curently on my 05' XR650L i have maxxis deserts. The sizes read as follows: Front- 80/100 -21 51m Rear- 110/100 -18 64m I was wondering what are the largest (tallest and widest) tires that i can fit on these rims? also what are the numbers telling me? height vs width? what is what? and what are the numbers before the "M" telling me? thanks, you are all bike gods!!