Tires for my ZR2

i searched the forum for what tires will fit and it seems like people are only asking about there normal blazers. i couldn't find anything about ZR2's..
Heres my deal. i want to put bigger tires on my truck without lifting it. being its a zr2 its already lifted a couple inches. So my question is what size tire can you fit on a stock ZR2 without lifting it and keeping it from rubbing. Right now its got the stock 31's but i was thinkin of 32 or 33 with a little more aggressive tread. new rims would be nice too. any suggestions?
i also read about back spacing. can someone explain to me what it is.

2000 ZR2 blazer 70 k miles
thanks

Anything larger than 31" will rub without modifications. Backspacing is also critical to not rubbing. Your stock wheels have 6" of backspacing. This is the distance from the wheel mounting face to the edge of the rim on the back side. A wheel with less backspace will stick out of the fender farther and have a tendency to rub on turns. For more info go to ZR2.com and search. These guys are the experts on ZR2's.

thanks