Race car suspension Class

[chriswh86]

interesting...mike, any photos of your ramp setup?

update -> I just had a brain far Mike. If I got scale pad leveler setup with built in roll off areas for each 4 wheels. I could just set my car on the scales and do what i need to do, then using the roll of part, i can put my tape measure on the roll off section and up to my frame rail and measure there...thats the only measurement id need to take really?

If i wanted shock heights etc i could attach a piece of metal to the roll off section that extends across to the next pad or something and measure to that piece of metal

this system would probably work good eh, i was thinking of a full pad leveler/roll off/roll off ramp setup, but i believe a scale pad leveler setup x4 with little roll off sections on the back of each scale pad area would work perfectly

such as> http://www.intercomp-racing.com/Products/25_SCALE_PAD_LEVELER_WROLL-OFF_PAD_822.cfm

or at least, if i can build my own and build the platform to extend toward the inside more on each tire, ill be able to measure to the frame rail

 

[Ranger Mike]

Roll off ramps easy to make
you need these to adjust the chassis...jounce the shock springs when both ARBs are disconnected
then roll it back on the scales after everything settles

 

[chriswh86]

interesting mike...and you adjust yours via shim plates under the wood?


New Question: I've used stagger tapes (only a couple times) and I've used a knock off longacre stagger gauge and i haven't really been happy with the stagger gauge setup, i find it to flex/sqwish a bit and i can be off on stagger by a 1/4" or so.

Im woundering if I should go back to the tape measure style of measuring or is there a better system I can use. I am looking for speed and consistancy

Cheers
Chris,

 

[Ranger Mike]

Tire stagger

You will get better results with the tape measure method. Use a stagger tape that is about 1/4 wide. I have both..but being on road course...not much point to doing this.
For round track stagger is everything. We used to run nitrogrn and bleeders in the wheels.
One tip...go to a horse tac shop and buy a curry comb..it is great tool to remove gravel from the slicks so you can get good measurments..

 

[chriswh86]

Interesting, good idea on the comb! we have treaded tires, so it will be crutial with the tape to get it in the middle of the tire each time for repeatable results...

Is there any good 1/4" wide tapes for stagger that have a good end on it for the tire etc or are they mostly all the same


Another question, My new car has aluminum lug nuts on course 5/8" studs, what's the best way/amount to torque them...Also, I may go with aluminum jam nuts as well, best just to snug them up on the radius rods and add a little extra quarter turn?

 

[Ranger Mike]

I think all the stagger tapes have long hook at the end..hoosier , longacre,,etc,,
use a torque wrench on the wheels...i like the kind that clicks when you reach proper setting..dont forget to back it off after use .
you do not need jam nuts on the lugs...on the suspension components of course...use jam nuts

 

[Ranger Mike]

Heat cycle machine

If you have that restrictive a sanctioning organization..you may want to look into building your self a trie heat cycle machine.

 

[chriswh86]

ahh yes, i forgot to mention, i ment using aluminum jam nuts for the suspenion arms, I was woundering how to tight they should be, before they break


im not sure I completely follow your reply on building a head cycle machine. I would however LOVE to build a tire shaving machine, get rid of half or more of that tread and see how the tires perform. I am still looking to see if anyone around here still shaves tires to see if that will be easier than building one

 

[MikeGaynor]

Mike (and the rest of you) thanks for giving me a couple of days of reading to go through this whole topic. It's tricky for me to pull out the information I want though as I'm not a) american, b) driving a live axle, c) using double wishbone front end, or d) racing round an oval... But still, lots of valuable information.

Now, I'm not sure if this is going to make me seem like an arsehole but I'm actually into drifting... As in, sliding a car around the track like Formula D. I don't wear flat peak baseball caps and I do have a huge interest in car setup but I think most people who like drifting don't really know what they are talking about when it comes to the physics of suspension. I plan on competing again in the UK so am building a BMW e10 2002.

My main objective in my latest "from scratch" build is to design a good suspension setup to provide LOTS of rear end traction (forward acceleration from the tyres, despite them spinning), whilst giving a savage self-centering effect on the steering. So from most of the discussions here my main interests are:

Roll centres front/rear to give control and balance during transitions (from a left to right slide)
anti/pro-squat in the rear to encourage as much traction as possible
ackerman/KPI/caster in the front to give a sharp steering response

So aside from my life story, and maybe encouraging some open conversations and thoughts about my points above, my main gripe is the effects of squat in the rear.

