I have a 71 that has original style rims. I currently have 70's all around. I would like to go with wider tires on the rear. (like 60's) Since I am a total novice on tires and rims my question:
Can I put 60's on the original rims that now have the 70's?

what i think I might do is buy a whole new set of rims and tires, so I can change them quickly. (I still like the original rims for shows, etc.)
If I buy new rims, what do i have to look for? do I have to worry about clearance in the rear?

The 60 and 70 in tire sizes has to do with the ratio of the width ofthe tire to the height of the sidewall. The width is measured in millimeters with 25.4 millimeters to the inch.

For example a 255/60/15 is about 27 inches tall. A 255/70/15 is about 29 inches tall.

The maximum width of a tire is limited by the wheel width with a 275 wide tire being as wide as practical for a 8 inch wheel. For your year car that would best fit the wheelwell with a 4.5 inch backspacing. 10 inch wide wheel can take up to a 305 width tire safely with 5.5 inches of backspacing on the 1970 if the rear axle is centered. You cannot go with more than 5.5 inches of backspacing with a 15 inch wheel as you will hit the shock mount.

If you go to a 17 or 18 inch wheel you can go up to 6.25 inch of backspacing with a 10 inch wide wheel. The larger diameter wheels allow for clearance on the shock mount by going outside of the contact point in the radius of the wheel.

If you are going to the maximum limits on backspacing it would be in your best interest to test fit wheels with that backspacing to verify clearance on your car. Accidents, frame specifications and the mounting of the body all come into play with these cars. The ability to have specifications for fit were not very good 30+ years ago.

thanks for your reply. I am still unclear on a couple of points. For a 255/60/15 would I want a 15x8 rims with 4.5 " backspacing? Likewise, on the 255/70/15 a 15x7 or is a 15x7 still ok for the 255/60/15?

here is what the sticker on the rims say, can someone tell me what it means?
15x7 5x4.5, 4.75, 5 +3 STD

Originally posted by freshayr:
here is what the sticker on the rims say, can someone tell me what it means?
15x7 5x4.5, 4.75, 5 +3 STD I can decipher part of it.

15x7 15" in diameter, 7" wide.
5x4.5 5 bolts in a 4.5" diameter circle.
4.75 4.75" of backspacing (depth from mounting surface to inside lip of rim)
The 5 +3 STD part has me stumped.

I may be wrong but the 5x4.5, 4.75, 5 probably means something else. Could you have a unilug design wheel that indicates that it is a:

5 bolt circle on 4.5",4.75" & 5" centers for different applications.

BTW: A unilug design wheel will have an oblong stud hole in the wheel to accomodate different applications and a spacer sleeve is used to make up the gap from intended application.

The standard GM wheel would be 5 X 4.75" bolt circle I believe.

The + 3 Std has me stumped as well. Maybe others will chime in.

Robert

Originally posted by Mytmouse:
I may be wrong but the 5x4.5, 4.75, 5 probably means something else. Could you have a unilug design wheel that indicates that it is a:Good point. I forgot the A-Bodies were 4 3/4"

I have a 71 Chevelle and want to put on 15x8 wheels with 4.5 inches back spacing front and rear with 255-70-15 tires all around will it fit?