By JohnJacob (38.27.177.90) on Wednesday, February 07, 2001 - 10:45 pm:

I found a place online that sells racing rims available in the 4x120 bolt circle. It talks about wheel back space and some stuff I don't know a lot about. Tell me what you all think...
http://www.diamondracingwheels.com/DIAMONDRacingWheels/RoadRaceSeries.htm

By Paul Krummenacker (208.140.33.251) on Thursday, February 08, 2001 - 01:30 pm:

here are some links that talk about backspacing

here is a really good page put out by Ronal, they are a German company that makes wheels, frequently seen on BMW, Porsche, etc.
http://www.allroadster.com/ronal/Wheel%20Choices.htm

this one is ok as well.
http://www.geocities.com/MotorCity/Track/3075/tires02.htm

Here is my understanding of wheel design: in a nut shell, your wheel is shaped kinda like this: ]|[ the line in the middle is dead center of the rim. Backspacing or Offset as it is also known, is how far you move where the lug nuts clamp on to the center of the weel in relation to the dead center of the rim. (confused yet?)

if your wheel has a 0 offset/backspace, the center of the wheel is exactly in the middle of the rim (if you chopped the wheel in half).

A Negative offset will move the center of the wheel toward the outside of the rim, moving the tires in toward the car. this will cause a narrower track = less stable

A Positive offset will move the center of the wheel toward the inside of the rim, moving the tires away from the car. this wil cause a wider track = more stable

HOWEVER!!! Too much Positive offset and you will be rubbing fenders with your tires. Also you will really change your steering geometry and you'll definately need to tweak on your alignment to get things to handle normal.

Too much negative offset and you will be rubbing the inner part of your wheel well.

I have a negative offset problem on my old Volvo that somebody put on aftermarket wheels. To fix this, the previous owner got some wheel shims that moved the wheel out by 3/8". this is a REALLY BAD idea, here is why. your lug nuts are only ~ 1.25" long (at most, many are 1" long. Your wheel is say 3/8" thick where the alloy wheel meets the hub, by sticking a 3/8" spacer in there you have now taken your 1.25" long wheel stud and left yourself only .25" to .5" for your lug nuts to grip onto!! If you have to run a spacer, then you need to replace your wheel studs with longer studs. Many SCCA classes require to have longer studs for racing.

having been out doing some testing in my Rally car, I can tell you, you definately want to make sure you have lots of lug thread, and your lug nuts are nice and firmly tightened down. After an hour of testing, I was inspecting the car and I found that one of the front lug nuts had walked itself out to the end of the lug. Not a good thing if I had been going all out and lost a wheel.

I'm going to contact diamond and see what they have to say about my specific application for rally racing. I'll let you know what I find out.

Paul