Since many buses have been sitting lately, this information may be of some interest.
There was a recent situation at the bus museum annex in Hershey, Pennsylvania where a bus had been sitting in the same position for a substantial time. When the museum people went to move it, they discovered that a front tire was flat. As it turned out, it was not a slow leak, but the tire had blown violently just sitting there. Since so many buses are sitting right now, we looked for an answer.
The following information comes from Marco Rabe, the head of research and development for truck tires in the Americas Region for Continental Tire.
If tires are parked in the same place for a length of time, environmental factors can affect the tire quality. Extreme temperatures, direct sunlight as well as chemical agents such as solvents, fuels, oils, hydro-carbons, paints, etc. can affect the health of the tire.
If vehicles need to be idled, the following steps can reduce a negative impact on tires.
- Inflate the tires to the maximum pressure (pressure on the tire sidewall). The pressure would need to be adjusted back to the recommended in-service levels before the vehicles could be driven again.
- If possible, ensure that the vehicles are moved from time to time to reduce local stress on the tires and avoid creating a flat spot.
- Cover the tires to avoid direct sunlight, while allowing for some ventilation to avoid high temperatures.
- Reduce the weight on the vehicles as much as possible.
- Avoid parking vehicles on black asphalt or other heat absorbent surfaces.
- Ensure that parking surfaces are free of oil, solvents or other chemicals.
If these precautions were not possible:
- Ensure none of the buses were parked on contaminated soil/asphalt which had the presence of oil, solvents or other chemicals. As long as this was not the case, one would not expect the tires to be compromised from being parked for several months during the pandemic.
- Flat spotting is not a safety issue and usually resolves itself once the tires are back in service.
In addition, the people at Continental Tire suggest the following:
If they have not already, they should check and increase the air pressure as described. Keep in mind not to move the vehicle with flat tires. Doing so will create a condition in the casing which can lead to a zipper failure.
They should roll the vehicle so that there is a new contact patch on the ground. Optimally they would move the tires so that the new contact patch is 180 degrees opposite from where it is now (~ five feet), but a minimum of one to two feet will help.
Before placing the tires in service, it is also recommended to check for excessive aging cracks in the sidewall. If they are in doubt, bring the tire to a TIA-certified tire professional for an expert opinion.
Flat spotting of an inflated tire (>90 percent of the recommended cold inflation pressure) is not a safety concern. The primary consequences of flat spotting is vibrations from the tire in the initial miles after being placed back in service.