Need advice on tires & rims

[Midnight Rider]

I have a 1985 ranger 4x4 with 235/75/R15 on it. A friend of mine has a set of tires and rims I want to buy. The rims are 15 x 10 with Cooper Discover 31 x 11.50 tires. My question is can I fit a smaller tire on these rims. I don't really want to mess with a lift kit right now, but he only wants $150.00 for all four tires and rims. The back is fine with these tires and rims but the front will rub, but the rims are real nice. Please advise me if you can, thanks. Also I heard someone talking about back spacing what is this, and should I be concerned about it?

 

[Skeleranger]

your tires are only about 9.5 inches wide so they wouldnt fit on the 10 inch rim. Thats still really cheap tho, mite want to just pick them up for the future. Backspace should be a concern as it is the distance from the back lip of the rim to the mounting pad or hub. it determines how far the wheel will be kicked out.