QUOTE(aaronchaiz @ May 2 2012, 02:30 PM)
Dude.. not necessary 18" will be heavier than 17" and even if it is.. for my case in example.. each rim heavier than stock rims for about, let's say 100-200gram? x4 is less than 1kg, u cant leave with that? Donut, yes it will be more expensive than 17" but metoo provided u with the calculation. Btw, donut can be heavier, give another 200 gram to it.. <2kg for rims and donut.. u go kurus ur body weight 2 kg to offset it..

the difference got so little? just 100-200grams?
i've done some research back when i was deciding on rims upgrades, and what i found is on a lightweight wheel like mine, for the same width of 8jj, the difference is around 1kg PER WHEEL.
info from enkei states that the RPF1 17"8jj is 16.05lb (aprox 7kg) while the 18"8jj is 17.95lb (8.1kg), i don't know how the other cheaper wheels are but i doubt they will better enkei's effort at reducing the weight difference between sizes.
so by getting 17" instead of 18", i save around 4kg of unsprung weight, and this is only on the rim's weight savings alone, cause 18" tires will also be heavier than 17" tires by around 1lb which is 400grams.
btw 1kg of unsprung weight doesn't equal to 1kg of bodyweight aka sprung weight.. keep this in mind...
my 3 cents