I'd just like to add to the conversation that the front wheel on bikes act like they're "spinning". When they meet a wall or bump, the front wheel creates an upwards trust. That's how those verticle wallrides that seem to drag/pull the bike up work.
This also affects bumps. I've had a few instances while stunting where the front wheel hits the bump first, pulls the bike onto the bump at a faster speed than I was originally going and then the bike bumps using the undercarriage.