the roller has 3 cylinders on which the bike "rides" on, so front and back wheels are turning. think treadmill for bikes. my husband used it in a doorway just in case he tipped over (which he did many many times). it will definitely take some practice until he has the bike going perfectly straight, as it does take balance.

the trainer has the back wheel elevatated and the resistance is set on the back wheel. the rollers don't have adjustable resistance, you use your gears.

some people love the rollers but you have to pay attention so you don't fall off! a friend of mine mentioned how he was watching a TdeF video and just about flew off because of the camera angle in on of the sharp turns (ie he tried to turn too! )