Roger10378 wrote:
Most of the 20 inch wheels are mounted with low profile tires so there is probably very little difference in diameter. Your bigger concern should be the load rating of the tires. Many of the 20 inch tires are for looks and not very high in load rating.
I have Michelin LTX M/S2 20" OEM tires on my truck. The 20" tire is less than 1" greater diameter than the 18" due to lower profile, which means the truck sits less than 1/2" higher than if it had 18".
But the 20" tires are rated for a hundred pounds greater load weight than the same 18" tires.