Question about corvette rally rims

[Don Barnes]

Are the wheels on a 1970 corvette 15x8 with a 4.25 backspacing.if not will these rims fit.

[Tom D.]

1970 corvette rally rims code AZ

1970 15x8 JJ (code AZ) wheels had -.50 offset, according to Colvin. Most wheels have a plus number for offset. I assume offset is the center plane to the bolt surface plane. I also assume he is measuring in inches...

Tom D.

[Don Barnes]

Do you know what the measurment is

If you lay the wheel on the face and take a straight edge across the whole wheel
and measure from the bottom of the straight edge to the back of the plate, my
wheels i have 4.25" that is called the back spacing right or am i measuring it wrong?

[Zachary K.]

Re: Do you know what the measurment is

My understanding of backspacing measurement is from the backside of the wheel outer rim (measured easiest with the tire off) place a straight edge across the wheel. Measure from that point down to where the wheel surface is that sits up against the rotor face.

[Joe L.]

Re: Do you know what the measurment is

Don-----

The term "backspacing" and "offset" define different METHODS to measure the same basic thing. In backspacing, the measurement is made from the rear of the rim to the plane of the center-section lug bolt mounting surface.

"Offset" refers to the displacement of the center section lug bolt mounting surface from the CENTERLINE of the rim. Displacements OUTBOARD of CENTER are POSITIVE and displacements INBOARD of CENTER are NEGATIVE.

Since an AZ Corvette wheel has an 8" wide rim, if the backspacing is 4.25", then the wheel would be said to have a POSITIVE 0.25" OFFSET. However, as Tom mentioned, Corvette "AZ" wheels have an offset of -0.50. This is the same thing as a backspacing of 3.50". So, if you are measuring them correctly and if the wheels are actually stamped "AZ", then they must have been modified (which is very unlikely).

[Duke W.]

Re: Do you know what the measurment is

Backspacing and offset are not directly related, which is why I don't like using it. Backspacing for a given offset can vary with flange design/thickness, so for a give wheel width (which is measured across the INSIDE of the bead mounting flange) it will not correlate exactly to offset.

Offset is easy to measure. With the wheel (with or without at tire mounted) laying outside surface down on a flat surface lay a straight edge across the inside flange (or tire sidewalls.) Measure the overall width from the straight edge to the surface and call this dimension "A".

Now measure from the straight edge to the wheel mounting plane and call this dimension "B".

Offset = B - A/2

and this will yield the correct sign.

Duke

[Tracy C.]

Like your logic...works with or without tires! *NM*