Optimal ride height for track setup
 

Looking for thoughts on how far to drop from stock height for track setup for ideal CG.

I am installing Bilstein B16 PSS10 on 2014 Sport where a professional race shop will be performing the setup. I am just looking to see what amount of drop those of you with track experience recommend.

Key input:
- Track experience 25+ days
- 75% Track Use / 25% Weekend Driver (I do drive it to track - 150 Miles)
- RS4 275/40/18 square
- SPL Upper Control Arms
- Hotchkins Front and Rear Bars
- No Aero
- Current Camber is -2.75...but expect it will go to -3.x

I'm literally getting rs4 in that size put on Monday. How do you like them?

I never found an answer when I was looking this up and from what I can see and measure, you don't have to worry about going so low that the roll centers end up below the road surface.

I'm at 26.5" from floor to bottom of fender. If you are on ots Bilstein you will probably need to run on the higher side around 27" or more to avoid bottoming out the chassis on the pavement on common road imperfections.

Edit: I am on 275/40/18 yokohama ao52

Been looking for these two posts on and off for the longest time, finally found them again. May find some of the stuff useful regarding BGTV8’s rationale on trying not to lower the car too much.

http://www.the370z.com/track-autocro...ml#post3100179

http://www.the370z.com/brakes-suspen...ml#post3776914

The Z does not have a linear camber curve in the rear. How can I explain this. This is just an example. Say you have your camber set at -1. Squat the rear inch, camber goes to -2. Squat 2 inches, camber goes to -3. In the Z, squat 1 inch, camber is -2. Squat 2 inches, camber is now -3.5. Also, the lower the rear. The more non linear the camber curve becomes. Lower the Z by 1 inch. Camber at -1. Squat 1 inch, camber is now -2.25. Squat 2 inches, camber now at -3.75. I don't know what the exact numbers are. But that's the way is was explained to me from AM Perf.

I don’t think this is related to height - in those two linked threads, there was a lot of talk about curing oversteer in those race cars. I noticed those cars had TRUE TYPE coilovers running heavy springs in rear...


Since those threads we discussed how true type required a different spring rate from divorced type. I wonder if those drivers would have solved their issues by going softer in rear accordingly

From my experience, going to low will cause understeer. I try not to go too extreme on dropping the ride height. It does help on tighter corner tracks.

Thanks for the replies...I just looking to see how much you track guys have dropped...1/2", 1", 1.25", etc and feel good about where you are.

Brendan - I am currently sitting at 27 3/8" on 18" wheels with stock dampers.

Rusty - I expect the suspension shop would set the appropriate Camber settings given the final lowered stance...would't they? I will remind them of the non-linear camber rate on squat.

Sharad - I have no need to go "real" low...this is not for looks...it is for performance. Hence my question as to what ride height seems to be working for those who track?

I do not have any understeer problems today (at Square and -2.75 camber)....my objectives are to be fully planted, car control (increase confidence on high speed turns) and address excessive outer tire wear.

It’s specifically BG’s response. It’s about the part where he discussed lowering CG via smaller diameter wheel + tire vs lowering via spring, leading to benefits on keeping a longer suspension stroke (also see how second post mentions lowering too much via spring messes up the roll center), and how he managed the gain in rear toe-OUT under braking (makes the rear end wander) during braking. Add what Rusty said, sort of finicky nature of camber change.

It’s not so much directly related. Just somewhat related.

I have been told that the rear camber issue can be fixed but it is expensive. Requires totally modifying the rear subframe and pickup points. I never got into the details of it but I may later on.

That's what i was told too. That to correct it, Some of the pivot points have to be move. It's not cheap and involving lots of engineering.

Yeap, I think MA-Motorsports can do it. Brian is the one that told me.

I wouldn't run any lower than two inches. Nismo stock is 28" floor to the finder well. There always trade offs. If you run a splitter you want to get as low as possible without causing issues. I run 26" front and 26.5" rear.

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The other thing about going too low. You are no longer in the middle of your shock/coil-over stroke. You are now closer to the bump stops. If you are riding on the bump stops in a turn and hit a bump. You don't have any travel to absorb the bump. Something not good is going to happen. The next thing is if hard on the brakes before a turn. You use up your travel and are on the bump stops. You hit a bump, guess what happens next. This may be one of the reasons for ice mode. Something to think about.

If you have a proper thread-into-body coilover, don’t worry about travel within your suspension components. The biggest problem is that lowering our double wishbone fronts causes unwanted alignment changes and limits suspension travel from the front upper control arm to the strut tower.

At stock height, the upper control arm will sit nearly perpendicular to the front knuckle; therefore, the camber/toe doesn’t not change a lot through compression/extension. Lower the car 1-2 inches, now that upper control arm sits at a 30-45 degree angle upwards. With the same amount of compression/extension, the camber/toe will change drastically more. Over bumps, the car will be easy to unsettle because your tire contact patch is diminishing.

Ideally, you would shorten knuckles and get full SPL arms to eliminate this unpredictability (similar idea for the rear to prevent unpredictable oversteer from camber/toe changes when lowered), but that’s a lot of $$$ and work to support a simple mod.

Basically the closer the ride height to stock, the better your car will handle. The alignment benefits really outweigh the slim benefits from low COG. Driver confidence is key. A low bucket seat will also help.