I am ordering a 15x8 ultra rogue 175 with 3.75 backspacing and -19 offset. A lot of people say 4 backspacing is ideal but the majority of ranger drivers buy -19 x 3.75.

 

Stick to the 3.75 to 4” BS on new wheels.
Too much BS, over 4”, and the tire will start to hit the body when turning and too little, 3.73”, and you lose caliper/brake spacing and things start to hit inside.

Factory specs are good for some things.
Most people I know buy the 4” BS so your call still.

 

Do you think the 3.75 backspacing would cause caliper/brake problems?

 

Usually not, I believe that is close to OEM BS.

My wheels have 4" BS, it was the closest I could get to 3.75".

When you get the rims, test fit one on the front and see if there is a clearance problems.
Do this before mounting the wheels.

 

for the caliper clearance, my wheels are 3.313" back spacing and theres no issue but the tires do poke out so it also depends how wide of a tire you have

 

I have BFG 31x10.5 A/T KO tires. The stock wheels on my truck are 15x7 D shape. So I should be problem free with a 15x8 3.75 BS? I don't think the wheel store will let me order them and then try them on to see if they fit before I pay them.

 

Pick your poison:

7" wide wheel w/ 4.50" Backspacing (+12 offset) - meaning 2.50" outboard. (Stock)
8" wide wheel w/ 3.25" Backspacing (-32 offset) - meaning 4.75" outboard. (aka - 2.25" further "out" than stock as well as being 1.25" inward less than stock)
8" wide wheel w/ 3.75" Backspacing (-19 offset) - meaning 4.25" outboard. (aka - 1.75" further "out" than stock as well as being .75" inward less than stock)
8" wide wheel w/ 4.00" Backspacing (-12 offset) - meaning 4.00" outboard. (aka - 1.50" further "out" than stock as well as being .50" inward less than stock)
8" wide wheel w/ 4.50" Backspacing (0 offset) - meaning 3.50" outboard. (aka - 1.00" further "out" than stock as well as being the same distance inward as stock)
10" wide wheel w/ 3.25" Backspacing (-57 offset) - meaning 6.75" outboard. (aka - 4.25" further "out" than stock as well as being 1.25" inward less than stock)
10" wide wheel w/ 3.50" Backspacing (-51 offset) - meaning 6.50" outboard. (aka - 4.00" further "out" than stock as well as being 1.00" inward less than stock)
10" wide wheel w/ 3.75" Backspacing (-44 offset) - meaning 6.25" outboard. (aka - 3.75" further "out" than stock as well as being .75" inward less than stock)
10" wide wheel w/ 4.00" Backspacing (-38 offset) - meaning 6.00" outboard. (aka - 3.50" further "out" than stock as well as being .50" inward less than stock)
10" wide wheel w/ 4.50" Backspacing (-25 offset) - meaning 5.50" outboard. (aka - 3.00" further "out" than stock as well as being the same distance inward as stock)