c3 rally wheels back spacing

[Sander B.]

what is the factory correct back spacing for the 15x8 rally wheels

4 or 4.5 ?

[John H.]

Re: c3 rally wheels back spacing

what is the factory correct back spacing for the 15x8 rally wheels

4 or 4.5 ?

Sander -

You'll have to measure it on a wheel, unless someone else has an "AZ" wheel handy and can measure it for you. OEM specs never used "backspacing" as a measurement; OEM specs used "offset", and all '69-'82 Corvette "AZ" 8" rally wheels had +.50" offset.

[Lawrence M.]

Re: c3 rally wheels back spacing

Sander,

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.

Larry

[Duke W.]

Re: c3 rally wheels back spacing

Sander -

You'll have to measure it on a wheel, unless someone else has an "AZ" wheel handy and can measure it for you. OEM specs never used "backspacing" as a measurement; OEM specs used "offset", and all '69-'82 Corvette "AZ" 8" rally wheels had +.50" offset.

John - The offset I have for the 8" Corvette Rally wheels is -0.5" (negative 0.5"). The 7" Corvette Rally Wheel is -0.28".

As the wheels got wider, the circumferential centerline of the wheel had to be moved outboard relative to the wheel mounting plane to provide sufficient inboard clearance, particularly with the rear spring ends. The '67 6" Corvette Rallys offset is +0.06", and the earlier steel wheels are +0.44". The KO wheels (including adapter) and '67 "bolt-on" aluminum wheels are the same as the '67 Rallys: +0.06".

So the "backspacing" of the 8" Rallys should be a little over 3.5", but this is not a very precise measurement.

The wheel width is measured from the inside of the tire mounting flange, but the backspace is measured from the outside of the tire mounting flange to the mounting plane, so it includes the overall width of the flange at its inside boundary, which probably adds about 1/8 - 3/16".

Duke

[Sander B.]

Re: c3 rally wheels back spacing

John - The offset I have for the 8" Corvette Rally wheels is -0.5" (negative 0.5"). The 7" Corvette Rally Wheel is -0.28".

As the wheels got wider, the circumferential centerline of the wheel had to be moved outboard relative to the wheel mounting plane to provide sufficient inboard clearance, particularly with the rear spring ends. The '67 6" Corvette Rallys offset is +0.06", and the earlier steel wheels are +0.44". The KO wheels (including adapter) and '67 "bolt-on" aluminum wheels are the same as the '67 Rallys: +0.06".

So the "backspacing" of the 8" Rallys should be a little over 4.5", but this is not a very precise measurement.

The wheel width is measured from the inside of the tire mounting flange, but the backspace is measured from the outside of the tire mounting flange to the mounting plane, so it includes the overall width of the flange at its inside boundary, which probably adds about 1/8 - 3/16".

Duke

Duke if you say the oem 8 inch wheels are 0.5 '' negative offset
shouldnt be the back space around 3.5 inch ?



i have 2 original 15x8 wheels
they have have a back spacing of 4'' (zerro offset)

bought 4 new repro wheels localy and while installing them
i discovered the tires hit the E brake brackets on the trailer arms

paragon sells repro's with a 3.5'' back space the say
and others advertise with 4.1/8''

thanks Sander,

[Duke W.]

Re: c3 rally wheels back spacing

You are correct, and I corrected my post.

I don't think any other Chevrolet models used 8" wheels, so one with 4" or 4.5 backspacing is aftermarket that doesn't conform to OE specs.

Duke

[John H.]

Re: c3 rally wheels back spacing

John - The offset I have for the 8" Corvette Rally wheels is -0.5" (negative 0.5"). Duke

Duke -

That's correct - typo on my part; offset is -0.5" (can't correct my original post - no edit function after someone responds to it).

[Duke W.]

Re: c3 rally wheels back spacing

...then I screwed up trying to correct your mistake...

Duke