tire width on a 69 Riviera

[lg69riv]

I have a 69 Riviera GS with stock rallys

Are the wheels 15x7?

and depending on what size they are

how wide can i go on the rear with out making the rear end sag down?

Thanks
Lou

 

[rcull]

They should be 15X7, and you will probably be happiest with 225/70. The chart shows even 255s:

http://www.teambuick.com/reference/wheels_tire_howto.php

Not sure what you mean by sag down.