Where the TPMS rubber meets the road

Four tiny footprints can speel the difference between winning and losing — on the track and on the street.

undercar motorsports racing TPMS tire pressure tire technology repair shop training technician training A/C training automotive aftermarket Adding or subtracting as little as one pound of pressure from a NASCAR tire can impact how the racecar handles on the track. And that can spell the difference between winning and losing in a competition that tries to even the playing field by regulating nearly every aspect of the car's construction. While your customers might not be running a 500-mile race, the tires on their cars play an even more vital role: protecting the safety of the occupants. It is up to you to make sure the tires are up to the task.

The Impact of Proper Pressure

Air pressure specifications are critical to several vehicle parameters. The proper inflation of the tires affects how a car handles, how well it stops, even what kind of fuel economy it can achieve. Correct pressure insures minimum heat buildup and maximum tread contact on the road surface. Low air pressure creates high heat and high sidewall loads that can lead to catastrophic failure. High pressures also reduce the tire's contact area with the road and increase the spring rate, which impacts the stability and handling characteristics of the car. As one source wrote, if your ties all have coffee stains on them, check your tires for excessive inflation!

Back in the late 1990s, there was a massive recall of Firestone tires. These tires would suffer tread separations on some SUVs equipped with them, resulting in rollovers that caused millions of dollars in property damage and personal injury. The federal government conducted an investigation into the causes of such a massive tire failure and responded by enacting the Transportation Recall Enhancement, Accountability and Documentation Act, otherwise known as the TREAD Act, on Nov. 1, 2000.

While this act focused on several areas of manufacturer documentation and reporting, one key result of the TREAD Act was the requirement of today's tire pressure monitoring systems (TPMS) as a mandatory vehicle safety system.

Early TPMS systems were indirect systems that used both information from the ABS wheel speed sensors and an incorporated algorithm to monitor tire pressure. We now see the more common direct system, using dedicated pressure sensors in each wheel (and often the spare as well) to keep an eye on things. Even this solution has its pros and cons.

On the pro side, a warning light is illuminated on the dash to let the driver know when a tire has dropped below what the National Highway Traffic Safety Administration (NHTSA) has decided is a safe level: about 20 percent of the tire's normal pressure. This, hopefully, will cause the driver to at least correct the problem before continuing in his travels.

On the con side, tire pressure variations of as little as 5 psi can impact vehicle characteristics and would go undetected by the TPMS. The concern is the increase of driver complacency and the elimination of routine pressure checks, even by the professional technician, choosing instead to rely on the TPMS as the fail-safe.

It is up to us to keep the TPMS working properly. These systems were phased in starting in 2004, and were required in all new cars starting with the 2008 model year. When performing any vehicle service, look for the TPMS warning symbol on the dash during the key on bulb check to help identify if that car is so equipped. Then, look for the solid on light that indicates a problem.

If the light is clear, and you're performing any type of tire/wheel service, use a TPMS test tool to first verify that the sensors are working properly on arrival. Notify your customer of any problems before you start the work. Once done, follow the service manual to make sure the system is properly returned to service. Some require a relearn procedure, even if all you did was rotate the wheels from front to back.

Keeping It Green

On Sept. 1, 2010, the California Air Resources Board (CARB) enacted its Tire Pressure Regulation. The premise for the regulation was that too many California cars were running around on underinflated tires and that was causing an increase in green house gasses. It's true. Underinflated tires add rolling resistance to a car, requiring more fuel to be burned and more emissions out of the tailpipe.

The regulation applies to all vehicles with a GVWR rating of 10,000 pounds or less and requires automotive service providers to:

check and inflate, with air or nitrogen, each vehicle's tires to the recommended pressure setting when performing any automotive maintenance or repair service.
indicate the same on the vehicle's invoice, along with a record of the final tire pressure settings.
perform the service with a tire pressure gauge that is accurate within � 2 psi
have access to a tire inflation reference that is no older than three years.
keep a record of the invoices for three years.

Of course, if you're running a professional shop, you already are correcting your customers' tire pressures when they're in for service and trying to educate them on the importance of checking it weekly. Only now, if you own a shop in the Golden State, you need to keep record of it.

