suspension seatpost, sprung saddle, carbon fork, and probably number 1: the fattest tires you can fit.

i guess the easy way to gauge this is check what size tires you are currently running, and see how much space you have between the tire and the top and sides of the fork, and between the tire and seat tube. all tires, although supposedly being 700 x 23 or 25 or whatever, all vary. but if you are running 25s and it looks like you have a ton of room, you could maybe pull off 32s.