I would like to do the same with a set of 275/30's on my G coupe 19's (8.5").

 

The OEM tires that came on my 07 were 225/45/18 and 245/45/18. If I replaced them with wider tires (say 245 F and 265 R), shouldn't they remain 45 rather than 40???????
(sorry if that is a really dumb question )

 

No, the aspect ratio (40 or 45 in this case) is not a fixed number, but is a relationship of cross section to tire height, therefore it varies with cross section. As the cross section of a tire increases so does it's sidewall height. In a 40 Series tire, the sidewall height is 40% high as it is wide, and a 45 series is, yep you guessed it, 45% as high as it is wide. Therefore a 245/45 tire would have a side wall height of 110.25mm or 4.3". a 265/40 would have a sidewall height of 106mm or 4.2". So as you can see the the tire heights are almost the same in both cases.

Lou

 

Thanks, makes sense now!!!!!

 

Ok, now that it has been established that the stock 18" x 8.5" rear wheels (2007) can take 265/40 and 275/40 tires, my question is this: Among the myriad of tire options available out there, who makes the 265/40 tires with the tallest sidewall or the 275/40 tires with the lowest sidewall?

 

275/40/18 on an 8.5" wheel. Nope And the question you asked, can be answered with a little investigative work here:

http://www.tirerack.com/tires/index....=true&index=xx

Lou

 

Why stop at 265, go to 305!

You will then get ultimate traction for your extremely powerful v6 that most likely puts down less than 250whp.

****ing dumbass

 

Dude, chill out! I'm just asking a question. If it it stupid for you, that's OK. As far as I remember, I never relinquished my right to ask stupid questions every now and then.

 

Besides, I have a stock HR. I think HR's put just a little more than 250 to the wheels so I think I could use all the traction available in the whole wide universe. But what do I know, I'm just a mere ignorant.

 

More pics of 275/40/18 on stock 18x8.5 wheels please!

 

The wheel will accept just about any 18 inch tire , doesn't mean it will work well. 275's do not belong on 8.5 inch wide wheels.

 

Yeah that's my dilemma, for a 18x8.5, all the "better" performance tires (RE01R/Kuhmo XS) out there are either:

245/40 (2% difference from stock with the narrowest width)
265/35 (3.6% difference from stock which may be too much)
275/35 (2.6% difference from stock but can't fit on a 8.5" wheel)

I'll be running a square setup so that shouldn't have an affect to my TCS (no VDC for me).

So yeah, what to do......this will be my dd and weekend track setup.

 

Seems to be some good choices here:

http://www.tirerack.com/tires/Compar...40&RunFlat=All

245/40/18 in front and 265/40/18 in back.

Lou

 

275 on a 9" wheel. 265 on an 8.5" wheel.

 

Thank Lou, but not for the tires I'm looking for:

Bridgestone RE01R
Dunop Durezza Star Spec
Kuhmo XS

 

completely forgot, the 265's are great and i finally have traction. The ps2's are gold!