[Subafreak]

Originally posted by longassname


The 35 series is only applicable to a 255 on an 18" wheel but lets only worry about width here first. You can go through a simple chart and pick out the appropriate series after you figure out what will fit. The bad news though is you really can't calculate what will fit on the inside side without taking measurements of clearances while the car is sitting on it's tires. The only way you could possibly do that is on an alignment rack.

With a whole bunch of calculation we can glean together some useful information about what will fit though, just but seeing what won't fit on the outside.

I'll do the math though and let you see what I mean.

The width of the wheel is critical.

Factory wheels are 7.5" wide with a +55mm offset. That means the wheel goes back 150mm from the mounting surface and sticks out 40 mm from the mounting surface.

My wheels are 8" wide with a +49mm offset. That means the wheel goes back 150.6mm from the mounting surface and sticks out 52.6mm from the mounting surface. So bascially the wheel sticks inwards the same amount as factory while sticking outward half an inch more. So in this case 74% of the wheel and thus the tire goes to the inside of the mounting surface.

In the case of the factory wheel 79% of the wheel and thus the tire goes to the inside of the mounting surface. So you're putting more rubber to the inside. What can you fit without rubbing on a factory wheel? I don't know. On the smaller diameter wheel you are going to have tire in an area that is tighter to the strut and the shape of the sidewalls will be a lot more bowed on the less wide wheel.

The real problem is in the case of aftermarket wheel. Most aftermarket wheels aren't available in an offset any larger than +42mm. This puts more wheel to the outside. An 8 inch wide wheel +42mm offset would stick out a whole 59.4mm from the mounting surface and a 7.5 inch +42 wheel will stick out 53.7mm from the mounting surface. In the case of the 7.5 inch wheel you're putting 28% of the tire to the outside in the case of the 8" wheel you are putting 29% of the tire to the outside.

So now you could take those percentages...factory 21% outside, 8" +49 26% outside, 7.5 +42 28% outside, 8" +42 29% outside and multiply by the crosssection width of the tire.

If we take my tires at 10.2 inches we see that @21% 2.14", 26% 2.65", 28% 2.856", 29% 2.95" of tire goes to the outside. I can tell you from looking at my car that the 28% and 29% instances will rub on the outside.

How big of a tire you can fit on stock wheels will most likely be determined by inside clearances.

So what are your wheels, where did you get them, and how much did you pay?