Right now I'm running BFG AT/KO 315/70/17 on stock rims.Not an ideal match,I know.First,this spring I bought a 6" Fabtech kit,but have not installed it yet.(Driveway still too wet).I also bought Helo Maxx6 Chrome 17x9 with -12 offset,which,according to my research,gives me 4.5" backspacing.My question to the experts here is,Can I mount up my new wheels with the BFG's,and run em' until it's time for the lift install?My rig is a 1999 F-150 4x4 5.4L Shortbox Flareside.

 

No, they will fit fine with the lift, but not without it.

 

Where will I see contact?With these big tires on the stockers,I get rubbing on the framerail at full lock.

 

Now I'm a bit more confused than before.After consulting the site where I bought the wheels,they list the wheels offset at 12,which I first assumed was supposed to be -12,but now I'm thinking it may actually be +12,making the wheels I bought 5.5" backspacing,right?How would this affect the fit of those large tires?

 

I'm not sure, but I think the Helo's have 5 inches of bs. A lot of mailorder places make a lot of typos. I'd contact Helo.
If you try to run that combo at stock height they are gonna badly rub the rear wheelwells and the front bumper's valance.