I agree with those who pointed out that wind speed isn't as much of a factor as the other characteristics of the wind. Buffetting gusts are much more difficult to ride than a steady wind. I've been out a few times where it was like trying to ride through a pillow fight with short blasts of wind of varying intensity and quickly changing wind direction. I'll take a steady 25-30 mph wind over that any day. I also agree with statements that it is "too much" wind when it becomes dangerous to the rider who can no longer adequately control his/her bike.