In any case. The tyre holder holds the tyre on the rim and prevents the tyre from "wandering" on the rim. Especially when using Mousse, the tyre holder becomes even more important. Since the valve hole in the rim is not used when using Mousse, you can also mount a second tyre holder depending on the cubic class. If you do not install a second tyre holder, you should make sure that you close the hole for the valve in the rim in any case dust-tight (with the rim tape, or a layer of "Gaffer Tape"), so that you exclude the penetration of dirt and foreign bodies over this opening and a leakage of the gel is prevented.