No one is discussing the diameter of the drum on rollers. Krietler rollers offer a variety of diameters - the smaller diameter will work you harder. I have the large diameter Krietler rollers with the resistance fan unit. It has three pulley settings and you can also open or close the air intake which contributes to the resistance provided. The fan also blows up at you offering a cooling breeze. Open the air intake flap all of the way and put the drive belt on the smallest pulley and you will push very hard to maintain 23 mph.

I learned to ride these in a door way but now simply place them about one foot away from a flat wall surface. They are easy to ride and much more fun than a fixed mag or fluid trainer.