Silver Comet

iTrader: (12)

I'm currently deciding on tire sizes on the moment for a near 500hp Rx-7 FC3S. I'm trying to take into consideration the circumference of the wheels compared to the OEM Rx-7 wheel to determine what will be the changes in gearing from the wheel being smaller or taller height wise. I have just removed 17x9 +22 RPF1's with 225/50/17 tires. I made them fit perfectly under the fenders via rolling/pulling modification.

From the specs given to me by the chart that FC3S Pro provided: FC3S Pro v2.0: Mods - Tires

I was running a near 4% increase in stock wheel circumference! I wonder what effect this had on gearing?

Now I'm trying to decide on a tire size that will give me more grip, a close relationship to the stock gearing, and that fits nicely with a 17x9 +22 rim.

Currently I'm landing on 235/40/17's for the front and 255/40/17's for the back, but have still been considering a square set-up of 235/45/17's. The square set-up would provide me the chance to be able to rotate rims on occasion to keep the wear about the same, but I would sacrifice the potential for more grip in the rear which I believe is a necessity for a near 500hp car that I would be getting from a 255 tire.

All the while all of these factors come into my decision I don't want my car too much lower than it already was so I have looking closely at the sidewall heights for the new tires compared to the old fitment that I had. It seems I'm going to have to bite the bullet and go lower regardless of my decision on tires.

Anyway looking for some input if you have any, I'll be pondering about this in my free time. Thanks!

EverythingBoosted

The taller the tire the more grip you will have as a general rule before you look at pressure, width and all that. I like the 255 option on the rear but I like the staggered look more than anything. As far as 255 vs 235 being that the 235 is slightly taller, the grip will be very close to the same so the 235/45/17 would be the best option IMHO.
Also a taller tire acts like lowering the ratio of the final drive. Ex.going from a smaller tire to a bigger tire would be like taking your FD and going from 4.10 gears to 3.90 gears if that makes sence.

HadaVette

iTrader: (3)

A tire with a 4% change in circumference (or radius, or diameter) will have an effective 4% change in gearing. Not a big deal in my book.

The tire compound will make more difference in traction than the small changes in tire sizes you are discussing. Check out some of the 200 treadwear tires popular in SCCA or HPDE road events.

My preference (yep, personal) is to stuff as much tire as I can under the fenders, and then tune the suspension to that. Which probably means a staggered setup. There will always be compromises, some budget dependant, some style related, etc.