When the Rubber Meets the Road

In the movies, a police chase always ends with the bad guy in cuffs seated in the backseat of a slightly scuffed patrol car. In real life, high speed chases are far messier, with one of the greatest risks being a tire blow out - and the ultimate sacrifice potentially an officer's or citizen's life.

Two years ago, as Florida Highway trooper Daryl Haywood raced after a fleeing car along Interstate 4, his patrol car blew a tire, spun out of control and struck a tree. He died instantly and the runaway motorist received 30 years in prison for what would have resulted in a speeding ticket if he'd pulled over when Haywood first flashed his lights.

Unfortunately, stories such as Haywood's are all too common. The poor condition of many roads and the very nature of police work fuel the prospect of a tire blow out.

Police vehicles subject tires to more severe operating conditions than the average passenger car. Over the course of a normal day, police drivers challenge their squad cars on several emergency calls, and perhaps a pursuit or two. These vehicles operate at slow then high speeds, corner quickly, turn on a dime and log considerable miles. Such stresses diminish tire life and performance.

"Two things cause a tire to fail - friction and heat," says Rick Longobart, fleet superintendent for the City of Inglewood, California. "The police vehicle is susceptible to both."

Longobart positions high speeds as the obvious contributor to tire failure - pursuit driving creates friction and friction generates heat. However, he emphasizes tire damage also develops when tires spin wildly as the vehicle rapidly accelerates. "Police tires are either running at high speeds or spinning, and both can cause the tire to fail," he explains.

A tire for every season
All tires are not created equal. The tire that meets the needs of patrol vehicles operating in the scorching desert heat may not be appropriate in a Northwestern drizzle or a Midwestern snow storm. Likewise, tires best suited to the Ford Police Interceptor may not be as highly rated for the Chevrolet Impala, and so on.

Most departments select tires offering both wet and dry performance capabilities, says Lance Miller, testing manager at the National Law Enforcement Corrections & Technology Center (NLECTC), which is a program of the National Institute of Justice that tests technology designed for law enforcement.

"We lack the luxury of driving exclusively in one or the other condition," he explains. "Everyone has to drive in most types of weather at some point, but how much of that you drive in plays a factor in the tire you select."

San Diego averages approximately 9 inches of rain a year. On a rainy day in this sunny, temperate climate, the number of citizen accidents rises 50 to 70 percent as rain water pushes oils and lubricants deep in the asphalt to the surface. Law enforcement vehicles cannot afford to be out of commission during these hectic times because of poor tire selection. By choosing a speed-rated tire, John Alley, San Diego Police Department's police fleet administrator, says squad cars stay on the road.

While maintaining the Washington State Patrol vehicle fleet for three years, Alley notes he employed pursuit-rated dry season tires during the summer months and pursuit-rated snow tires over the winter months. In some areas, Alley fitted studs to the tires to maneuver safely on black ice. "I had to take extra precautions to make sure I had speed-rated snow and mud tires, and studded tires," he says.

Navigating tire ratings
All tires mounted on patrol cars must be rated for pursuit, explains Miller, who headed the bi-annual NLECTC tire testing program from 1995 until the final test in 2001.

Passenger tires, typically purchased for vehicles that will not see such severe service, are not recommended for police duty. "You are going to lose the speed rating, and if the vehicles were involved in a pursuit, the tires could introduce unfavorable handling characteristics," says Miller, who spent nine years as a police officer and small-town police chief. "Speed-rated tires used on police vehicles have more in common with high-performance tires on sports cars than tires used on a civilian version of the same car used by police."

Tires rated W to Z pass muster as pursuit-rated tires, with "Z" being the highest available.

If a tire races along at 150+ mph at anything less than a Z rating, it would likely disintegrate, Longobart stresses.

The U.S. Department of Transportation also requires tire manufacturers to grade passenger vehicle tires on three performance characteristics: treadwear, traction and temperature resistance. These ratings also factor into police tire selection.

Treadwear. This rating refers to the general hardness or wearability of a tire's rubber compounds, which directly translates into how long and how well the tire will hold up. A tire with a lower treadwear ranking may only be rated to last 40,000 to 50,000 miles, while one with a higher treadwear score may withstand 60,000 to 80,000 miles. For instance, says Alley, Goodyear rates its Eagle RSA17 at 260, which means it wears about 2.6 times as well as a tire ranked at 100. "From my days in law enforcement, I can tell you we certainly didn't get that kind of mileage out of our tires," Miller admits. "But even so, treadwear is a critical consideration in an agency's purchasing decision. Treadwear ratings directly impact how soon you may need to replace the tire."

Temperature. Tires are made of rubber, and heat is its natural enemy. Any time a tire rolls down the road it generates friction which produces heat. The faster one drives the greater the turning forces exerted on a tire and the more heat produced. Manufacturers design tires to expand and dissipate this heat build up under severe operating conditions to ensure they maintain integrity. This is what temperature grade speaks to. Temperature grades, from highest to lowest, are A, B and C. These rankings represent the tire's resistance to heat generation. The Goodyear Eagle RSA17 puts its pursuit-rated tire at an A, says Alley, who's been with the San Diego PD for eight years.

Traction: There is both wet and dry traction. Manufacturers design tires with specific characteristics and performance metrics in mind. In some cases, the manufacturer tries to hit that sweet spot offering a blend of both wet and dry performance. Traction ratings, from highest to lowest, are A, B and C. They represent the tire's ability to stop on wet pavement. Again, Alley says Goodyear puts its Eagle RSA17 at an A rating.

