Those Sonoma County hills are pretty special. At the Terrible Two double century yesterday, two guys on a beautiful Ibis tandem (equipped with rim brakes only) crashed on the Geysers descent. The explanation I heard was that they cooked their rims and blew a tire off. Three other tandems completed the ride no problem, but it does underscore the fact that if you're going to be riding in that kind of terrain you should pick (and use) your brakes very carefully.