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Tire-Pressure Monitoring Systems (TPMS) Guide:
The federal government has mandated that all new passenger cars, multipurpose vehicles, trucks & buses weighing 10,000 pounds or less be equipped with tire-pressure monitoring systems (TPMS). The systems must indicate when one or more tires have lost 25% of their recommended inflation pressure, allowing consumers to avoid the resulting unsafe driving conditions. The rule is being phased in, with 20% of the affected vehicles required to comply by model-year 2006, 70% by 2007 and 100% by model-year 2008.


Generally speaking, there are 2 different types of tire-pressure monitoring systems. Indirect systems have been around for more than a decade. These devices use the vehicle's anti-lock braking system to monitor each wheel's rotational speed. As a tire loses pressure, its rolling radius decreases and its rotational speed increases. A malfunction indicator light (MIL) is triggered when one or more tires' rotational speed reaches a predetermined threshold in comparison to the other tires. In a direct system, each tire is equipped with a sensor that measures actual pressure. The measurements are then sent via a wireless radio-frequency transmitter to a receiver, which analyzes the signal and reports the results on a monitor mounted within the cabin of the vehicle. An under-inflation state in any tire activates an alarm.

A federal court in 2003 found that indirect system was not as reliable since it could fail if all four tires were under-inflated or if two tires on the same axle were under-inflated. NHTSA published a new rule in April 2005 requiring that the system be able to detect a loss of air pressure in each of the four tires.

The ability to reprogram the systems was another disputed topic. SEMA requested that the systems be reprogrammable in order to accomodate alternative tires with different pressure thresholds. If the car comes with tires inflated at 32 pounds, the warning light will come on if a tire drops to 24 pounds, which is 25% of 32. However, if the car owner then installs low-profile tires with a recommended pressure of 40, the warning light should come on at 30 pounds. But unless the TPMS is reprogrammed, it won't trigger until 24. That means the tire is now 40% under inflated, which would defeat the purpose of the rule and give the driver a false sense of security.

NHTSA did not want to mandate reprogramming. The agency believes that it will be a voluntary feature of TPMS in the marketplace and is unaware of any problems that would prevent reprogramming. Such problems are unknown at this stage, since the systems are just now coming into the marketplace in large numbers.

Once consumer get used to seeing something on their new vehicles, they want it on their old vehicles as well. Once they start using TPMS - esp. aftermarket model with its ability to display current pressure at any point and to warn of low tire pressure - they feel naked when they're driving a vehicle without it.

A consumers must understand that a TPMS system will eventually pay for itself through reduced tire wear and increased fuel economy. Right now, DOT says that we waste about 4.2 million gallons of fuel a day due to low tire pressure. That's a little over 2 billion gallons a year, and we're sitting with a U.S. reserve of about 900 million gallons, so we're wasting over 2 times that. The tire industry and the government tell us that somewhere around 32% of all tires are running at least 30% low. That means that those tires are dangerous on the road, which affects insurance, vehicles and health. The Insurance Institute for Highway Safety said that 200,000 accidents last year (2005) were caused due to blowouts. In addition, you wear a tire out roughly 10% faster for every 10% it's under inflated. So if we're 30% low on 32% of the tires, that's a lot of wasted tires and a lot of wasted resources that will be used to replace them. We like to think that, aside from providing safety and savings in fuel and tire wear, we're also providing people with an opportunity to help environmentally.

Amount of Under-inflation Wasted Fuel Added Tire Wear
3 psi +1% +10%
6 psi +2% +30%
9 psi +4% +45%
* What's more, under-inflated tires are dangerous. Cornering & braking are affected, and a low tire is much more likely to blow out. Remember, your tires lose air constantly, even when the car isn't being driven.

Reasons to always keep your tires properly inflated (i.e. prevent under-inflated & over-inflated tires):

