Saw mention of much debate over anti-squat on another thread.......

so thought I would put the cat among the pigeons and start a fresh debate!!

What is the concensus here (for those with "unusual" suspensions as the std book version doesn't allow for much alteration!)

I will voice my opinion later

yes , i made mine so that it had some .

quote:

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Originally posted by NS Dev
Saw mention of much debate over anti-squat on another thread.......

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Matt @ Procomp's your man on this subject!

As far as I can tell with my limited knowledge, anti-squat is a very difficult subject.

Simple theory dictates that the more you have, the more directly vehicle weight is transferred to tyres to create traction.

Conversely, experience in very traction-limited conditions (grasstrack) where a race is usually won or lost in the drag for the first corner, PRO-squat geometry has worked very well for me!!!

I have found that the benefit of this is that the rear suspension is wound up by the initial start, cushioning the initial shock to the tyres, then releasing that shock progressively as the dampers allow the springs to unwind again.

maybe this is not a scientific solution but it seems to help get off the line exceptionally well. With anti-squat, the shock into the tyres can actually be felt on launch, followed by soaring wheelspin which requires throttle feathering to limit.

Hi right as you know i use geometry witch works verry verry well IE 200bhp locost style will do verry quick o-60mph and indesantly quick o-64 feet time with is capable of leaving two black lines for 22.5 feet if you use to manny revs of the line all with a open diff and a driver with a sensative right foot.

Know the question is why dose that geometry work and is it actually antisquat. Dose anti squat exist.

This is a can of worms and should be an enjoyabe debate.

cheers matt

No no no no no! I will not get drawn in to this.

You debate all you like, I'm off!

Cheers,
Syd.

i believe that cars car be designed so that they dont dive or squat, but its debatable how useful this is for any given application. For circuit racing on tarmac in a light car id not bother myself. Drag racing may be a different issue.

[Edited on 11/9/06 by JoelP]

Well lets looks at drag racing where the launch is all important.
Years ago when the gasser cars were around they realized that weight transfer onto the rear wheels gave them more traction. Weight transfer is visibly seen in squat so they thought the more squat the better. Problem is after about 60ft the car unsquats suddenly and unloads the rear tires. My camaro was like that, would come out of the hole good then blaze the tires at the 60ft mark (not a drag car). It is incredibly difficult to launch a car like that.

So, later on someone figured out that the whole opposite/equal reaction thing applies to cars. If you try to lift the back of the car up using the power of the engine, the tires are going to get forced into the ground just as hard. Add weight transfer to it and you get some major loading of the tires. Because you are using the engines torque to gain traction it is a fairly smooth loss of traction as you get going faster and unload a bit.

Pro drag cars generally run at LEAST 100% antisquat. If you watch them launch from behind you can usually watch the back end come up.

If you want an example you can take a hotchkis (leaf sprung) camaro into the 9s with stock rear suspension and Cal-tracs and DOT slicks. Try doing that with no antisquat.

So why dont road race cars use antisquat? Well they do.... when they can. Not many modern road cars with solid rear axles anymore and IRS won't gain much antisquat. The 4th gen camaro with solid rear had a torque arm for anti-squat. The torque arm is about the simplest way to think of anti-squat. The shorter the arm, the further away from the COG and the more antisquat you get (also from leverage). Problem is you get brake hop if its too short.

The book 4 link (+ panhard) actually does allow for some antisquat. If you angle the arms up a bit and raise the sideview IC you are gaining antisquat. Simplest way to think of how that works is to think the tires move forward first and try to drive under the car lifting the back. Also the twisting axle is trying to push against the lower link will lift the back if the lower link is pointing upwards. Anytime the tires are lifting the back of the car up, the tires are getting pushed into the ground just as hard. Add to it the fact you are hard on the gas and are transfering weight to the rear and you can see why it works.

For loose surface racing I have no idea. I would guess its very likely that other factors are more important.

If Ive missed of screwed anything up let me know. Id hate to lead people the wrong way.
Cheers.

quote:

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Originally posted by C10CoryM
If you watch them launch from behind you can usually watch the back end come up.

