Chains,as with gas mileage claims, your mileage may vary. My last chain(a high quality replacement) lasted only 1500 miles, even with regular cleaning and lubing. Heavily loaded panniers, stop and go traffic, and road grit took it's toll on the chain, yet my summer bike, which is lighter, with out panniers(backpack only) has several hundred more mile on it's chain, but still has almost "like new" stretch readings. Also, my winter commuter just recently broke a rear axle, making me realize that I need to upgrade to a better hub/wheel assembly, but for a few hundred dollars more, I can get a bike that will better meet my needs, and then I can put my current commuter into backup/recreational status.