Why is it necessary to check your tire pressure frequently over the summer? Heat is one of main reasons when it comes to changes in tire pressure, therefore the rider must be alert and on top of constant pressure and temperature changes. If not careful around tire pressure, the motorcycle’s behavior could change and become a safety concern.
These changes of pressure are based on principles of physics. It is important to understand that pressure can be measured using different units of measure such as BAR or PSI and the increase or decrease of air volume. Pounds per square inch (PSI) is the primary unit of measurement in North America.
The air inside the tire is trapped, this way we can increase or decrease pressure as the tire expands and contracts. As pressure rises, particles of air strike against the inside tire walls as they have less space by the fact that they are being pushed and tire swelling is occurring. When temperature changes this process becomes more complex, as air is a gas that expands with hot and contracts with cold temperatures. Ultimately, there are physical laws that explain the behavior of air pressure and temperature in the tires, but we won’t go more into depth here, just the necessary to understand the concept. If interested in further theory details, research Boyle’s Law, Gay-Lussac Law or the Archimedes.
The rule of thumb is that for every 5° temperature difference, tire pressure will become around 2% higher or 2% lower depending on temperature. In summer, especially in mountain areas, very high temperatures can be reached during the day while they can be very low at night, with a difference of up to 20°, this means tire pressure can vary up to 8%. With so much temperature difference over a day it is important to check tire pressures at the beginning and end of the day. Always try to check tire pressure under the shade or away from sunlight if possible, as the sun’s rays can alter values. Apart from ambient temperature, heat by friction should also be accounted for altering tire pressure. Friction transmits heat to the inside of the tire, increasing in many occasions by 2.9 to 5.8 psi. If going to the track, check tire pressure after a few laps and try to return it to the one initially marked by the manufacturer.
Normally with tire warmers or not, pressure is set lower than usual-around 2.8 psi– as it will go up on track. When tire warmers are used, it is recommended to go around the track twice and then come into the pits to check for tire pressure by finding out the difference from the manufacturer’s recommended. If pressure is not the same, adjustments should be made for an exact match. Without tire warmers, the procedure remains the same, but includes four warm-up laps instead of two.
Even though a two to eight percent may not sound like much on paper, remember that manufacturers have advised a specific pressure number in order to extract the maximum performance of the tire in every aspect, so it is crucial in real life situations. These small deviations influence directly with the bike’s behavior. If pressure is higher than suggested, handling, grip levels, leaning ability and tire wear can be negatively affected. Excessive rear wheel spin under acceleration, ultra-sensitive lateral movements and abrupt turn-in can be some expected characteristics on an over inflated tire.
Another important aspect when dealing with a tire’s maintenance and pressure is looking after the tire’s valve, cap and leaks -no point on checking tire pressure if a leak is present-. When consistently checking for tire pressure, if the tire has pressure variables outside ambient temperature (2%), is possible the tire is losing pressure due to a defective valve or a puncture. If this is the case, we recommend going to a tire specialist near you to find out if the tire can be repaired or replaced.
Don’t forget to check your tires!
Until next week!