I just ordered a set of wheels, 20x10 with 4.5" backspace and -18 offset.. Im going to be running 38x15.5x20 tires.. think i will have rubbing issues under the truck??
I have 18x10" wheels with 5" backspace, so the center of the tire is moved IN 1/2" compared to your wheels. With 35x12.50s the tread is 1/4" outside the fender and the tires clear the frame/spring by 3/4" at full lock. My next tires will be 37x12.50 and should come right to the spring. 38x15.5 is a big, wide tire. You really need less backspace and a flare to run them. I'd look for something in the 13.5" width range and they'll fit a lot better and your highway mileage will improve.
Something is off in those specs....a 10" wide wheel with a 4.5" Back Space is -25mm offset.
The tires will definitely rub the springs close to full lock, you'll also get some sidewall flex while driving from running a 15.50" wide tire on a 10" wide wheel.
I've seen quite a variance in offset specs from what you would expect based on wheel width and backspacing. I think its just differences between manufacturers in how they are measured. Really if a wheel was 10" outside edge to outside edge, then 0 offset would be 5" backspace, but that is 1/2" or 12.5mm from what you are expecting things to be DC. Am I thinking of this wrong, do they measure wheel width at the inside bead area and backspacing from the mounting flange to the back edge?
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