How To Know When To Replace Your Car’s Tires

In most states, you’re legally required to replace your tires when the depth of their treads reaches 2/32″. At that point, the grooves have become so worn that your tires provide very little traction. They become a safety concern to you, your passengers, and other drivers.
On dry road surfaces, shallow grooves rarely pose a problem. There’s sufficient traction between the road and rubber to give drivers plenty of control over their vehicles. This is the reason race cars use slicks. On wet roads, however, shallow grooves are dangerous. The moisture has less room within the treads; with nowhere to go, it causes your vehicle to hydroplane.
In this article, we’ll take a contrarian look at your car’s tires. You’ll first learn how to use a penny to determine whether your treads are legal (i.e. deeper than 2/32″). We’ll then explain why letting them reach that point may be unsafe.
Using A Penny To Measure Tread Depth
You can purchase a tread depth gauge at nearly any auto supply store for under $10. It is worth the expense (you’ll understand the reason in a moment). Most people forgo the gauge, however, and instead use a penny to test their treads.
The process is simple. Insert a penny into the grooves of your tire with Lincoln’s head positioned upside-down. If the coin submerges to the point that any part of Lincoln’s head is covered, it means the tread depth is at least 2/32″. The tire is legal. But it may still be unsafe, which means the penny test can be unreliable.
The Problem With The “Lincoln’s Head” Test
Your tires are equipped with wear indicators. These are bars molded into the rubber by the manufacturer in order to let you know when your treads have reached 2/32″. Nearly all tires have them. The problem is, that tread depth may be unsafe, depending on where you live.
As mentioned earlier, when the roads are dry, there’s plenty of traction. Even tires that are bald are relatively safe. So, if you live in a region that receives very little rain or snow, allowing your treads to reach 2/32″ should be fine. On the other hand, if you live in an area that receives a lot of rainfall and snow, you should replace your tires earlier. On wet roads, you’ll lose traction long before the grooves reach 2/32″.
If you frequently drive on wet roads, consider replacing your set when the tread depth reaches 4/32″. If you drive in snow on a regular basis, replace them at 6/32″.
As a side note, you can perform the penny test with a quarter to identify when the grooves of your tires reach 4/32″. The top of Washington’s head is the marker.
A Closer Look At Your Treads
To understand the reason moisture causes a loss in traction, it important to recognize what occurs between moisture and the treads. The pattern of the grooves is designed to direct water, and bite into snow. Unlike air, water cannot be compressed. When your tires make contact, the moisture enters the grooves, and is moved through them. As long as there is plenty of room, you’ll retain traction.
At any given time, only a small area of your tires will make contact with the road’s surface. The shallower your treads, the less water required to fill them. This causes the area of your tires that touches the road to shrink. As it becomes smaller, you’ll begin to hydroplane. This problem is even more pronounced with slush (from snow) since it quickly fills in the treads, and often remains there. It robs your tires of traction.
To recap, determining the right time to replace your vehicle’s tires depends largely on whether you drive on wet or slushy roads. While 2/32″ may be the legal tread depth in most states, replacing your set when they reach 4/32″ or 6/32″ may be more appropriate.