Why do you do this?

Do you consider anything with a 70% aspect ratio a performance tire?

No. Anyone running a 205/70Rwhatever is not interested in handling, period. Why use them as an example? This is the handling not the resto forum.

I have 245/40R17's (24.7") going and some sheet metal mods and attention to backspacing is needed. Anything more than that and you will be cutting metal out. Remember we are talking about over all tire height now, not rim diameter.

Years ago I ran 245/60r14's in the back of my 72 Swinger and it would rub the inner fender in hard turns. That was with about a finger's width of clearance between the leaf and the sidewall and about the same between the rolled fender lip and the sidewall. I probably could have gone taller, but it would have just hit the inner fender sooner. The sidewall would also rub the side of the leaf in hard cornering, which I put down to sidewall flex due to the high aspect ratio, which a 70 aspect would just aggravate. What that Swinger needed was a shorter sidewall height and more spring rate, already had a rear bar in it.