Any experienced wheel and tire people out there?

OK, here is my delima. I have a 1999 GT vert and I am going to upgrade my stock 1999 GT 17" rims and tires with fresh 18" ers. What I want to do is close the wheel openng up some. I know that you may say lower the car but due to where I live I do not feel that I can do that with out possibly hurting the car. So, this is what I am thinking. Intead of going with the stock size of 245*40*18 I was thinking of 255*45*18. Will these fit with out hitting? If so, how deep will the wheels need to be? Will I need the wheels to have a different offset? Any help on this subject will be helpful. Thank you for your time. Take care all.

While you can mount those tires to those wheels, you will probably want to know that doing so will cause your speedometer to read incorrectly because you are changing the rolling diameter of the wheel and tire.
Also, for every centimeter that you may close the wheel gap by adding to the tire's sidewall, you will also raise the car off the ground an equal amount - giving your car a 4x4's stance.

Yea, I know that it would pick the car up a bit but how much difference will there be between the 245*40*18 and the 255*45*18? Should I think about 255*40*18. I am not worried about the speedo. Thanks.

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Originally Posted by MrWhipper

Yea, I know that it would pick the car up a bit but how much difference will there be between the 245*40*18 and the 255*45*18? Should I think about 255*40*18. I am not worried about the speedo. Thanks.

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The difference in sidewall heights would be 45% of 255mm (114.75mm) instead of 40% of 245mm (98mm) - a difference of 16.75mm on each side of the wheel.
By running the 255/45/18 instead of the 145/40/18, you'll close the wheel gap by 16.75mm and raise the car up off the ground by that same amount.

have you considered springs that only lower it by 1"?
I've seen many lower theirs 1.5 to 2" and have issues;

I'm 1" lower and even have an extra low x-pipe -before the x-pipe I never hit the ground and with it hanging down about an inch itself I very rarely hit and if I do it's very minor.
I also should mention I live in an area with really crappy roads with massive frost heaves and bumps- so my advise is the right springs with no more than a 1" drop combined with the right tires might be the best combo and balance of both worlds.

I agree with Nicole. American Muscle (formerly Mustang Tuning) offers a set of springs that lowers your car 1 1/8" in the front and 3/4" in the rear. This might be a good spring set for what you have in mind.

http://www.americanmuscle.com/sprang...-d-series.html

I want to thank you both for your time with my questions. It is funny, after reading your first post droptop I thought about a spring kit after changing the tire size. I just want to make sure but will the 255*40*18 fit on the front and back with out hitting? Also, How wide will the rims need to be? will I need to change the rim offset? Thanks again.

I'm running 275/35/18 and 265/35/18 on my car with no rubbing problems. You should be able to get a 255 under your car with NO problems. You should be able to fit those 255s on something as narrow as an 8" wide wheel.

Once again Thank you for your help. I wanted to post this link. It is great for tire size, speedo change ect. http://www.miata.net/garage/tirecalc.html

I purchased my new rims. They look great on my black 99 vert. Again thanks for all of your help. I have a pic at my site. I am planning on getting more pics as soon as the weather changes.

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Originally Posted by MrWhipper

OK, here is my delima. I have a 1999 GT vert and I am going to upgrade my stock 1999 GT 17" rims and tires with fresh 18" ers. What I want to do is close the wheel openng up some. I know that you may say lower the car but due to where I live I do not feel that I can do that with out possibly hurting the car. So, this is what I am thinking. Intead of going with the stock size of 245*40*18 I was thinking of 255*45*18. Will these fit with out hitting? If so, how deep will the wheels need to be? Will I need the wheels to have a different offset? Any help on this subject will be helpful. Thank you for your time. Take care all.

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Hello, Low profile tires can be a real pain these days, For myself I use a 15in. rim. But to fill the wheelwells, I got a taller tire and width, Works out the same, But cost so much less to take care of. Just a thought, SargsStangs