Introduction
Tire tread depth is an important indicator of how much the tire has worn and to know the amount of tread remaining in the tire. Note: A single visual inspection or just one measurement is not sufficient to evaluate a tire, this is because of uneven wear and also the incorrect positioning of the probe. Different measurement methods can lead to wrong conclusions.
A tire tread depth gauge provides a better assessment of tire tread depth than simple visual estimation or even a single measurement. To get accurate results, measure in the right place. Then consider the results in the context of a full tyre inspection.
The following guide shows you how to check the depth of the tire tread, including where to take the measurement and how to use that measurement when carrying out a tire check.
Why Accurate Tire Tread Measurement Matters
You can’t reliably measure tire tread by visual inspection, since a tyre may look to have adequate tread from the outside while the inner or outer shoulder is actually more worn. Furthermore, tread measurement can show the differences.
Constant measuring of tread depth enables the technician to compare the wear on various sections of the tire and also to assess the wear on all tires. Tire shops and repair facilities can use this information to make maintenance recommendations and explain their findings to customers.When checking the tyre it is not enough merely to look at the lowest measurement reading; it is also important to take into account both the position of the measurement and the difference between the various measurement points.
Can You Check Tire Tread Depth Without a Gauge?
Yes, in the section referred to as ‘tire wear and damage’ we explain how to describe the depth of the tire tread without having to use a special tool for this purpose; the ‘penny test’ or ‘coin test’ is a simple method of checking whether the tread of a tire is worn.
The tire tread can be assessed for obvious wear using the coin test. This test does not measure tread depth in millimetres or inches, and it also fails to show differences in wear between the inner, central, and outer parts of the tread.
Although these methods may be useful for spotting obvious wear, the coin test is not a technique for measuring tread depth and so can be quite different from the real tread depth. It also cannot measure the inner, central and outer parts of the tyre separately.
Use these for a preliminary check but not for a tire tread gauge. Make sure you measure multiple locations and use the measurements to compare tires.
When Should You Use a Tire Tread Depth Gauge?
A tire tread depth gauge is more useful than a simple visual check for detecting tire wear.
- Checking tires before replacement or seasonal maintenance
- Comparing tread wear across different areas of a tire
- Investigating possible uneven tire wear
- Inspecting vehicles in a fleet or workshop
- Recording tread depth for service reports
- Tire wear between the left and right sides of an axle
A depth gauge needn’t be inaccurate; the accuracy of a tire tread depth gauge is determined by the right position, the choice of the best measurement points, and the consistent use of the tool.
For more details regarding the different types of gauge, their features, and the criteria for selection, please see our comprehensive guide to the tire tread depth gauge.
Prepare Before Measuring Tire Tread Depth
Good preparation helps prevent measurement errors. Park your vehicle in a safe area in the parking lot. Measure the tire tread in a place that is wide enough for your measurement. Check the tire for visible damage like embedded objects, cracks etc. Remove stones, etc., that could get into the groove of the tread and hinder a correct measurement with the tire tread gauge. Make sure the tire tread gauge is clean and ready for measurement. Also check if a battery-powered gauge has enough power.
Remove any stones, etc., which might cause the gauge to come into contact with the tread groove of the tyre. Make sure that the tool is clean and in good condition. In the case of a battery-operated gauge, verify that it has been left on or that it has enough power.Tell us which tyre you measured, for example the front-left tyre, the front-right tyre, the rear-left tyre or the rear-right tyre. This will be useful when you come to look at your results later.
Where Should You Measure Tire Tread Depth?
Tire tread depth is measured at various points across the width of the tire and may differ because of the tire’s inflation, its alignment, the vehicle’s suspension, and other factors relating to vehicle maintenance.
Measure Across the Tread Width
Check three main areas:
- Inner shoulder
- Center tread
- Outer shoulder
Take the tire measurements from the indent of a suitable tread groove rather than on top of a tread block. Continue to take measurements in the same manner for all three test areas.
Note the difference between the inner shoulder, central, and outer shoulder readings; do not average them to get a single value. Instead, record the difference.
Measure at Several Points Around the Tire
Uneven tread wear may happen due to irregular wear around the circumference of a tire. Measure at different points to pick up any unusual wear.
Measuring multiple points helps you identify wear patterns and provides a useful reference for future comparisons.
Do not take the most severe or the least severe wear as the only criterion. Your aim is to determine the general amount of wear on the tyre, not to arrive at a particular figure.
