Which backspace for a 15 x 8 rim?

Hi all, I have been searching extensively on the web for the last 3 weeks to find the best set up of a/t tires to go with my 92 b2200 2wd, and I've decided on going with some 205/75r15 general at2's which obviously means that I need a set of 15's to fit them on my truck. I have been battling with figuring out what the best backspace is for me to have the least amount of modification and best fit after picking out a set of rims (15 x 8 pro comp rock crawler series 51's) and the options are as follows 3.5, 3.75, and 4.0 backspace. I apologize in advance if someone has already posted about this but I can be a bit thick headed as well and I would really appreciate it if someone could explain to me how and why whichever number is the best choice. If someone has already fitted a rim this size to their b series before you help would be very much appreciated.

Thanks

On a wheel that wide, you want about 5.5 back space, so they may not work for you... unless you want them sticking out wider than the fender.
You might want to look for a 15x7 wheel.

so in that case would a 15 x 7 (pro comp series 52) in a 3.75 backspace be ok?

On a 15x7 a zero offset puts the mounting surface dead center of the wheel. That would mean that the backspace is 4 in. 3.75 might not be enough, but you can break out a tape measure and check what works.

Also, here's a little calculator to play with.

Yeah been playing with that calculator too, gonna have to do a little digging to find another set of powder coated gloss black rims in my price range that has a similar design and a 4 in backspace, thanks for all your help I really appreciate it.