Fire Truck Tire Pressure

Recently I got a call from a Fire Department asking why the tire pressure indicators provided with their new truck did not match the tire pressure stamped on the sidewall of the tire. This is a question that is being asked more now that tire pressure indicators are becoming more commonly used.

While it may seem that the tire pressure stamped on the side of the tire would be the recommended tire pressure to use, it is actually the maximum tire pressure to carry the maximum load the tire is rated for. Generally we are not loading the tire to its maximum rating for several reasons:

• The axle rating is based on the lowest capacity of axle, suspension, tires, wheels, frame; the tire often has a higher load rating than these other components and so we are not using the maximum load rating.
• We do not generally load the axle to its maximum load rating.

We obtain the recommended tire pressure from load and inflation tables published by the tire manufacturers. The axle loads we use are the ones we measure when performing the ULC or NFPA required weight tests with ballast simulating equipment and personnel loading.

It is important to use the correct tire pressure for the following reasons:
Underinflated tires flex more and build up heat, causing premature tire failure and potential blowouts. They also hydroplane at lower speeds and increase stopping distance.
Overinflated tires are more susceptible to impact damage and may cause handling problems.

NFPA 1915, Standard for Fire Apparatus Preventive Maintenance Program, recommends checking your truck's in service weight annually. This would be a good time to make sure that you are using the correct tire pressure based on the load and inflation tables published by the tire manufacturer.

We'd be happy to answer any questions you may have or help you with tire pressure calculations, feel free to contact us.