Stig

I've just got hold of a set of GT500 wheels for my '07 GT/CS. Shame to change the 18" Bullitts, but I've got the GT500 brakes too and they won't fit behind the Bullitt spokes.

Thing is, I'm not sure what tyre sizes to run? The GT500 runs 285/40x18s on the rear and 255/40x18s on the front (I think).

The rims I have are 9.5" wide.

What's the max width I can go to? I thought it was 275 - but the GT500 says different?

mikes rx

Factory fronts are 255/45/18's, not 40's. Rears are 285/40/18. I am putting 255's on mine at all four corners. That way, I can rotate them. The 285's from the rear may not fit in the front, so that might be where your 275 number comes in.

Keep in mind: wider tires mean more rolling resistance. Sure, our cars have the power to move them, but it is still rolling resistance

I had cobra rims with 275/40/17's on my 2000 V6. When i sold the car, I detuned it, put back the original intake, and put back on factory bullitts (245/45/17), and the car seemed equally as fast (because there was less tire to move).

All I can say is that 275 is a WIDE tire, and I can only imagine what 285's are. To give a comparison: most full size truck tires aren't even that wide from the factory...

...but the wide tires sure do look good on the car

Stig

Thanks Mike,

Thanks to this handy site http://www.carbibles.com/tyre_bible.html I found a neat calculator that ensures that the speedo reading isn't affected either.

See tire size calculator.

From that, I'm going for 285/40x18 at the rear and a 255/45x18 at the front.

These give the closest rolling diameter to the original 235/50x18s with about 0.5mph difference at 70mph.

I can live with the increase in rolling resistance, given the wide/low rear aesthetics I'm looking for.

Incidently, my previous car had 355/30x18s running on 13" rims at the rear

GottaHaveIt

You did remove the little one before you replaced the tire & sold correct ! lol at lease you used breaks in the picture good shot !

06GT

I have the 18x9.5 GT500 Wheels from Mustang Tuning, I'm going to try to fit 285/40/18 Nitto 555s on all (4) corners.

Stig

I'd be very surprised if you didn't have rubbing issues on the fronts at that width.

70MACH1OWNER

Hey Drew... take this for want it is worth. I have Steeda 18 x 9.5 wide rims with 275 wide Nitto's mounted on all 4 wheels coming soon... I hope. However Steeda told me that 275 wide on a stock ride height car was as wide as you can go without rubbing. If you car is lowered it would seem to going to be in trouble with the 285's
Scott

06GT

Yeah, I've thought about this...anyone running 285s up front that can clarify how much rubbing there is?????

Maybe I'll just order 275s just in case...275/40/18 should be OK (maybe some slight rubbing, no big deal), I'm planning on ordering the 555's also

RonG

I have the GT500 rims w/ Nitto 555 255/45/18s on all four corners. I also did this so I could rotate the tires. I like the way the tires work on the car. However, I think the 9.5" rims are a little wide for the tires from a cosmetic perspective. It looks like the tires are bulged out a bit. Granted, I'm really getting nit picky at this point since I love the overall look of the GT500 rims.

Ron

mikes rx

Ron, you don't happen to have the factory splash guards on yours, do you? The factory mudflaps seem to fit the 235 tire perfectly. I am wondering what the extra 3/4to 1 inch of tire will do, in conjuction with the different offset that the GT500 wheels have to compensate for the wider wheel.

If needed, I guess I could take the guards off. But, I actually like the way they look (I'm probably the only one). And, they really do help prevent getting dirt and stuff thrown all over the rear bumper

06GT

Or you could move out here to Arizona, and get rid of the mudflaps altogether

06GT

Supposedly 295s will fit on a 18x9.5" wheel.

70MACH1OWNER

I will Drew if you will sponsor me and the wife.
Scott

Stig

Personally, I wouldn't risk it! 285s are maxxing it as it is really.

RonG

I don't have the splash guards on my car, but there is still plenty of room between the tires and the fender. I would think the guards would fit w/ the 255 tires. The 285s or 295s might be a problem.

BTW. I bought some 2003 mustang tri-bar center caps off ebay and they fit perfect. There are different caps available if you want something besides the cobra emblem.

Ron

mikes rx

I'm not worried about clearance and fitment, I'm worried about how they look and how well they cover the tire (ie-when looking at the car from behind, does the tire stick out past where the guard is)

RonG

Okay, now I see what you mean. With 255s you will not have a problem. I don't think the tire position looks that much different from the factory 18" wheel/tire combo. I don't remember all the details, but I believe the rim offset is 50mm. This tucks the tire well under the fender (maybe a little too much). I will probably get wider tires for the back when these wear out.

06GT

I'm mounting the GT500s on Friday, with 255/45/18 fronts, and 255/40/18 rears, Nitto 555s

Pics to follow later this weekend probably.

05BlackGT

I really want more tire, so I'll be test fitting 295/35/17's up front as soon as I get my new front struts installed. I'm hoping they will work with the extra clearance of a true coilover strut.

mikes rx

If my calculations are right, that tire size has a MUCH smaller diameter than the factory:

Stock diameter (235/55/17) = 27.177 inches
Your tire size (295/35/17) = 25.130 inches
SN95 tire size (245/45/17) = 25.681 inches

Therefore, your overall diameter is even less than the SN95 wheels,

Maybe you typed the tire size in wrong.

Also, I think that tire size is too wide for the front. I don't even think 285's fit in the front too well.