What size rear tires for 94 Blaster?

The ones on my stock rims are 21-10-8 but I'm not 100% shure that their the original oems. I'm not shure what you mean by a set, but rockymountain atv is where I buy all my tires and rims, cheapest place to get them new.
 
im going to get the maxxis razrs from rocky mtn atv, so fronts i want to order 21x7x10s , and rears choices are (20x11x10 , 20x11x8 , 20x11x9 , 22x11x9) i have stock rims. so rears i need 20x11x8s?
 
For the rears you need something with an 8 at the end. The rest doesn't matter. if you buy bigger a/m rims then you need tires with a bigger id ( inside diameter)
For example. 18x11x8 will fit the stock rims. Later on you buy a 9" rim, now you need 18x11x9
 
ok so i need the 20x11x8 rears, do these tires have alot smaller circumfrence than stock bubble tires? enough to effect the gearing alot or no?
 
ok thanks for the help, im also ordering new brake pads off of ebay for 94 blaster, screw in style, cable operated pads, anyone have a guide of how to change then, i havent found it on here yet...