My car uses a BMW e36 rear end, which has a trailing arm, with two diagonal/forward pointing (from the hub into the subframe) arms one above the other. The trailing arm controls the fore/aft forces from the wheel, the upper and lower track control arms control the side to side forces from the wheel, as well as controlling camber gain. Together they all form a complex sort of semi-trailing-arm suspension system where the wheel ultimately cambers and toes all over the place under compression and extension depending on the lengths of the arms.

I want to know whether I should be looking to use anti-squat to push the wheel into the ground by mechanical leverage of the suspension arms (the wheel trying to ride under the CoG), or whether to use pro-squat (or less anti-squat) to allow the CoG to shift backwards over the rear wheels and use the springs to push the wheels down into the ground.

Quoting something Ranger Mike said earlier in the thread, regarding the effects of lateral forces acting on the tires, it was made clear that roll is good as it uses the springs to push the outer tire into the ground, rather than using a higher roll centre to reduce the amount of roll and convert it into lateral shear force on the tire through the suspension arms. Does this translate into longitudinal forces and the CoG on the lines drawn to calculate anti-squat?

 

[Ranger Mike]

welcome and thanks...pls clear up one thing..when drifting..you want the car to respond instantly to your desire to spin the tires..right?
and all efforts are to achieve this? or is handling also in the equation?

 

[MikeGaynor]

Thanks for the reply Mike. I'll try and clarify on your questions.

The car should be responsive to direction changes, and should have the grip/drive to push itself out of corners, but the spinning of the wheels is going to happen any way - there's no need to try and artifically sharpen the response of the rear wheels breaking traction. Beleive it or not drift cars should be built to have as much rear end grip as possible, so to make it slide you have to be going faster and driving harder (which is in turn an advantage when competing). If your car is on a tight rope trying to spin the wheels at the slightest touch then you end up drifting a track much slower than the opponent.

Everybody has different ideas but in my opinion I just want a "solid" feeling car which has as much rear end acceleration traction as possible. Since the throttle is constantly being adjusted you have to allow for a predictable change from accel to deccel forces but ultimately you want the most traction for the acceleration, without it brake-hopping as a result (brakes and handbrake are used occasionally).

"handling" in the traditional sense isn't really applicable, but certain aspects of it need to be considered. Just try and think of it being a drag race, whilst sliding around corners. Maybe like dirt racing (where most of the focus is on the rear end) but on smooth tarmac rather than rough dirt.

I imagine in an ideal situation my inside front tire would be off the ground when mid-corner, assuming a drift angle of around 45deg to the track, giving full weight transfer to the rear end for forward acceleration.

Apologies for this whole thing sounding amatuerish compared to racing, but it is still very competitive as a motorsport and I think suspension design really hasn't been developed beyond off-the-shelf bolt on parts.

 

[MikeGaynor]

https://www.youtube.com/watch?v=qzChg2Wetrg
(I hope that link works)

Excuse the poor quality but this was me a few years ago in the grey e30, it shows so well that I am losing ground on the opponent cars in every battle. The idea is for the chase car to show that they can be inches away from the lead car, but with more angle and style and precision. If you are the chase car then having huge mechanical grip gives a huge advantage as you can close the gap between you and the car infront at will.

For those of you with minimal experience of the effects of grip on spinning wheels, the rules seem to work basically the same but the effects of tyre temperature and the lateral forces deforming the rear wheels are greatly reduced as the tyre is already spinning.

 

[Ranger Mike]

i am not too up on drifting...about the only thing i can say is set up the chassis to road course specs..as close to 50 - 50 as possible..avoid bump steer fnt and rear..min camber build as possible..aero up as much as possibnle..reduce weight to bare min..add tuneable 3 way shocks as minimum...go with aftermarket ARB...lighten up any rotating weight to bare minimum

 

[MikeGaynor]

Thanks Mike, that's the general idea for what I was going for anyway. Whilst not being an expert on drifting, hopefully you can help clarify my below thoughts re: squat. From reading elsewhere it seems that IRS is not as sensitive or effective with anti-squat but I still have to mount my trailing arms somewhere and still have free reign of the height of my rear roll centre so I want to put it all in the best place for traction. Thanks.

my main gripe is the effects of squat in the rear.

