Just messin around with Mixerman3D's models
From left to right it is: Barey doing a handplant, Kleiner doing a kickflip, and Grigori doing a stall on his pegs.
Facepunchforums.com, look in model releases and find mixerman3d's models, it comes with a stiff bike and a bike where the tires pedals and handbars can all move, plus 4 kinds of ramps.
just extract everything from the mixerman3d model pack thing you downloaded to the sourcemod/gmod/mod folder and then it should all be good. If it still doesn't work, go to Mod manager in the gmod main menu and enable it.