tires foe SQ5
 

What choices do I have for new tires. Currently there are 255/40R21 on the ground.
Can I use a 20 inch and get by? More choices.

Your wheels are 21", you can't magically install 20" tires on them.

So no, you can't install 255/40R20 tires on 21" wheels.

You could certainly go to tirerack and buy new tires and wheels that are smaller, but the same overall diameter so the speedometer remains accurate.

265/40/21 will fit stock wheels and the prices go way down because the options increase. They will also be slightly wider as well. Not sure why you would think a 20" tire is going to fit a 21" wheel lol.

265/40/21 or 255/40R21

265/40/21s
 

Hi,
me and other peeps are very pleased with Atturro 805z, some 420$ for the set(yes, 4 tires...). I'm on my second very happy set, after Dunlops, Michelins Lats Sports.
Great tire, fantastic for the $$.
I'm on 21x9.5 ET32 Rims, HAS KW.

CHEERS,
BOB