my dad is buyin a brand new gmc duramax...and we have some 18 inch rims that we we're going to put some 305/r18 bfg's on it..
do u guys think he will need a lift kit? he was thinking maybe a 4in.
ne suggestions?

 

I run 315/55/20's on my 07 Classic Chevy, and I have no lift.. They rub every now and then in a sharp turn if I hit a bump.. but I just have my torsion bars cranked all the way up.. the Correct way to do it would be with a levelling kit..

The 305 in the tire size is the width, you need to know the 2nd number as well to figure up actual tire height.. its a ratio.

But, he should have little to no rubbing with the 305's if he turns his bars up..

 

You need to check the backspacing of the rims. If they are less than 5 inches or so it won't work. The problem is the rear portion of the inner fender. There has been alot of discussion about this problem at other sites...

If you lift it, the amount of lift required and backspacing issues would be dependant on the lift manufacturer. Each has their own recommendations. I'd check with which ever lift company you are considering.

Just for gee whiz info, on my 05 I ran a 285/75R16 on a 10" wide wheel just by cranking the bars and some slight trimming. That's with 4.5" backspacing. I tried them on the 08 and they hit the rear inner fender big time. So I tried the bars and it still hit. If I more backspacing it would work but....

 

My 35's rub with a little more then 4" of lift. But as Rescue said it is all in the backspacing and I am not trading my wheels in to eliminate a little rubbing.

 

just like everyone has said if you have less then 5" of backspacing it will rub no question about it. I have seen guys buy wheels and already had tires then they get upset because with the wheels they are rubbing now so if you already have the wheels check the backspacing just take a piece of flat bar or something and measure on the rear of the wheel where it would meet the hub to the lip of the rim that will tell you your backspacing i believe