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quote:

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Originally posted by Gav

quote:

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Originally posted by C10CoryM
If you watch them launch from behind you can usually watch the back end come up.

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No that i know, however from simple observation i thought that was due to the rapid acceleration of the tyres which increases the tyres diameter hence the the backend raising?

[Edited on 11/9/06 by Gav]

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HI right now what C10CORYm is describing is exactly what i have and what i have been thinking for some time one interesting thing is are you measuring 100% at the point of the COG along the wheelbace or at the front axle center as i have seen both used to calculate the % of squat.

Inorder to take the best advantage of this we have had to spend a lot of time developing dampers to work with the coilover spring setup at the rear aswell.

And also some people say that it really only works whilst getting of the line i find that by adding a bit more to the inside of the car perdomently the right for the uk circuits this helps keep the wheel on the ground and resist axle lift due to torque out of the tighter corners. And when wet it dose seem to be able to get the torque down to the ground better than the other cars on the grid wich are running no antisquat but they are also of a shorter wheelbase.

cheers matt

quote:

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Originally posted by C10CoryM
Well lets looks at drag racing where the launch is all important.
Years ago when the gasser cars were around they realized that weight transfer onto the rear wheels gave them more traction. Weight transfer is visibly seen in squat so they thought the more squat the better. Problem is after about 60ft the car unsquats suddenly and unloads the rear tires. My camaro was like that, would come out of the hole good then blaze the tires at the 60ft mark (not a drag car). It is incredibly difficult to launch a car like that.

So, later on someone figured out that the whole opposite/equal reaction thing applies to cars. If you try to lift the back of the car up using the power of the engine, the tires are going to get forced into the ground just as hard. Add weight transfer to it and you get some major loading of the tires. Because you are using the engines torque to gain traction it is a fairly smooth loss of traction as you get going faster and unload a bit.

Pro drag cars generally run at LEAST 100% antisquat. If you watch them launch from behind you can usually watch the back end come up.

If you want an example you can take a hotchkis (leaf sprung) camaro into the 9s with stock rear suspension and Cal-tracs and DOT slicks. Try doing that with no antisquat.

So why dont road race cars use antisquat? Well they do.... when they can. Not many modern road cars with solid rear axles anymore and IRS won't gain much antisquat. The 4th gen camaro with solid rear had a torque arm for anti-squat. The torque arm is about the simplest way to think of anti-squat. The shorter the arm, the further away from the COG and the more antisquat you get (also from leverage). Problem is you get brake hop if its too short.

The book 4 link (+ panhard) actually does allow for some antisquat. If you angle the arms up a bit and raise the sideview IC you are gaining antisquat. Simplest way to think of how that works is to think the tires move forward first and try to drive under the car lifting the back. Also the twisting axle is trying to push against the lower link will lift the back if the lower link is pointing upwards. Anytime the tires are lifting the back of the car up, the tires are getting pushed into the ground just as hard. Add to it the fact you are hard on the gas and are transfering weight to the rear and you can see why it works.

For loose surface racing I have no idea. I would guess its very likely that other factors are more important.

If Ive missed of screwed anything up let me know. Id hate to lead people the wrong way.
Cheers.

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Surely the only point at which the tyres are being 'pushed' into the ground is during the fractions of a second that the rear end is actualy moving up (i.e. the reaction force pushes the tyres down).

Once the chassis is raised, I can't see that there will be any extra force pushing down on the tyres. In fact raising the rear end up would tend to transfer weight to the front, assuming that the cars COG is somwhere above the axle line.

a trick also used by drag racers - they load the suspension up on one side so if they have an open diff - on launch , they have equal weight on either tyre , giving really good traction .

so that backs up the unequal side to side setup .

also raising the cog gives more weight transfer to the rear on acceleration , another reason why drag cars sit the arse right up in the air .

[Edited on 12/9/06 by Volvorsport]

quote:

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Originally posted by MikeRJ
Surely the only point at which the tyres are being 'pushed' into the ground is during the fractions of a second that the rear end is actualy moving up (i.e. the reaction force pushes the tyres down).

Once the chassis is raised, I can't see that there will be any extra force pushing down on the tyres. In fact raising the rear end up would tend to transfer weight to the front, assuming that the cars COG is somwhere above the axle line.

