I'm riding a fixed-gear century this weekend along with my roadie friends.

Even though I've ridden a few road-bike centuries and one double century (the Seattle to Portland Classic two weeks ago in 10 hours and 30 minutes) I am nervous:

I did a 35 very hilly miles yesterday on the fixed and it left me sore. Fixed riding is definitely harder than road riding, all things being equal.

How many of you ride centuries on your fixed?