What is the smallest and largest OD possible without having to have a flash tuner to compensate for the size difference? I heard that a light goes off if the tire size changes to much from stock.

 

Id like to know the answer to this as well. I just bought new 18" rims but the tires i want dont come in the size i want (255/45/18). So in addition to wanting your question answered, anyone want to suggest a tire size as close to that as possible? thanks!

 

Remember plus sizing (or minus sizing) your tire combo will not change anything.

Example:

Stock 255/55/17

+1 = 255/45/18
+2 = 255/35/19
etc..

The only problem is when you change aspect ratio and size at the same time, then you need to consider compensating for increased rolling circumfrence of the assembly. Again, a little won't kill you, but a lot can't be compensated for on the speedo. It's the speedometer / odometer that you're really worried about here, more then the CEL illuminating.

HTH.

Also, as to tire sizes, Tire Rack is an excellent source of info, you can see what diameters and footprints different manufacturers have as well as sizes offered. Most performance tires are not really the same size, even when marked as such between brands, and they change with wheel width, etc... so you have to do some homework here and you'll come up with a tire that will fit all your size requirements just fine.

 

SilverHorseRacing,

The CEL light will kill me if I have to look at it everyday so I want to make sure I don't get it with 275/30/20 or 275/35/19's (26.6" or 26.5" OD's). I really don't want to flash the PCM because i'm worried about warranty issues for now. Eventually I will because I'm definitely going with a SC but until then, I don't want any issues. And I'll probably go with the intercooled Whipple if Ford warranties it. If not, probably a Saleen since they do have 3yr warranty coverage available. Just waiting to see.

S197 V6,

What mfr are you looking at? The following mfr's make that size:
Goodyear
Michelin
Pirelli
Continental
Bridgestone
BFGoodrich
Yokohama
Dunlop etc.....

 

S197 V6,

What mfr are you looking at? The following mfr's make that size:
Goodyear
Michelin
Pirelli
Continental
Bridgestone
BFGoodrich
Yokohama
Dunlop etc.....[/quote]

Its not that i cant find tires in that size, its just that the dont have the ones i REALLY wanted in 255/45/18. So i was just wondering what other size i could possibly using without messing things up.
PS: these are the one i am looking at...http://www.tirerack.com/tires/tires....+Pole+Position

 

http://www.discounttire.com/dtcs/sea...55&ar=45&rd=18

 

http://www.miata.net/garage/tirecalc.html

 

Good choice! It's my pick too. Want them in the sizes stated above depending on what rims I find that are 19" or 20" and lighter than stock.

You could use 245/45/18's or if you have at least 18x9's you could just go with 275/40/18's. That would give you a nice chunk of rubber and would look sweet!!! 275 width's are about the widest you can use up front without rubbing. Good Luck and hope this helps!

 

The one on Miata.net is good but this one is the best I've found. Even does rim width and offset.

http://www.bigcustomwheels.com/info_specs.jsp