Fisher: Summer heat means 'road gator' season

The summer driving season will soon be upon us, but what will it be like this year?

Last year, courtesy of the pandemic, it was almost non-existent. Most people stayed locked in at home afraid to venture out. The highways were almost empty at any time of day.

This year there is hope that, as people continue to get vaccinated into the spring and summer, the Centers for Disease Control and Prevention will relax some of its guidelines and restrictions and a more "normal" summer can be enjoyed by at least those who are vaccinated.

It is expected that outdoor gatherings will increase as a safe way for individuals to get together. So, for the first time in ages, we can likely have that barbecue with friends.

Outdoor dining and drinking with appropriate spacing and physical barriers also likely will be a summer staple for many throughout the country and beaches, where people can remain fairly spread out, will be a relatively safe way to enjoy the warm weather, too.

This is good because according to weather experts, this summer is going to be hotter than usual. June through August is expected to be hotter than average from the West Coast to the Mississippi Valley and western Great Lakes.

The northern and central Rockies into the northern and central Plains are expected to be in for a really hot summer while the East and Southeast are expected to be near or slightly warmer than average this summer.

So what does this mean for the summer driving season this year?

With the hot weather and pent-up need to get the heck out of the house, people are going to go somewhere. And with the economy heating up too, truck traffic is expected to increase as well. I'd say the highways are going to be bustling again.

And what does that mean for tires? Heat is a tire's worst enemy when it comes to removal miles, irregular wear and service life.

With hotter ambient temperatures expected, I'm sure there will be a rise in the "road gator" birth rate as well.

Road gators are those long strips of tread rubber and belt package that are thrown off a tire that is run flat or underinflated.

Excessive heat is generated by the increased deflection of an underinflated tire's sidewall. The lower the inflation pressure, the more a tire will deform or flex, which results in an increase in tire temperature.

This increased deflection and resulting high temperature causes the rubber compounds throughout the tire, but especially in the shoulder and bead area, to break down and fail. At continuous operation above 250°F, the rubber will begin to revert and cause the belt package to separate from the casing.

Naturally when the belts separate from the casing, the tread comes with it, and a road gator is born.

You may be wondering why you don't see as many road gators the rest of the year, while they seem to propagate like bunnies in the summer, even though you know tires are run underinflated year-round.

That's because summer elements, such as hot temperatures and blazing sunlight, affect tires. Tires absorb heat from the pavement.

When ambient temps get higher than 100°F, some road temperatures can reach almost 200°F. In addition, when a tire is exposed to direct sunlight, it naturally will absorb heat, too.

The hotter road temperatures make tread compounds "softer." This altered rubber state wears faster and acts as a magnet to nails and other road debris, leading to an increase in the incidence of punctures during the summer, too.

Heat also is 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.

A tire's contact patch can be up to 18% larger 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. These temperatures, combined with heavy loads and high speeds, exacerbate tire failures and our highways become the breeding ground for road gators in the hot months of the year.

So what can we do about it?

Well, if you are performing yard checks for any of your fleet accounts, you need to be much more vigilant this time of year. Each tire will require a thorough external examination 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 pounded through the tread and belt package and eventually cause a leak.

Checking tire pressures properly is vital. Whenever possible, check inflation pressure when the tires are cold or at ambient temperature.

This means tires that have not been run for at least three hours.

I know it's a pain to check the pressure in every tire, but if the equipment you are inspecting does not have a tire pressure monitoring system (TPMS) that you can access to get accurate pressure readings, you have to use a calibrated service gauge to check the pressure of each tire to find those that are underinflated.

Since the odds of finding underinflated tires increase in summer months, I guarantee you will find more tires to be serviced this way than just bump-checking them.

If the cold inflation pressure is greater than 80% of the fleet's target pressure, you can add or bleed pressure in the tire as necessary to meet the target inflation pressure.

If the inflation pressure is 80% or less of the target pressure, the tire must be considered flat and should be deflated, removed from the vehicle, demounted and inspected for punctures or other damage.

Otherwise, if the tire is just aired up, the leaking valve stem or puncture will continue to lose air and eventually fail the tire.

Keep in mind that reinflating a tire/wheel assembly that has been run flat or underinflated can result in an explosive zipper rupture, which will ruin your day.

If the tires are hot when you check them, a regular tire gauge can't determine the cold inflation pressure since tire pressures change with increased temperature. There is about a 2 psi increase for every 10°F increase in tire temperature.

For example, a tire inflated to 100 psi at 70°F will have a pressure of 104 psi at 90°F and 106 psi at 100°F simply due to the increase in ambient temperature.

When you add in pressure increases due to operating heat, it is normal for tire pressure to increase as much as 20 psi when trucks and buses are running, so expect the pressure readings to be higher than the target pressure.

Therefore, if pressure must be measured when tires are hot, look for consistency between tire pressure measurements.

Both steer tires should read about the same, all the drive tires should measure about the same and all the trailer tires should be about the same.

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, the tire pressures are acceptable. In some cases the actual hot inflation pressure could be higher than the maximum inflation pressure on the sidewall.

This is not a safety issue as tires are designed to withstand this normal pressure buildup.

The maximum inflation pressure is for cold tires only. Never bleed hot tires to reduce inflation pressure unless directed to by a TPMS that calculates cold-inflation pressure.

If the actual hot pressures measured across the same axle differ by more than 20% from each other, the low pressure tire(s) most likely have an air loss problem and should be treated as flat. If the difference is less than 20%, the low-pressure tires can be inflated to match the other tires' pressures.

Before re-inflating a tire, though, determine if there is a problem with the tire, such as a puncture or leaking valve stem.

Make the proper repair and then inflate the tire to the target pressure. Otherwise, the tire just will continue to leak and fail another day.

If one or two tires have pressures much greater than the others, the cause may be overload due to unbalanced loading or heat resulting from unbalanced brakes or direct exposure to sunlight. (The sun beating down on one side of a parked vehicle can cause a 10-15 psi increase in tire pressure.)

Finally, don't forget to make sure metal valve caps are installed.

Properly inspecting and maintaining your fleet accounts' tires is one of the best ways to ensure road gators are prevented and keep the roadways safe from these predators. Hopefully the only place you'll see a gator this summer is at the zoo.

Peggy can be reached via e-mail at [email protected]. Her previous columns are available at www.tirebusiness.com.