The importance of tread depth

Tire School

The importance of tread depth

Fast facts: Ways to check tread depth

  • Tread wear indicators are spaced evenly through the main grooves in the tire tread. If they are flush with the level of the tread, then the tire must be replaced.
  • If you have a tire tread depth gauge, insert the probe bar into the groove and push the shoulders flush with the tread. Check the top of the gauge to see the measurement.

Your tires form the essential bond between your vehicle and the ground. The tread grips the road as you drive. But if it’s not deep enough, your car loses traction and suffers extended braking times. Shallow tread grooves make it harder to control the vehicle in wet weather and the chance of aquaplaning increases. To ensure your safety, measure the tread depth as part of your regular vehicle maintenance.

Tread is the rubber on the tire that touches the road. New tires have an average tread depth of 8 to 9 millimeters (10/32 to 11/32 inches). As you drive, the tread will wear down. A tire with a tread depth below 1.6 millimeters (2/32 inches) lacks grip. Braking distance and vehicle control are impaired. These tires are not safe for driving and must be replaced.

Please consider that safe driving in wet and snowy weather conditions is affected by the tread depth, the pattern design and the rubber compound of the tread of your tires. On wet or snow-covered roads braking performance will progressively decline with lower tread depths. On wet roads there is an additional increased risk of aquaplaning with fading tread depths.

Therefore, check your tires regularly, reduce your speed on wet and snowy roads and consider replacing your tires in good time.

Ensure your vehicle is equipped with the correct winter, summer, or all-season tires.

Tread Wear Indicators

Tread wear indicators, or wear bars, are spaced evenly through the main grooves in the tire tread. If they are flush with the level of the tread, then the tire should be replaced.

Several winter tire models are equipped with winter tire wear indicators.  If they are flush with the level of the tread, the tire is no longer suitable for winter driving conditions. In some locations, they may also no longer legally qualify as winter tires.

Tire tread patterns and their many uses

Fast facts: Different types of tire treads

  • Symmetrical tire tread patterns deliver smooth driving, high directional stability, and low rolling resistance.
  • Directional tire tread patterns provide high protection against aquaplaning, excellent handling on snow and mud, and very good road-holding at high speeds.
  • Asymmetric tire tread patterns offer excellent handling, high curve stability, and good grip in wet conditions.
  • To maintain optimal safety and performance, avoid mixing tire tread patterns where possible.

The tread is the part of the tire that makes contact with the surface of the road. And if you take a look at different tires on the market, you’ll notice a great deal of variety in their tread patterns.

Why are they so different? Because a tread pattern is a unique design that enhances a vehicle with grip and handling for specific driving conditions. Just like in a detective novel, you could identify a make of tire by the tracks it leaves on the road.

Every tire tread has four constituent parts:

  • Ribs are the raised section of the tread pattern, made up of tread blocks;
  • Grooves are deep channels which run circumferentially and laterally around the tire;
  • Tread blocks are the raised rubber segments that make contact with the road surface;
  • Sipes are small, thin slots molded into the tread blocks.

Taken together, the ribs, grooves, tread blocks, and sipes can be arranged in a unique pattern to modulate the tire’s performance in critical areas like noise, handling, traction, and wear.

And that in turn provides tire manufacturers with the ability to develop tread patterns to address specific driving needs like wet braking, dry handling, aquaplaning (hydroplaning) resistance, and traction on ice and snow.

How many tire tread patterns are there? Quite a few. But broadly speaking, we can distinguish between three categories of tire tread pattern. Which one does your car have?

Symmetrical tire tread pattern

The most common type of pattern is symmetrical; it’s suitable for passenger car tires, but not for high-performance use. Tires with this design have continuous ribs or independent tread blocks across the entire face of the tread, and both halves of the tire feature the same pattern.

Key features:

  • Smooth driving
  • High directional stability
  • Low rolling resistance

Tires with symmetrical patterns provide the owner of the vehicle with the most flexibility for tire rotation without affecting day-to-day performance. They’re also quiet, long-lasting, and fuel efficient. However, they are less adaptable to changing conditions on the road. So even though symmetrical patterns deliver steady grip on a dry road, they won’t be as effective in wet conditions as other tires.

Directional tire tread pattern

A tire with a directional tread pattern is designed to roll forward in one direction only. It has lateral grooves that meet in the middle of the tire tread, resembling the shape of an arrowhead. Its purpose is more than sporty aesthetic, however. The V-shaped grooves are more capable of resisting aquaplaning (hydroplaning) at high speeds by displacing water more efficiently through the tread pattern.

Another benefit of directional tread is extra traction, which provides excellent handling on snow or mud. For this reason, a good all-season or winter tire is highly likely to have a directional tread pattern. The extra traction is also useful for performance tires on high-performance vehicles.

Key features:

  • High protection against aquaplaning
  • Excellent handling on snow and mud
  • Very good road holding at high speed

The point to remember about directional patterns, however, is that tire rotation becomes a bit more complicated. They can only be rotated vertically – for example, from the front of the car to the back – otherwise, the pattern will be oriented in the wrong direction when fitted to a wheel on the other side of the vehicle. That would render the benefits of the tire tread useless.

You can keep track of the correct orientation using the arrow indicator printed on the sidewall of the tire. It’s in the same direction as the pattern, pointing in the required direction of travel.

Asymmetric tire tread pattern

A tire with an asymmetric pattern features two separate tread designs, one on the inner half and another on the outer half of the tire. It looks unusual, but both halves serve a distinct purpose.

The inner tire tread is responsible for water displacement and protection against aquaplaning (hydroplaning). The outer tire tread has rigid tread blocks for higher lateral stiffness, which provides high grip when cornering and driving on dry surfaces, and quieter interior noise. This combination of features makes asymmetrical tires especially popular for use on ultra-high-performance cars.

Key features:

  • Excellent handling
  • High curve stability
  • Good grip in wet conditions

However, just like a directional tire pattern, care must be taken with tire rotation. Vertical rotation between front and back are the options here. Indicators on the sidewall will guide correct fitting.

Do not mix tire tread pattern

When buying new tires, avoid mixing different types, sizes, or brands of tire on a single vehicle. For best results, source the identical make and model of tire to the ones you already have on your wheels, to maintain optimal performance characteristics.

Another thing to keep in mind when replacing tires; replacing a pair of tires is safer than replacing just a single tire. The newest tires should be fit on the rear axle, and partially worn tires to the front axle.

If this isn’t possible, then drivers are advised to ensure that the replacement tire has the same tire tread pattern as the other tire on the same axle. Mixing the patterns will impair the handling characteristics of your car; it could even be dangerous.


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