Race car suspension Class

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

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Ranger Mike

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 completly 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

(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.

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, dont 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

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...

Attached Files

HP required to overcome Aero drag.pdf (113.5 KB, 23 views)

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