back space
 

What is the required backspace for 35 inch tires on a JK?

Required?

The general recommendation for a 35x12.50 is a 4.5" backspace. Recommendation. There are variances in tire height and width, in actual measured lift height, in the choice of fender flares and whether someone is ok with trimming or adding washers to steer stops, and the list goes on.

Is the backspace measured from the inside of the wheel or the outside of the rim? I am currently running stock 18inch wheels with 34 inch tires with 1 1/2 inch spacers. I would like to move to 17 inch wheels and 35's and get rid of the spacers. Hope this isn't a stupid question. Vehicle is a 2007 JKU Sahara with 2 1/2 Teraflex lift.

Stock rims should be 6.25" backspace. Minus the 1.50" spacer, gives you an effective backspace of 4.75" right now. So new rims with a 4.50 would put those same tires 1/4" further out (assuming the same width rim.) Then there are the variables of new rim width, actual measured height and width of the tire, etc.

There are plenty of diagrams online that will show backspace better than I can explain it, but it is measured from the back edge of the rim to the inner mounting surface.

Nope, not a stupid question. People ask about this and offset all the time. It's just that there is not a single 'correct' answer that will work for everyone, too many variables.

The most common setup is a 9 inch wide wheel with 4.5 inches of backspacing.