raleighBahn

Hey folks,

I know next to nothing about about suspension dynamics (have read some excellent posts including Clark's Garage, etc), so some newbie questions. I mostly drive my car on the street (once a week, about 45 minutes unless I have something specific like PCA). I just did my first HPDE (VIR) and hope to try out some autoX. To the extent possible, would like to see if I could make some tuning or modifications to make it the most fun for the intersection of these three activities (mostly street, 2 - 3 HPDE per year, handful of AutoX). I know all cars (and drivers) are different, but perhaps there is a starting point I can get to for a known good suspension setup and adjust from there (of the items below, all settings as I received the car, except the new wheels). Car seems to understeer. Example: Coming out of Turn 1, VIR, tires really howl and have to take wide radius after apex and really open the wheel. Want car to sit down and dig in. Maybe my new tires (below) will be partial answer.

Current setup:
1989 951 (M030, LSD, etc - S spec)

Engine: Turbo S, no mods of any kind

Wheels/Tires:
Set 1: 996.362.124.00 (7, 55) 205/50ZR17, 996.362.126.05 (8.5, 50) 255/40R17, Riken Raptor (not great, but lots of tread) - (used at first HPDE)
Set 2: 986.362.124.01 (7, 55) 225/45R17, 986.362.126.06 (8.5, 48) 255/40R17, Dunlop Direzza Sport Z1 Star Spec. Just got these from Lart - suspect they will be vastly better. See photo at bottom of car with the new wheels.
Set 3: Original 16" Club Sport wheels, no tires mounted.

Q1: There is no spacer plate on the rear hub as per bulletin 9303 on 17" wheels. Are these needed?

Q2: I suspect the Dunlop better for Track - for AutoX as well?

Sway Bars:
Front: 30mm (968 M030)
Rear: 16mm (stock)

Q3: Very happy to find I had the upgraded front bar, surprised the 3-way 968 bar wasn't there as well. Read on for the rest and let me know if this is no-brainer swap out.

Front suspension:
Rebuilt front Koni Sport Struts - Yellow Adjustable. 951.343.521.00.
Coil-over Kit (front) Hyperco 300lb springs
Settings: Half turn counter-clockwise from soft/stop


Rear Suspension:
Rear Shock - Adjustable Yellow Koni model #8040
Settings: Two half-turns - Clockwise (Firmer) //3 half turns is total range

Q4: As far as I can tell, torsion bars are stock and no coil over kit. What should be done to balance the 300lb springs in front, if anything?

Brakes:
Stock (for 951S). Stock brake pads. Stopped pretty well at VIR, would like a little more bite. Recommendation on front and rear pads that are hybrid? Do not want full blown race pads that need warming up at this point.

Alignment:
See attached photo below
Attachment 829289

New Wheels and tires (set 2) from Lart

car_slave

Your car will understeer a lot with that setup. Find an aftermarket 19mm or 20mm rear sway bar and stiffen the rear shocks. If want more you're going to have to run 27mm or 28mm rear torsion bars to match the 300 lb. springs in the front. You could just put softer springs up front, which might be cheaper and better for the street. The new tires you have will be great for auto cross and track.

raleighBahn

What do you think about the oem 19mm 968 3-way rear sway bar that is usually paired with the 968 m030 bar I have up front? There is also a lindsey one that is 5-way.

car_slave

Both should be fine.

raleighBahn

Thanks man. Thinking I'll go incremental approach and not change everything at once. Will do the new rear sway bar (on lightest setting initially) in addition to the new tires I have. Take it to another HPDE and see where I'm at. The car did after all stay in good control and never got squirreley. Don't want to change everything and then watch my rear end pass me The sway bar can be dialed in a little between runs and perhaps the front Koni if needed. If still under steering after event, rear torsion bars.

Rob 3

Your comment on the incremental change is a good perspective from my humble opinion. Then you learn what works and what doesn't for you as well as how it all ties together. What works in a twisty small radius set up doesn't necessarily work in higher speed large sweeper. If you've been doing this for a couple years and you need to make change, then you can try a couple things at once, but for now its better to isolate each change to see if its what you want and you also know exactly what the impact was, not having to guess which change did what. Something you might find helpful is Carroll Smith's "Engineer in your Pocket"...