The "spinsters" may have a young, charasmatic instructor shouting positive encouragement at them...but you have Zeus, the god of weather, blustering at full fury in your face, daring and defying you to proceed against his winter wishes, throwing down endless frozen roadblocks, continually ratcheting up the degree of difficulty while dropping the degree of temperature, as the incessant howling hounds of traffic surround you in a constant dark din of danger and peril. It's a death-defying, blood-warming, life-affirming, breath-stealing experience you won't get on a trainer, no matter how lovely the leotard.

On the other hand, I don't have the personal discipline to spin. I bike to work and back because once I start the ride I can't stop 'til I get to work or home.