Quick tire size question

[Coup D E'Tat]

Will 245/45/17's fit without rubbing on a 7" wide, +42mm offset wheel on a 2G? Thanks in advance.

 

[jtmcinder]

I doubt it. I'll bet it will rub the vertical link in the rear.

And you really don't want to put 245s on 7" wheels, anyway.

- Jtoby

 

[Coup D E'Tat]

So, you don't think it'd even be worth trying? The reason I ask is because, through the dealer, my uncle gets free replacement tires for his Mustang, so I figured that I could get his tires and slap them on.

Spacers or something wouldn't help the problem at all? I'm just trying to save myself some cash, is-all.

 

[jtmcinder]

Oh, a spacer will make it fit, although this will require a rolled fender lip in the rear. And a smaller tire would work on these wheels without doing anything. I just answered with regard to 245/45/17s on a +42mm wheel on a 2G.

- Jtoby

 

[Turbo Shogun]

Interesting...

What about 245/40's on a 17x7.5"?

Reason I'm asking is they don't make Kumho MX's in 235/40/17.

They make Dunlop SP Sport FM901's in that size, though, but I read the reviews, and even though Best Motoring gave that tire a rave review, I'm not gonna risk $400+ for a mediocre tire...

Not to mention they were testing tires on MX5's in the rain.

 

[jtmcinder]

I, personally, would never try to run 245/40/17s on a 17x7.5 wheel. If I had 17x7.5 wheels, I'd back off to a 225/45/17 and probably run Azenis.

- Jtoby

 

[Coup D E'Tat]

Originally posted by jtmcinder
And you really don't want to put 245s on 7" wheels, anyway.

- Jtoby

What would the downsides/potential downsides of this be?

 

[Groomz]

Tire companies design tires to fit a certain range of rims. Say from 7-8 inches wide and tested on an 8 inch rim. A 245 tire is not designed to fit a 7 inch rim. Neither are 235s. 245s would need at least 8 inch wide rims to work properly, just because the tire fits a rim does not mean it should be on that rim. Go to www.tirerack.com and check the tires specs, it will say what size wheels that specific tire will fit.

 

[jtmcinder]

Realize that my comments are mostly about serious driving, such as when autoXing. It probably makes no difference driving sensibly on the street. With that said....

The reason you don't want to undersize the wheel for the tire is this. When you undersize the wheel, the inward pressure on the sidewalls both weakens the sidewall and slightly bends the tread. The slight bending of the tread lowers grip a little, assuming the same tire pressure and the same tire on a wider wheel. Not that big a deal with modern tires. However, the weakening of the sidewall forces you to run much higher pressures to keep the tire's shoulder from rolling over in a hard corner. The higher pressure exacerbates the bent-tread issue a little, which lowers grip a little more - but still not a big deal - but it also greatly reduces the tire's compliance, which lowers grip a lot. So you actually can end up with less grip than if you ran a smaller tire on the same wheel.

Cliff notes: For maximum grip, you want to run the lowest pressures that prevent the shoulders from rolling over. Undersized wheels require more pressure to avoid roll-over. Therefore, undersized wheels reduce lateral grip.

I don't know if a 7.5" wheel is one of the cases where a 225/45/17 will end up having more grip than a 245/40/17 (for the same kind of tire). But I know that an Azenis has so much grip than an MX that a 225/45/17 Azenis is definitely a better choice for a 17x7.5" wheel. In fact, a 225/45/17 Azenis could probably beat a 245/45/17 MX on an 8" wheel. By the end of next year, I might know this for sure.

If Azenis came in 245/40/17, there would be no debate as to what to run on a 2G. We'd all have 8" wheels and these tires.

- Jtoby

 

[Coup D E'Tat]

Alright, so it isn't "supposed" to be on the wheel. Basically what I would like to know is if the tire is going to blow off of the wheel or something dangerous. My 235's I have right now don't seem too wide for the wheel? On Goodyear's website, it has different max/min (rim width) sizes for some of their tires, and the tires that I will be getting (Goodyear Eagle F1 GS's) are reccomended for 7.5 to 9.0". Now, after reading this I think that I could get away with running them, unless someone here has some first hand experience or something along those lines? I mean, .5" is a lot, but I really don't think anything should happen?

**Edit - Right after entering the above, I saw your post Jtoby. I do no autocrossing, and will not be driving these very hard through turns (especially with winter coming.) I was just looking for an answer along the lines of safety (probably should have mentioned that in the original post .) But, I thank everyone for the help, and I'm going for it, and I guess we'll just have to see what happens!