Grip can be defined as “the ability of a tire to adhere to the road surface.” Three general factors can affect grip – either positively or negatively. Those factors are: the driver, the vehicle and the environment. Last month I focused on the driver and how smooth inputs, simple weight transfers and controlling speed can enhance vehicle control. This month we’ll touch on vehicle and environmental factors.
Tires: Tires provide grip. Correct, well maintained, properly inflated tires will enhance grip. Incorrect, worn, damaged or improperly inflated tires will decrease grip, leading to a degraded level of vehicle control. Police vehicles generally are supplied with all-season type street tires. All season street tires are a compromise lying somewhere between high performance street tires and winter specific tires. The tire construction and tread design of all season tires allows for “adequate” dry, wet and light snow operation. Mixing different types, sizes (unless specified by the vehicle manufacturer) or brands of tires on the same vehicle disrupts vehicle handling. Also, it is recommended that winter specific tires be used on all four wheels during the winter driving months. Placing winter tires only on the front or rear of a vehicle will cause an imbalance in handling characteristics. Proper tires, with proper inflation pressures, are also imperative to the proper function of Anti-Lock Braking, Stability Control and Traction Control systems.
Tires must be properly inflated to function at their optimum. Under or over inflated tires can be hazardous (especially severely under-inflated tires). Check tire pressures weekly, at the very least. We advocate using the recommended vehicle manufacturer cold tire pressures. Information on the proper inflation pressures can be located on the tire placard posted the door edge, door post, glove box or fuel door. Also be aware of the instrument panel warning icons indicating severely low tire pressures.
Worn tires will not perform well, especially in wet or snowy conditions. The purpose of tire tread is to remove water and snow, mud etc. from between the tire and the road surface, thereby maximizing the tire contact patch. If these substances cannot be removed, the tire will not make effective contact with the road surface (e.g. hydroplaning) and vehicle control will be severely degraded. Tires have wear bars in the tread grooves. If your tires are wearing to the point where the wear bars are close to becoming exposed, it’s time to replace the tires.
Suspension: Worn suspension parts such as springs, dampers (shocks), ball joints, linkages and bushings will be detrimental to vehicle handling. These parts should be checked and replaced as needed on a regular basis by your department’s vehicle maintenance facility.
The driving surface plays a major role in grip. Dry surfaces provide more grip than wet surfaces. Snow provides less. Packed snow even less, and ice virtually none. Debris like sand, oil, dirt, gravel etc. also effect grip. Environmental changes can occur rapidly and unexpectedly. Drivers should be looking far enough ahead in order to analyze the road surface and prepare to react to any possible change. As the driving surface changes for the worse, the driver must slow down appropriately and be as smooth as possible with the controls. It is always preferable to drive proactively by making adjustments ahead of a problem as opposed to being reactive by trying to fix a problem after it presents itself.
Remember, as discussed last month, the most important factor in maintaining grip is the driver. The driver has the ability to comprehend, detect, adapt or react to vehicle and environmental issues. If the driver does not act proactively or reacts inappropriately, a loss of vehicle control could become a serious reality.
Our EROC programs at DriveTeam train police officers to better understand themselves, their vehicles, and the environments in which they operate those vehicles. Our instructors are proud to present these programs with the goal of keeping police officers safe while performing the task that many do most frequently – driving.
Lead Range Instructor
EROC Blue Division