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Tire Tread Depth Tests & Tire Wear Indicators

When tires are new they look very different than a typical set that has seen 20,000, 40,000, or 60,000 miles. Over time, tire tread depth wears down along with the tire’s performance in rain, light snow, and other conditions where traction is compromised. Hydroplaning resistance is also greatly reduced as a tire ages. Most tires start out with between 8/32 and 10/32 of an inch of tire tread depth. To help deal with such small increments of measurement, certain tire tread depth and tire wear indicator tests were developed for the average person to be able to check their tires.

Believe it or not, coins are great tire wear indicator. For example, just about everyone knows the tire tread depth “penny test.” Tires need to be looked over periodically to measure tread depth, and the penny test is fine in a pinch. It is done by holding a penny heads-up, upside-down and sticking it into the deepest part of the tire tread. If the tread comes up to the top of Abe Lincoln’s head, it means the tire still has 2/32” of useable tread, the legal minimum in most states.

For many years tire manufacturers have incorporated tread wear indicators (TWIs) also known as wear bars, into all tires. These small raised “bars,” between 1/32 and 2/32 of an inch in height, are located in the deepest part of the tread. The concept behind incorporating TWIs into a tire is that once the tire tread depth is worn down to the point that it is no longer safe, the TWI will show, visually indicating the tire needs to be replaced by bridging the gap between tread blocks.

The advent of TWIs could have been the demise of the so-called “penny test,” but it lives on – with some good reason. TWIs are not located everywhere on the tire, so a penny can be used effectively to make sure some sections of tire tread depth are not lower than the areas where the TWI are located. Uneven wear can occur due to a number of factors including over- or under-inflation of a tire, emergency braking, and alignment or suspension problems. Still, as tire wear indicators go, the “penny test” is mostly useful at the end of a tire’s life and may only show that you may need to replace your tires immediately, not how much life they may have left. This is where the “quarter test” comes in.

Similar to the “penny test,” the “quarter test” is a tire tread depth test that’s done by holding a quarter upside-down and sticking George Washington’s head into the deepest part of the tire tread depth. If tread covers Washington’s head, this shows that the tire has at least 4/32” of tread left and is still perfectly useable. Performance will not be as good as new tires would be when driving over standing water or in other adverse conditions, but it is not as severely compromised as it could be. In terms of tire wear indicators, if your tires pass the “quarter test,” the tire tread depth should still be relatively safe (and legal).

Any tire shop can fit your car, but at The Tire Choice and Total Car Care we combine great prices, exceptional service, and a comfortable waiting area featuring amenities like wireless internet. Come by one of our many locations to find out the difference between The Tire Choice and just another tire store.


Tips and Facts

Tip: Don’t have a penny? The Tire Choice will check your tire pressure and tread depth free of charge.
Tip: Make sure your tires are properly rotated, aligned, balanced, and inflated – all of which reduce tire wear.
Fact: Since 1968, U.S. law has required all tires must be made with tire wear indicators.
Fact: Tire wear patterns can indicate different problems with your tires. For example, a worn center tread means overinflated tires.


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