Mike Simard

Hi Struan.
I have a dedicated racer and have some random thoughts on suspension setup.
My car races in NASA which has weight/power classes and I've run it with 229 or 440 hp with 640whp available. Race weight with me and fuel is 2800lbs. I've always been in sorting out mode and never competative but I've learned some things.

Spring rates others quote are low IMO. Because of the motion ratio of the 928 both front and rear, it takes more spring than you think. Most people don't understand the formula for calculating wheel rate and I blindly tried springs on my car until I bothered to break out the calculator.

I've run several different combinations such as numbers you see here on RL but they were all too soft. Now I run 2000 lb/in front and 900 rear. That is about as stiff as you can go but it gives a good wheel rate and works really well for me.

A 928 with a 2000 lb spring is equivalant to a strut car with 500-600ish.

Another important detail I've found is that the damn rear adjusters move!
I wondered why my car was plowing badly one time and just happened to notice the steering wheel wasn't centered any more. Turns out the eccentric adjusters had moved and I had silly toe in. Both rear wheels!

IcemanG17

Sturan
Okay so the car is loose with excessive wear on the outside front tires....this tells me you are overheating the outside edge of the tires...so you need MORE camber in the front....I am running 225/50-16 street tires all around on my lemons racer with 2.4' camber (maxed out) and the tire wear is very even across the tread.....it is slightly toe in in front and neutral in the rear.... our racing weights are almost exactly the same....

If you are happy with the slightly loose handling, I would leave it.... you could try playing with tire pressures to tune it a bit too.... remember loose is FAST..... another option that might help you is aero mods.....a stronger rear wing might help too

RKD in OKC

Ha ha ha, handles neutral till pushed hard...Everything handles neutral until pushed hard The limits of traction is where the balance is not before.

Without seeing the tire outside edge tire wear it is difficult to tell if it is from lack of negative camber, too low tire pressure, or just normal for your driving style. A good way to check for camber and pressure is to measure the temps across the tread, but not too close to the edges. Preferably with a temp probe you can stick into the rubber and as quickly as you can coming off a hot lap. I 4 wheel drift thru corners and wear the outside corners off my tires, but not the outside 1/4 of tread that I would consider wear from not enough negative camber. Looking at the temps you should be able to tell if you need more negative camber up front. Even temps across the tire and you are good.

If it were me, I would put a little more negative camber in the rear, say .8 to 1. That should give you a little more rear grip adding throttle in the corner and increase corner exit acceleration. With 255 in the rear you should still be able to power oversteer with ease. It will also make throttle lift rotation in 4 wheel drift more about the front grabbing more and turning in instead of the rear coming around.

Loose is faster than understeer and definately a lot more fun, but neutral is faster than loose.

Also because of the Weissach rear end steering you feel like you are really hanging the rear out loose in a 4 wheel drift compared to other cars.

Lloyd

I agree with Mike. My 1978 car weighs about 2800lbs. and I am running an adjustable LEDA coil over suspension with 2000lb. Hypercoils on the front and 750lb on the rear. The calculation for the "wheel rate" justifies the numbers. I thought this set up would be crazy stiff, however it is not that way at all. Maybe it is the tuning of the shocks and springs. Racer's Edge in Knoxville designed the set up and I have been very happy with it for 4-5 years running on many tracks in the South east.

ROG100

http://www.youtube.com/watch?v=Jkqj44OZTAE

Kiwi 928 in action

James Bailey

running DOT "slicks" I use Kuhmo and do 15-20 minute sessions. I found that 3 1/3 negative camber made for even tire temps at about 32lbs cold.... 2900 lb 928 , Eibach springs , run very low with 225x50x15 tires stop sway bar works for me on short technical lots of turn tracks. To get the "extra" negative I used S-4 upper and early lower A arms and had to shim the lowers out to get it back to only 3 1/2 neg. I max out the caster and have been known to let go of the steering wheel and let it self correct when it gets interesting I have no horsepower 198 RWH and have to run it as a momentum car yet it will power oversteer if need !

struan

hi again, got the membership thing sorted this morning. Have just returned from workshop,and after reading your advice have increased front camber to 2 degrees,and rears to 1.Will try it and see how we get on.
heading off tomorrow for round 3 this weekend. At same circuit as round 1 so I will have some data to use for comparatives.On Friday we will be doing fuel consumption tests, as well as see how the suspension change works (or not). AS the race weight is critical in our events,and my car is underweight with dry tank, we only want to carry minimum fuel load,so it will be interesting to find out how much we use per lap. I will report progress during w/e if time permits.
One thing I will be doing as soon as we get home is drop out the springs and get them checked to see what we have in there.
Thanks for all you comments so far. HAPPY NEW YEAR!!

ROG100

Good luck at the race Struan, show the lawn mowers a good clean set of heels 8>)

mark kibort

Do you know why you have to run that much camber and get even tire wear??

I think you know the answer

You shouldnt recommend set ups that will kill handling and burn through tires unless you futher qualify your set up.

Ill give you a hint. Dots and eibach springs.

ask Mark A how the "Estate" handles with the set up I suggested.

struan

Hi again,I'd almost forgotten about this, we did ry a few a things, however the lowering helped the most.At all 3 circuits we race on lap times came down by 2-3 seconds. end result was 4 consecutive fastest qualifying laps and 8 class wins and 1 second from 9 races. Ended the season 3rd overall in class,our blown headgasket being the spoiler in that I got no points at that meeting. Still 3rd in class, also picked up Rookie of the year, most improved driver, and the dubious honour of the "Gardner Trophy" in recognition of a major off road excursion.All in all quite pleaseing.
Picture just to show that we really do exist.