Re: !5" rim performance vs. 17" wheel performance (vuu16v)
it depends on what tire you are using... sidewall stiffness differs between brands and models of tire... along with tread pattern, material used, etc... yes, a light wheel does help, but... more weight on the outer edge is what matters the most... ie., light tires will help more due to less rotating mass... shaving material of the center of the wheel will have very little affect on the acceleration/deceleration... but will affect ride (depending on amount of material removed... a 15" wheel/tire can ride as harshly as a 17" w/t depending on what tires are chosen... the old toyo proxes t1 plus had very stiff sidewalls, which made them a harsh riding tire, but very predictable with lots of grip (for a road tire)... the t1-s is the same construction (different tread pattern) with a softer sidewall, they are more comfortable, but do not perform anywhere close to the older model (imo)
ride and feel are also affected by suspension and alignment... some tires work better with more camber, some work better with less... air pressures will also vary between tires... so just trying a new set of tires will not always give you a subjective view...
i personally have 15" volk te-37's w/ 205/50 bridgestone potenza's... 34 lbs. per corner... on a slightly lowered car (~2.0") with modifications to the front suspension to keep camber curve and roll center the same as stock height, a relatively soft spring rate and modified rear trailing arm...