satx

Does wheel offset only apply to the wheel dimensions, independent of what tire size is wrapped around them? Specifically, I will have 18 x 10 wheels in the rear with 2" outer offset. I was considering either 295/35 18, 285/40 18, or 305/35 18 tires around them in the rear. The offset measurement of the wheel was determined when I was considering 295/35 18 tires, but I did not know if that offset was just based on the wheel measurements (as opposed to tire size). Any input?

thx

JoeJP

Its generally only for wheels. I don't think 305/30's fit on a 10" rim.

Poco

It does depend.If you want the wheels sticking out past the wheel well and the section width of the tire can also stick out far enough for some scrapage on the fender(even on the inner fender) when hitting bumps.It would also depend if your car is lowered,then your wheel and tire combo may not fit at all.

Philostang

Joe and Poco are right...

Strictly speaking, offset is a measurement of a wheel (regardless of the tire mounted on it), and it measures the distance the mounting surface is from the centerline of the wheel. The value of knowing offset is really not related to everything fitting inside the wheel well, that's what "backspacing" is usually used to determine (how much room do I have to clear suspension components, body panels, etc.?). Offset is used to in conjunction with other suspension geometries to determine the minimal wheel scrub radius, among other handling characteristics. (Of course, to do all that, you do need to know at least how tall your tire is...).

Anyway, as a rule of thumb, try to stay close to the factory offset to maintain the engineered-in optimization of the suspension geometry (note, this isn't 1965 when scrub radii were wildly inappropriate as they came from the factory...there's a good, good reason most cars today--even rear wheel drive--have positive offsets). On our cars +45mm to +50mm is the correct offset. If you want a tire/wheel combo that comes closer to the fender, play with the width of the wheel and the section width of the tire--don't mess with the offset (Ford engineers spent a lot of time getting this right, and as you will note when Saleen and Roush took the project in their hands, they still used +45mm offset for their wide wheel offerings).

Speaking of Roush, they managed to fit a 275/45/18 tire mounted onto an 18x10" wheel w/(I'm almost certain) a +45mm offset. Things got pretty tight like that, so for your larger sizes I bet you would need to go with +50mm offset, and even then, I'm not sure things would fit...and then there's interference on the suspension side to worry you.

I saw a guy running 18x9.5" wheels w/+45mm offset using 285/40/18s. He was maxed out just up to the fender's edge, and reported a bit of rubbing (suspension side) on sharp turns (wheel lock) when hitting a sharp dip (coming off of a driveway past the curb), but the car looked great!

Hope some of that helps.
Best,
-j