Tire Size for 18x9.5 Rims?

[89mercury]

I was looking at some 18x9.5 rims for my 89 Mercury. They have 4.5” of backspacing. I was thinking of using a 255/45/18 or a 285/40/18 tire. Would the 285/40/18 rub in the front? Or would it be ok?

[DuceAnAHalf]

285/40 is a big tire, i doubt it will fit up front.

[89mercury]

BFG G-Force T/A KDW
285/40ZR18 is 11.4" on a 10" rim
255/45ZR18 is 10.1" on a 8.5" rim

I may have to use 285/40/18 in back & use the 255/45/18 up front.

[DuceAnAHalf]

the 285s should fit in the back, im running a 325/5015 on the rear of mine, thats 13.5" section width and 28" tall, with 5" of BS they would fit just fine. Not sure about the fronts though

[mrltd]

Good god those are expensive tires....I fit 275/40/17's on the front of mine without any issues. Not as wide rims on my car though.

[89mercury]

Good god those are expensive tires....I fit 275/40/17's on the front of mine without any issues. Not as wide rims on my car though.

Mrltd, what is the backspacing on your rims?

I was going to put 255/45/18 on all 4 rims, those would have cost around $500 for all 4 cheapo tires. But while looking at 18x9.5 rims I noticed that the new mustang GT500 uses 18x9.5 rims. The GT500 uses the 255/45/18 in front with the 285/40/18 out back. So now I’m thinking about 285/40/18 on at least 2 rims maybe all 4 and those suckers are expensive $1000+ for 4 new tires. That’s more than the rims I was looking at!

I picked those 2 sizes because they are very close to the overall diameter of the stock 215/70/15 tires.

[mrltd]

Something like 4.5.... They are mustang wheels with 1" spacers...

[89mercury]

Something like 4.5.... They are mustang wheels with 1" spacers...

Are your rims bullitt 17x8 part#M1007J178? Those show to be 5.72" backspacing. With a 1" spacer that would be 4.72" overall. Do your tires rub on the front during a turn?

[mrltd]

Sounds about right... No rubbing at all. I am running the 98-02 brakes, which could make a difference.

[89mercury]

Sounds about right... No rubbing at all. I am running the 98-02 brakes, which could make a difference.

A big brake upgrade is the main reason I am looking at new rims & tires. I want to convert to 2000 cobra brakes; 13" front & 11.66" rear.

[89mercury]

I think the 285/40R18 tires will fit. I looked up that a 255/50R17 tire is 10.4” wide mounted on an 8” rim. So the tires have added 1.2” on each side of an 8” rim with 4.5” of backspacing.

If the 285/40R18 tire I want is 11.4” wide mounted on a 10” wide rim. It should be 11.4” or smaller mounted on a 9.5” wide rim? If correct, then a 9.5 wide rim would have about 0.95” of tire added on each side and as long as I have a 4.5” backspacing it should fit. Right?

[mrltd]

A big brake upgrade is the main reason I am looking at new rims & tires. I want to convert to 2000 cobra brakes; 13" front & 11.66" rear.

Have fun with that...Our brakes are offset quite a bit from a mustangs setup. Some different rotors (2 piece wilwood/brembos) in the correct offset and some custom brackets would make the caliper install possible.

[89mercury]

Have fun with that...Our brakes are offset quite a bit from a mustangs setup. Some different rotors (2 piece wilwood/brembos) in the correct offset and some custom brackets would make the caliper install possible.

The offset is different. Here is a 12.44" 2000 C.V. vs. a 13" 2000 cobra I wonder if the offset difference is greater than 0.30"?

[mrltd]

Yeah, it's WAY more than .3"..... More like 1" or more. We've discussed it before. Not really worth it. Upgrading to the 4 pot calipers on the vic rotors would help.

http://www.grandmarq.net/vb/showthre...ighlight=cobra