Gauging The Pressure
Let us take you on a journey. This journey starts where all good adventures do, at the beginning. That would be ground zero, or 0 psi to be exact. From here we will slowly build in psi all the way up to 30 plus. On this adventure we will make important stops to talk about certain psi ranges and how to run them, the pros and cons of that psi, what types of tires you can use, and the dangers to avoid. We talked with tire industry experts to get this dialed in but we also want to stress that every tire and motorcycle manufacturer has tire and tire pressure recommendations and those are the safest for you and your bike. Using a tire that isn’t designed for a particular bike or for a particular terrain should be done with extreme caution.
The only time you run zero psi is when you have a multi cell solid foam insert known as a mousse insert. These are sized to fit specific rim widths and tire sizes. The build characteristic of the mousse is designed to simulate a feel of 12-15 psi when new. Over time the product will breakdown and shrink due to use and heat causing the product to no longer fill the carcass cavity and keep the bead seated, rendering it unusable and needing replacement. During installation you should use supplied mousse gel (a silicone lubricant) to help reduce heat due to friction and assist with mounting, while using the tire fitted with mousse it is best to avoid high pressure washing at the bead seat as to not wash away the lubricant. The lifespan of the mousse product varies amongst users depending on service conditions and use exposure. The use of a mousse is desirable in extreme off-road conditions where a rider has the desire to finish the ride without risk of a puncture or failure. Professional MX guys run them outdoors to eliminate the variable of a flat costing a DNF; GNCC, National Enduro, Desert, Extreme off-road racers rely on them when pit distances do not allow for easy service.
Trials tires are the only off-road tires that are designed to run at such a low psi and that is only when they are properly fitted on tubeless trials type rims. The reason such a low psi can be accommodated is due to the build characteristic of the tire. Generally the trials tire consists of radial casing design and contains an interlinear in the casing which allows for tubeless application. The radial tubeless design incorporates a different style bead seat and softer sidewall construction. The low pressure allows for the flexibility to maximize the footprint and mold the tire to the riding surface. By design the speeds of trials are lower and this should be kept in mind when cross applying the tires for general off-road riding.
Ideally if you choose to run psi in this range at the minimum you should choose ultra-heavy duty type inner tubes (3mm – 4mm thick) you still run the risk of “pinch flats” from debris and square edge hits, but the thicker rubber tubes offers added protection. Another consideration would be choosing tires with added construction strength or additional carcass plies, generally noted with A/T (all terrain) Dessert or Rally markings. This is not a common pressure range and would most likely only be considered for Enduro Extreme & Super Enduro application. There are a variety of “Bead Lock” systems or products on the market which fall into this pressure range category (Tube Saddle, T Lock Concept, Tube Guard, Tubliss, etc.). All of these systems are in place of running the basic inner tube, but keep in mind that TT (tube type) off-road motorcycle tires are not intended to be used in a tubeless application. The air will not seal inside the tire and if a foreign object is introduced (a cut or puncture) the tire will be rendered out of service.
Now we are entering into the realm of motocross and off-road riding. According to the design of these discipline specific tires, in general, this is the operating range sweet spot. Every rider will have a preference or comfort level which they prefer, a balance or risk (failure) vs reward (traction) within this range. In general a tire that is designed for Mid-Soft soil application will have wide spacing of blocks (tread) combined with a pliable casing and is meant to dig into the soil. This would require a psi towards the upper end of this range. Unless the rider is trying to cross applicate its use and then they would consider the lower end of the PSI range to maximize plant and footprint. Likewise a tire that is designed for Mid-Hard soil application will have close block spacing to maximize footprint and a more rigid casing requiring upper PSI range for stability of the added grip. When cross application of the Mid-Hard pattern tire for use in groomed, soft or muddy soil, one would consider the lower end of the PSI range to optimize casing movement with added flex to help clean the blocks and follow the ground.
This is the ideal pressure range for Enduro application when using F.I.M. and DOT approved knobby tires in an off-road primary application. When using knobby style pattern tires that may see some sustained speed runs or pavement riding, the concern of temperature build up causes one to avoid running low pressures. Additionally this discipline generally sees a wide variety of terrain and hazards suggesting that to finish the ride (by avoiding pinch flats) the added psi is warranted.
This PSI range is suggested for dual-sport 50/50 and 80/20 style riding. Generally this application is reserved for a purpose specific type machine and one should always refer to the manufactures suggested psi rating, as weights and loads can vary greatly within this category.
For bigger enduro and on/off road dual sport bikes, bikes with a lot of luggage, and/or adventure bikes, you start looking at the 30+ psi range. This is known as the 90/10 category and generally limits the off-road riding to fire roads and gravel trails. Again it is always best to refer the machines manufacture suggested inflation pressures and tire recommendations by unit. Paying critical attention to if TT (tube type) or TL (tubeless) type tires are necessary due to wheel sizes and rim styles. With the weights and loads of this machine category it is critical not to use too low psi when on-road speeds are sustained as the results could be seen in a drastic reduction of tire life and possible failure.