Tread Wear Indicators: How to Use the Wear Bars

What are tread wear indicators?

Tread wear indicators, usually called wear bars, are small raised projections molded into the floor of a tire's tread grooves. Federal Motor Vehicle Safety Standard 571.139, which covers new pneumatic radial tires for light vehicles, defines a treadwear indicator as "the projections within the principal grooves designed to give a visual indication of the degrees of wear of the tread." The same regulation defines a groove as "the space between two adjacent tread ribs."

The purpose of the wear bar is to provide a visual check that needs no gauge. When the bar becomes level with the tread blocks on either side, the tire has reached the depth at which it should be replaced. Federal standards require new pneumatic tires to incorporate a tread wear indicator, so you will find them on essentially every passenger and light truck tire sold.

Where to find the wear bars

Wear bars sit at the bottom of the principal grooves, the deep channels that run circumferentially around the tire. They appear as small flat bridges spanning the groove from one tread rib to the next. Look for a series of bars spaced at regular intervals around the tire, usually in the groove nearest the shoulder.

Because tread wear is not always uniform, check several points around the circumference of each tire. A bar in the center of the contact patch may be flush while one near the shoulder still shows depth, and that difference is worth investigating before you buy a replacement. If the wear pattern is uneven, the cause may be an alignment or inflation problem that will damage a new set just as quickly.

How to check the wear bars

On a fresh tire, the wear bar sits well below the tread surface, hidden inside the groove. As miles accumulate, the bar moves closer to the top of the tread. The moment the bar is level with the surrounding tread blocks, the tire has reached the wear limit and should be taken out of service.

A quick finger test works well: run the pad of your thumb across the groove. If you can feel a distinct recess where the bar sits, you still have some margin. If the surface feels flat and smooth from the bar to the tread block, the tire is at the limit. Repeat the check at several spots around the tire, including the inner and outer shoulder grooves.

Many drivers also use a coin as a rough check. Insert the coin into the groove with the head pointing down. If the top of the head is covered by the tread, you have depth to spare. If the head is visible above the tread, the tire is near or at the wear limit. The wear bar itself remains the most reliable reference because it is molded to the correct depth.

If you notice an uneven wear pattern, see our Learn article on tire tread wear causes for a deeper look at what might be going on.

What it means when the wear bars are flush

When a wear bar is level with the tread blocks, the tire has lost most of its groove depth. At this point, the tire's ability to evacuate water from the contact patch is significantly reduced, increasing the risk of hydroplaning on wet roads. Stopping distances on wet pavement also lengthen, and the remaining tread offers little cushion against road hazards.

Replacement is the only safe action when the wear bars are flush. Do not wait for cords to show or for the tire to fail. Worn tires are a leading cause of weather-related crashes, and the cost of a new tire is far lower than the cost of a collision.

If you are comparing tires for your next set, use our buying guides to see spec-based picks for your size, such as the best 17-inch tires or best all-season tires. For general replacement guidance, see our Learn article on when to replace tires.

What to do about your wear bars

Questions

What do tire wear bars look like?

Wear bars are small flat rubber bridges that run across the bottom of the tread grooves, perpendicular to the direction of the tread. They are usually spaced every few inches around the tire and may be harder to see on a new tire because they sit deep in the groove.

How often should I check my tire wear bars?

Check them at least once a month, along with tire pressure. It is also a good idea to check them before a long trip or when you notice any change in handling, noise, or wet-road performance. A quick visual check takes less than a minute per tire.

Can I drive if the wear bars are flush?

No. A flush wear bar means the tire has reached its legal wear limit and is unsafe for normal driving. It will have poor traction in wet conditions and a higher risk of hydroplaning. Replace the tire as soon as possible.

Do all tires have wear bars?

Federal safety standards require new pneumatic tires for light vehicles to have tread wear indicators, so essentially all passenger and light truck tires sold in the U.S. include them. Temporary spare tires and some specialty tires may have different requirements, so check the tire sidewall for markings.

What is the difference between wear bars and a tread depth gauge?

A wear bar gives a visual reference without any tools, while a tread depth gauge measures the remaining depth in 32nds of an inch. Both are useful. The wear bar is set to indicate the minimum safe depth, so if it is flush, the tire is worn out even if a gauge shows a slightly different number due to measurement location.

Why is the tread wear indicator sometimes called a TWI?

TWI is the abbreviation for tread wear indicator, and it often appears as a small triangular or arrow-shaped mark on the tire sidewall. This mark points to the location of the nearest wear bar, making it easier to find the bar without scanning the entire tread.