I have a 81 k5 blazer with a 4 inch suspension lift. I want to run boggers. What is the biggest size without them getting into the fenders?  

The largest i would go on a blazer would be 33 inch to be safe, or maybe 35's,  you also have to consider engine size to move those bigger tires. It will slow you down a lot. Also a piece of advice, if you are considering running boggers on the street they will wear out pretty fast and they are expensive.    

33's only.....my friend has a 82 k1500 with a 4" lift and we tried 35" boggers....the first left turn bent the fron bumper an wrecked 2 front tires on the inner fender well........i told him 33's would be better,  other 35" tires work ,like BFG at's with a slight rub