Tires I'm going to get measure 40"x16"x16". Where I wheel the maximum width is 80". I don't want tickets. What backspacing wheel will I need to be legal? I don't want to have to narrow the axles to achieve this. 77 K20 is the rig the wheels and tires will be going on.
Do you have a tape measure? Can you do simple math?
Lets assume your front axle is 68" wide. Lets also assume that your tires measure an actual 16" wide.
If you have a wheel with zero offset (centered), your overall width would be:
axle width + tire width = 84".
Welp, that puts you 4" over. You need to come in 2" per side. That means your wheels need to be offset 2" towards the vehicle centerline.
Since you didn't mention the wheel width, here is what you need to do to figure your backspacing:
(wheel width / 2) + offset = backspacing (towards vehicle centerline)
(wheel width / 2) - offset = backspacing (away from vehicle centerline)