Tires and Tire Pressure

The reason we spend a lot of time talking about these subjects can be found in a comment made by a Bridgestone engineer – “Tire pressure affects every aspect of the tire, including the load-carrying capacity, tread contact patch shape—where the tire touches the road—and size and handling characteristics.” 

Therefore optimizing tire pressure will increase the safety and security of the principal and is essential knowledge for the Security Driver and Executive Protection Practitioner.

As we have often said, tires are the only part of your vehicle that makes constant contact with the pavement. 

To obtain the vehicle manufacturer’s suggested inflation level for your executive vehicle, take a look at the tire sidewall and the label often located in the door jamb. If it’s not there, check the owner’s manual. 

Recently, we were asked why tire sidewalls often show a pressure rating, shown in maximum pounds per square inch (psi), that differs from the vehicle maker’s recommendation.

How do they determine the recommended pressure that appears on the tire and the recommended pressure on the sticker located on the vehicle or in the vehicles’ manual?

To get the answer, we did go to the standards set by the Tire and Rim Association (TRA) in the United States and the European Tire and Rim Technical Organization (ETRTO). We looked at their guidelines in developing tire sizes’ maximum psi and maximum load levels.

The maximum tire pressure is precisely that, the maximum pressure the tire can safely hold. But within that, there is the ideal pressure to maximize the performance of the vehicle, and that is the tire pressure recommended by the vehicle manufacturer. 

Tire manufacturers develop ideal tire pressures based on various factors such as how much load the vehicle puts on its left front wheel during a right turn at 60 mph. 

We assume that the tire manufacturer drives the vehicle at the maximum handling capability of the vehicle tire combination at a speed of 60 MPH. This is our assumption, and it seems to make sense.

Through rigorous testing, the vehicle’s recommended tire pressure is determined, with the idea of balancing considerations of performance, fuel efficiency, safety, and overall longevity.

Check PSI Once a Week

The key to maintaining proper tire pressure is checking psi levels at least once a week or more. But according to the tire companies and the National Highway Traffic Safety Administration (NHTSA), not many people do that. Just 19 percent of drivers properly check and inflate their tires, even though tires tend to deflate by about one psi a month. According to the agency, about a quarter of all cars have at least one tire that is significantly underinflated. As a Security Driver or Executive Protection Practitioner that can’t be you.

Tire Pressure Monitoring System

At some point, almost everyone has seen the tire pressure monitoring system (TPMS) warning light appear on the dashboard. Its purpose is to warn you that at least one or more tires are significantly under-inflated, possibly creating unsafe driving conditions. The tire pressure readings are provided by pressure-sensing transmitters mounted inside each tire and sent to a central computer (ECU) for display on the dashboard. The problem is that the warning light on the instrument panel does not come on until there is a 25-percent drop in tire pressure. By the time the warning light is displayed, you and the passengers are in a very unsafe vehicle.

If you have attended a protective driver training program, you should know how much tire pressure affects a vehicle’s ability to corner, drive out of an emergency, and stop.  A while back, we produced an episode on TPMS, and we mentioned that by the time the TPMS light comes on, the driver would lose 15 to 20 percent of the vehicle’s emergency capability. That means if the vehicle/driver combination could escape an emergency at 40 MPH, they could not avoid the same scenario at 32 MPH if the TPMS light is on.