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.