Biggest tire to fit a 68

Hello all, new to the forum. I have a 68XR7 built 390 with a 9inch rear. Looking to put some bigger meat on the back. What is the biggest tire I can fit on a stock 68 without modification. It would be 15x8 wheels. I’m looking at M/T 275/60/15. Some guys online are saying they’ll fit and others are not… Figured I would ask the experts here for a definite answer… Len

Any thoughts guys? I’ve tried to search but can’t seem to find much for a 68…

Seems like a lot of folks are migrating to 16” or 17” rims…I posted this earlier.

I assume that size tire is going on a 10” wide wheel? I would recommend pulling measurements on the car based on the wheel size and offset you plan to use to make sure it will clear.

Edit: my fault, you said 15x8s. Same advice applies.

To fit 275s your wheel backspacing will need to be spot on and you’ll probably need to raise the rear ride height. Here’s a few shots of my car with 245/60/15s on 15x8 with 4.5" backspacing. I’ve seen another 68 at Carlisle with 255s on the back, and it looked big.

I’ve got 15x8 rims on the back of mine with 255/60-15 tires. The twist to mine is I have a '59 Ranchero differential that is 2" narrower than the stock differential (57.5" vs 59.5"). I have the standard fare Torque Thrust D rims with 4.5" of backspacing. It may take a little more backspacing to get them under the lip with a factory 9". I’ve never rubbed, but my car isn’t currently sitting particularly low.