[scottsee]

because they spend all their $ on wheels and tires. And not on performance like they should. Wheels and tires have to do with your racktime, but not to the degree that you would notice when stock, or mildely modified. but to answer your question. 17 are typically lighter, and less expensive, and have a softer ride then 18s. as for why every race car isnt running 12's....i guess stickers just don't produce horsepower...