Just a real quick question before I head down to the tire shop. Will a 315/ 70/ 17 fit on the stock spare tire mount when it is mounted on a 17 moab rim? I think it will be tight but I am not sure. Thanks

 

the 265/75/16 on stock steel was tight on the carrier for mine. with a spacer maybe 315 will fit.

 

I have 35x12.50s mounted on my stock wheel and on the rear carrier (no spacer). It takes a bit muscle to get it on, but it works - push it on the carrier hard and start to thread the bottom bolt, after a few turns you can start the other bolts, continue until tight.

So, it works on the spare carrier. HOWEVER, the tire rubs my rear upper FT adjustable control arms (from the looks of it, it would rub factory arms as well) and the stock rim will rub most rear extended sway bar links. From my calculations, if you get 8" wide rim with 5.5" or less of BS you will be fine (for these problems at least). I will know for certain later this week if I am correct, as I am getting a new spare wheel for the 35" spare tire.

 

The rim width will not matter...the BS should be about 4.75" for a 12.5" section width tire (305 - 315 mm)

 

315 x .03937 (1mm) = 12.4" wide tire
12.4" x .7 = 8.681" (aspect ratio = 70 = .7 = amount of sidewall from rim to tread dia. on one side)
8.681" x 2 = 17.362" ( total side wall expressed in dia.)
17.362" + 17" rims = 34.363" dia tires (nice)

I have similar on my 2d X on stock rims which have a back spacing of 6.25", fine for narrow tires.
I had to use 1.5" spacers (legal here in AZ.) to avoid rubbing controll arms, cleared fender and body no problem with 3" lift.
I use a 1" spacer on spare mount and it sits down in the stock bumpers relief perfectly snug to the door etc.
It also gives me a working rear view window, something I consider important, with no brake light mods needed.
If I changed out rear bumper It wouldn't fit and I would have to do "something".

Back spacing is the key up to 35" tires, bigger than that you're gona deal with other requirements.

 

I ran a spacer from Expedition One when I had 35x12.5 on my stock rims. It lifts the spare up and pushes it out. Fits perfectly. The backspacing isn't right for a larger tire on the spare stock mount. The link below is where I bought it at...

http://www.expeditionone.biz/JKsparetirebracket.htm

 

It wont fit without a spacer. I have 5.75 inch backspacing and needed a spidertrax 1.5" spacer to get it to mount.