Ok, so I have never had to purchase tires before as I have always 'borrowed' bikes in the past. I was on the dunlop website and it seems like a 756 front and 739 rear would be the best combination given that some of what is ride is hardpack and other stuff is loose. My question comes to tire sizes. It looks like 110/100-18 is the only size close to the factory 120/80-18 size. Is this a good tire choice for the bike? The bike will see little to no pavement with these tires.