I'm sure your personal experiences mimic my own. Nearly every car I've ever serviced had at least one tire that was grossly underinflated. This was a potential accident waiting to happen, and at the very least a situation that could leave the driver sitting on the shoulder of the road with a flat.

Now I don't know about you, but if my wife had to change a tire on the side of the interstate during rush hour after just having left the shop, I would be upset, too.

If you're not checking those tires today, start doing so now. If the spare is readily accessible, check it, too. You'll be performing a professional service for your customer, and might add a few sales to the bottom line in flat repairs, tire sales and related suspension/alignment work. And your customers will appreciate your thoughtfulness.

ALTERNATIVE 'FUEL'

What About Nitrogen?

You've seen the ads stating that substituting nitrogen for the air in your tires will make them last longer and give you better gas mileage. With an average cost of gasoline now more than $3 per gallon, is this a worthy claim? You'll find lots of conviction on both sides of this argument, so let's take a look at the realities.

First, nitrogen is used in racing, heavy equipment, commercial trucking and aircraft applications. The claim for the trucking/heavy duty crowd is that nitrogen, being a larger molecule than oxygen, will be less likely to leech through the tire and helps maintain proper pressure. If pressure is consistently correct, then tires run cooler, meaning they last longer. Correct tire pressures also impact fuel economy. And using a dry source of gas eliminates contaminates in the air that lead to rubber aging and wheel corrosion. In these markets, the claims are well documented.

But does that make it effective for passenger cars? After all, air is already 78 percent nitrogen and even the best equipment cannot deliver a 100 percent pure nitrogen charge. In a study done by Consumer Reports, the difference in static air loss over time was negligible. Senior tire engineer and project leader Gene Petersen notes one important variable is the quality of the air used for conventional inflation.

"Not all air is of equal quality," Petersen writes. "Moisture, oil from the air compressor, and other pollutants can affect tire integrity."

I've had personal experience using nitrogen instead of air in two of my own cars, a 2001 Isuzu Rodeo and a 2006 Kia Sportage. In both, tire pressures remained consistent, requiring no additional service after the original fill. When the Isuzu was sold, the tires had more than 70,000 miles on them and still had life left. And I've seen tires on dozens of vehicles sporting the blue or green valve caps indicating a nitrogen fill has been performed, many of which were just as underinflated as any others I had checked.

Using nitrogen may provide some benefits, but it is not a substitute for routine checks of tire pressure. It is the maintaining of proper pressure with a clean, dry source that will insure long tire life and maximize a vehicle's fuel economy potential. If anything, nitrogen generators help provide that source. Of course, so would a good filtration system mated to your existing compressor.

DRAG RACING SCIENCE

Top Fuel Flex

Are you a drag racing fan? Even if you're not, you've likely seen a photographer's favorite shot: the one taken of those huge slicks at the moment of launch where the sidewall wrinkles up. But what is that all about?

According to Dave Auffenberg, Goodyear project leader for tire development in drag racing, sports cars and dirt racing, that crinkle effect happens on every launch. It's supposed to happen.

"The whole wrinkle wall concept of drag tires is the same as storing energy in a spring," says Auffenberg. "As the car starts to move, the tire grips and the sidewall wrinkles. It is storing potential energy. As the tire unwinds, you are taking the stored potential energy that you get from the tire winding up and turning it into kinetic energy as the car moves and that springs the car forward."

Putting the proper air pressure in the tire is critical in making the most of that potential energy. According to Auffenberg, if the pressure is too low, tire shake and too much spin can be the result. If the pressure is set too high, the tread face can't get the maximum grip on the track surface. And in a sport where the difference between winning and losing is measured in thousands of a second, this has got to be just right.

Most of these great shots are photos of bias-ply tires. In the NHRA, all three of the top professional categories (Top Fuel, Funny Car and Pro Stock) use this type of tire. Radial designs are also in use, and they wrinkle, too, just not as much.

"It's different with a radial drag tire. (Radials) have a more consistent dynamic footprint," says Auffenberg.