What you need to know about TPMS

 

 

Why?

 

In 1999/2000 Firestone was forced to recall 6.5 million tires due to a rash of accidents blamed on the construction of the tire. The primary cause for these failures was determined to be low tire pressure. That incident prompted the Federal government to force new standards to protect the public from the dangers of tire under-inflation.

In 2001 NHTSA National Highway Traffic Safety Administration conducted a study of 11,530 vehicles and found that nearly 40% of all vehicles tested had one or more tires under-inflated by 20%. Nearly 30% of the vehicles tested had one or more tires under-inflated by 25% or more.

 

Under-inflation is the leading cause of tire failure. Combined with excessive highway speed and heavy loads, tire sidewalls can begin to deteriorate quickly, vehicle handling becomes sluggish, and the tread can start to separate from the rest of the tire. The physical tire damage may go undetected by the driver for many miles. Even if the tire is later inflated to specification, the damage is already done and a potential accident is waiting to happen. A tire that is under-inflated by as little as 7% (3psi) will reduce tire life by 10%

 

The study showed what most of us already knew. Consumers do not check their tire pressure often enough if at all. This prompted Congress to pass the TREAD act or…get this.. The “Transportation Recall Enhancement, accountability and Documentation Act”. Sounds like trouble already. An Act with that goofy a name can’t be well thought out. And it isn’t!

 

TREAD Act of 2000

 

The TREAD Act was passed in the fall of 2000 following the Ford/Firestone crisis. Congress wanted to make tires safer for the motoring public. The TREAD Act has nine components that affect the tire industry.

 

Ø      Tire testing standards

Ø      Tire labeling requirements

Ø      Tire Pressure Monitoring Systems

Ø      Early warning reporting system

Ø      Safety recalls in Foreign countries

Ø      Sale or lease of recalled ties

Ø      Reimbursement prior to recall

Ø      Acceleration of recall

Ø      Disposal of recalled tires.

Tire Pressure Monitoring Systems (TPMS)

 

The TREAD act requires the installation of tire pressure monitoring systems that warn the driver when a tire is significantly under-inflated. It includes all passenger vehicles with a gross vehicle weight of 10,000lbs or less. That includes almost all Passenger and Light Truck vehicles with the exception of vehicles with dual rear wheels. The TREAD Act is very specific in that a TPMS system need only warn the driver in the event that a tire is determined to be significantly under-inflated. According to the specifications of the Act, this could mean a tire would need to be under-inflated by as much as 25% before the TPMS telltale would alert the driver. The current TPMS mandate applies only to passenger cars, SUV’s, vans and Light trucks below 10,000 lbs GVW. However a “phase II” ruling covering vehicles heavier than 10,000 lbs is already in the works. Although the current mandate began with 2004 model year vehicles, TPMS systems were first seen in the US on some 1997 vehicles. Regardless, by September 1^st 2007, all vehicles sold in the US must have tire pressure monitoring systems.

 

See the final legislation here:

 

http://www.nhtsa.dot.gov/cars/rules/rulings/TPMSnprmPost2Cir/TPMSnprmPost2Cir.html

 

TPMS phase-in schedule

 

Ø       20% of vehicles manufactured between October 5^th, 2005, and August 31^st, 2006.

Ø       70% of vehicles manufactured between September 1^st, 2006, and August, 2007

Ø       100% of vehicles manufactured after September 1^st, 2007.

 

 

 

TPMS System types

 

Indirect TPMS

Ø      Uses the ABS system to determine differences in tire pressure

Ø      May be difficult to recognize

 

Direct TPMS

Ø      Uses separate sensors mounted in the wheel/tire assembly

Ø      Allows actual measurement of tire pressure

 

Indirect TPMS

 

An indirect TPMS system uses the anti-lock brake system wheel speed sensors to detect an increase in wheel speed that may be due to an under-inflated tire. As tire pressure decreases the diameter of the tire also decreases. To keep up with the other tires on the vehicle the under-inflated tire will need to rotate faster. The increased rotational speed will generate a higher frequency output of the ABS wheel speed sensor. Indirect systems compare diagonally opposed wheel speeds to identify under inflation. Some new indirect systems monitor the resonance frequency of the tires along with the wheel speed differences.

 

Indirect TPMS – How it works

 

Ø       [(LF + RR) – (RF + LR)] / Average Speed

Ø       If < threshold value = OK

Ø       If > threshold value = TPMS Warning

 

Indirect TPMS uses a fairly simple formula to determine if one or more tires are severely under-inflated. The system takes the sum of two diagonally opposed tires and subtracts that value from the sum of the other two diagonally opposed tires. This value is then divided by the average of all of the wheel speed sensors. If the total is less than or equal to the threshold value, no TPMS warning will be issued. However, if the total is greater than the threshold value, the TPMS telltale will be illuminated.

