BMI also has a huge review on wheel/tire width/size on a g37. Yes absolutly a difference in performance. Smaller diamerter + lighter = better drag times, larger diameter + light weight = better cornering. My gas milage sucked with 18'' wheels just fyi.

 

I can tell you how it feels going to heavier than stock wheels. 1st, in high speed cornering you can feel all the extra wieght in the steering wheel, especially on uneven ground, the suspension will wallow more w/heavier wheels. 2nd, I have a section of road that I do high speed runs on, it's 8/10's of a mile long on a country hwy, I can exit the last corner before the straight at roughly 70. With the heavy wheels I can only top out at about 145-6 before I have to start shutting down, with stock wheels I can hit 150 and still have a little room.

 

We can't tell you if its worth your money to shave weight, just like deepblue said - it depends on your situation, are you going from heavy 18" boat anchors to lightweight 17"?
Generally speaking if money is no object any weight reduction is a good upgrade to our car.

 

Purely for performance, I'd invest in the driver. But for looks and bench racing, lighter wheels will help.

 

I was able to feel a difference on my IS300, my stock wheels are 22lbs, I went with 14lbs Kosei racing wheels and could feel a difference even with bigger(heavier) tires mounted on the lightweight wheel.

 

Did you keep the same wheel size? That is a huge reduction in weight.

 

Does anyone know the unsprung weight ratio
in regards to actual weight?

I've heard 4:1 and also 2:1

And...aren't the OEM brakes very heavy???
Woudn't changing that out save quite a bit
of rotational weight?

And I know my Goodyears are very heavy compared to
some Falkens and Contis!

 

I went from the stock 16" (~19lbs) wheels on my '01 Prelude to heavier 17" wheels (~24lbs) with the similar diameter tires and lost .4 of a sec and 2mph in the quarter. The 17" wheels had "grippier" tires, too.

 

Even better would be lighter 17" or 18" forged wheels. Less rotational mass with added width.

 

Don't think it would be noticeable going from AP1 wheels to other lightweight wheels.
Going from heavy 25 lb or so after market wheel to a lieghtweight 14-15 lb wheel I would bet you would feel a very noticeable difference.