Friction drives, dry roads and wet ones

Rubbee, from Lithuania, is the friction drive on this catalogue: a powered roller against the rear tyre, street versions in the 250 W class, and the option to lift it off. Other rollers exist. The physics does not change with the logo.

The tyre is the clutch

The roller needs a square contact and a tyre that is not glazed, cut or running soft. Pressure is part of the tune. A knobbly tyre can walk the roller sideways. A bald slick in the rain can spin the roller without moving the bike. Neither is fixed by turning the assist up.

• Look at the stay or the dropout the clamp uses. It has to be a structural tube.
• Check the spring still has travel after the bracket is tight.
• Listen for a rub at full suspension travel, if the bike has any.
• Plan on inspecting the tread where the roller runs.
• The pack, if it is in the roller body, is small. Read the watt-hours before you plan a long ride.

Friction drives are specialist in the fit engine because the mount is the whole product. A universal claim is a sentence, not a measurement.