rquiles36@yahoo.com

I just purchased 20x9 all around Shelby wheels . I’m wondering what tire size to go with. I’ve got an 06 Legend Lime dropped with the Eibach pro plus kit

m05fastbackGT

I ran 275-35-20" Nitto G2's on 20x9.5" wheels as a square setup. I'd would go with either 265-40-20" or 275-35-20" as a square setup. You can also go to tire rack.com or discount tire.com as they both have recommended tire and wheel size specs on their websites. In the meantime, welcome to TMS

Bert

two things you want to be aware of, to size the tires:

1) keep the overall diameter of the new tires about the same as the old ones -- you can look up your old tires on Tire Rack (or anyplace that has the information) and check the diameter (on the "specs" page). I am not sure about yours, but most mustang stock tires are about 27.2" overall diameter. You want your new tires to be about the same, within about 1/2" or less. If the diameter of the new tires is bigger than the old ones, the speedometer will read a little low (meaning you wil actually be going a little faster than the speedometer says) ; if the new tires are smaller than the old ones then the speedometer will read high.

2) The width of the tires should be sized to match the wheels. Again you can look up the new tires you are considering on Tire Rack, and check the "specs" tab for the "rim width" for that particular tire. You want 9" to be within the range of recommended widths. If you use tires that should have a wider wheel, you will not get full benefit of the added width; basically you will be paying for rubber that does not touch the road. I'm pretty sure that 255 is about the widest that will have a 9" wide wheel in range; 265 is pushing it and 275 is too wide, I'm pretty sure. But look it up for yourself, don't take my word for it!

m05fastbackGT

Although tire rack has the measured rim width at 9.5" for a 275-35-20" tire. 275 is not considered as too wide for a 20x9" wheel. If you also check the specs on Tire Rack, rim width range for a 275-35-20" tire is between 9"-11" As long as the rim width is within the specified ranges? 275-35 series tires are considered to be within specs for a 20x9" wheel. The OP can also go with 255-35-20" tires on 20x9" wheels as a square setup which has a measuring rim width of (9") and rim width range between 8-10"

Bert

I checked and I see you are correct, rim width for the 275/35-20 that I checked was 9-11" , so it is "OK" . . . but personally I would not do it on my car. Notice 9" is the extreme low end of the range.

For fairly crisp handling you want the rim to be at least the measuring width, preferably wider. On narrower wheels the tread curls around and up off the ground at the edges, so you end up paying for rubber that is not touching the ground. I'd probably go with 255 or 265 at the widest on the front, and 255 of 265 or maybe 275 on the back, if I was looking for the appearance of wide tires and not so concerned about how they actually perform.

Your mileage may vary, it's up to you, I am just trying to help.

m05fastbackGT

Yes, I'm fully aware that 9" is the extreme low end of the range, but even then a 275-35-20" tire on a 20x9" wheel is approx just 1/4" per side wider. Therefore nothing to really be concerned about other than for just a slight bulge over the rim. Also, Ford installed 285-40-18" tires on 18x9.5" wheels (rear) as "OEM" and 255-45-18" tires on 18x9.5" wheels (front) as "OEM" for the 2007-09 Shelby GT500 models. Despite 9.5" as being the extreme low end of the rim width range, Ford never the less paired the 285-40-18" tires with the 18x9.5" SVT wheels anyhow. At any rate, I think it's pretty safe to assume that if the engineers over at Ford had any concerns over the 285-40-18" tires as being too wide on 9.5" wheels? Ford wouldn't had selected those sizes, to begin with. I do however agree from a performance and handling perspective that it would be best for the rim to be at least the measuring width or preferably slightly wider for optimal crisp handling. Knowing the OP is wanting to run a square setup on all 4 corners, I would highly recommend going with 255-35-20" tires on a 20x9" wheel which has an optimal measured rim width of 9" and stock height of 27" as his best choice for his particular application.