I am getting ready to put new tires on the jeep and was going to put them on the stock wheels with wheel spacers. But now am wondering if I would be better off with wheels that have the proper amount of backspacing.
So what would be the optimal backspacing to run 35" tires ?

 

to run 35X12.5 wide tires, you will need 1.5'' wheelspacer or 4.5-4.75 of BS aftermarket wheels

Your stock wheel have 6.25'' of BS

 

I run 4.75 of backspace with 35x12.5x17 (KM2s) and I think it's perfect (no rubbing). If you want the wheels\tires to stick out more go with 4.5 on down. I prefer the tucked in look and it's less stress on the hubs.



Here is some good info that I copied from the AEV site.

Offset
What the book says: Offset is a measurement from the mounting surface of the wheel to the centerline of the wheel. This measurement is typically expressed in millimeters and can be positive or negative. In the case of all newer factory Jeep wheels, they are all a "positive offset," meaning that the mounting face of the wheel is outboard of the centerline.

What the engineer says: Many aftermarket wheels come with a generic offset that is designed to "fit" as many vehicles as possible so that dealers only need to carry one wheel. The issue here is that the wheel doesn’t really "fit" any application...this is why you see Jeeps with the tires sticking out three inches past the flare. This may be OK in sunny southern California, but guys who live where it snows can be in for all sorts of white knuckle handling, not to mention a huge mess on the side of the car. With the proper offset, even 35" tires can stay neatly tucked under the Jeep. It's a common misconception that you need to have them stick out to clear.

Backspacing
What the book says: Backspacing is the measurement from the wheel mounting surface to the rear lip of the wheel. Backspacing is not used in the wheel industry because it really doesn’t mean much unless you know the width of the wheel and what kind of construction was used to make the wheel. Backspacing can be helpful if you are comparing the exact same width and type of wheel.

What the engineer says: Let's say that for your performance requirements you decide on a 16 x 7 wheel with 4" backspacing and end up with the outside edge of the wheel 3" outboard of the wheel mounting surface. Your friend, on the other hand, purchases a 16 x 10 wheel, also with 4" of backspacing - and ends up with an outside edge that is six(!) inches outboard of the wheel mounting surface. So while your Jeep looks great with the 16 x 7 wheels and 4" of backspacing, your friend's Jeep has tires sticking out three more inches on either side - a totally different look. And even if you like that look, you still end up with the handling and mudspray issues described above. The other factor in backspacing vs. offset is how the wheel is made. Wheel width is measured between the bead seat surfaces on the inside of the wheel. Backspacing is measured to the rear lip of the wheel, so if you have a thick bead like many aluminum wheels do, or a different type of wheel weight seat, you may not end up with what you want.

Scrub Radius
What the book says: Scrub radius is the radius measured from the centerline of the wheel to the pivot axis of the steering knuckle.

What the engineer says: A typical late model Jeep has the wheel approximately centered over the pivot point of the steering; when changing offsets, it is critical to take into account how the steering system was originally set up in order to avoid handling problems on the road. If you have a positive offset wheel stock, and decide to switch to a negative offset wheel, you’re scrub radius just increased drastically. What happens is one wheel travels in a forward arc, while the other travels in a rearward arc. You just changed your steering geometry to resemble a 150 year old wagon…and your Jeep will drive like it too

 

I have a set of 16" wheels BS 4.5 and a set of 15" with a 3.75 BS. the 15" stick way out and sprays alot of mud, snow and what ever else you drive through. Looks cool though.

 

I have 33s with 4 1/2 backspacing and they stick out a tiny bit. I think 4 1/2 is the perfect backspacing for the JKs