what are the widest tires i can put on my stock RS wheels?

 

you can put 235/60-15 front and 255/60-15 rear. i did on my 91 v6.

 

You also need to pay attention to what size of tire is allowed on a particular rim. This would be a safety consideration. You can go outside the allowable and people have. But you could blow a tire off the rim just hitting a pot hole if the bead and rim did not have the correct contact surface. The Tire and Rim Association has standards telling what rim a particular tire is designed for, and what an optional rim would be. If you reply what size rims you have, I can check the book and tell you what sizes are allowed on that rim. Some of the tire sizes may not even be manfactured by anyone. But each size of tire is designed for a particular rim width. It does not tell you if that tire will fit the car.

If you have 15x8 rims, then these tires are designed for an 8 inch rim.

265/70r15, 275/70r15, 265/60r15, 275/60r15, 255/55r15.

These are allowed on a 8 inch width rim.

235/75r15, 245/75r15, 265/75r15, 235/70r15, 245/70r15, 255/70r15, 235/65r15, 255/65r15, 295/65r15, 225/60r15, 235/60r15, 245/60r15, 255/60r15, 295/60r15, 225/55r15, 225/50r15, 245/50r15, 265/50r15, 275/50r15, & 295/50r15.