Technical Tips > Brakes, Suspensions, Steering, Wheels & Tyres

Tyre Combo for 18x8 ( Front and Rear )

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craigh:

--- Quote from: Vettech on December 09, 2016, 04:47:02 PM ---Confusing topic, I thought 73-76 used 15x8" offset: -1mm backspace 4.5", Std OEM tyre 225/70R15.
So? if you go up to 18" dia - do the other diamentions  stay the same esp if the width remains at 8" ?????????

--- End quote ---

Normally if you +size a wheel you aim to keep the new rim offset the same as the original.

So if its 15" x 8" 4" backspace today you would go to 18" x 8" 4" backspace.

If you went with a wider rim  you would modify the backspace to have the rim so the increase in width is evenly distributed in and out.

This is not always possibly but it allows the suspension geometry etc to work as intended.

Go to this site to play around and it will show you visually what the changes are and explains how offset and backspace are related.

http://www.rimsntires.com/specspro.jsp

As for 8" C3 rims I thought they were all 4" backspace

bfit:
From what I have seen earlier c3 have 15x8 4.5'' BS
Later c3 I think with the alloy wheels are 15x8 4'' BS
LIMITED observation I only have only worked on one later c3 A 79 model
The rims on that are 8'' with 4'' BS  stock vette rims
Bfit

craigh:
I had a look at 2 sets I have here, 71 & 76 both 15 x 8" 4" backspace.

From NCRS c3 guide on steel rims.
The back space on a 15 x 8 Rally wheel for a Corvette should be 4 inches. The back space on a 1968 15 X 7 Corvette rally wheel is 3 3/4 inches.

So 68"s were narrower at 7" wide then it went up to 8" for 69.

Just to confuse it more In GM cars of the era corvette was the only one using 4" backspace with 8" rim, the camaro etc with 8" uses 4.5" backspace.

So in 40 years I imagine a lot of things get swapped around between cars etc etc.

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