My car uses a BMW e36 rear end, which has a trailing arm, with two diagonal/forward pointing (from the hub into the subframe) arms one above the other. The trailing arm controls the fore/aft forces from the wheel, the upper and lower track control arms control the side to side forces from the wheel, as well as controlling camber gain. Together they all form a complex sort of semi-trailing-arm suspension system where the wheel ultimately cambers and toes all over the place under compression and extension depending on the lengths of the arms.

I want to know whether I should be looking to use anti-squat to push the wheel into the ground by mechanical leverage of the suspension arms (the wheel trying to ride under the CoG), or whether to use pro-squat (or less anti-squat) to allow the CoG to shift backwards over the rear wheels and use the springs to push the wheels down into the ground.

Quoting something Ranger Mike said earlier in the thread, regarding the effects of lateral forces acting on the tires, it was made clear that roll is good as it uses the springs to push the outer tire into the ground, rather than using a higher roll centre to reduce the amount of roll and convert it into lateral shear force on the tire through the suspension arms. Does this translate into longitudinal forces and the CoG on the lines drawn to calculate anti-squat?

 

[Ranger Mike]

i would concentrate on up grade to LSD..i assume you already have limited slip diff
go to strut tower braces if you do not have alrerady
coil overs
add driver seat
unless you really want to get serious and buy suspension software, don't monkey with any of the geometry...oh you could if you have lots of time to do trial and error but it is better to have a map when going into unknown territory..

 

[MikeGaynor]

I'm happy to buy suspension software but need to know what I should be aiming for with anti squat... The whole thing confuses me. On one hand I have the theory that more squat means more weight transfer and more of the springs pushing my wheels vertically down, on the other hand less squat means more of my suspension trying to push the wheels down and into the floor. Since I don't have a live axle I'm limited to more linear force vectors on the rear tires rather than torque twisting the arms, but I still need to know roughly what I'm aiming for.

Thanks for the general advice too but I'm a bit beyond the "drivers seat" and "tower brace" stage of modifications :) That's why I'm here! I'm literally offering subframes up to a hollowed out bare shell with no front chassis rails and no rear floor pan. Once I've sorted the basic geometry out I will then continue the build. Full roll cage with tower and subframe ties, welded diff, coilovers, spherical/rosejoints throughout the suspension, reduced weight to a bare minimum etc, but the backbone of the whole build pivots around (excuse the pun) my suspension geometry.

I can find out where my roll centres are easily, with suspesion software, and can plot how it will move to keep it as stable as possible, but I need to know where things should be for optimum traction beyond "keep the tires flat on the floor". The car is going to be around 900kg with driver so I need to make the most of what little weight there is into more forward traction.

Even if you ignore my drifting question, just treat my question like drag racing, and hopefully clarify the theory behind anti squat as not many people who know what they're talking about share their knowledge online! Just try searching for "e36 anti squat" and you get a few pages of BS on the entire internet.

 

[Ranger Mike]

if that is the case Mike..then why not set up as 4 link and tune from there?

 

[MikeGaynor]

Because I don't have access to any decent live axles or spares and I think it's a backwards step in terms of unsprung weight and traction over uneven surfaces.

 

[Ranger Mike]

HP required to overcome Aero drag

4 link is the hot set up on dirt...nuff said

 

[Ranger Mike]

I ran across this when doing Aero research. This was written by one savvy guy...

 

[b00sted]

Wow, there's a lot of good information here.

I ran across this forum while doing a Google search. I'm teaching myself SolidWorks and want to eventually design and build my own car...A tube-chassis design similar to a Locost/Lotus 7, but with round tube, a safer cage, and much nicer suspension.

Anyone here own this book? http://books.sae.org/book-r-146
It was recommended to me by another guy on a drag racing forum. After looking through the table of contents and reading a few of the reviews, it sounds like it will be a good thing to have on hand.

 

[Ranger Mike]

Welcome..if I had an extra $100 I would buy it

 

[rick7343]

Anyone got any theories on the front vs. rear roll center heights?