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Hi yes it should only be acting on the rear whilst momentry in squat but it dose allow the car to leave two black lines equal for a considerable distance. shurly if it is only momentry it wouldent leave such long lines for such a length.

funnily enough the last time i demonstrated this to a driver was at donnington so i wonder if the two black lines are stil there in the padock as you go in on the white ish coloured concrete in front of you. If it is there i will show you on sunday Nat.

cheers matt

not sure Matt.

Certainly what you describe will no doubt aid traction exactly as you suggest.

Really difficult to cut to the exact science if it all though.

On the grasser, the long travel means that the shock loading on the tyre is absorbed by the springs compressing, then the dampers allow a controlled release of that energy, which minimises wheelspin.

Obviously the grasser is mid-rear engined, but (with pro-squat geometry)we can make 0-60mph in 4.5 secs uphill on wet mud, which says something for traction.............. on the flip side, so can another club members car with anti-squat, so who knows!!!

On tarmac, you have to be REALLY brutal with the car to get any wheelspin at all, normally it just lifts the front clean off the ground and goes off like a rocket, but never have timed it on hard surfaces. Took it on the kart track at stretton just outside leicester and from a standing start it hit the limiter in 2nd, which is 72mph, on the straight where the prokarts hit 50mph or so after exiting the corner!!! lol

also know it hits the limiter in 2nd (again 72mph ) in 2 streetlights distance down the road, but again no idea how far that is (and less said about that the better!!! lol)

quote:

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Originally posted by MikeRJ
Surely the only point at which the tyres are being 'pushed' into the ground is during the fractions of a second that the rear end is actualy moving up (i.e. the reaction force pushes the tyres down).

Once the chassis is raised, I can't see that there will be any extra force pushing down on the tyres. In fact raising the rear end up would tend to transfer weight to the front, assuming that the cars COG is somwhere above the axle line.

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quote:

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Originally posted by MikeRJ
Surely the only point at which the tyres are being 'pushed' into the ground is during the fractions of a second that the rear end is actualy moving up (i.e. the reaction force pushes the tyres down).

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now thats a concept i understand - except there are two ways to do it in skiing.

Jump up (top most travel = lack of traction)
squat down (as you drop down, you actually reduce the weight on the skis during the drop down)

I've spent the last year or so biulding anti-squat into my Sylva Striker for autotesting and it really does work. The article I found most interesting is this one:

http://www.afcoracing.com/tech_pages/4link.shtml

On a 4 link axle if you slope the trailing arms up towards the front of the car then as the axle pushes forward, the arms will push down at the back forcing the tyres into the ground. Just try holding a stick against the wall with your hand and pushing if you angle the stick up towards the wall then your hand will go down.

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Surely the only point at which the tyres are being 'pushed' into the ground is during the fractions of a second that the rear end is actualy moving up (i.e. the reaction force pushes the tyres down).

Once the chassis is raised, I can't see that there will be any extra force pushing down on the tyres. In fact raising the rear end up would tend to transfer weight to the front, assuming that the cars COG is somwhere above the axle line.
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The above isn't true. All the time you accelarate the c of g is trying to push the back of the car down, so the anti-squat can try and conteract that and give the tyres more bite.

If you get to the point where the back of the car is raising then you've gone to far.

quote:

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Originally posted by Steve Morten
The above isn't true. All the time you accelarate the c of g is trying to push the back of the car down, so the anti-squat can try and conteract that and give the tyres more bite.

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Mike,
You're quite right, it's all about compromise. If you didn't have suspension at all then you wouldn't need anti-squat but the tyres wouldn't be in contact with the ground much.

Hi but if it will pull 3-4 cars lenght on thoes whithou it of the line and 2-3 lenghts out of the tighter corners it has got to be worth using.

The only time it has ever caused me any problems under braking was at pembrey whilst braking for the hairpin at turn 1 but given the speed caried down to that corner and the fact it is a hairpin it is about as bad as it gets and that just neded the damper going up 1 click to controle the axle tramp.

cheers matt

Some words of caution;

In roll or one wheel bump or droop, unequal length or non-parallel trailing arms WILL impart a large torque reaction into the axle housing, trying to tear the mounts off the casing.

