Colorado's bike to work day is later in the year. The weather in May is just too unpredictable (she says, looking out the window and seeing the rain turn to big white fluffy things).

*checks*
ahah.

http://www.dot.state.co.us/BikePed/COBikeMo.htm

COLORADO BIKE MONTH
June is Bike Month

BIKE TO WORK DAY
The Fourth Wednesday of every June

So, is it May for the rest of the country?