  • Vehicle Safety - Proper tire inflation greatly reduces the potential of a tire blowout that can lead to unwanted road-side emergencies, damage to vehicle, and even personal injury.
  • Convenience - Aftermarket TPMS can conveniently and continually check your tires to ensure they have proper inflation and correct tire pressure.
  • Accuracy / Reliability - Aftermarket TPMS will allow drivers to quickly respond to an audible beep and a visual alert emitted by the TPMS alarm when the tire pressure falls to dangerous levels. Aftermarket TPMS can usually detect any air leakage in seconds.
  • Improved Fuel Economy -
    • The Department of Transportation estimates that 5 million gallons of fuel per day (over 2 billion per year) are wasted due to low tire pressure.
    • Under-inflated tires increase the rolling resistance of vehicles and, correspondingly, decrease their fuel economy.
    • Properly inflated tires save fuel and that saves you money at the pumps!
    • Wi-GaugeTM can help your vehicle to get the best possible fuel mileage by ensuring your tire pressure is constantly operating within the correct range.
    See: MythBusters Tire Pressure Test - dated 11/04/2010
  • Enhanced Vehicle Performance -
    • Tires with low air pressures skid and hydroplane more easily.
    • Aftermarket TPMS, through proper tire inflation, will allow optimum performance of your vehicle with greater stability, handling and braking in both wet and dry conditions.
  • Increased Tire & Tread Life, and save MORE money! -
    • When a tire is under-inflated, more pressure is placed on the casing of the tire, causing the tread to wear more rapidly than it would if the tire were inflated to the proper pressure.
    • Properly inflated tires can extend the life of tire treads and casing by as much as 35%.
    • Aftermarket TPMS helps to ensure maximum tire and tread life by monitoring your tire pressure/temperature and maintaining proper tire inflation.
    • As petroleum price goes up, tire price goes up accordingly. Now you can hit 2 birds w/ 1 stone.

Why aftermarket (DIRECT) TPMS are so much better than OE-installed (INDIRECT) TPMS:

  • OE system can't identify the specific problematic tire, you have to test all 4 or 5 (incl. spare) tires to figure out.
  • OE system can't indicate the actual PSI drop or real-time pressure ratings in the problematic tire(s), instead it reacts with a primitive beep & let you do the guess work.
  • OE system doesn't always indicate the temperature of each tire, many aftermarket models do.
  • OE system warns only when tires lose 25% or more of their recommended inflation pressure, most aftermarket models have different alert levels with up to ±1 psi accuracy.
  • Most OE systems cannot be reprogrammed to work with aftermarket low-profile tires at all.
  • Some OE system utilizes valve stem sensors in opposing to aftermarket systems' screw-on valve cap or strap-on sensors, as a result, valve stem type is very unforgiving in terms of compatibility, most wheels (esp. aftermarket ones) are NOT compatible with valve stem sensors. Compatible wheels need to be specially engineered so that they can accomodate such sensors.
  • Some OE system relies on the vehicle's anti-lock braking system (ABS) to detect under-inflation, while aftermarket sensors broadcast data via a wireless transmitter (e.g. RF) to a display panel w/ a central receiver.
  • OE system works by comparing the rotational speed of each wheel in normal driving mode & relies on a tire that is substantially under-inflated having a roller diameter that is smaller than its counterparts. Aftermarket system's display panel analyzes the data & tells the driver which tire is under-inflated & the actual pressure on each tire.
  • OE valve stem sensors are very difficult to be replaced, as a result, you need to get new wheels!
  • Many OE sensors require the use of counterbalance to balance the weight of the sensor, aftermarket sensors usually don't.
  • Most aftermarket direct TPMS are battery-operated, they can operate while the vehicle is stationary.
  • Aftermarket direct TPMS will not give false positives if the vehicle is being driven on gravel or bumper roads, has mismatched tires, or a tire that is out of balance/alignment.
  • OE systems are engineered to meet the NHTSA law without incurring any extra expenses, in other words, for a lil' more, they could have used many better aftermarket systems and offer much greater peace of mind but they chose money over functions, how sad.

Sigma Automotive Aftermarket TPMS:


NOTE: TPMS is meant for use only as a tire pressure monitoring system that measures and monitors tire pressure and temperature and which can alert you of a pressure leak or a low-tire situation. TPMS is a lot more than a tire gauge, but it will not prevent a catastrophic tire failure (tire blow-out) due to tire damage or defect.

The weight of a TPMS sensor is enough to create an imbalanced assembly: Tires & wheels are manufactured to be perfectly balanced, so adding a sensor (regardless of type) that weighs anywhere from 1 ~ 1.5 ounces is going to have a negative effect on the rotating assembly. If the goal is perfectly balanced UHP (ulta high performance) tire & wheel assembly when the sensor is in place, then the mechanic must invest in the right equipment & constant training. By utilizing the correct "pin-plate" & the advanced features of modern balancers, technicians easily can apply a tape weight to achieve static & dynamic balance.


Home Safety TPMS :

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