Best to angle both trailing arms up and keep them parallel. This also alleviates the suspension locking at a certain point, which I suspect is what is giving some of the benefits being discussed here.

Cheers,
Syd.

Your right syd. You have to build a bit of compliance into the bushes so don't use rose joints. Anyway most race cars don't have a lot of suspension travel.

The other thing you have to be carefull of if you have top and bottom arms angled the same, is that, as you roll, say on a right hand turn then the left rear wheel will move back slightly and the right will move forward slightly thus steering the back of the car out as in oversteer. Thus is great for us Autotesters but I don't think it would be good at speed. It tell's you how to conteract this in this article I posted earlier:

http://www.afcoracing.com/tech_pages/4link.shtml

Hi compliance in the bushes is also the secret to getting it all to work nicely.

cheers matt

sorry for short reply in a big rush.

And how many locost racers are utilising a rotating trailing arm mount (bird cage type thing) on the diff casing??

Compliant bushes just spread the load, but can't stop the forces acting. ie They soften the effect of the twisting, but don't stop it.

The article mentioned above states that arms shorter than 17" are not effective, because of the high longitudinal movements with rotation. Where does all this sit with a Locost with 12" arm lengths?

And lastly, none of this works with wishbones, no matter how much some may want you to think otherwise. All you end up doing is buggering up perfectly good(?) geometry.

Cheers,
Syd.

Hi Syd,
I guess the reason they go on about birdcage is because they are talking about oval track racing so they are going to need more suspension movement than in a seven.

The twisting effect on a live back axle is there whether you angle the arms up or not. The shorter the arms the more the twisting. Maybe thats why they prefer longer then 17" arms. Anyway my axle hasn't broken yet, and thats after 2 years about 50 events and 2 drivers. In fact I guess the twisting effect acts like a rear anti roll bar?

All I did when first trying mine was to add more mounting holes at the front. I put 3 holes in at 3, 5, and 9 degrees. If it didn't work I could always move them back.

As for independant rear & wishbones I agree I don't see how you can biuld anti-squat in.

Sorry for the delayed response.

Obviously anti squat has its place in racing. How much, and what compromises you are willing to take depends on your car and type of racing.

Drag racing it is one of the primary concerns. Second only to a straight launch. Autocross and low speed road racing where it's more about traction than exit speed it is still a high priority consideration.

High speed road racing or open road events where speeds rarely reach below 70mph......... there is much more important things to worry about.

With loose surface racing, I have no idea. Never really played like that although it does seem fun . I would guess it has no real effect until you sweep the track down to the hard pan.

In a 4link with fixed axle brackets (no birdcages) most of the antisquat comes from the twisting force of the axle (pinion trying to turn up on acceleration). This is why you generally end up with a setup like the first diagram I posted. The top link pulls straight back on the chassis (no effect) and the lower link is pushed forward and up on the chassis.

The Afco article is talking about a 4 link with birdcages. You still need something to control pinion angle. They generally run a pull or push bar
( http://www.racepartsoutlet.com/PartDetail.cfm/ID/3531 )
which is a "torque link" from axle to chassis. This uncoupled link is where they get most of their antisquat from. Angle it down and when the pinion rotates it lifts the chassis up. Brake hop can become an issue of course which is why they sometimes add yet another uncoupled link to control pinion angle on braking. Did I mention the oval track guys are well known for uncoupling forces and adding links?

So in the article posted using birdcages, the only antisquat you are getting is from the forward thrust of the tires which if the links are angled up in front will try to lift the chassis as well. You wont see much more than 25% antisquat that way.
This is also how it works with a SLA IRS system. Yes Syd, it does work. Whether you opt to use it or not is your choice, but it definitely does work.

If you take your upper and lower A-arms and angle the fronts upwards you get the same lifting effect when the wheels/hubs thrust forward. See attached pic. Sorry for the lousy doodle but I'm too lazy to do a nice one

Are there more important things to worry about? Yes, but if you are drag racing or doing low speed road racing (probably what most locosts are doing) and you need more traction I would opt for some antisquat.

