I understand 4.25 is the stock backspacing. Would like to know would a 4.00 flat backspacing work ? Without headache

 

I have a 95 E150 and I always made the assumption that 3.75" was the stock backspacing for 15x6" rims and 235/75r15 wheels. I am currently running 3-5/8" backspacing wheels with 255/70r15 tires (29x10") with no issues.

Basically what you are doing by decreasing your backspacing, from 4.25 to 4.0, is moving your wheels outward. If you have floating axles in the rear, this puts a smidge more stress on your wheel bearings, but it's negligible at worst. If you have semi-floating axles, it's not a concern at all. On the front, kicking the wheels out increases the chance that they may rub during turning, but only with tires pushing 30"+

If you're looking at wheels with 4" BS that aren't an incredible width like 9"+, and you are intending to use tires no more than and inch larger than factory-spec in diameter, then I would say from experience that this should work great.

 

Thank you! I was planning on doing 16x10

 

16x10? I'm pretty certain that your wheels are going to stick out quite a lot if you use that size all the way around.

These are my 15x8 rims with 29.1" tires:

 

I have 16x10 on now, but with 4.25 backspacing. I use different tire size as I'm going for different look. I use 255 50 16"s on my rims . No rubbing at all, turning etc.

 

I'm running 15 x 10 aluminum slots in the rear with a 3.5" B/S with 275/60/15 tires to fill out the fender flares and improve the rear gear/final drive ratio (from 3.55 to 3.67). Fronts are 15x 8.5's with 235/70's with a 3.75" BS. No issues with either size wheels or tires. a 1/4" difference in B/S will make no difference anywhere.