they work just like your bike works as your rideing it . the spinning of your wheels keeps you up right when your rideing you bike so this spins your front and back wheel creating the same effect only you dont move lol. they do work i guy i work with has one for his sun.

 sorry if im just being stupid, but would a DH bike work on it if it had a street/slick back tire on?

 Yes, they are really great, more realistic then a trainer!

 HOLY SHIT
ITS LIKE A DYNO FOR YOUR BIKE

 Does this actually work?

 how does it stand up?