22" rears are usually used for alot of XC racing, they are too large for most anything else imho.

I run 22 fronts simply b/c they are off my old 400ex and 20" rears. Most people run a 21 or 22 front and 20" rear for most riding.

 

I'm thinking previous owner put the 22 in the rear for added ground clearance. up here in northern jersey all the trails are all very rocky. I'm more curious about the 21's in the front. should the front tires be smaller then the rear? I thought the fronts should be taller then the rear?

 

Well yes, usually fronts are larger. But since they put 22's on they arent.