63 wheel offset

[Michael G.]

I don't have 63 wheel without a tire on it to measure, so, does anyone know what the offset of the standard 63 / 64 steel wheel is? (offset=distance from mounting surface of wheel to outermost point on rim)

Thanks,

[Joe L.]

Re: 63 wheel offset

I don't have 63 wheel without a tire on it to measure, so, does anyone know what the offset of the standard 63 / 64 steel wheel is? (offset=distance from mounting surface of wheel to outermost point on rim)

Thanks,

Mike------


I can tell you what the off-set is but i can't tell you what the distance is from the mounting surface of the wheel to the outermost point on the rim. That's because the latter dimension is not off-set; it's backspacing. Off-set is the displacement of the wheel mounting surface from the centerline of the rim.

The offset of the wheel is +0.44"

[Duke W.]

Re: 63 wheel offset

I don't have 63 wheel without a tire on it to measure, so, does anyone know what the offset of the standard 63 / 64 steel wheel is? (offset=distance from mounting surface of wheel to outermost point on rim)

Thanks,

What I think you're asking for is the so-called "backspacing", which is the distance from the innermost point of the wheel to the mounting plane. It vary for wheels of the same width and offset due to differences in thickness of the tire mounting flange. For example an aluminum wheel of the same width and offset will likely have slightly greater backspacing because the flange is thicker than a steel wheel.

"Wheel width" is measured between the insides of the mounting flange. "Offset" is how much the mounting plane is away from the center of the wheel width, and high negative offset will yield a "deep dish" wheel.

You can estimate backspacing as follows:

Backspacing = wheel width + offset + flange thickness

Offset may be either positive or negative and flange thickness is probably between .090" and .120".

I prefer using offset when comparing wheels. Joe gave you the '63 - '66 base steel wheel offset. KOs (with adapter) and '67 steel and aluminum wheels are +.06"; '68 7" Rally wheels are -.28", and all '68-'82 wheels are -.50"

Duke

[Michael G.]

Re: 63 wheel offset

Thanks guys, I can calculate what I need from that information. What I'm tying to do is determine, when I switch to a seven inch wheel and 215mm wide tire, where in the old tire envelope do I put the new tire/wheel. I'm intending to locate the new tire on the old tire centerline, that's why I need the current off-set. With the number you gave me, I can tell the wheel builder how to relate the mounting surface to the centerline of the new wheel.

On a C2, if there's a better place to locate the new, wider tire than on the old tire centerline, please let me know. Obviously, it been a long, long time since I was a GM chassis/body designer, but with he proper coaching from you guys, I can probably dredge up the old skills and handle this

[David L.]

Re: 63 wheel offset

[Duke W.]

Re: 63 wheel offset

Thanks guys, I can calculate what I need from that information. What I'm tying to do is determine, when I switch to a seven inch wheel and 215mm wide tire, where in the old tire envelope do I put the new tire/wheel. I'm intending to locate the new tire on the old tire centerline, that's why I need the current off-set. With the number you gave me, I can tell the wheel builder how to relate the mounting surface to the centerline of the new wheel.

On a C2, if there's a better place to locate the new, wider tire than on the old tire centerline, please let me know. Obviously, it been a long, long time since I was a GM chassis/body designer, but with he proper coaching from you guys, I can probably dredge up the old skills and handle this

You can use '68 Corvette Rally wheels, but you'll have to shave the horizontal fender lips. Some guys claim that 7" zero-offset G-body Rally wheels will fit, but rear spring clearance is likely to be insufficient. That's why 7 and 8-inch Corvette Rally Wheels have negative offset. Positive offset 7" wheels are out of the question.

215/70s will look and work fine on '67 6" Rally wheels, and they will accept the '63 wheel covers. Fender lip clearance can be gained by adjusting camber in the negative direction, and at full lock the tires might rub the steering gear carriage bolt heads.

Duke

[Michael G.]

Re: 63 wheel offset

Thanks Duke. This car is a 63, but, other than the body, its not stock (disc brakes, Tremec, rack and pinion, EFI, etc). I'd prefer not to cut anything on the body, its already painted. My plan is to have special wheels made, either 17" GT-40 wheels or a 17" version of the stock C2 knock-offs. As such, I can set the wheel offset at whatever the ideal is, I just need to know what that is.

[Tracy C.]

Re: 63 wheel offset

.........
You can estimate backspacing as follows:

Backspacing = wheel width + offset + flange thickness

.....
Duke

Duke, Did you really mean 1/2 the wheel width in your equation?

[Duke W.]

Re: 63 wheel offset

You are correct! Thanks for pointing out the error.

Offset = 1/2 wheel width + offset + flange thickness

It's too late to edit the prior post.

Duke

[Patrick B.]

Re: 63 wheel offset

Thanks guys, I can calculate what I need from that information. What I'm tying to do is determine, when I switch to a seven inch wheel and 215mm wide tire, where in the old tire envelope do I put the new tire/wheel. I'm intending to locate the new tire on the old tire centerline, that's why I need the current off-set. With the number you gave me, I can tell the wheel builder how to relate the mounting surface to the centerline of the new wheel.

On a C2, if there's a better place to locate the new, wider tire than on the old tire centerline, please let me know. Obviously, it been a long, long time since I was a GM chassis/body designer, but with he proper coaching from you guys, I can probably dredge up the old skills and handle this

The critical spot for inboard tire clearance is the emergency brake cable or bracket whichever is closer to your present tires. If 7 inch rims with the same offset as your 5.5 inch rims are used, the rim will be 3/4 inch closer to the trailing arm. If your present tires are closer than 3/4" to the emergency brake cable or bracket, you have reason for concern. If there is much more clearance, then you could consider more positive wheel offset to reduce the chance of fender lip rubbing. The sidewall width of a 215/75 R15 tire would not increase the whole 1 1/2" when mounted on a 7" rime versus a 5.5" rim but it is a conservative assumption when gauging clearance with the emergency brake cable.

[Michael G.]

Re: 63 wheel offset

Patrick, complicating matters will be the change to 67 trailing arms and disc brake rotors. I need to check those (I don't have the chassis here today to do so) after I install them, to see if the location of wheel mounting surface or the park brake bracket changes. I can compensate for any changes, though, so long as I know where the issues are I'll be able work it out...