Teardrops n Tiny Travel Trailers

wheel question
My current tires are 205/75R15 on wheels with 3.5" of backspacing. There is 5.5inches from the wheel mounting service to the side of the trailer.

I have a set of 235/85R16 tires. I want to mount them on 16X7 wheels but can only find wheels with 4" back spacing which is going the wrong way. I think I need to keep at least the original 3.5 of BS? Would these tires rub on a 4" BS wheel

http://www.tirerack.com/tires/index.jsp All the info you need can be found at the Tire Rack. Your tires cross sectional width can be factored into your existing idler hub face spacing and new rim backspacing, just do the math.