I've only found one article with much info... it stated that the front roll center should be 50-66% of the height of the rear or the car will understeer going into the corner and oversteer coming out...

That is exactly what my car is doing, and I've been trying softer and softer RR springs. It is getting better, but still not good... I have a The rear RC is pretty fixed since we have to run the stockish 4 link in the rear...

If the rear RC is around 22", then my front should be at least 11''... sounds crazy!

Opinions?

 

[Ranger Mike]

my opinion
stk clip heavy car with iron heads should have frt roll center 2.5 inch above ground.
ifin you are pushing goin int and loose coming out...frt springs way too soft...going into the turn.. the weight is coming forward and washing out rt ft tire grip...tire shear...and weight is staying there ...up front...so coming out the car is way too nose heavy and rear tires do not have enought weight to hook up the rear drive tires,,,results- they spin instead of driving off the turn..

 

[rick7343]

OK thanx...

But there is less than an inch front shock travel, and softening the outside rear spring is helping, which would seem that the front wants to roll more than the rear...(?)

 

[rick7343]

Interesting... I was down in the big city today talking to one of the leading race shops and they said the light hollow Hotchkiss bar can't be preloaded... they are not strong enough...hmmm...

I suspected the bar was twisted when I set the car up last weekend... (crap!) Maybe that's why adjustments didn't have mush affect...

We are stuck with stock mounted bars... Have to find a solid bar now I suppose...

Why can't things be simple anymore...?? lol

 

[chriswh86]

Rick - What springs are you running? Getting a large sprint split up front or in the rear could be crutching a bigger issue

"I suspected the bar was twisted when I set the car up last weekend... (crap!) Maybe that's why adjustments didn't have mush affect..."

Sounds like you are setting your car up with the sway bar attached? it shouldn't be while scaling and setting ride heights etc...

 

[rick7343]

Lf. 600. Rf. 650
Lr 200 Rr 175. (4 link)
Car has never felt hooked at all until I increased outside air pressures, always felt greasey lik it was always sliding...tires squealing , etc... just starting to make some progress.

The idea was to run softer front springs and bigger bar (1-3/8" 540lb) to be able to get the front CofG down in the corners, But the shock package was too stiff to let this happen...So I put the springs back in that the race shop that built the shocks advised (current)

Seems the presures the other cars are running are too soft for my car and the tires get greasy, but running too much seems to take a while for the tires to get hot enough to stick really good...

How is optimum tire pressure determined?

I called the manufacturer, they said to start at : rf 36,rr 34,lr 32, lf 30 and drop a couple psi if needed... most top racers in the class say no more than 28 hot in the outside and 16-18 hot on the inside... at 16 hot on the inside I can feel the lf tire fold over and hop coming out sometimes...

One of the fast cars that passed me the other night looked like he was sliding all over... not hooked either... had more power than me and got the job done though!
we have to run Towel City recap on 8" Hoosier casings... Also have to run a lot of extra stagger to make them work..

wonder if we all are missing something?

 

[Ranger Mike]

Rick, you are limited to running hard tires in this racing class. The lite spring big ARB idea is not working for this car on this track. Forget about getting Center of Gravity down in the corners...why would you want to do that? What is the purpose? CoG is a starting point but the Roll Center is where everything happens.

Hard tires require RT front weight in order to increase traction and properly turn the car in a corner. They require rear weight in order to hook up and driver off the turn. Springs control amount of weight transfer ,,, Shocks control rate of transfer. Tuning these two are key to making the car handle.

Tire temperatures are indication of how good the actions above are working. You should have no more than ten degree spread over the inside, center and outside tire temp readings.
Adjust tire pressure until you get the 10 degree spread.

I had a driver once who insisted on running 10 psi on Hoosiers when the Hoosier tech said 20 was minimum..car bottomed out..no wonder..but some people just will not listen and want to run the “ hot setup” without understanding what is really going on...

Go back to more conventional spring / ARB set up and work on the right front wheel geometry. Reduce bump steer, reduce camber build, add Ackermann. On rear , eliminate and roll under/over steer to avoid mixed signals...when you get the car to turn going in ..then work on hooking up the rear end...my opinion

 

[rick7343]

"Rick, you are limited to running hard tires in this racing class. The lite spring big ARB idea is not working for this car on this track. Forget about getting Center of Gravity down in the corners...why would you want to do that? What is the purpose? CoG is a starting point but the Roll Center is where everything happens.."

