I want a big bad rear tire that will always take me to the top of the hill, instead of clogging up and spinning out somewhere before the top. Been readin' and looking at pretty tire photos, and reading reviews.... I looks like the IRC M5B is the Beast that I'm looking for. But I'm not certain what sizes will fit my 08'. The manual calls for a 110/100-18 64M , but tires rarely come in the exact sizes called for... The IRC M5B is available in a 110/80-18 , a 120/80-18, a 130/80-18, 140/80-18 ,and a couple other diameters. I think the 110/80-18 is the best fit, but maybe not. Which of these sizes will fit the WR450? Which is closest to stock? Which size would you chose, if not the stock size, and "why"? Also have you tried this tire? What's your favorite tire for getting up big loose and/or muddy hills?