There are two main types of tire pressure gauges: fixed workshop gauges and portable pocket size gauges. The objective of this procedure is to show you how to use a tire pressure gauge and interpret the readings correctly.
Part 1. Preparation and safety
- Use a tire pressure gauge and interpret the readings correctly.
Whenever you perform a task in the workshop you must use personal protective clothing and equipment that is appropriate for the task and which conforms to your local safety regulations and policies. Among other items, this may include:
- Work clothing - such as coveralls and steel-capped footwear
- Eye protection - such as safety glasses and face masks
- Ear protection - such as earmuffs and earplugs
- Hand protection - such as rubber gloves and barrier cream
- Respiratory equipment - such as face masks and valved respirators
If you are not certain what is appropriate or required, ask your supervisor.
- Do not inflate tires above the pressure recommended by the tire manufacturer. If you do, the tire may explode or the wheel rim may give way and cause a blowout. The result will almost certainly be personal injury.
- Make sure that you understand and observe all legislative and personal safety procedures when carrying out the following tasks. If you are unsure of what these are, ask your supervisor.
Points to note
- There are two main types of tire pressure gauges — fixed workshop gauges and portable pocket size gauges.
- The two most popular types of pocket tire pressure gauges are the pencil type and the dial type.
- The pencil type looks similar to a pencil and contains a graduated sliding extension that is forced out of the sleeve by air pressure when it is attached to the tire valve.
- The dial type has a similar fitting to the pencil type but includes a graduated gauge and needle.
- Each gauge measures pressures in either pounds per square inch (PSI), kilopascals (kPa) or bar.
- One bar is equivalent to 100 kPa and 14.5 PSI.
- One PSI is equivalent to around 7 kPa. Some gauges have scales for both units of measurement.
- Pocket type tire pressure gauges are inexpensive and more accurate than the gauges provided by service stations. Service station gauges are often damaged by weather, misuse or being run over.
- There may also be a significant difference in readings between one service station tire pressure gauge and the gauge from another service station.
- If the same pocket type tire pressure gauge is always used to check tire pressures, then there will be no variation of readings.
- The tire pressure will vary from vehicle to vehicle, its use and driver preference. Recommended tire pressures are located on the vehicle manufacturer's tire decal. The recommended maximum tire pressure is located on the tire sidewall. Never inflate the tire above the recommended maximum pressure. The tire may explode, or the wheel rim may give way and cause a blowout.
Part 2: Step-by-step instruction
- Remove the valve cap
First, remove the valve cap from the tire valve. Be sure to place it where you can find it later!
- Fit pencil gauge to the valve
Make sure the graduated sleeve is seated into the gauge body, and then push the tire gauge chuck firmly onto the head of the valve. If air escapes, adjust the angle and your hand pressure until no more air leaks out.
- Read the scale
When the graduated sleeve slides out, remove the gauge from the valve without moving the sleeve and examine the scale.
- Add the numbers
Read the bottom number, then count the marks. Add them up, and you’ll find the tire pressure
- Examine dial gauge
When using a dial type gauge, check the graduations on the dial. They may be in pounds per square inch, or if it’s a metric gauge they will be in kilopascals or bar. Many gauges have all three graduations: PSI, kilopascals and bar. Once again, remove the valve cap and put it in a safe place.
- Attach the gauge to the valve
Attach the dial pressure gauge to the top of the valve. Adjust your hand pressure and angle, so that no air is escaping from the valve.
- Read the gauge
When the needle has jumped, remove the gauge from the valve, and read the dial. The numbers are by tens, and the marks between are units.
- Reset the gauge
Reset the dial gauge to zero by pressing the button on the neck of the dial. Repeat the procedure for all wheels. Remember to replace the valve cap on each wheel as you go.
- Check your results
Check your tire pressure readings against the specifications in the shop service manual. You will also find a tire decal listing the recommended tire size and pressures. This is usually located on the driver’s door, driver’s door pillar or glove compartment lid.