I did the 104 mile/blue route yesterday with 40mm Ramblers. I would not have wanted to be on a narrower tire. We still hit 42mph downhill and did 24mph in a pace line on pavement, but the few miles of single track and the last gravel section would have been tough on narrower tires, and there were plenty of 35 mph downhill gravel sections that a narrower tire would have been sketchy. But, I didn't win, so what do know. I averaged about 14.5mph and the pros averaged like 22. Unreal.