 

Pros and cons of Indirect TPMS

 

                  Pros

 

Ø       Uses existing hardware

Ø       Allows early compliance

Ø       Cost to service is much lower to consumer

Ø       No batteries to go dead after a few years.

Ø       New technologies can detect 4 tires with low pressure

 

                  Cons

 

Ø       Early systems won’t notify driver if all tires are low.

Ø       Early technologies hard to identify

Ø       Early systems not as accurate

 

Direct TPMS

 

Direct TPMS is differentiated from the indirect system by the presence of a sensor in each wheel that measures tire pressure directly. Direct TPMS is considered to be significantly more accurate than the indirect system. The tire pressure sensor is typically am integral component of the valve system.

Some OEM’s, like Ford, and many aftermarket systems use a sensor which is mounted to the wheel with a large band clamp. Ford refers to this as a wheel mounted TPMS, Typically, the sensor is located 180 degrees from the valve stem.

 

 

The presence of standard rubber valves in the wheels normally indicates the vehicle uses an indirect tire pressure monitoring system (TPMS) that compares tire revolutions when the vehicle is in motion by monitoring the ABS speed sensors.

However, beginning with the 2007 model year, some vehicles have begun using a rubber valve stem direct TPMS that is hard to distinguish visually from a standard rubber valve stem.

 

 

 

Only the rubber TPMS valve's resistance to gentle bending confirms its design.

If a direct TPMS system is in use and the air pressure has been released from the tire, the aluminum tire valve (along with its attached tire pressure sensor) should be unbolted and allowed to gently "drop" into the still-mounted tire and wheel. This will help protect the tire pressure sensors (some exceeding $200 each when purchased from the new car dealer) from being broken during bead loosening and tire dismounting.

The tire should be removed from the wheel following the tire machine's instructions. Before the tire is reinstalled following the tire machine's instructions, all original TPMS aluminum sensors should be fitted with a new rubber grommet (also called an o-ring or seal), aluminum retaining nut, special nickel-plated valve core and O.E. valve cap (shown below).

Rubber Grommet, Aluminum Retaining Nut, Special Nickel-Plated Valve core and O.E. Valve Cap

It is important that all components be torqued to appropriate values to prevent air leaks. Attempting to reuse the original rubber grommet, valve core and retaining nut may result in an air leak. Additionally, it is important to retain the original aluminum TPMS sensor's valve cap.

Note: A standard brass valve core (shown below right) used in an aluminum tire pressure sensor valve stem will experience galvanic corrosion and the brass valve core will eventually seize in the valve's aluminum barrel.

 

Only special nickel-plated valve cores (shown above left) should be used in aluminum tire pressure sensor valve stems.

 

 The valve stem on many TPMS sensors acts as the antenna for transmitting the wireless radio frequency information to the TPMS controller. In some cases, a TPMS sensor may be equipped with a metal cap from the factory. This metal cap may in fact be a part of the antenna assembly and should not be replaced with a plastic or chrome cap. In any case, the TPMS valve stem cap should be equipped with an O-ring to prevent Air loss through the valve core.

 

Pros and cons of Direct TPMS

 

                  Pros

 

Ø       Display actual pressure information for each tire

Ø       Provides service direction for the customer

Ø       High visibility, which encourages safety

Ø       More accurate

Ø       Faster learning system

 

                  Cons

 

Ø       Expensive

Ø       Easily damaged

Ø       Limited battery life

Ø       Many different learning procedures

Ø       Slows down the workflow process

Ø       Requires new procedures from tire service personnel

 

TPMS and Nitrogen

Ø      How do you identify a tire filled with nitrogen?

Ø      How will nitrogen affect a TPMS sensor?

Ø      What if a tire equipped with TPMS is already filled with nitrogen?

The latest buzz-word in the industry is Nitrogen. Nitrogen composes 78% of the air we breathe. One real benefit is the fact that Nitrogen is dry; that produces less corrosion of the wheel, which is a large cause of pressure loss. Nitrogen does not have any adverse effects on the TPMS sensors or the overall operation of the system. Nitrogen is an inert dry gas that has a larger molecule than Oxygen, So in theory will suffer less pressure loss over time. When a tire is inflated with Nitrogen, a unique green valve stem cap is supposed to be installed. Be careful when servicing cars equipped with TPMS and also have Nitrogen. Remember that the metal valve cap in some TPMS sensors are actually part of the antennas that transmits the radio signal. Removal of these caps may cause the signal to interrupt.

TPMS is sure to be a challenge for all tire dealers that like to do the job right the first time. With a little training and a small investment in equipment you can be prepared for this new technology. A lot of your competitors will not be. Summit Tire has TPMS equipment and training literature available for you. We will also be holding ongoing off-site training sessions throughout 2007. Please contact us if you need any help with TPMS.

smckenzie@summittire.com