"We use Goodyear because it's the manufacturer's original equipment," he says. "Also, if we have to change one tire, we could not put on a different tire make or model. If we did that, we'd have to replace all five tires, and that would be cost prohibitive."

Most departments employ a competitive bid process to purchase tires. Alley notes his agency bids competitively every five years. But he adds they spec a single tire brand.

"We've found that if we stay with one manufacturer it reduces our costs overall," he says.

Keep it up
Ultimately, a tire's ratings won't mean much if a department fails to maintain its tires.

Over- or under-inflated tires signify a significant problem on the road, says Alley. Under inflation ranks as the leading cause of tire damage and failure, and can increase fuel costs by 3 to 5 cents a gallon - something today's cash-strapped agencies can ill afford. Over inflation stimulates heat build up and boosts the risk of high speed blow outs. Out-of-balance tires trigger uneven wear and vibration, creating unstable conditions at high speeds and shortening tire life.

"Under inflation is one of our biggest challenges," Alley admits. "Tires naturally lose air over time."

For this reason, motor technicians in this California department inspect tires daily before each shift. While manufacturers recommend vehicles be brought in every 5,000 to 7,000 miles for maintenance, San Diego pulls its patrol cars for routine repairs every 3,000 miles. At this time, technicians remove the tires and inspect them for damage, set air pressure to 35 psi, then balance and rotate them. They replace any tires at 4/32-inch or less tread. Technicians plug holes in tires only once, after that the tire must be changed out.

Longobart's department also services its vehicles every 3,000 miles. At these maintenance intervals, technicians inspect the vehicle from bumper to bumper, including the tires. Because severe service shrinks tire life expectancies, technicians must guesstimate tire wear from interval to interval. Though a tire may appear to have another 3,000 miles left on it, technicians must downgrade its useful service life and often change it prematurely. The tire may then be used as a spare or retired because it may not last until the next service interval.

Even so, daily checks are critical. "A tire can be worn out between intervals - even if it's being used the same way between services," Longobart states. "It only takes one high speed pursuit, or an officer spinning the wheel one too many times, for it to wear out."

Putting the onus on officers to inspect tires before each shift and educating them on how driving tactics impact tire integrity also helps safeguard tire life, he adds. User groups within the Inglewood department encompass tire maintenance and vehicle operation.

These groups drive home the message that vehicle maintenance is part of an officer's responsibilities. "They don't just get in the vehicle and drive," Longobart says. "They must check the brakes, make sure there's gas, and inspect the tires for proper inflation and other problems."

Blow-out protection
Even if a department does everything right from selection to maintenance, the risk for blow outs remains. "No matter what the tire brand, as long as there are potholes in this country, no tire is going to keep us safe," says Rick Cole repeating the words of a Greyhound executive he once did business with. Cole is the chief executive officer of Tyron Automotive Group USA, a Burbank, California-based company that manufacturers blow-out protection. "This is true for law enforcement, too," he adds. "Our roads are getting older. They are cracked, have potholes and ruts. Regardless of whether a tire is high speed rated or heavy duty, there is always a chance that if you hit a pothole at high speed, the tire's going to go."

When a tire deflates, air pressure no longer holds it in its correct place on the wheel. As a result it becomes free to move about and the tire's beads can slip over and into the wheel well, causing the tire to flail or flap about. The driver loses steering control and the flapping tire may cause serious damage to the vehicle and passengers.

The Tyron wheel band attaches over the wheel well after the tire has been fitted, to support a deflated tire and prevent it from slipping into the wheel well after a blow out.

The device holds the sidewalls vertical, keeping the wheel off the ground. This increases stability after a tire fails, and in turn maintains steering, braking and cornering control.

"With Tyron in place, our officers can drive on a flat tire and get it to the garage for repair," says Longobart, who used Tyron wheel bands as maintenance superintendent for the City of El Segundo, California. "They also enhance the safety of the driver because if there is a blow out at high speeds, the tire maintains stability allowing the vehicle to come safely to a stop."

Run-flat tires also are peaking the interest of some police departments. However, to date not a single U.S. police department uses them. The main reason for their lack of popularity is expense, says Cole. Equipping a vehicle with run-flats runs upward of $1,600 for tires that offer little more than 20,000 miles. "A department the size of the Los Angeles Police Department replaces tires every 30 to 60 days," he points out. "If you quadruple or quintuple the cost of tires, you make it well beyond the reach of any department budget."

Today's run-flats also do not handle well in high speed turns or on wet pavement, making them a danger to the police fleet, he adds. They negate the spike strips often employed in high speed chases. And being directional, meaning a left tire can only go on the left side of the vehicle and vice versa, would require patrol vehicles to carry two spares in their already overcrowded vehicle trunks.

Even so, Longobart predicts as the technology improves and the price comes down, manufacturers will eventually spec run-flats on all police vehicles. The challenge is creating run-flats that perform like today's pursuit-rated tires, Alley adds. But this may happen sooner rather than later as Ford Motor Co. and General Motors Corp. conclude their work on run-flats designed with police service in mind.

With technologies like these, the day may soon come where police chases no longer spells disaster but play out like they do in the movies: the patrol car intact and the bad guy in the back.