OK, so I have a 02 blazer xtreme. I bought some 18x7.5 wheels with +38. Tires are 245/55/18. My calculations give that a 5.25" backspace right? So .75" would work, but to get them to sit the same as factory I would have to do 1.25" on each because the wheels are .5" less wide than stock, is that right? But then I have one wheel and tire calculator telling me I need 1.5" and another calculator saying 1.75". So I'm really confused. Then I've read the rear wheels are tucked in farther than the front, so to get them even with the fronts what would I do for the rear? I've seen .75" more on each side, and I've seen 1.5" more on each side... Also, are my front bore and rear bore both 70.3? I've seen somewhere that front is bigger than rear... Appreciate any help.

 

99% sure the hub (I think this is what you're referring to as bore?) is the same diameter front and back. As for the rear axle being narrower than the front, this is correct. It is a shade less than 3" narrower total, and most people use 1.25" or 1.5" spacers on the rear to even it with the factory front.


For the spacers, I think you'd be safe doing something like 1.25" front, and 2.5" rear. With your tires that are 0.75" less backspacing than factory, and 0.5" narrower than the factory 16x8 Xtreme rims you have 1.25" total inset for the outside face of the rim compared to factory rims. 1.25" will get you really close to factory on the front. If you want to widen the rear track to be close to the same width as the front, I'd suggest to use the 1.25" from the front, plus another 1.25" to compensate for the narrower rear axle for a total of 2.5".


Of course, any suspension changes you have done may play into that too, considering that if you've lowered the truck you may need to be a bit narrower to clear the fenders.