I have a Trek 520 with Mavic T519 rims and Panaracer Pasela 700 x 35c tires. I'm planning a trip on the kinds of surfaces you find on the C and O Canal Path (dirt and loose gravel). The 35's I have on the bike now sometimes wash out a bit on the looser gravel surfaces. Does anyone here have any experience with the maximum size tire that a Trek 520 can accept? Will a 29" tire fit on the Mavic rims that I'm using? Can anyone recommend a tire? Thanks!