New Shoes' Numbers

I am putting 275-40-20 on 20X9" on front of my 2010 SS, with 275 fitting nicely on 9".

I am following the guideline "305/35-20 = 28.4" tall, 10.0-10.5 wheel" in putting 305-35-20 on 20X10" on rear.

However, for their 305-35-20 PZero, Pirelli recommends rim width range of 10.5-11.5" with meas. rim width 11" and sect. width 12".

So, am I safe with my rears?

I guess I'll have some bulge, perhaps 1" over each side of the wheel? Same bulge fronts and rears? It could give an old school, good look, but am I safe with my combinations?

Online, I see most use 10.5" or 11" for 305.

Michelin, on the other hand, is OK with 10-12" wheels for their comparable Pilot Sport PS2 305-35-20, whose meas. rim width is 11" and sect. width is 12.3"

10" wheels should be fine with a 305/35-20 tire. Bridgestone, Goodyear, and Michelin all approve rim widths from 10" - 12".

I like your tire size/wheel width combo as 9/275 = 10/305. And I always think wider rubber looks good…as long as it doesn’t stick out past the fender lip.

Have you considered going with a 315/35-20 for the rear? This tire will be the same height as your stock tires whereas the 305/35-20 will be slightly shorter. But the 315 would probably be better mounted on a 10.5" wide rim minimum. I have 275/40 and 315/35 size tires on my '96 but I don't know what size tires/wheels fit the 5th gens.

I think my brand, Pirelli, is on the conservative side with their recommendations, just covering themselves. Thanks for the reassurance on these other brands who are OK with 10/305.

Yes, I think this combination is gonna look good. Of course, I am simply moving the stock rear 275s to the front and buying new 305s for the rears. Saves some $ that way, anyway.

I really like these certain wheels which come in 20X10 but no larger. So, 315s are not for me, although some others do run 315s on wider wheels on their 5th Gens.

Yes, the height of my 305-35-20s will be 28.4" compared to the stock 28.7" but not enough to mess up the systems since it's still within .5" difference.

If I do get any bulge, the tires will wear faster, but anyway, just as long as they don't blow out.

Then with these bigger and heavier wheels and tires, I'll have to up the horsepower to compensate, heh heh.