I have the stock polished 18 x 8 1/2, 235/50-18. Will a wider 275/45-18 work? If yes, will it bulge over the edge of the wheel and be noticeable?

Thanks in advance,

 

Yes, a 275/45-18 wheel will fit your stock wheel, that width is the minimum most manufacturers recommend for that tire size. It will bulge out a little bit too, since your 8.5" wide wheel is actually about 9.5" from outer edge to outer edge, but a 275mm wide tire is 10.8" wide, so there will be 1/2" to 3/4" of bulge on either side. Another downside to that tire size is that there are very few tires available in the 275/45-18 size (the very good Continental ExtremeCOntact DW is available though), it is also taller than stock, so left uncorrected, your speedometer and odometer will be off by about 2%. Personally I'll be getting 255/45-18 tires next spring for the stock 18x8.5" wheels I picked up this year.

 

Some say the 8.5" is too narrow for 275/45.
IMO 255/45-18 is a better size for the stock wheel.

 

Thanks for the suggestions, much appreciated.

 

Agreed, 255 is better. If you go 275, the 40 series is the correct height, 26.6" overall. 285/40-18 is the actual correct height of 27", as used on the rear GT500s 2005-2009.l.

You can split the difference and go 265/40 as there's a fair number of those on www.onlinetires.com, but it's a bit shorter overall. Still lists 8.5 as min width. Most 275s say 9" min width.

Or, go get them cool 2010 GT500 9.5" wide 18" wheels for $600, and fit the full boat 275 on there easily!

 

What do you mean by "correct height"? The stock 235/50-18 tire is 27.2" tall, the 275/40-18 size is 26.6" tall like you said, and the 275/45-18 size is 27.7" tall. The 275/45-18 is actually closer to the stock diameter (just barely) than the 275/40-18. In reality they will be about the same amount off, just one is taller than stock by about .5", the other one shorter than stock by .6".

The wheel width recommendations for a 275mm wide tire are different for different aspect ratios. For a 275/45 tire, manufacturers recommend a minimum wheel width of 8.5", so his stock wheels would be fine. For a 275/40 tire, manufacturers recommend a minimum wheel width of 9".

 

Plug in the values here, great site for comparing

http://www.rimsntires.com/specs.jsp?item=Wheel-Tire

 

Correct height means least chance of rubbing/interference from the suspension. The actual desired height is 27" or so (27.2 for the GT, 27.1 for the GT500, but with wear those will both go to 27" eventually), the extra height and width of a 275/45 tire might generate rubbing or interference in the front especially if he's lowered. Stock wheels shouldn't be a problem with it, though.
But if you honestly think the width difference between a 275/45 and a 275/40 on a 8.5" wheel is that significant, feel free to think so, but he's still pushing the width limit for that size regardless.

The best tire for that wheel size is the 255/45.

 

It doesn't matter what I think, I'm just giving the manufacturers recommendations. Tire Rack is a great resource for giving complete specs on tires, including dimensions and wheel size recommendations. What you seem to not understand, is that the lower the profile of the tire, the wider the wheel needs to be for any given width of tire. That's why a 275/45 fits fine on an 8.5" wheel, and a 275/40 tire needs a 9" wide wheel.

 

Thanks Keith, I'm now much better educated on the matter Don't know how I'd get along without that explanation.

Obviously if you put a 65 series tire on there you can go much wider as it will bulge out along the sidewall. AND you can fit a 275/40 on there fine if you want, despite what the 'manufacturer recommendations' say. Most tire shops won't do it, but it'll go on.

What I'm saying, and I'll make it painfully explicit for you in the hopes that I won't need more of your edumacation, is that a 275 is pushing it width wise for a performance tire on an 8.5" wide wheel. AND that the 45 series on an 18" wheel should be a 255, not a 275. He's welcome to put that wide a tire on, but it's not ideal, no matter what the sidewall ratio is, and I don't think many people would recommend it. You obviously are not one of those many.

Amazingly, my internet browser goes to TireRack as well, and amazingly I looked at the same specs as you. Sheesh

 

Typically two up / one down... 235/50-18 > 255/45-18 > 275/40-18

That how manufacturers go up in size when they put wider tires in the
back to keep them relatively the same diameter as the front.

 

Here's a few random thoughts....

• 2003-4 SVT Cobras came from the factory with 275/40/17's mounted on 9" wide wheels, so an 8.5" width wheel isn't a huge problem, IMO.
• I run 275/40/17 drag radials on 17x8" Bullitt wheels. Great in a straight line at the dragstrip, but a little uneasy in fast corners. Some of that is likely due to the drag radials tread (or lack thereof).
• On my 18x8.5 factory fanblade wheels I run 255/45/18 Continental Extreme Contact DWS tires and they're awesome, but I believe there's a little more room for a wider tire, say 265 or 275.

 

I'd agree with all those, probably the DR effect with their soft sidewalls, but maybe also not such a well supported tire.
Ideally for corner carving you'd have as wide a wheel as possible and as close a vertical sidewall as possible. Not saying you can't go wider on narrow wheels, but it's not ideal.
Depends on what he's wanting them for and if it's both front/back or just the back. Personally I wouldn't go 275/45-18 on the front on a 8.5" wheel, but it's not like the tire will explode (just maybe slip off the rim a bit and drag the nose of the car all over the asphalt and cause you to crash into that berm and kill the little doggy you were trying to avoid --- nah, just kidding).

 

Just buy a set of these!...
anyway notice the stock size on the 302R is 275/35R18
275/45's are too tall, you'll notice a power loss on the low end.
The stock rims on the '93 Cobra were 17x7.5 with 245/45's, 275/40's are only 1.18"s wider (and thicker than 245/45's) so they'll be fine on 8.5" wheels

 

LOVE those wheels, and they're only $637 a piece!!

 

Wow, didn't realize they were 10"s... nice



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To Cinque35 - that picture of the wheels is excellent! If only I were rich...

 

Way to short, the optimal diameter for the street car is 27", on a 18 x8.5 - a 255/45R18 at all four corners probably offers the best combination of lateral grip, ride comfort, steering response, and load carrying capability (especially an XL version) as well as wheel protection.

BTW for anybody interested, the formula for determining tire OD is

section width x aspect ratio (expressed as a decimal number) / 25.4 x 2 + rim diamter = overall tire diameter.

e.g 255 x .45 / 25.4 x 2 + 18 = 27.03