MAKE SURE HRE will sell you the 21" tires with the wheels...the tires are on major back order with no ETA!! HRE is hoarding some sets. Frankly I do not think its worth the hassle to go 21" rear: More $, $$$ Tires, Rare tires, non-std sizing, more weight. You'd probably be just fine running the 20" in the rear and do yourself a favor in the long run. Just my .02 :)