Help your tires stay cool…even when they’re hot

Tires become hot during long-distance and high-speed trips, and the heat increases tire pressure. Would it make sense to reduce the pressure slightly before a long/fast trip, so that the extra heat would just bring them back to the recommended pressure level? Pima Pumsi

No. Certainly and absolutely no. Lower pressure can partially and briefly “compensate” for thermal expansion, but it will also generate even more heat! Even to the point of causing a blowout if the tire casing is weak.

Sustained high-speed cruising generates a lot of heat, in five main ways.

The first is the heat of the roadway, which can easily reach 50 degrees Celsius or more on a sunny day. It’s too hot to walk barefoot.

Second, there is always some heat-generating friction between the tire tread and the road surface; even at constant speed in a straight line, the wheels are still “driven” (not just rolling) with enough force to propel a load weighing more than a ton. When the car brakes, accelerates or corners, friction increases – sometimes significantly.

Third, the tire wall constantly flexes with each rotation and causes friction between the particles of the carcass material itself. The more the housing flexes (in degree and/or frequency), the more heat is generated.

At 100 km/h – even on a smooth, straight and flat road – each part of the carcass flexes at least 10 times… per second! Add to that braking, acceleration, cornering and perhaps a rough surface and the degree of flexion also increases.

Fourth, the tread wiggles, twists and rubs, even slightly, all the time. When changing pace or direction, this action can be much more than light – enough to scrub the tread as if it were being sanded.

This effect can also be exacerbated in the event of faulty caster, camber or wheel alignment angle or brake adjustment… and even faulty shock absorbers which allow the wheel to bounce.

Fifth, brakes generate a huge amount of heat (braking from 100 km/h to zero generates enough heat to boil a liter of water) and under severe usage conditions they can literally get hot.

By conduction and radiation, this can make the rim (which is in permanent contact with the air inside the tire) too hot to the touch.

Far from lowering the pressure at the start of a long and fast journey, you should in fact take particular care to ensure that the pressures are “at least” as high as the recommended level, and even consider increasing it (!)… d between 5. and 10 percent.

This gives the tire a greater volume of air to absorb and dissipate heat and reduces the amount of flex with each rotation. The tire will still become hot, even hot, and the pressure will still increase, but to a lesser extent than if it was underinflated to begin with.

You can prove it to yourself. Increase the pressure on three tires by a few psi and reduce the pressure on the fourth by a similar amount.

Drive 20 km quickly, then feel the tire temperature. The softer starting tire will be noticeably warmer than the other three. And don’t forget that heat also softens the tread and makes it wear faster.

During a brief stop during a long journey, it is a good “early warning” system to feel the temperature of all the tires and their rims.

That they’re all a little warm is no cause for concern; if one is much hotter than the others, either the pressure in that tire is too low, or the brakes may seize that hub slightly.

Another indicator to watch out for (over a longer period of time) is uneven tire wear. Depending on the pattern of wear, this may indicate a constant pressure error or misalignment/caster/camber adjustment or improper brake adjustment.

Tires are an excellent diagnostic tool; the checks are quick, the symptoms are clear and finding the fault is a double advantage because repairing is always cheaper (and safer) than suffering the consequences of negligence.