IcemanG17

I figured it would be good to put all this data in one thread for easy reference.... Here is the data I have:

On Casper, running 275/645-18 (same as 275/35-18) all around on 18x10x65mm wheels my actual ride height is 95mm front and 140mm rear...the front is VERY LOW..but my suspension has full heim joints and can go lower than stock shock 928's.....For reference the Estate running stock bilsteins with -1.5 coils eibach springs was at 120mm front and 150mm rear

Alignment.....currently I am running LOTS of camber due to the low front height....I am at 3' in front, 2.5' in rear with zero toe all around...my caster is 4.5 & 4.9' and the thrust angle is near zero.... I have noticed excessive front tire wear on the INSIDE drivers side tire...which is odd considering Thunderhill only has 3 right turns vs 13 left? When I 1st checked it it was over 3.5' on the drivers front, which is now 3'....should be better.....

I know Kibort runs 110mm front & 135mm rear with 1.7' camber in front and a bit over 2' in rear....but he is on stock koni shocks....

My spring rates feel quite high....800+ front and probably 500 rear

What is your race-track 928 set at and why?

OBehave

I think this is a great idea as I have been playing with my 85 and now Hanson car. First thing though is the need to clarify the camber values you are using.
Your 3' and 2.5' rear are negative or positive camber? I will assume it to be negative as that is what is more favorable for racing but let's please be clear as to -3' or +3'.
as far as toe, you should make absolutely sure there is no play in the steering components and you would want a little toe in so when the car is moving forward the wheels tend to turn outwards just a little. So for instance by setting the toe to 0, when the car is driving forward it could actually give you a toe out of 1/16"-1/8" or more depending on the tightness in the steering joints.
Toe out wears ties on inside,toe in wears tires on outside. negative(-) canber wears tires on inside and positive (+) camber wears them on the outsides.
And massive wheel spin wears them evenly.

IcemanG17

Ed
Negative camber.......since its what you need.....

Interesting about toe out wearing tires on the inside....might be worth a slight toe in......I'll check how these tires wear....

GregBBRD

This should be interesting......

I've always found alignment discussions, at the race track, very humorous. People end up running around making changes on their own car to what their buddy is running....without thinking about the differences, from car to car.

Almost impossible to compare camber readings...since the height of the car changes the positon you might be on any given "camber curve".

It is possible that a car with 2 degrees of negative camber with sits higher than a car with 3.5 degree of negative camber might actually have more negative camber when the suspension is compressed to the same height as the car with the higher camber reading!

Front toe is also very interesting on the 928. As the cars get lowered, the "angle" that the tie rods sit at gets really wacky. Under braking and acceleration, some very "nasty" things will be happening on a highly lowered vehicle. (The "bump steer" goes absolutely nuts!) These cars really need to have the springs removed and be run through a "toe" curve" to see what actually is happening.

Everything I've set up has some significant "changes" to this "curve". Until you do this, you will destroy front tires, on the inside....

ubercooper

My weight dist is different, but here they are anyway

2600lbs
Konis
850 front springs
650 rear springs
928 SP sways full stiff
295 front tires
335 rear tires

For now...
120mm front
140mm rear
0 toe rear 1/16" toe in front
1.5 front camber
1.9 rear camber
Caster 4

Lizard928

Brian,

With the car that low Greg has nailed it on the head.
You need to make some changes.
Make yourself a bumpsteer kit (not too difficult).

Also measure your tire temps inside out and middle. Adjust your camber based on this.
Run 1/16" of toe in on your car (front) and the same to zero on the rear.

If you cannot get your camber down to acceptable levels and you are running early suspension then replace your lower a-arms with later arm to achieve less camber.

puyi

And remember, too much camber or too caster make the car more sensible to rolling. So you have to optimize these 2 factors.
Toe is only relative to understeer or oversteer. If the car understeer go toe in positive way and "vice-versa". The optimisation should be the heat of the tire. It is not relevant, Camber is even more important in that way but is really nothing compare to pressure tire adjustment. With slicks, the tire pressure has to be 2 kPa @ 85-95 °C. If your tire over heated, you should begin with more air in it, so if you have beginning the race session with 1.6 @ 20 C, lets go to 1.65 and so on until you get the good pressure and T°. The adjustement of Camber goes 2 ways. The first one is to make the car the more simple to drive. It is to make it neutral. Second, it influences tire pressure and T°, so if you simply learn about that, fisrt and second are not independant facts. Then it is always an optimization between to antagonist factors. If you change the brand of tire or even the type of tire in the same brand, all your adjustment has to be re done!

Puyi

John Veninger

Not sure my car's height, but I have is pretty low. I focused on corner balancing more that height.
Camber runs -2.1 front and -2.5 rear. Front toe 1/16 out. Rear toe 0.
Springs are 900 front and 450 rear
We need someone to make some drop spindles to get rid of the silly control arm angles at the low height!

IcemanG17

Great info from Doc as always......I will have to take some temp readings to see what is going on.....