On the topic of tread, you might know that several years ago the Rubber Manufacturers Association (RMA) ran a campaign to encourage drivers to regularly monitor the condition of their tires....
In this RMA campaign they invented the acronym "PART" to help people remember the 4 steps they recommend: Pressure, Alignment, Rotation, Tread. These steps should be done at least once a month and before any long trip.
Today, I'd like to tell you about the Tread step.
First, let's define the tread. It is the part of your tire where "the rubber meets the road", the band of rubber and groves which surround the circumference of your tire.
As you drive, or use your tire, the tread gets worn down little-by-little until eventually it is all used up. Under ideal conditions, with your car in perfect mechanical shape this will take possibly 2 or 3 years, but certain driving habits, less than perfect roads and weather, and mechanical defects can cause this wear to happen more quickly. Tires approved for sale in the USA have a treadwear rating stamped on the tire sidewall.
When the tire is new, the thickness of this band of rubber varies depending on the design and model of tire, but when it gets down to 2/32nds of an inch (slightly more than 2mm) the tire is effectively worn out and needs to be replaced. In fact, many areas have laws which make it illegal to drive with a tire which has less than this depth of tread.
Tire professionals use a special little tool, a depth gauge, to measure tire tread, but there are two simple methods which anyone can use to quickly determine if the depth of the tread is over the minimum requirement.
The first method is built in to most tires made today. These are wear bars, which appear as little bumps in the grooves of a tire, placed at regular intervals around the circumference of the tire. These wear bars are exactly 2/32 of an inch in thickness so that when the level of the surrounding tread is higher than the wear bar, the tire still has useful life. When the tread is level with the wear bar the tire needs to be replaced.
The second method involves using a US penny. Place the penny in a tire's groove with Lincoln's head entering the groove. As long as a part of the head is covered when the coin is fully inserted in the groove, there is more than sufficient tread depth, but once the top of Lincoln's head is visible, it's time to change that tire.
When you're checking the tire make sure you look at several sections around the complete circumference and look for signs of uneven wear. You may have irregular tread wear if there are high and low areas or unusually smooth areas. Also make sure no nails or other objects are embedded in the tire. If you notice any of these conditions you need to check with a tire dealer as soon as possible if you see problems.
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Accutire Digital Tire Air Gauges help maintain accurate air pressure. Available at The Tire Rack.