How to Measure Tire Tread Depth Correctly
1. Set the gauge in the correct position.
Start by inserting the probe into the tread groove and place it against the base of the groove. Check that the gauge is properly positioned with respect to the tread. It is to use the probe straight into the groove and not at an angle. Also make sure the probe is in full contact with the groove.
The following steps apply in most cases, but may differ depending on the type of gauge you are using and the particular design of the probe supplied. Although some gauges measure actual groove depth, others measure to the top of the tread. Refer to the operating instructions for your gauge model.
2. Apply the same method to every reading.
When comparing the measurements, it is necessary to use the same method of contact and a tire area that is comparable.
All technicians must use the same inspection method. Do not use different contact angles or measure different areas. Record any changes to the procedure.Although a digital display makes tyre measurements easy to read, it does not remove the operator from the error loop; the operator must place the measuring tool in the correct position to take accurate measurements.
3. Take the readings and compare them.
Take note of where the tire was, when the measurement was taken and the position of the measurement (for example, inner, centre, or outer in the case of a single tire).
Then compare:
- Different areas across the same tire
- Tires on the same axle
- Left and right tires
- Readings from previous inspections
If you want to carry out repeated measurements and make digital records of your tire inspections, you should use a digital tire tread depth gauge such as the UDIAG TT300 Tire Tread Detector. This device shows the measurement clearly on its screen and that data can be recorded and transmitted to the TreadX App, where records of the tire’s position on the vehicle, the vehicle itself, and all the measurements taken can be stored. Further details about the UDIAG TT300 are available here.
How to Interpret Tire Tread Depth Readings
It should be noted that the minimum tread depth reading may be useful, but when you are comparing different measurement points on the tyre consider whether there are consistent wear patterns.
For example, a tire may show:
- Lower tread depth on the inner shoulder
- Greater wear in the center of the tread
- More wear on the outer shoulder
- Significant differences between several points around the tire
The tire wear patterns may be linked to tire pressure, tyre alignment, the suspension parts, tire damage, tyre number and other factors. We need to investigate further to identify the root cause of the reading.
No single measurement can give a complete description of the tire; it has to be considered together with the wear pattern and the other measurement points on the tire.
When Does Tread Depth Suggest Further Inspection?
Further inspection is appropriate when the readings approach the applicable legal limit, vary significantly across the tread, or show an unusual wear pattern. Always consider the regulations in the relevant market and the tire manufacturer’s recommendations.
Remember that the legal minimum is not the same as a recommended replacement point. Tire age, inflation condition, tread wear indicators, cracks, bulges, cuts, and sidewall damage also affect the replacement decision.
If the tread depth appears acceptable but the tire has visible damage or severe irregular wear, do not rely on the measurement alone.
At What Tread Depth Should Further Inspection Be Carried Out?
If the tread depth measured is close to the standard for the market, or if there are significant local variations, or if the wear is unusual, further inspection should be carried out. The legal minimum limit for tire wear and the limit recommended by the manufacturer for replacement should be compared, and other factors which affect the decision to replace the tires should also be taken into account.
It should be noted that the lowest legal limit for tread depth is not necessarily the same as the limit beyond which a tire should be retired and replaced; in addition to this, various other factors must be considered, such as the tire’s age, its recent history of inflation, the way its tread has worn down against the tread wear indicators, the presence of cracks, bulges, cuts and any damage to the sidewall. One should not ignore any visible signs of damage.
A tire replacement decision should consider several factors together:
Measure the remaining tread depth. Compare it to the minimum required numbers and the manufacturer’s recommendations.
Does the tire tend to wear evenly across its inner, central, and outer sections?
Other indications of wear and damage include surface cracks, bulges, cuts or punctures, and the ageing of the tyre’s surface etc.
The way the vehicle is used (for example, the amount of load, the mileage, the conditions of driving, etc.) together with its maintenance record.
A tread depth gauge gives useful measurement data.
Conclusion
To measure the tread depth of a tire, measuring just one point is not enough; you should measure in the proper position and take readings at several spots on the tire, such as the middle and the outer edge, then record these readings.
The coin test gives a quick indication of the tread depth, but is less accurate than using a tire tread depth gauge to give a specific measurement. When deciding whether to replace a tire, consider the depth of tread, the wear pattern, any damage to the tire and the relevant guidance or recommendation.