i got a 86 f 350 box truck and was wondering whats the widest you can go in the rear? ( tires ) how much space needs to be between the tires? inch? 2 inch?

 

On my 1999 dually I run 305-70-16's on stock rims . I had to get some spacers to do it ,I found a guy out in California an ex - drag racer that makes very high quality ones . Mine were hub eccentric yours should be lug eccentric .Ford Truck Enthusiasts Forums - 1996pwrstrk's Album: Dually adapter
This is Fred's link check his site out and give him a call he's a real nice guy ,if you want to go the spacer route WheelAdapter.com > Wheel Spacers

 

Do a search on the internet, there is a tire size limit for the stock rims. If the sidewalls touch while loaded, I have heard that is a very bad thing.

 

Yep, VERY BAD thing, I seen the end result of tire sidewall rubbing, a totaled truck and a munged up friend. He got a set of new tires on his dually chevy, the biggest he could find. Only 10-20 miles he went before the sidewalls blew out flipping the truck! The other set was almost ready to blow out too. FHP investigation found the sidewalls were rubbing and there was some brew ha ha over it.

 

yea my little set up didnt last at all. big mistake, lotta extra work, but noone hurt or nothing. its cool because ill just use em on my silverado ( needs tires too )

 

average tire size on duelly's are 235/85/16's,anyway thats what we run on our rollback and its a 84 f350