These temperatures, combined with heavy loads and high speeds, exacerbate tire failures.
Heat is also created by the friction between the tread and the pavement. When a tire runs underinflated, the tire footprint length becomes elongated at low tire pressures, resulting in more rubber on the road, which generates more heat than when properly inflated.
In fact there is 18-percent more rubber on the road when a tire has only 70 psi versus 100 psi, a pressure that most fleets target.
Tires running at 75 mph versus 55 mph will generate extra heat, too.
The hotter road temperatures also make tread compounds "softer."
This altered rubber state wears faster and acts as a magnet to nails and other road debris, which is why punctures tend to increase during the summer.
As a result of all of these factors, our nation's highways become the breeding ground for road gators in the hot months of the year.
So what does this mean to you? Well, if you are checking tires for your fleet accounts, you need to be much more vigilant this time of year.
Inspect tires more closely to find puncturing objects that could cause leaks as well as cuts and snags. Remove nails, screws and other road hazards from treads even if they are not puncturing the casing.
As tires wear, these objects will be pushed in deeper and eventually cause a leak.
I know it's more time-consuming, but unless the fleet can provide you with inflation pressures supplied by its tire pressure monitoring system (TPMS), use a calibrated tire gauge to check inflation pressures.
The odds of finding underinflated tires goes up in the summer months, and your gauge or a TPMS are the only way to identify them. If you use a gauge, I guarantee you'll increase the number of tires you find that require service.
However, the trick to using a tire gauge is to understand the effect that temperature has on inflation pressure.
For years you've heard that you should only check tire pressures when the tires are "cold," which means that they have had a chance to cool down after running on the road. (This usually takes about three hours for commercial truck tires.)
This is still true. The inflation pressure inside a tire rises as heat is generated during normal operation.
Test have shown that the air inside an 11R22.5 tire can reach 160 degrees F or more in over-the-road operations, depending on inflation pressure, road temperature, ambient air temperature, altitude and other factors.
So if the ambient temperature was 70 degrees F when the tire originally was inflated, the pressure could rise 10-20 percent just from normal operation.
It is not unusual for the difference between the cold inflation pressure and the hot pressure to be as much as 15-20 psi.
In addition, great changes in ambient temperature also can seriously affect inflation pressure.
The rule of thumb that is easy to remember is that inflation pressure will change 2 psi for every 10 degrees F change in ambient temperature.
That means if you are in Tucson, Ariz., now, and the ambient temperature is 120 degrees F, a tire's inflation pressure would increase 10 psi from its original pressure of 100 psi that was set when the temperature was 70 degrees F. (You can calculate this using this equation: 120 degrees -70 degrees/10 X 2 psi.)
Conversely, if it's the middle of winter, and someone hated you enough to have you check tire pressures in Duluth, Minn., when the temperature is 0 degrees F, there will be a drop in inflation pressure of approximately 14 psi (70 degrees minus 0 degrees/10 x 2 psi) and instead of having 100 psi, the tire would have 86 psi.
Besides ambient temperature, you also should consider sun exposure.
Tire inflation pressure also can increase if the tire and wheel assembly are just exposed to the sun on a hot day.
I've seen as much as a 9 psi increase in a tire that was inflated to 100 psi earlier in the day from just sitting in the sun. So keep that in mind, too.
Basically, if the fleet doesn't use a TPMS that can convert hot inflation pressures to cold, you are taking a guess at what the pressures are in tires.
So never bleed air from hot tires and be sure when adjusting inflation pressure, that the vehicle has been parked for at least three hours.
If the actual cold pressure measured is greater than 80 percent of the target pressure, adjust the pressure in the tire on the vehicle to meet the target inflation pressure.
If the actual cold inflation pressure measured is 80 percent or less of the target pressure, consider the tire to be flat and remove it so that it can be inspected properly.
There is usually a reason that causes tires to have a 20-percent drop in inflation pressure. This is also an OSHA requirement for servicing truck tires, wheels and rims.
If you have to check tires when they are hot, look for consistency.
Both steer tires should read about the same; all drive tires should be about the same, as should all trailer tires. If the actual hot pressures measured across the same axle are within 5 psi of each other, and they are all higher than the target pressure, tire pressures in these tires are probably acceptable.
If the measured pressures differ by more than 20 percent from each other, the low pressure tires may have an inflation problem and should be treated as flat.
Otherwise the tires with lower pressures can be inflated to match the other pressures.
In some cases the actual hot inflation pressure may exceed the maximum inflation pressure marked on the tire sidewall.
This is not a safety concern. Both tires and wheels are designed to withstand this normal pressure buildup that results from operational heat.
It's good if inflation pressures can be checked twice as often in the summer as in the winter months due to the increase in punctures and increased vulnerability tires have to underinflation and damage from road and internal tire heat.
Quickly addressing punctures and other low-pressure conditions is the only way to make road gators an endangered species.