[ChrisCantSkate]

i typed up a long reply and IE crashed... im gonna do a cliffnote version.. if you want me to elaborate more i will...

the farther out the weight of the wheel is located the more tq it uses to spin idealy a light small rim ouw be the best, but you can compromise for a heavyer small rim or a lighter large rim. there is a downfall to larger rims though, the thin tire wall will not flex enough to put a long contact patch. you may have a 7inch wide tire, but only 3 inches long are touching the ground... 21 square inches... now if you have a 6 inch wide tire but can get 5 or 6 inches long (even more with deflating, but im kinda exagerating/pulling numbers from my ass for an example, cause a 7 inch wide tire on a thin rim can only expand so far wide, but a small rim can go wider, but lets keep this simple) so 5x6 is 30sq inches. thats more of a contact patch.

now onto the light big rims robbing tq.. the easyest way to show this.. get a 1 ft long pole and put a 1lb wieght on it, spin it up 45degrees or even enough, just so you feel the weight of it. now get a 3 ft pole and do the same thing. now take a 2lb weight and put it back on that 1 ft pole and do it again. im doing this in my head, so im not calculating the actual force, but the 2ft weigh spinning on a 1 foot pole should feel lighter than a 1 lb weight ona 3 ft pole... translation.. you need less force to turn the heavyer weight since its located closer to the center. i have 16lb 17's that are 7.5 inches wide (215 tires) and a 40 sidewall (86mm i think) i nkow my stock rims were 19 lbs, and 6.5 inches wide, i had 195/55/15s i think(whatever maintaines the stock diameter compaired to 125/40/17) and it was noticeable the better traction i got off the line with those time. i never had a chance to take the 15's to the 1/4mile since i sold them, but its a very common to use smaller wheels to put more power to the ground.

a guy i know with a very very powerfull 240sx (has a longer kill list than anyone here) dyno'd better with 17lb 14's than 13lb 18's. he has a meaty tire on the 18's so he can get good launches on the street.

well i said i wasnt going to make it long, and i basicaly went over all my points im more detail than i planned, but ok... i think ya get the point

contact patch = lenght x width of your tire
rotational mass matters. the lighter and smaller the rims the better. you can compromise size for width(its hard winding a 15x8 tire with the correct offset for fwd) if you can keep a decent contact patch for off the line acceleration. wider and bigger is better for handling, cause the sidewalls wont flex as much and you have a large lateral grip

if anythings confusing, tell me, i typed this fast, and am more than willing to explane anything. im not saying anyones wrong, consider this a lesson on matching size and weight.