I have friends that goto Track Days frequently on their motorcycles. If the first session is very cold they use their old tires and don't ride real hard because they don't want to shear their good newer track tires.
After the track warms up they will put on their newer tires and ride much harder. They discuss cold tire shearing as the reason they don't use their newer tires during this first morning session when the track is cold and dirty.
What is cold tire shearing?
Cold tire shearing occurs when the temperature of the carcass of the tire is cooler and the surface temperature of the tread get's very hot.
The surface of the tire begins to tear off or shear. You hear a lot about this in various race series for cars and motorcycles where they don't allow tire warmers or the ambient temperature is very low for a race or practice session.
Conditions that can contribute to this effect
Over inflated tire when it's cold. We would start our tire pressure in the morning at about 28 to 35 pounds, after coming in we would have the psi raise up to as high as 38 to 40 psi. If you start at the OEM recommended or the stamped maximum on the tire you could go into practice at 42 psi and come in at 46 psi plus. Higher pressures can be dangerous though as you will have less mechanical grip (friction).
Riding too hard on the cold carcass rather than just running the tire in for a lap or two
Poor weight distribution. Reduced rake in the front by raising the forks in the triple clamps too aggressively can load up the front end too much. Lower the forks in the triple clamps too aggressively can put too much weight on the rear.
Dampening and springs. Setting compression dampening too high or cranking the springs (front or rear) can also contribute to this condition.
The core issue frequently over inflation in combination with cold tires and cold track. Your friends caution in the morning is well served. Go out on old tires, clean the track and do laps with the rest of the field, take it easy and ramp into the fresh tires as the sun begins to heat up the track.
The tires will look like this
