Tyre mousse (bib mousse)

A mousse is a ring of closed-cell foam fitted inside an off-road tyre instead of an inner tube. Because there is no air to lose, the tyre cannot go flat from thorns, nails or pinch flats. Michelin's Bib-Mousse was the original; many brands now make them. They are standard in enduro, rally and hard enduro.

Fitting is tight and needs plenty of special lubricant, good tyre levers or a mousse fitting tool. The ride feels like a tyre at roughly 0.9 bar when new; as the foam ages and shrinks it becomes softer.

Heat is the enemy: long fast road sections or sand at high speed can cook a mousse. Use the recommended gel, check the mousse when changing tyres and replace it when it has lost its shape or shows cracks.