getting new rims and tires and want alttle bit wider stance right now got 38x12.5x15 sx's on eagle 589's with 3.75 back spacing would 2 1/2 back spacing be to far back i'm looking at getting 36x13.5x15 iroks on some just plain steel wheels (diy beadlocks in the future) not worried about tire scrubing the fender cuz me and the sawsaz are good friends and i have 8" total lift

 

Got a tape measure? If so figure it out yourself. 3.75->2.5" backspace change is 1.25" wider, 12.5->13.5" wide tire is 1/2" wider (to the outside edge) so your track will widen 1.75" each side or 3.5" overall. I'm surprised you can run 38s on 3.75" backspace wheels and not rub the frame or springs. I rub with stock 3-3/8" wheels and 33x10.50s and with 33x15.50 SXs on 2.5" backsapced 15x10 wheels.

 

they dont rub but are damn close they are also 10" rims not 8's most run