17x9.5 wheels with 54mm offsets fit the car fine. It's ideal for the fbody. Shouldnt rub on inside nor outside.

The guys with corvette 50mm wheels who you are talking about probably had 17x11 inch wheels. I have these in my car. I put in a small spacer, did some BFH, and rolled my fenders slightly. 315/35/17 tires.

So what's the deal with your 275/45/18 tire? Did you mean to get a taller tire, or is that what the carid dope said was the right size?

 

I don't know about why OP is running 275/40's, but I am because it is actually closer to the factory size than 275/35. When I did the calculations, they were slightly taller than the stock tires, where as the 275/35 was significantly shorter.

I can't remember by how much now, but I know it would have made my speedometer off by a good bit.

 

You need to do this

 

275/40/17 tire diameter = 25.7 in

275/40/18 tire diameter = 26.7 in

275/35/18 tire diameter = 25.6 in

I'm getting this info from here: http://www.miata.net/garage/tirecalc.html

So I think the 35 is more appropriate and believe the combination between the extreme offset and the larger tire probably contributes to quite a bit of rubbing.

 

Taller tire plus low offset means fender lip rubbing. Pay someone (or rent) to roll your 1" tire-cutting fender lips and problem solved. An adjustable phb wouldnt hurt either

 

Where can I get one of those?

 

Amazon, you can get them for around $180-$200. Just be sure to use a heat gun

You can also use a rubber mallett with a heat gun, however to fully roll the fenders you will need the tool. It's almost impossible to hammer them cleanly

 

Ok I'll try it. Thanx alot guys!!

 

Havent had a chance to roll my fenders yet, but I came across a cheap set of stock springs and installed them. So far so good. No rubbing yet. Haven't tried a launch yet.

 

Launch was good

 

A 275/40/18 tires aren't the issue the offset is. With the correct offset and rolled fender lips you should never have any rubbing, except under the most extreme conditions.

Believe it or not the tires don't rub at all that low.

 

I agree that the offset is the biggest concern here but adding an extra inch doesn't help. Our cars have different tolerances. Some cars fit large tires fine, others don't. A taller tire bulges out in different spots compared to a shorter tire