I've run BF Goodrich Radial T/A's (235/60-15 front and 245/60-15 rear) and am currently running Grand Prix 245/60-15 Performance GT's on my 76 Monte Carlo. The BFGs had a smoother ride, but the GP's have better traction. Not a clue what I have on my 86 Grand Prix right now, but I can tell you that I will be getting rid of them as soon as I have money for 15x7 Rally II's. I'll probably go for the BFGs for the smoother ride because it will be my driver. So my suggestions would be:
If you're going for performance, go with the Grand Prix Performance GT's. If you're going for smooth ride (daily driver), go with BF Goodrich Radial T/A's.
If you're going for performance, go with the Grand Prix Performance GT's. If you're going for smooth ride (daily driver), go with BF Goodrich Radial T/A's.