Wheels (again)

[cherokee]

If there is one thing I just can't get my mind around it is wheel sizes. Simple question.

Will these fit:

13x7 4x100, 38mm offset approximately 5.5” backspace
I would like the tires to be 20.0 x 9.5-13 tire.

-----

If they do not fit what is the backspace, or offset or whatever that would be needed for a 13x7 wheel?

Thanks for the help, I did try to search, but everyone likes to go with larger wheels I need to stay with 13's.

Thanks for your help, this stuff is just a mental block with me.

[RallyBob]

Originally Posted by cherokee If there is one thing I just can't get my mind around it is wheel sizes. Simple question. Will these fit: 13x7 4x100, 38mm offset approximately 5.5” backspace I would like the tires to be 20.0 x 9.5-13 tire. ----- If they do not fit what is the backspace, or offset or whatever that would be needed for a 13x7 wheel? Thanks for the help, I did try to search, but everyone likes to go with larger wheels I need to stay with 13's. Thanks for your help, this stuff is just a mental block with me.

I lent my old 'GT-4' wheels and tires to a forum member here to autocross with. They were 13 x 7" three-piece alloys (Keizer knockoffs), with Hoosier 20 x 9.5 x 13 slicks. They fit his stock GT body with no flares, and his car is extremely lowered. The backspacing is 4" on these wheels. Keep in mind that with the cantilevered-sidewall slicks, the tires bulge another 1.25-1.5" past the edges of the rims!

Here's Travis' GT with my wheels and tires fitted.

Bob

[GTJIM]

For a GT:

The 'off-set' at ET38 (38mm) needs to be reduced to ET28 (28mm) by use of a 10mm spacer on the front to get the steering geometry into spec. This does depend on the actual diameter of the tyres so you have a range of between 1/2"(12.7)mm and 3/4"(19.1mm) spacer thickness you can use on the front and still be "close enough". A 3/4" spacer would reduce the 'back-space' by that amount 5.5" - 0.75" = 4.75" which should just about clear things on the front.

At the rear wheels you can space a bit further because "steering Geometry" is not so involved there - the rear wheels don't turn! So you can use wheel spacers to centre the wheel under the rear guard - once again about 3/4" to get the wheels out far enough to clear the body (the lip along the chassis rail is the thing to keep clear of here).

The 'back-space' is the distance the mounting surface is away from the inside edge of the rim. The 'off-set' is the distance the mounting surface is away from the centre of the rim. Larger Positive 'off-set' moves the rim inwards.

HTH

[cherokee]

Thanks for the help guys.

[jvandyke]

Originally Posted by RallyBob I lent my old 'GT-4' wheels and tires to a forum member here to autocross with....

Want to sell 'em?
Yes, it's me, still looking to fill my Stienmetz flares better (especially on the back)

Ultimately I'd like some sort of mag rim, (still like the slot mags) and as wide as I can get away with. I guess I'm after the look that Gil and Kyle got, wide and low.
Anyway I made this to help me get it straight. Maybe it will help others.

[oldopelguy]

Please, when you ask a question about wheels, specify which model of car you are looking for.

Formulas you need to do your own math:


Rim Width / 2 = Centerline
Centerline + Offset + Rim Lip = Backspacing

8" wide rims / 2 = 4" Centerline
4" centerline + 0.63" Offset + 0.25" Lip = 4.88" Backspacing