COG height of bike and rider is close to 100% of the wheelbase, so my calculation of 1100mm COG height must be in the ballpark, but how close?

I measured my CoM height as 1120mm (on my old bike) using a pair of scales, in an "attack" position. It's hard to be more accurate than that though, because my body position definitely changes a bit when I pedal, and even the gradient of the hill you're on affects both body positioning and the resultant anti-squat.

In theory, the ideal value of anti-squat is about 100%. What's really clever about Dave's design - the part that IMO is absolutely ingenious and he may well be pissed about me posting in public since it's a concept that's pretty hard to patent - is the way it decreases after the usable sag range. What this means, potentially/theoretically at least, is actually BETTER bump absorption if you're pedaling than if you're coasting, as well as a combination of efficient, firm pedalling and low pedal feedback.

Say you had ~100% anti-squat over the first 50% of the travel, then it tapered off down to 0% for the 2nd half of the travel (not based on any actual bikes but just for the purpose of explanation). When you're pedalling, you create a higher than average vertical load on the rear axle (say you normally have a mean value of 600N on the rear wheel whilst coasting, but when pedalling you increase it to a mean of 800N). While you're on smooth ground and the bike is at say 30% of its travel without moving, there is a constant extending force opposing only the extra 200N of vertical load at the tyre (the vertical load is what's trying to compress the bike past its sag point, and the extending force is what's cancelling it out). When the bike hits a bump and the amount of anti-squat begins to drop off, the extensive force might drop to 100N even though the compressive force (from the rearwards weight shift) is the same since chain tension is the same and you're still pedalling forwards with the same effort.

So that means you now have an extra 100N of vertical force on the axle that was previously being cancelled out, now acting to compress the suspension further/more easily than it otherwise would have had you simply hit the same bump at the same speed whilst coasting. This means suspension that moves more freely, better wheel tracking, lower change in normal reaction forces at the tyre, and as a result, better traction. It also means that, since decreasing chain extension is the primary means of decreasing anti-squat, you get less pedal kickback as the bike moves further into its travel, which means that unlike bikes that "lock out" when you pedal, you don't feel like someone kicked you in the feet when you pedal over a bump. As Dave has said about half a billion times too, it lets you set up the damper for the real riding (cornering, jumping, rough stuff, whatever), not to stop your bike bouncing around like crazy.

DW-link is the real deal when it comes to efficiency and pedalling prowess. There are of course physical imperfections that can't be overcome, such as the rider's mass moving around as I mentioned before, differing sizes of the riders, differing riding positions (seated vs standing whilst pedalling etc), and the fact that changing gears/chainlines affects the anti-squat rates, but these are factors that are common to all bikes anyway (except some gearbox bikes that have only a single chainline to optimise, instead of 9/18/27 variations). I'm not so sure I agree with some of Dave's damper curve setups when it comes to what's ideal, but there is no question about the pedalling efficiency.

rbx · Jan 22, 2009

SOCKET:

I understand that DW link lowers anti-squat values as you get deeper into the travel...buts so dose any SP,FSR suspension design but DW does it more agressively perhaps!?

Also you can design a suspension with a gearbox that has the same amount of anti-squat at sag when comapred to dw-link but with zero chain growth.

boogenman · Jan 22, 2009

jackalope said:
^^
Huh???

Rather than type a 4 page long explanation, he just gave a brief summary and said "look here" if you want a more in depth answer. I didn't see where he said a DW link is better than "X" or that you should buy a Pivot unless you're a D-bag.

Geeez I guess you are angry about that old Trek!

I was not ripping DW one bit, just commenting on his quick response and stating that he is a true 'suspension junkie'. The sales pitch was a joke, you know poking fun at something. Go slit your wrists dude, or take a chill pill.

C4dev · Jan 22, 2009

Sorry DW - I've been running around like crazy recently! I think socket has effectively posed the same question much more effectively (and directly) than I have.

Socket said:
"mashing" on the pedals, as well as generating oscillatory power output, also tends to create vertical motion of the rider/bike's CoM. Unless the maxima/minima of the vertical accelerations involved were in phase with the chain tension maxima/minima (which I think they'd be somewhere near 90deg out of phase since max chain tension would be at about 9/3 o'clock pedal position, whereas max vertical acceleration of the rider's mass would be at closer to 6/12 o'clock) then the vertical motion alone of the rider would move the bike up and down in response, in addition to varying your anti-squat amounts. I don't think an ideal geometric solution exists for this - biopace sounds good in theory but screws up other things, like constant chainline/anti-squat anyway. Aerodynamic load can certainly be countered, being a force that changes at typically low frequencies.

This was the engine I was talking about!

Steve M · Jan 22, 2009

rbx said:
SOCKET:

I understand that DW link lowers anti-squat values as you get deeper into the travel...buts so dose any SP,FSR suspension design but DW does it more agressively perhaps!?

Also you can design a suspension with a gearbox that has the same amount of anti-squat at sag when comapred to dw-link but with zero chain growth.

What the DW-link does that nothing else does, is keep the anti-squat at a more or less constant rate of around 100% for the first maybe 40-50% of the travel (sorry if this is not 100% accurate, it's just a conceptual explanation) which means that wherever you choose to run the bike's sag set up, it'll still pedal much the same. It also doesn't use excessive anti-squat in the parts of the travel BEFORE the sag point, which means you don't get pedal kickback effects when the rear wheel is compressing after extending into a hole in the trail. Anyway, after this point roughly half-way through the travel, the anti-squat begins to drop off fairly sharply, to the point where at the end of the travel it may have zero anti-squat or even pro-squat in order to reduce chain extension effects. Singlepivots and FSRs don't have that level of control, which is due in part to the fact that their radii of curvature for the rear wheel aren't able to be as tight as that of 4-bar linkages of various arrangements (such as DW-link). They simply aren't able to make such rapid changes to the anti-squat levels.

You can get good results that are similar to the DW-link, in terms of whether you think it "bobs" much or not, with other conventional means, as you say by having 100% anti-squat at the sag point (and there are certainly other means that may have never been built that could actually replicate the DW-link pedalling characteristics without infringing on the patents), but the DW-link arrangement is technically brilliant when it comes to pedalling efficiency IMO. It all depends on whether you think close enough is good enough really - some people reckon their FSR bikes pedal well enough and are happy to trade off some of the pedalling efficiency for what they believe to be a smoother ride.

hbracca · Jan 22, 2009

So after reading this and a few other threads, reading a moto suspension book or two, and a couple of actual prototypes under my belt I think I am starting to get a good understanding of the the pedal/brake induced forces and the design to enhance/counter those forces.

I would like to hear peoples thoughts on the brake induced forces. I understand that "brake jack" (where the suspension extends or firms up under braking) is bad. I personally like to have a bit of "brake squat" to balance out the compression of the front fork under braking. I would imagine that to much of this would be bad for traction and in the event of larger hits under braking, would probably allow the suspension to bottom easier. I personally don't use a ton of rear brake, so I don't think I would notice the disadvantages of this as much, but everyones riding styles are different.

What are your thoughts? Others talking about it helps me (and others I would imagine) to understand the true advantages/disadvantages in "real-world" bike riding, as opposed to all of the marketing hype in the bike industry.

Thanks a ton,

-Hollis

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