Tuesday July 14th, AM. Tried new dirt for the first time right between Whipple and the "bridge to nowhere". Then right before the bike path along the 84, a large piece of metal ripped the rear tire's sidewall. 1st epic commute flat! Sidewall punctures are the only weakness of the Conti Gatorskin + Mr. Tuffy's setup. Last time I hit a piece of metal it didn't get past Mr. Tuffy's and just pinged the frame on each revolution. Managed to get the tire to hold a new tube at a low pressure. Had been making great time until then, so after the setback took some leisure time to explore dirt by the dumbarton: rode underneath the bridge and tried all the dirt possible. Various cranes hauling dirt stopped my progress a few times (some kind of wetlands restoration project). Grabbed a new gatorskin at Chain Reaction Cycles in Los Altos.