ej_racer

Hello,

Can anyone tell me what will be the perfect size of tires to get for an 18 inch rim? I like them pretty thick. maybe a 245 perhaps? will that work?

CHESTON

iTrader: (19)

i think you should tell us what the width of you rim is too. that would help.

also, what kind of car you have would help and/or filling out your profile. sedan, wagon, forester? also stock body or wide-body?

off hand, 235 or 245s are what people mostly run from what I have gathered here.

also, what kind of suspension setup do you have? stock, just springs, coilovers, fully tricked out?wider widths may need more camber, etc.

ej_racer

I have a subaru wrx sti 2007 4dr, I have tein lowering springs with stock struts.

CHESTON

iTrader: (19)

245's should fit fine.

next queston is what profile you want...the 08/09 STIs run 40 series tires.

Only bad thing (if you care) is that the speedo will be off a little bit either way you go with 245s. 40 series tires make your speedo run slow, and 35 series tires make your speedo run fast.

i'll be putting on some 235/40/18 later this summer when the money's there, i've got an 06 STI. this should keep my speedo spot on.

not sure if you're trying to stuff 255 in your STI's pants, but if you are, try asking some of the autocross guys on here.

ej_racer

Yea i guess is should stick with the 245/40's? does it matter for the speedo to run slow?

ej_racer

I want my speedo to actually stay the same? is that possible?

CHESTON

iTrader: (19)

I use the classical standby calculator: http://www.miata.net/garage/tirecalc.html

[standing on soapbox]
my preference is to keep my speedo as close to accurate as possible. It bothers me when it's off. and i don't know if you've noticed, but even on the stock STI rims/tires, the speedo is off. usually 1-3mph off "fast" at 65mph IIRC.

doing some poking around on the internet, i found that supposedly the stock STI in Japan comes with 235/45/17. using above tire size calculator, and since I was going to 18's, let me to my decision to use 235/40/18s. this is within 0.1% spec of a JDM size 235/45/17.

with 245s, like earlier post, 40 makes the speedo "slow" and 35 series makes it run fast. but, by my math, a 235/40/18 would make the speedo spot on.

anyways, if you have to have bigger and spot on speedo, the next size up is (GULP): 265/35/18.
[stepping down from soapbox]

CLIFF NOTES:
-use the link above to calculate for speedo calibration.
-Stock USDM STI speedo runs fast
-Web info says JDM OEM tire size is 235/45/17
-for 18" rims, i recommend a 235/40/18 to keep speedo on track.