Aluminum is a harsher ride. You will feel every bump in the road, more so than you would with steel. Over a long distance, the bumps and jolts from that harsher ride will add up. With a good steel bike, the steel will be a bit springy, and absorb some of the bumps and jolts. I'll never understand why Cannondale chose aluminum for a touring bike (I mean, sure, aluminum is light, but the harshness of the ride makes it an inferior material for long distance touring, in my opinion.).