For most of my riding I use old style toe clips and straps; so my feet
are attached to my pedals, but not really locked in. The straps are at
most moderately tight.
It turns out that for me, that's sufficient for jumping. I learned the
skill in the 1970s, partly because one route to work had some nasty
railroad tracks. It's done by pushing my torso suddenly upward with both
arms and legs (ideally starting from a crouched position) then pulling
the bike upward with both arms and legs. But take care to keep the
steering pointed straight! You want a straight landing.
I haven't tried to jump a railroad track for a long time, but for years
it was a regular event on my ride to and from work. I did it even with a
briefcase on the rear carrier.
It's possible without toe clips or clipless pedals. I can do it a bit,
but not as well as with toe clips; and I'd bet YouTube has instructions.
I _think_ the physics goes like this: You pop your torso up, then pull
up to lift just the front wheel. This raises the bike center of mass.
Then while your body is still elevated, you quickly push down on the
bars as you contract your legs to take force off the pedals. The bike
rotates around its center of mass, so while the front wheel is dropping,
the rear wheel is rising.
At least that's how it feels to me. I think the same physics applies,
more or less, to jumping a skateboard.
Maybe someone will dig through YouTube and find instructions.
--
- Frank Krygowski