What should the distance be from top of tire to under side
of flatbed? Unloaded.
I don't want the tires rubbing when loaded
2002 Ram 2500 4X4 reg cab long bed.
Thanks

 

Usually you figure on the axle hitting a suspension stop, usually a rubber pad between the axle or spring and the frame. Allow an inch clearance unless you need to chain it for winter mountain passes, then you need more, like 3 inches. (chains tend to slap a little.)

You can also design the bed so the tires come up through it almost to the top surface when loaded. Often one car tandem trailers are set up like that.