# Tire-pressure gauge

A tire-pressure gauge, or tyre-pressure gauge, is a pressure gauge used to measure the pressure of tires on a vehicle. Proper tire pressure is crucial for vehicle safety, fuel efficiency, and tire longevity. Tire gauges come in various types, including analog, digital, and dial gauges, each offering different features and accuracy levels. Tire-pressure gauges can be used both professionally and casually and come in many different sizes.
Since tires are rated for specific loads at certain pressure, it is important to keep the pressure of the tire at the optimal amount. The precision of a typical mechanical gauge as shown is ±3 psi (21 kPa). Higher precision gauges with ±1 psi (6.9 kPa) uncertainty can also be obtained.

## How tire-pressure gauges work

Many modern cars now come with built-in tire pressure sensors that allow all four tire pressures to be read simultaneously from inside the car. Before 2005, most on-board tire-pressure monitoring systems (TPMS) used indirect pressure monitoring. The anti-lock brake sensors detect one tire rotating faster than the rest and indicate a low tire pressure to the driver. The problem with this method was that if tires all lost the same pressure then none would show up against the others to indicate a problem. However, research has shown that both direct and indirect tire pressure monitoring systems are equally effective.
Tire-pressure gauges measure air pressure using various methods:
Mechanical methods, like analog and beam gauges, use mechanical pressure sensors. For example, in dial gauges, a diaphragm or piston moves in response to tire pressure, causing the needle on the dial to shift. In beam gauges, the pressure causes a lever to move, which then aligns with a scale to indicate the pressure.
Electronic methods are digital gauges that use sensors to detect tire pressure and convert this information into an electronic signal. This signal is processed and displayed on a digital screen. Electronic gauges may include pressure transducers or strain gauges to detect changes in pressure.

### Accuracy and Calibration

The accuracy of a tire gauge is critical for ensuring proper tire pressure. Most gauges are accurate to within a few PSI or kPa. Regular calibration is necessary to maintain accuracy. Many digital gauges come with automatic calibration features or can be recalibrated manually. Analog gauges may need to be recalibrated by a professional if they show signs of inaccuracy.

### Usage and Maintenance

To use a tire gauge, the valve stem of the tire must be accessed. The gauge is then pressed onto the valve stem, and the pressure reading is taken. For accurate results, it is important to perform this task when the tires are cold, as pressure can increase with heat from driving.
Regular maintenance involves keeping the gauge clean and free from debris. Digital gauges may require battery replacements, while analog gauges should be checked periodically for accuracy and mechanical wear.

## History of tire-pressure gauges

Underinflated tires can lead to a range of issues, from minor problems such as premature tire wear and reduced fuel efficiency to severe consequences like tire failure, tread separation, and blowouts. Schrader, a prominent manufacturer of tire pressure monitoring systems, reports that underinflated tires significantly impact road safety, contributing to approximately 250,000 accidents, 33,000 injuries, and 660 fatalities annually.
Because of statistics like these, laws have been put into effect to regulate monitoring tire pressure in vehicles. TPMS, or Tire Pressure Monitoring System, is a safety feature integrated into vehicles (or added as an aftermarket component) that continuously monitors tire pressure and alerts the driver if the pressure in one or more tires drops below acceptable levels.

## Types of tire-pressure gauges
### Analog gauges

Dial gauges feature a round dial with a needle that moves to indicate the tire pressure. The pressure is usually displayed in pounds per square inch (PSI), bar, or kilopascals (kPa). Dial gauges are known for their durability and ease of use.
Pen-type gauges are compact gauges that resemble a pen and have a small dial or scale for reading pressure. They are portable and often used for their simplicity and convenience.

### Digital gauges

Electronic gauges use electronic sensors to provide a digital reading of tire pressure. They often come with backlit screens for better visibility and may include additional features such as memory functions for storing previous readings or automatic shutoff to conserve battery life.
Smart gauges are equipped with Bluetooth technology to sync with smartphones, allowing users to monitor tire pressure through a mobile app. These smart gauges can provide real-time data and alerts.

### Beam gauges

Beam gauges use a mechanical lever and a scale to measure tire pressure. They are less common but offer a straightforward, no-frills approach to pressure measurement. Their accuracy depends on the quality of construction.

## Regulations on tire pressure

Since September 2007, all new automobiles below 10,000 lb (4,500 kg) in weight sold in the United States are required to incorporate a Tire Pressure Monitoring System, which is capable of monitoring all four tires and simultaneously reporting under-inflation of 25 percent of cold placard pressures in any combination of all four tires. TPMS known as Direct TPMS are capable of TREAD Act legislation requiring simultaneous pressure measurement for each tire pressure.