Credit: Intercomp, tire durometer gauge
Trials Tire Pressure
I'll mention this here because if you are new to trials, the very low inflation pressures may come as a surprise. A rider just starting out with our trials club asked me to have a go on his bike and report what the heck was wrong with it. It was basically unrideable - not hooking up anywhere. I asked him how much air was in the tires. Same as his sportbike, 30 psi. Well, 4 psi in the rear is fairly standard. The front would be slightly higher, maybe 5 psi.
The pressure gauge can make a big difference too. The nice digital one I have for normal use is inaccurate at those low pressures. I bought a special Moroso analog gauge used for drag racing slicks. It tops out at 15 psi. Once you get accustomed to those pressures, you can get a pretty good idea of the pressure just by pressing on the tread and seeing how easily it deforms.
When I started in trials I did not realize just how important the tires are. Although having an excellent front tire may be nice, it's really much more important to have an excellent rear tire. It's not uncommon to “flip” the rear tire halfway through its useful life to again have sharp blocks on the leading edge of the tread.
At low speeds (say, less than 30 mph) the aerodynamic resistance of the vehicle is usually much smaller than its rolling resistance. Thus, when attempting to optimize the range of an off-road EV, tire pressure is worth considering. Although not specific to trials tires, the following quote from Wong's Theory of Ground Vehicles is applicable.
“Inflation pressure affects the flexibility of the tire. Depending on the deformability of the ground, the inflation pressure affects the rolling resistance in different manners. On hard surfaces, the rolling resistance decreases slightly with the increase of inflation pressure. On deformable surfaces, such as sand, high inflation pressure results in increased ground penetration work and therefore higher rolling resistance. Conversely lower inflation pressure, while decreasing ground penetration, increases the deflection of the tire and hence hysteresis losses. Therefore, an optimum inflation pressure exists for a particular surface condition.”
The coefficient of rolling resistance for sand can be 2 - 3 times that of medium-hard soil. Even with very low inflation pressures, concrete offers much lower rolling resistance than soil or sand. You probably already have a feeling for this just from pushing a motorcycle around on various surfaces.