Only a tricycle can backpedle.
Or a unicycle.
We need a photoshop of Kerry and Obama
both trying to ride the same unicycle.
“Forward! Back up! Forward! Go Back!
And it’s pretty hard when you only turn to the left.
I prefer to say “back-paddle” — as in furiously paddling backward to avoid the rapids ahead. (Which seems an apt metaphor for Kerry, at almost any time.) Boats, canoes and paddles have been around since before recorded history, while bicycles have been around less than two centuries. It seems very likely that someone used the “back-paddle” metaphor long before anyone mentioned backpedaling. Plus, as you point out, you can’t peddle backwards on a bicycle. You can back-peddle a bicycle with coaster brakes — but, that only stops you.