Tires are supposed to be 60 duro, they "ball up" like slicks a bit..

Center of gravity down... why are lower cars faster around the corners?

"Hard tires require RT front weight in order to increase traction and properly turn the car in a corner. They require rear weight in order to hook up and driver off the turn. Springs control amount of weight transfer ,,, Shocks control rate of transfer. Tuning these two are key to making the car handle."

How much weight is too much for the right front? I would like to use all the tires...

How much is too much rear weight..local guys are saying 50% rear is too much...

Other teams are saying their roll centers are way left to keep weight on the left front...Mine is almost in the canter @ 3.5"


"Tire temperatures are indication of how good the actions above are working. You should have no more than ten degree spread over the inside, center and outside tire temp readings.
Adjust tire pressure until you get the 10 degree spread."

I made a mistake by listening to others on camber (6 degrees) and tire pressure... less camber and more air works better so far... with 28lbs hot in the RF it just gets greasy... I will reset with temps... I had eliminated bump... not sure how to accurately measure ackerman... ?

"Go back to more conventional spring / ARB set up and work on the right front wheel geometry. Reduce bump steer, reduce camber build, add Ackermann. On rear , eliminate and roll under/over steer to avoid mixed signals...when you get the car to turn going in ..then work on hooking up the rear end...my opinion "

Bump is almost zero, camber build is less than a degree per inch...

Am going to fix the rear roll steer since the back of the car jumps over a bit when fuel is applied in the corner...

Last race ,it finally started feeling hooked up on the rear, so it's not really that far off... everyone says it looks good... it doesn't feel good yet, and not much feedback thru the steering wheel.. I changed gearing for last race and lost ground, so it looked worse than it was... new, modern custom cam on the way... engine is old and tired...

Thanx Mike!

I was really frustrated because chassis adjustments and changes weren't making any difference until I got some laps on the tires and finally added air..

 

[Ranger Mike]

[QUOTE=rick7343;4032703

Center of gravity down... why are lower cars faster around the corners?

In general low cars turn better simply because the distance between the CoG and the RC is shorter. But the assumption is the weight tranfered thru the RC is going where it does the most good. Having RC located to the left is not going to plant the Rt ftont tire As EFFECTIVELY as having it plant when the RC id off set to the right side when turning left

 

[rick7343]

So would it nbe wrong to assume with a heavy car and only 8" tires that there is already enough weight on the rf tire to plant it?

The fast guys and most successful race shop all tell me their roll centers are left... they just won't tell me how much..lol

They said on some of their bump stop cars (late models)the RC is outside the car to the left to keep the front left down... so they are tying to elimnate body roll...

Both my outside tires get really hot and get greasy after a few laps, so I think I have too much body roll, so the moment arm on the front would need to be shorter to combat the roll, correct?
(I have tried a lot of rear springs to try and match the rear roll to the front since the rear has a short moment arm..)

We only have 2 nights left, and I doubt I will make tomorrow night... It is our anniversary and time is limited since they put me on shiftwork ... (I am not quite married to the car, my wife keeps telling me...)

The car is actually pretty good in the corners right now, I am underpowered compared to those darn crate engines... It just doesn't really feel "hooked"...

 

[rick7343]

Does moving the RC left have something to do with the angle between it and the tire contact patch relative to the RC height?
I think Mitchell wrote that the height of the RC doesn't matter as much as the angle between it and the tire contact patch...

So you could have a higher roll center,but moved to the left, and it would act similar ro having a low roll center?? There must be something or why do it?? It must change the action of the moment arm too by changing the angle of it also...??...

One of the fastest cars here in my class has the same front clip and a pair of 400 springs in it... so it is possible... Have to say, he is always adjusting his though...

 

[Ranger Mike]

400# spring guy it racing a go kart chassis which has just about zero camber change. I suspect rear end goes loose and he dirt tracks it out of the turn..his success I think is due to driver... Anyway

On way to Bahamas until Thursday

 

[rick7343]

Nice!