6+6 Stang

here ya go i know 30 and 35, heres what i'm talking about

Overall Diameter: 26.97 in 685.03 mm 285/40R18
Overall Diameter: 27.03 in 686.56 mm 255/45R18

your telling me this is same look at the calculator using those 2 size only, i'm not one that got smart first, i never start crap on here, he could be less wise.

6+6 Stang

and heres mine tell me they are same dia..

-
295/30R20 Overall Diameter: 26.96 in 684.78 mm
255/35R20 Overall Diameter: 27.02 in 686.30 mm

that's why going with this size when time for tires rears taller than front

285/35/20
245/40/20

ejanderson05gt

Well, I suppose my comment was two-fold. One for the broken grammar that made your post next to incomprehensible, and two for exactly what Mike Maples said.

So, without trying to "cut you done," all I can say is this: +1 to Mike's post.

6+6 Stang

ok give you that, subtract 3 posts back, your saying the calculator is wrong, i disagree, front tires are taller, I'll leave it at that and not comment on this topic any further, take it up with 1010tires tell them they are mistaken.

Mike Maples

Calculators are a pretty good tool but tire manufacturer's specs are a lot better place to start.

You will notice that no manufacturer makes a 285/41ZR18 or a 255/39ZR18 because they just label them to the nearest "5" for the aspect ratio. Both B.F. Goodrich tires in question are spec'd by the manufacturer as 27" OD because they make them to match for people who want staggered sets.

And a difference in OD of less than 1/10th of an inch would never be visible even if the tire was sized exactly as calculated. Some manufacturer's tolerances may be greater than that for the same size tire and with all 4 tires the same size you will likely get that much difference between the fronts and rears before the first rotation.

I apologize for my tone...it's been a long hot day. But I'll stick with my comment about tire sizes.

6+6 Stang

I'm not disagreeing with you, and I'm not splitting hairs, but after going from 19's to 20's, having the speedo get out of sync, you start googling , research, whatever, paying to have one tune to calibrate the 20's, another tune for the stock 19's cause a switch in winter, maybe I just read into these things too much, I try too trust manufacturers but when you see these calculators you second guess. sorry for all have a good night, I apoligize for being illiterate, and sorry for typo's.

ejanderson05gt

Mike, again, taking the words right out of my mouth. Calculators are nothing more than a tool. They should be used as a reference point, not a definitive answer. 1~2 mil's isn't noticeable, especially considering that, as a diametric measurement, you'll only account for half of the difference on each side. Every tire can be different from the manufacturer, but the tolerances are hardly noticeable.

808muscle

Well I guess the question has been answered.

starbai

A+ would read again.

Sleeper_08

To reiterate what was said above 255/45/18 and 285/40/18 are exactly the same 27" OD per Tire Rack. They also happen to be the same size tires as on early GT500s

http://www.tirerack.com/tires/tires....ce+T%2FA+KDW+2