With 4links its so easy to give yourself the adjustablility so why not? Adjustable length links and a couple more holes in your brakects is all you need. Then you can play around and tune to suit each situation. I like versatilty in my toys.

Cheers.
Rescued attachment antisquat.JPG

Could mountain bike makers Ellsworth's instant centre suspension be adapted to work for anti squat?

They use it to control chain torque to prevent the suspension from bobbing when peddaling.

quote:

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Originally posted by jroberts
Could mountain bike makers Ellsworth's instant centre suspension be adapted to work for anti squat?

They use it to control chain torque to prevent the suspension from bobbing when peddaling.

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Hi C10CoryM,
Your post is explains a lot to me thanks.

This bit especially:

"In a 4link with fixed axle brackets (no birdcages) most of the antisquat comes from the twisting force of the axle (pinion trying to turn up on acceleration). This is why you generally end up with a setup like the first diagram I posted. The top link pulls straight back on the chassis (no effect) and the lower link is pushed forward and up on the chassis. "

I didn't realise the top link pulls all the time on accelaration. I thought it was just initially as the drive kicked in?

That might explain why some of the Irish autotesters are mounting the shocks forward of the axle rather then on top?

So if you have both links pointing up, then does the top link counteract by pulling the axle up, against the bottom link pushing the axle down into the ground? and would you get more traction by pointing the top link down?

Stephen.

Firstly I should be more careful with what I type.
"In a 4link with fixed axle brackets (no birdcages) most of the antisquat comes from the twisting force of the axle"
In some cases depending on axle pivot location (leverage) and a few other factors you may actually get more antisquat from the forward thrust. I don't think it is very common, but it is possible.
Anytime the tires are trying to accelerate the vehicle there will be torque trying to lift the front of the pinion. How much force depends on how much acceleration there is. At 100mph in a locost there will be very little, but it will still be there. At 10mph in a 1000hp camaro with slicks...... lots.
The autotesters may be moving there shocks for any number of reasons. Reduced wheel hop on acceleration would be my guess.
So we understand that there are two types of antisquat. One from the forward thrust of the axle (lets call this Jacking Anti Squat), and one from the torque of the axle (Torque Anti Squat).
Lets start with JAS (and yes I am inventing abbreviations )

4link suspension can be thought of as a swing arm. If you draw a line through your upper and lower link pivots in Side View you get your Instant Center where the lines cross. This is also your Swing Arm length. This is the point where your rear axle pivots on while moving.
Due to the weight transfer/ height of CG if you draw a line from the rear tire and ground point to the CG height and front axle point you get whats called the "100% line".
If your IC is below that line you get less than 100% AS. If above, more than 100%.
So with this, you can calculate what percent JAS your car has. I will let you draw out some examples of different link angles on your own and see where the AS ends up.
So now lets look at the TAS which is simplest to think of as a torque arm with no other pinion angle control (say a 3 link or a 4link with birdcages).

So when you step on the gas the big blue arm is trying to lift in front due to the torque of the differential. The front of the arm is fastened to the sprung mass (chassis) The shorter the arm, the less leverage the arm uses against the differential and the further away from the CG (more leverage). Now go back to the swing arm length/height of the 4link. This is your torque arm and is what acts on the CG to reduce AS. The shorter it is, and the further away from the CG the more AS you will gain.
Ok, so that's looking at the two AS as uncoupled forces. Now if you try and think about how a 4link locost with solid axle brackets it gets really complicated really fast. Now that the two forces are coupled they fight each other, and help each other. To be honest, I don't think I could reliably calculate out the forces involved. You can see why un-coupling the AS from the swing arm is so popular.
It allows you to have your SA exactly how you want it, while being able to tune the AS accordingly.
After all that, I want to say again that everything is a compromise. Short SA have some major flaws, specifically wheel hop on braking.

Not going to re-read that so I hope I have done OK .
Cheers.

Hi that sounds like a perfect description of what i also belive to be true about antisquat.
The only thing i would add further is that to get this lot working in a locost type setup is that it needs a lot of playing with the dampers on the rear to get the best controle of the axle movment and espesialy when you start to get towards the point of wheel hop under braking.

I knew this would be an interesting debate.

cheers matt