I am considering the 18" GT3's at the moment as an alternative to my OEM 16's. I'm in the same situation as the original poster. I will probably go visit one of the local club guys and try out his car with the 18's. That will probably be my best gauge of performance changes.

 

A great article about suspension tuning as well as describing handling charteristics and the usual geek speak, unsprung weight, preload and all that fun stuff. Including a bit about upsizing your wheels.
SCC Making it stick


I know they have a few more artices if you poke around that describe plus sizing its benifits and drawbacks in more detail.I also remember reading recently a article in their mag about rotational inerta. I don't know if its hit the website yet.

 

oh yeah and the "flywheel effect" refered to in that article comes from here:
SCC technobabble

rotational inertia with math as reguarding a flywheel. but the same hold for a wheel weight, if you are inclined to crunch the numbers.

 

What do you guys think of added unsprung weight as a wear factor for the wheel bearings and suspension? Is this something that should be considered or is it so negligable that no consideration at all need be taken?
When I finally do add wheels ,at this point in my education, I'm pretty sure I will stay with 17" and go as light as possible.
Looking foward to all responses. Thanks

 

I went from stock 16's to 18's and I could tell a difference but not enough that it would make me switch back. My car isnt tracked or anything so its not a big deal to me. What you might want to consider if you do decide to track your car and having a extra set of wheels with some nice tires on it.

 

OEM 16s w/ track rubber for "go"
Semi-Light 18s for everywhere else.... of course, when you go FI, it really does not matter how heavy the wheels are... you'll be getting wheelspin anyways

weight is very overrated... unless you're running 30lb wheels or your last name is schumacher, I don't think anyone should worry. plus... 18s look so hot

 

I just uped to 18's a few weeks ago(Ultraleggeras) -to me- I noticed that the car seemed a bit more "hesitant" to speed up from a standstill. Once the momentum gets going you can hardly tell tho. I dont quite remember how much heavier than stock they are but if your like me and willing to sacrifice some speed for show than its all good.

 

Running 18" HRE445, 8.5" front, 10' rear, P-Zero Pirellis, +56 front offset, +68 rear (but I'd go +71 if I had to do it again)=handled better IMHO with the wider rubber all 'round