Thanks, that's great info. I am a little worried about the weight of Marathon Plus, but it's an old, steel bike, and I'm switching from steel rims to an alloy, so I'm thinking I will still come out ahead. Plus between the axle-mounted fenders and front rack and the internal hub, I'm willing to take on a heavier tire if it means means not having to disconnect all that crap to change a tire. Knowing that I could go as low as 21 (or 17) mm really opens up my rim options. Thanks again.