My least favourite thing about riding is punctures, with border crossings taking a very close second. Both nuisances result in an unwelcome pause and wasted time, which I hate more than anything. Border crossings can theoretically be avoided, but punctured tubes are irregularly reoccurring annoyances for the fearless adventurist. With that in mind during the preparations for Prometheus 19, I decided to run the expedition on mousses.
Nobody uses mousses on expeditions
Mousses completely remove the risk of punctures, but also yield other benefits. They give constant amazing traction and a less bouncy feel compared to tubes. Another plus is that there is no need to carry tubes, tyre irons, a pump etc. in the tool kit, reducing weight significantly. However, there are drawbacks too, as mousses are expensive, and you’re stuck with a single pressure setting for every section of the route. Furthermore, mousses can fail without warning if run carelessly. Admittedly I was a little apprehensive to commit to the mousses, but the benefits seemed to outweigh the risks. Running an expedition on mousses was a learning experience and it did not go entirely smoothly.
Lubrication kills friction
The greatest enemy of mousses is friction, as it generates heat and abrasion, which both damage the mousse. Friction between the tyre and the mousse is generated by the plastic deformation of the tyre under the load of the bike and rider. To reduce friction, mousses are installed with a silicone based lubricant, but it does not last forever inside the tyre. You could just keep running the mousses and replace them with tubes when they fail, but that would be very expensive and require carrying everything necessary for riding with tubes. Since I usually gravitate towards a lighter gear configuration, I popped the mousses every 3 000 km or so, to inspect and lube them. My 21” Michelin BIB front mousse now has 10 000 km on it after three lubes from installation. In all service breaks the mousses were still in decent shape in terms of lubrication, so I will stick to the 3 000 km lube interval in future expeditions.
Speed is heat
Riding speed is proportional to the thermal load induced by friction on the mousse. From the tyre’s perspective, it has a hot spot rotating around its outer sphere during riding. The faster the riding speed, the more passes around the tyre the hot spot makes per minute i.e. more speed equals more heat. The good thing is that on off road expeditions speed is usually pretty low, with the exception of transits on tarmac. To keep the thermal load manageable, we kept cruising speed on transit below 90 kmh (55 mph). During off road sections we were up to 140 kmh (85 mph), but as they were mostly short lived sections, they did not seem to have any effect on the mousses. I guess the greatest risk is high speed in high doses.
Light is right
As mentioned above, friction between tyre and the mousse is generated by the plastic deformation of the tyre under load. So obviously the higher the load, the more deformation and consequently more friction. The rally guys such as Lyndon Poskitt and Ionut Florea successfully run mousses on their 690/701 rally bikes, but I dare say that’s probably the heavier end of the scale of reasonable use. I have the feeling that mousses are mostly practical during off road expeditions on light single cylinder bikes. Frankly, I have zero experience in multi cylinder adventure bikes, but judging solely by their mass, I find it hard to see how a mousse would be able to provide adequate support under the load. If anyone has any experience in this, I’m all ears.
The perfect fit
A final consideration for the health of the mousse is correct tyre size. In the front I ran a Michelin M15 BIB Mousse for 21” 90/90 and 80/100 tyres. It was originally inside a 21” Michelin AC10 80/100, then a Michelin Starcross 80/100. The mousse was fine throughout the 10 000 km. In the rear I ran a Michelin M18 Enduro BIB Mousse for 18” 120/90 tyres, initially inside an 18” Michelin AC 10 120/90 and later inside a Metzeler Six Days Extreme 140/80. When we stopped to inspect and lube the mousses after 1300 km from the tyre change, the mousse had started to split on the inside ring. As the mousse had been in pristine condition just 1300 km earlier, and the damage was on the inside ring and not the side walls, I believe the damage was due to the lack of support from the side walls of the wider tyre I.e. it allowed for the mousse to be overly squashed vertically. The traction was amazing though. Either way, the damaged Michelin mousse was replaced by a Metzeler E-18H1 – Medium Enduro mousse for 18” 140/80 tyres. It was in pristine condition during inspection and lubing 3 000 km later and has now 4 300 km of use.
Changing mousses is a ten minute job if you have the right tools; a proper mousse changer and five good tyre levers. I have the Rabaconda “3-minute mousse changer” and KTM PowerParts tyre levers. To be honest, the Rabaconda for me was more of a “two hours of frustration, swearing and sweating bullets” mousse changer initially, but once the correct technique is dialed in, it can be done in three minutes. Either way, I can’t imagine trying to lube the mousses without tyre changer, so finding a workshop with the correct tools is essential during expeditions.
The mousses were a big win, and I would not go back to tubes lightly. It can be argued that more time, and definitely money, go into dealing with the mousses, as opposed to fixing the odd punctured tube. But the fact is that expeditions are chaotic by nature, and any small amount of added control is welcome. Lubing a mousse inside a workshop is much preferable to fixing a flat in rain, while exhausted, hungry and cold. The battle will be there either way, but dictating the field is crucial.