I found this awesome game called Freerider where you make your own tracks for a BMX bike and other vehicles, pretty cool has its own forum where users share tracks..
FreeRider 2:
OneMoreLevel.com - Free Rider 2
FreeRider 2 Track Forums:
Free Rider 2 - OneMorelevel.com Forums
One of my FreeRider 2 tracks:
MTB/BMX 'Loops' track, Sub Smooth, VERY Smooth if you play it right.. =) - OneMorelevel.com Forums
Enjoy! if you make a track post it here!!
Hellson