I have a 2000 4X4 Dually that I already have a 3" lift for and I am having problems figuring out what tire size that I can use with towing that won't interfere in the rear. If I have to use spacers I am alright with that. just don't know where to even start looking for advice or the spacers.
Thanks

 

Wheels spacers are illegal in most states, maybe even all I think. They're also sketchy, especially if your gonna be towing with lots of weight on the back, and I imagine there will be since its a duelly.

As far as I know (I'm not a duelly expert) you'll probably have to get new wheels that are made for wider duel rear tires.

 

with a truck made for towing and hauling like yours... a set of 18 or 20's with a larger tire might be best..mainly to keep the sidewall size down so you still retain good towning hauling characterisitics

 

or if your gunna do alot of towing and lifting it i would get one of those conversion kits and get some tractor trailer wheels on it. my friend has them on his chevy and the thing is sick!