myo6mustanggt

I'm looking into buying stock 18 mustang rims from a 08 these will fit my 06 gt convertible right will it affect my speedo or something else thanks

houtex

Goodness.

There we go.

Yes, they will fit. If you get the correct size for the '08 Mustang then there will be no speedo correction needed. If you get a different size, you'll need to try to match up the outside diameter of the tires, if possible, or accept a slight difference in the speed indicated.

This is what I'm doing on my 275/40-18s. They're a little less big than the original 2010 GT500 wheel size should be, and ditto the regular '06 GT 17s I had (235/55-17)

I'll be gettin' the 285/40-18s in back, and the 255/45-18s in the front the next go round, as I want the slightly larger tire for both the speedo correction and they will look a little better in the wheel wells, although I'm also thinkin' the 285s all way 'round, but... turning rub.

http://www.rimsntires.com/specspro.jsp

Use this to compare your current tire size with what you'll wind up with.

Hope this helps!

07 Boss

A 235/55/17 is bigger than a 285/40/18 as far as the speedo is concerned. Your speedo will read higher than it is now if you make that switch.

06 Screamer

I've had the 285- 225 combo on my car for over 7 years and double checked everything, even as going as far as comparing the speedo with my gps. It's so close its not even an issue. I even tried putting the 285 in the front to check for rubbing, it fits fine and it rubs the inner liner just barely you have to notice. It fits under the top of the wheel opening of the fender, but you go look at it from the front it sticks out way past the front bumper.

06 Screamer

Did this when I was taking the 235/55-17 snow tires off in the spring and putting the GT500 set back on. The 285 is on the passenger side.

07 Boss

No it's not that big of a difference, about 1/5 of an inch. If your 285 up front is sticking out, that is the offset/backspacing of the wheel, not the tire size. Unless one is trying to put a 285 on a 8" rim or something lame like that.

houtex

It's all of 0.7% difference. 60 on the speedo is 59.6 on the 18s, in those sizes, so no real difference. Heck, you'd wear that out on the 17s during the course of their lifespan.

Whereas going to the 275/40-18s, it's 1.8%, or 60 is now 58.9, or a whole MPH. Which goes up (down) as you get wear, so you might be two MPH off at the end of the tire life, potentially.

I live with it. It's not bad until you get up there in speed. 75 indicated is about 71 actual, for example... and it just gets worse and worse. But that's about as fast as I go normally on the way outta town highways.

---

As far as the 225 issue, that doesn't measure your speed. So you can put 175 on there (not that I would, but hey) and it won't matter. It's only the rears.

Not sure if you were saying anything of the sort, but I thought I'd throw that out there for info in case.

07 Boss

My rear tires are almost 29 inches tall which makes for about a 10% difference in revs per mile.

And width matters when discussing tire height because you have to multiply it by the aspect ratio to determine side wall height.

05YellowGT

I've found the best way is to measure the actual diameter of the tire, it can be considerably different from what you get using the aspect ratio to calculate it. This is because the actual dimension that one manufacture says is a tire's width can differ from what another one says is the same width, it depends on how they measure it. I run 285/30/20 and that calculates out to 754.4 revs per mile using the aspect ratio, but when I measure the actual diameter and use it instead, I get 740 which matches the speed on my navigation unit.

07 Boss

That's true, every manufacturer is different. That's why Nittos run small. But if you don't have the actual tire you have to do the math.

Stoenr

Most of you have handheld tuners that can match the tires rev's to calibrate speedometer, no big deal. OE speedo's are off by a few mph as is from factory.

Imatk

If you have a tuner just go into the revs per mile and change it.

https://tiresize.com/calculator/

Gigantor

I have a set of stock rims from my 06 GT. They are the 18" fan blades and have tires mounted on them with usable treads. They are all in excellent shape. Let me know if you're interested.