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tires January 21, 2016

Low Pressure and Worn Tire Tread Contributes to Accidents

When was the last time you checked your tire’s air pressure? Don’t remember? What about your tire tread? Many drivers forget about these details as they may not seem to affect everyday driving. However, according to a 2012 National Highway Traffic Safety Administration (NTHSA) study the dangers of low air pressure and worn tread on your tires are immense and have been shown to contribute to accidents.

The Importance of Proper Tire Inflation

When a tire is underinflated, the majority of the car’s weight shifts from being spread out evenly across the width of the tire to being concentrated on the tread that is located just under the sidewalls. This means that as the tire rotates, the sidewall gets continually flexed, or squished, and heats up. This affects both performance and safety. According to NHTSA, tires underinflated by 25 percent or more are three times as likely as properly inflated tires to be cited as factors in highway crashes.

The government acknowledged this and passed the TREAD Act, which requires all motor vehicles sold after September 1, 2007 to be equipped with tire-pressure monitoring systems (TPMS). This is an electronic system designed to monitor the air pressure inside the pneumatic tires on various types of vehicles. TPMS report real-time tire-pressure information to the driver of the vehicle, either via a gauge, a pictogram display, or a simple low-pressure warning light.

For those vehicles equipped with TPMS, don’t ignore its warnings. For those drivers with vehicles not equipped with TPMS, buy a tire gauge (they cost less then $5) and use it to check each tire’s pressure monthly. Pick a memorable monthly date or add a reminder to your calendar so you do not forget. This simple routine could prevent a serious accident.

The Importance of Proper Tire Tread Depth

Tread depth is a vertical measurement between the top of the tread rubber to the bottom of the tire’s deepest grooves. In the United States, tread depth is measured in 32nds of an inch. Average new tires used on cars typically start with 10/32″ to 11/32″ of original tread depth. Tires fail Virginia State Inspections and are legally “worn out” when they reach 2/32″ of remaining tread depth.

But common sense tells us that you may not want to wait until your tires reach 2/32” to replace them. Whereas NHTSA found that about 26% of the tires with tread depths of zero to 2/32 inch contributed to crashes, 8% of the tires with 3/32- to 4/32-inch tread depth also created problems in crashes according to NHTSA.

This is especially a concern in climates like Northern Virginia, where we experience wet roads often—especially in the summer months. We recommend consider replacing your tires when they reach approximately 4/32″ of remaining tread depth. Since water can’t be compressed, you need enough tread depth to allow rain to escape through the tire’s grooves. If the water can’t escape fast enough, your vehicle’s tires will be forced to hydroplane (float) on top of the water, losing traction. Without traction, your vehicle cannot respond to the steering wheel or the brakes, presenting serious safety issues.

The good news is that it’s pretty simple to get a sense of your tires’ remaining tread depth: all you need is a penny or a quarter.

To measure the tire tread, place a penny in the groove between the treads with Lincoln’s head upside down. If part of Lincoln’s head is always covered by the tread, you have more than 2/32″ of tread depth remaining. Alternatively, place a quarter into several tread grooves across the tire with Washington’s head upside down. If part of Washington’s head is always covered by the tread, you have more than 4/32″ of tread depth remaining.

The Quarter Test

The Penny Test



Proper tire inflation and tread depth work hand-in-hand. Bottom line: Check your tire pressure and tire tread depth to protect yourselves and others on the road.

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