If you`re having trouble finding tread depth indicators, just look for a small “TWI` marker (profile wear indicator) along the sidewall (see images below). The depth of the tyre`s tread is also part of it. There are still many reasons why your tires and what they are mounted on could give you a headache at the time of WOF. We make a brief overview of the rules and regulations so that you can prepare for the next WOF visit. The main grooves are the wide grooves of the tread where the tread depth indicators are located. All other grooves are secondary grooves that can wear out during the life of the tire. Tread depth indicators (also called tread wear indicators or TWIs) are the projections inside the main grooves that tell you how far the tread is worn and usually about 1.6 to 2.2 mm thick. If you have trouble finding tread depth indicators, simply look for a small “TWI” mark along the sidewall (see Figure 7-1-1 and Figure 7-1-2). Well-balanced wheels ensure smooth, vibration-free operation, improve tread life, and extend the life of your vehicle`s suspension and steering components. The image below shows how hard a tire hits a wet road at different speeds. The faster you drive, the less effective your tires are if the tread depth is not up to date. The rule now stipulates that a tyre must have a tread cutting depth of at least 1.5 mm (excluding tie rods or tread depth indicator strips) in all main grooves containing formed tread depth indicators and over the entire circumference of the tyre.
When was the last time you checked the tread of your tires? According to the NZTA, the legal minimum tread depth is 1.5mm, but consultants say tyre grip in wet conditions decreases once the tread is less than 3mm. See how easy it is to check the tread of your tires with a 20-cent coin. But what can you do about it? After all, WOF controls serve our security. That is certainly a good thing. But there are holes and they can be in the tires (almost literally too). New vehicles only require a WOF check every 3 years, which is a real concern in terms of tread depth. Anecdotal evidence suggests that the number of dangerously discreet vehicles is increasing. Virtually all tires have shaped tread depth indicators. However, a small number of tires, such as retreaded tires or older tires, may not have molded tread depth indicators.
For these, the NZTA has retained the old requirement of at least 1.5 mm tread depth over 3/4 of the tread width and the entire circumference of the tire. Land Transport Rule: Tyres and Wheels 2001 has been amended to include new tread depth requirements. These requirements came into effect on November 1, 2007. They take into account new tread designs and allow for a more consistent examination of tread depth during vehicle inspections. Some high-performance tires have asymmetrical treads to improve handling and performance. These tires have an inner and outer tread pattern so that the pattern is not symmetrical over the entire width of the tread, and must be placed to fit a specific side of the tire with the corresponding side of the rim, as shown on the tire. If you move these tires from one side of your car to the other, the tires should not be removed from the rims and turned over, as this will cause the rim to fail. Even with a 6-month check-up, the tread can become weak in the meantime and fall to a dangerously low limit.
This is also not surprising, as the minimum requirements reduce the road contact area to just 5% when you`re on a wet road, as the tire struggles with water drainage. It is therefore not surprising that there is a call for an increase in the minimum. To measure the tread depth of your tire, place a 20-cent New Zealand coin in one of your tire`s center circumferential grooves. If you can see the whole number 20, it means your tire still has a tread of 2mm or less and it`s time to think about investing in new tires to make sure you stay safe while driving. Since this is the only part of the vehicle that adheres to the road, the tread depth of your tires is very important for the safety of your vehicle. Checking the tread depth of your tire is easy and only takes a few minutes. You can use a tread depth tester/gauge yourself or go to a local repair shop and ask them to check it out for you. Tire repairs must legally bring the tires back to the “safety tolerance” at the time of manufacture.
Approved vehicle standards apply. What are the main grooves and profile depth indicators and how can I find them? The main grooves are the wide grooves of the tread where the tread depth indicators are located. All other grooves are secondary grooves that can wear out during the life of the tire. The following shows different profile models with profile depth indicators (and therefore main grooves) and the width at which you should mark (NZTA image). Most tires have molded tread depth indicators that protrude from the tire`s tread when it reaches the minimum depth. The legal minimum tread depth is 1.5 mm in all main grooves containing these shaped tread depth indicators. These shall be at least 1,5 mm over the entire circumference of the tyre. Tyres on the same axle must have a number of fundamental characteristics in common. This means the same size, the same type of carcass (mixed steel layer, radial fabric offset, cross-angle/fold, run-flat) and the same profile type (mixed asymmetric, directional, normal road, etc.). Below are some guides to help vehicle inspectors measure tread depth against the new requirements for different types of tread patterns. The main grooves are the wide grooves of the tread where the tread depth indicators are located. All other grooves are secondary grooves that can wear out during the life of the tire.
Check your tires regularly to make sure there is enough tread. The minimum legal depth is 1.5mm, but the more profile you have, the better the grip and the safer you are. Tread markings and depth indicators are usually located in about six locations around the tire. It is important that these are not confused with the flat sections that are part of the profile template. In the following, different profile templates with profile depth indicators (and therefore main grooves) and the width in which you should measure marked, are displayed. Tread depth is measured in the main grooves containing tread depth indicators. However, there are tread patterns where the main grooves cover different widths of the tire tread. This means that to pass a WoF or CoF, some tires must have a tread depth of 1.5mm over a greater tread width than other tires. This is especially true for side-grooved tires (those that end at the edges of the tires), as shown in Example 1 in Figure 7-1-3.