Rim and tire gurus?

[FastFord58]

Hello, all.

I am trying to figure out backspacing and offset for my car. It is a 1988 Coupe, but it is using a 2003 Cobra suspension. Front spindles and the rear IRS are both 2003.

I have 2003 Cobra rims with 275/40 Khumo Ecsta Supras, but they stick out an inch eac side because the suspension is an inch wider on both sides of the car.

I have googled and visited some sites, but they have confused me a little bit. I need to know what I have to measure to figure offset and backspacing on a 17X9 rim so that it is not sticking out of the car.

The 03 rims have a 6.12" w/approx. a 25mm offset.

Thanks in advance.

ff58

 

[Mustang5L5]

Did you use the Cobra or Fox control arms??

 

[FastFord58]

Fox tubular control arms.

I have figured out that a 17x9 rim with a 50mm offset will work, but I'm not sure about the backspacing.

Is the offset dependent on the backspacing?

 

[backfocus]

Offset is the distance between the center of the wheel to the mounting point. Backspacing is the distance from the back of the rim to the mounting point.

So if you have a 8" wheel with a 0 offset the backspacing would be 4". The closer the mounting point is to the front of the wheel is positve offset. If the mounting point is pushed back toward the back of the wheel (from the center of the wheel) is negative offset (as with deep dish wheels).

So yes, offset is dependant upon backspacing.

Here is a good link for finding correct wheel sizing and getting the maxium wheel and tire size.

http://www.rodandcustommagazine.com/techarticles/custom_tires_how_to/