Baskspacing, offset, etc.


Founding Member
Dec 1, 2000
Oceanport, NJ
Trying to figure out if I can run the 05 wheels on my car. I am under the impression from my reading that backspacing is a function of offset.

I have read that the new style wheels are 6.295" of backspacing. I have also seen that they have 45mm offset (1.77"). The calculation that I have seen for backspacing is half the wheel width + offset. Being an 8" wheel; 4+1.77=5.77 which isnt much different than the earlier wheels.

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You're going to need spacers.

I have non-original width 14x7 styled steel wheels with a 4-1/4" backspace on my '66 and this only leaves me with about 1/4" clearance with the front a-arms.

Backspace is the distance from the rear "face" of the wheel (the part in the center with the 5 bolt holes that goes up against the rotor/brake drum) to the very outer edge of the rim (the edge on the inside side of the car).
The way that I was taught (which may or may NOT be correct)...

Backspacing and offset are two different ways of expressing the same info.

They both tell you how far in or out the wheel will sit in relation to the face of the hub. The hub being the flat surface that the studs stick out of (the center of the brake rotor... ya know)

BS tells you how far it is from the hub (mounting surface on the back side of the wheel) to the INSIDE edge of the rim (the back edge of the wheel, toward the inside of the wheel well).

OS tells you how far it is from the hub (mounting surface on the back side of the wheel) to the CENTERLINE of the rim. Positive offset would move the rim out making it look very deep (like most old cars), negative would move the rim in making the wheel look very shallow (like most new cars).

So if you have lotts of backspace, the wheel looks very shallow, if you have lotts of (positive) offset the wheel looks very deep.

At least that is the way I understand it.... maybe somebody on here who sells wheels can verify if this is correct or not.

:flag: :nice:


And a chart that lists offset for various backspace, based on rim width: