They are called mousse but they are not desserts. These foam core inserts for tires are currently used on Enduro and motocross bikes, but only at a competitive level
Tar and dirt, mud and sand, ice and snow, as well as hot and cold, wet and dry, are the main environmental conditions that affect that fragile balance that determines the grip of our vehicle. And much of this alchemy depends on the internal pressure of the tire, the force contrasting the loads and traction to which a tire is subjected.
To cope with changing environmental conditions, tire specialists have been studying, for over a century now, tire compounds, treads and casings with versatile characteristics, trying to stretch as far as possible a blanket that looks always too short. A balance largely determined by what is inside a tire that supports the tire preventing its excessive deformation that could be caused by a number of external forces.
Cars, motorcycles, quads and trucks ... all vehicles must face an inexorable fate: when tires are inflated with correct air pressure, everything they will meet on the road - absolutely everything - will try to release that air trapped between the tire and the rim. A partial remedy exists, at least in certain conditions: the simplest solution has existed for at least thirty years, and is represented by the mousse, a foam insert which replaces the inner tube.
Donuts for all!
Created by Michelin’s development center, always looking for ways to cope with the problem of tire deflation, both in civil, industrial and military purpose, the mousse made its appearance in the mid-80s, in the wake of problems encountered during major off-road competitions. Starting with motorcycles, the Bib-Mousse (named after Bibendum, the French manufacturer’s mascot) was subjected to extensive on-field testing, then transferred to the automotive industry, equipping cars competing in some of the most demanding races in the World Rally Championship.
The successful experimental participation of Jean Ragnotti’s Renault 11 Turbo, equipped with ATS system (Appui Temporaire Souple – flexible temporary support), during the Greek Acropolis Rally in 1987, where tire resistance has always been one of the determining factors of the race, earned Michelin the Technological Innovation Award, attracting the attention of many sports teams. That is until 2008, when the Federation Internationale de l'Automobile (FIA) forbade their use in championship competitions, decreeing after twenty years the gradual abandonment of their development. At least for four wheelers.
In view of the facts, after Michelin, other manufacturers too started looking at mousse inserts, almost exclusively for use on motorcycles, focusing their attention on issues raised during enduro and rally marathon competitions, where tires are put to the test in extreme conditions. Nowadays we can count on many specialized brands: off-road enthusiasts can rely on a number of premium brands such as Michelin, Dunlop and Pirelli flanked by less known, but no less valuable, brands like Mefo Mousse, and three Italian brands such as Goldentyre, Technomousse and WDS Equipment ( a late comer yet much appreciated among bikers ).
The competition in this niche sector is entrusted to very personal interpretations. Starting from the basic formula, namely the compound of the mousse, which must guarantee the required stability and durability needed in particularly severe use.
The foam can substantially be divided in two main families: those based on polyurethane or butyl rubber (the same used for inner tubes). But every manufacturer is extremely jealous about the fillers used during the production process, instrumental in shaping the final product by molding and vulcanizing or by extrusion, previously shaped (with sausages cut to size), or by injecting directly into the mold the liquid emulsion. The formation of cells inside the compound seals air/gas within a myriad of these small cells, which simulate the pneumatic action originally exercised by compressed air only, providing a support similar to that of a tire inflated between 0.9 and 1.2 bar.
Directions for use
Notwithstanding that their use is not permitted on public roads, the use of foam inserts finds its natural use in off-road motorcycle racing as in motor-rally, enduro, rally-raids and at times in motocross, as well as for recreational rides on private land.
Fitting these inserts can be quite a challenge, as well as reducing friction between rim and casing, that is why abundant silicone grease is used, often supplied by the manufacturers themselves. Before opening the throttle a short break-in is recommended, essential to bring the tires to the correct temperature favoring the expansion and complete adhesion to the inner walls to prevent unbalancing or internal rotations. Furthermore small gas cells expand (someone guarantees on the presence of nitrogen in them), increasing the elasticity and filling action of the material.
Beware though, their lifespan is very limited: rather than mileage, time should be considered; you can hardly count on a single tire mousse lasting through a few days of competition, and definitely not later than 6 months from its first use, even if used occasionally. Even their storage is limited in time, since they must be used within 18/24 months of their production before the chemical decay of this unstable material begins.
Offered in two or three configurations - cross, enduro and desert – suitable to equip the best off-road motorcycles, tire foam inserts show different characteristics according to the size of their section, ensuring a flexible support. It is possible, furthermore, to manually shape the foam insert carving some grooves or through holes to reduce its resistance, just like riding with slightly deflated tires.
There is no lack of hybrid solutions as well, once a part of Dunlop’s offer and now present only in the German MEFO Mousse catalog, where the foam ring is cut in half and "stuffed" with a smaller tube (such as those on mountain bikes) which further sustains the foam. A trick used by some tire mousse specialists on either new or nearly exhausted foam inserts (and not meant for this solution) to extend their life, or making it possible to regulate the tire changing the pressure in the small tube placed inside them.
Building on the consensus reached by the run-flat performance offered by tire mousse inserts, recent alternatives have appeared on the scene, such as TireBalls, small inflatable rubber balls, strung in sequence between the rim and the tire instead of an inner tube, guaranteeing internal pressure also in the event of a puncture. But that's another story which deserves specific attention.