Currently, I have a set of 19" Niches (Form) on my Q40 (8.5///9.5). Tires are 245/40///265/35. The wheels are about 29lbs each. Someone I know introduced me to SCCA and I wanted to give it a try. I bought these primarily for the "objective" cosmetic upgrade from the factory 17"s and because I was able to get them new for pretty cheap. I was wondering how much of a difference (performance) switching back to the 17"s (7.5 squared) would make on the course. The OEMs come about 7lbs lighter, and are narrower. If I did switch back I would replace/ upgrade the stock Eagles to a different brand/size 245/50.

It would be my first time and I will likely suck so the difference in wheel size could be seen as negligible for now; however I just wanted to hear your opinions on if switching was worth it in the semi long run- plan on getting RPF1s or something alike in a year or so if I get into the course.

I do have hotchkis F/R SBs installed, had eibachs on but swapped back to factory springs, still got them though.

 

I assume you still have your OEM 17s, a 245 is pretty wide for a 7.5", I wouldn't go more than a 235 on them. I'd run 18s if they are ok by SCCA rules, 18s are a wheel upgrade option for the G37 (not sure if they still offered that pkg for the Q40 though).
If you can run 18s I'd look at all rear 18x8.5 sets (they came in staggered 7.5/8.5 sets typically) and run a 245/45 or 255/45 all around. Much better tire selection in 18s as well.

 

Thanks for your input. I was wondering how much difference 5 to 7lbs of unsprung weight has, as well as an inch difference in rotational mass has, meaning is it vastly noticeable to an amateur driver? Would you consider 29 lbs heavy?

 

I was running boat anchor 20s then went to my current 18" Wedssport set and dropped over 10 lbs per wheel, and it was slightly noticeable, combined w/ good summer tires it's one of the best upgrades I've done. My Weds are 19 lbs, so yeah, I'd say 29 lbs are a bit on the heavy side. Don't know what the SCCA allows but if you can source some light 18s that would be the way to go. For a budget setup Konig makes some nice looking 18s that are under 20 lbs and cost $200 or less per wheel.
https://konigwheels.com/wheels/flow-formed-wheels/

 

Been looking at the Konigs, specifically the Dekagram in 19". The sizing I'm interested in is 8.5 +30 in front and 9.5 +35 in the back. The same size as my 19s now- would rather not need to spend on tires at the moment and my tires are still pretty new. However, the front offset on my current set is +35, and with the bit of tuck it has I'm guessing a +30 would be a better fit? I am not planning on lowering my car anytime soon and would like to know if there would be a slight poke with a 245/40 tire.

Anyway, the wheels are 19lbs each, which is 10 lbs lighter on each wheel I have now.

Thanks again for the tip on brand!

 

Should fit just fine, will be pretty flush at stock height but no problem tucking the tires in the fenders.

 

Thanks for all your advice!