Saturday, January 12, 2008

Shall I Check the Tires, Sir?

Some of us may recall the days of full service gas stations. For those who don’t, take a look at the scene in “Back to the Future” where Marty (Michael J. Fox) watches a car pull into the Texaco station in his home town in the 1950s. The attendants leap into action – one checks the oil, another pumps the gas, a third washes the windshield, and a fourth checks the tire pressure.

Why does the tire pressure matter? An underinflated tire experiences higher rolling resistance. This excess friction generates excess heat in the tread. This had three consequences. First, excess heat increases wear – the tire gets old faster. Second, excess heat compromises traction. Finally, underinflated tires use more gas. The difference is significant. By raising the tire pressure from 24 psi to 30 psi the car’s mileage will improve by 3% to 4%. See the US Department of Energy site on fuel economy here. And most cars are not running at the correct tire pressure. To verify this, check the pressure on the next rental car you use. You will find that the tires are usually low. This increases road comfort – most Americans like a soft squishy ride. The rental car companies don’t care – the cost of replacing tires is part of normal maintenance and already figured into their operating expense. Most users refill the gas tank rather than pay the high charge the rental car companies impose.

Three to four percent may not seem like much, but that matches the total contribution that the Arctic National Wilderness Refuge will provide should it be exploited to capacity. But more pragmatically, what can individuals do? By checking tires, each of us can benefit individually by spending a little bit less for fuel, driving with a little bit more safety and having the tires last a little bit longer. Could manufacturers do anything? Yes, and they already have. Many newer model cars have tire pressure sensors built into the rims, so the driver doesn’t have to get into a service station and scuttle around with a tire pressure gauge, getting road dirt on one’s fingers and clothing. Should newer models have a warning light to alert the driver? Should States require tire pressure checks as part of the annual safety inspection? Or should responsibility remain with the car owner, as sovereign?

This is a particularly interesting test case in that the benefits to the individual and to society are perfectly aligned. By keeping tires at the optimal running pressure, the individual gets a safer, longer lasting, more economical car, and society gets safer traffic and reduced fossil fuel consumption. The only losers in the bargain are the tire manufacturers, who sell fewer replacement tires, and the gas companies, who sell less gasoline. Tire manufacturers like being known for safe, long-lasting, economical tires, and all offer tips to improve these qualities, such as Goodyear and Michelin. Tire manufacturers grade their tires on three parameters: wear, traction, and temperature resistance. The US Department of Transportation describes this grading system here.

States are free to determine whether to inspect cars for safety, emissions, or neither, and how frequently – annually, on sale only, or at some other frequency. About ten states only require emission testing in metropolitan areas, such as Atlanta, GA, which helpfully summarizes inspection programs nationally here.

A tire pressure gauge is inexpensive. Serviceable models cost under $5 at any car parts store, top of the line digital models cost $15 or so. They fit in the glove compartment. Checking the tire pressure takes a few minutes and will save a few dollars.

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