I'm new to the site guys so any help will be appreciated!! I am running the factory 17" x7.5 alloy wheels which are the tear drop/ fan blade style OEM wheels. I do not know what the factory back spacing is. I do need to know what back spacing I will be okay to run on 285/70s with a new aftermarket wheel which are 17x9. They offer a 5.5" back spacing and a 4.5" . I'm on stock suspension still and I don't want any issues clearing ball joints, etc. this is on my 99 f150 sport 4x4. Any help??? Never fooled with back spacing before.

 

Iirc the stock wheels are either 4.5 or 5".

If you ever plan to lift the truck in the future go with the 4.5" backspacing. All lift kits require that. And I doubt you'd have any rubbing with them. The only thing I can see them possibly rubbing is the corner of the valence when the tires and the suspension are at weird angles, and that's a quick fix, just takes about ten minutes and a box cutter to trim a little off and it isn't noticeable. Another option is to crank the torsion bars to level the truck, and then you'd definitely have no problem. You'd just need to get an alignment after.

 

I would go 5.5 if you like the tires tucked in tight to the body and 4.5 if you want them to stick outside the body. And yes most lift kit spindles recommend 4.5" backspacing or less.