15's no bigger then 35's...WRONG go check out Interco they got sizes up to 44's on a 15" rimyes...cheaper than the 18's and have a ton of upgrade options. 33-40'tires
15's cheap but no bigger than 35's
16's limited selection of tires
17's more expensive of the two (wheels/ and tires) but you can still manage to stay light.
18's - expensive/heavy
20's - mall crawl