cleoent

Well when the time comes to order new tires, i've decided i'm going to go with 245/40/18's.

My question is, my stock tires (225/45) run at 32-34 PSI to keep the TPMS happy, if i go with a bit lower profile of a tire will I have to up the tire PSI to the upper 30's therefore upsetting my TPMS and having the light come on?

I only ask because the light drives me bonkers, and i'd really like to avoid it at all costs

GeorgeH

iTrader: (2)

I ran my 245/40-18 T1-Rs at 32 psi on stock rims and they worked fine, although they were a *little* softer in the sidewall on the limit than I liked. I solved that by going to an 8.5 inch wide rim.

It really wasn't a big deal, though. I didn't get the rims because the handling was bad and/or driving me nuts, but rather because I had two bent stock wheels, so it was a good excuse to upgrade. Unless you are hypersenstive to sidewall flex you should be fine on stock rims.

Besides, jacking the pressure up will just cost you grip anyway.

cleoent

Yeah i'm aware of losing some grip with higher pressure. I just kept reading on here that people going with lower profile tires had to jack up their pressure, i was thinking i'd have to do the same but perhaps not! Yahoo

mikeschaefer

i run 35-38 psi depending on my mood and never see a tpms light come on

that's on both stock tires and the 245/40s i'm running now

swoope

iTrader: (5)

the tpms sensor does not know what size tires you have. it just reads pressure. i think it goes off at 26 psi. on the low side.

beers

rotorhead335

Well, I have what I hope is a related question. I see people going to 17-inch tires. Perhaps they are edgy drivers or even weekend racers and need to save money on frequently replaced tires. Good enough. But

1. peformance-wise, is ther an advantage to smaller tires?

2. A tire dealer I talked to said that Mazda put a lot of time and energy into setting up the RX-8 to run "just so"--the great handling we know and love. He thought, however, that changing sizes, profiles, widths, etc., risked decreasing performance, I guess because the suspension/wheels/tires would not be the "ideal" or standard set-up. Could some of you experienced people weigh in on this?

Thank you,
Jeffrey

GULAMAN

There's a thread sorta related to this in the Competition board:
Linky here

Basically, going to 17" and keeping the same aspect ratio will decrease the rolling diameter of the wheel/tire, thus changing the car's effective gearing. this *can* be an advantage, such as in autocross where you are trying to keep the car up in the revs in 2nd gear. the other issue is weight; the smaller wheel/tire package will ostensibly contribute less unsprung weight and less rotational inertia to overcome.
p.s. let's not turn this thread into an argument like in the link...just go pile onto the other thread if you wish!

rotorhead335

Thanks, Gulaman. - JT