275/60/15 will fit nicely on a 8" wide rim with a 5" backspace. They will fit on 7" Buick rim but they bulge alot. You may be able to go bigger but you definately need to measure BOTH SIDES of your car to see how your body is centered (or not) on your chasis. Mine is approx 1/2" off side to side.
I am running 275/60r15's on 15x7 buick ralleys on my '68 GS. They fit perfect. I would not recommend anything bigger unless you go with 5 inch back-spacing. I bought my car with weld prostars on it. They were 15x8's with 235/60r15's and the sidewalls rubbed even though the quarters had been rolled. The rims had 4inch back spacing. I sold the welds and bought some stock buick ralleys because I was replacing the quarters and I had no intentions of rolling the new quarters. The 275's look ok on the 15x7's-they dont bulge nearly as much as I expected.
How much back-spacing is there on a 7" wide Buick rally? I'm finding hard to picture you having clearance issues with a set-up that was approximately 1.5" narrower than what you have now per the calculator site I use now. How old is your rear suspension and do you run lowering springs? I question this, because I'm going to try and run 16X8's w/225 60's on my 68 w/4" backspacing . o No:
The buick ralleys are 4 1/4 backspace. If you bring the wheels out a 1/4 inch and add another inch to them to make it 4 inch back space 15x8 wheel, it makes a huge differance on the '68. You essentally have brought the wheel out towards the wheel lip 1 1/4". The wheel lip is not round on the '68 which creates clearance issues. If you are planning on running a 16x8 wheel, I would recommend a 5 inch backspace. This would tuck the wheel in more towards the inner fender. I have not tried this, but I have been told that it will work on these cars. Also, I would recommend a little bigger tire than a 225/60 16. The gs is a big car. the 225 60 16's are standard issue on newer cars such as the '96 to 2000 chevy lumina or buick regal. A peg leg gs or skylark should be able to roach one of those tires running on 3 cylinders!:laugh: Just my opinion. The 275's I put on my gs give it the perfect muscle car stance on the stock suspension and they tuck into the wheel well the way they were ment to be.
I made a mistake, my rims have a 4.5" backspacing. Also, I don't much care for the big/little look as far as tires go. I need to be able to rotate the tires for maximum life and only want to have to carry 1 spare. Anyways, the 225's are definitely an improvement over the stock width 14's.
i have a set of weld stars used with slicks 15x8 5 in back space for sale 150 for both rears near chicago
