Well, I am getting new tires, and am wondering if 21's would fit on the back? Just wondering if they will fit with the stock heel gaurds? And is 23in front and 21in back tires a good combo?

I fit 22" shredders and 22" dirt devils in the rear with stock and aftermarket heel gaurds. 23" in the fron will add more clearance. You will gain more top speed with the bigger tires. It's all your preference.

23/22 is a real good combo for woods riding since, as said above, you'll get lots of good clearance, but you'll probably want to gear down a little then too.

i run 22inch front ITP HDs and 20inch ITP HDs rear. i ride some nasty technical trails out in Perry County APV and i dont have any trouble. i love the side tread that the HDs have. it helps alot when i get in the rutted out stuff.

i just got the same tires u run trial rider what gears u running ? right now i am 13/40 with stock motor just got jet kit and full system lrd

I run stock 14/40 im, pretty sure.

Oh and i have supertrapp slip on.