So, when are your tires actually worn out? This is a question a lot of us ask ourselves. For many, the answer is when they no longer pass a safety inspection. But waiting that long can have a serious impact on your safety.
The U.S. Federal government doesn’t have any laws for tread depth, but 42 of the states, and all of Canada, do have regulations. They consider two-thirty-seconds of an inch to be the minimum legal tread depth. Two other states, including California, consider one-thirty-second to be the minimum and six states have no standards at all.
Since 1968, U.S. law has required that a raised bar be molded across all tires. When tires are worn enough that this bar becomes visible, there’s just 2/32” of tread left. But does that older standard give you enough safety?
Well, Consumer Reports issued a call to consider replacing tires when tread reaches 4/32”. And the recommendation is backed by some very compelling studies. Now before we go into the studies, you need to know that the big issue is braking on wet surfaces.
We tend to think of the brakes doing all the stopping, but you also need to have effective tires to actually stop the car. When it’s wet or snowy, the tread of the tire is critical to stopping power.
Picture this: you’re driving over a water-covered stretch of road. Your tires actually need to be in contact with the road in order to stop. That means the tire has to channel the water away so the tire is actually contacting the road and not floating on a thin film of water – a condition known as hydroplaning. When there’s not enough tread depth on a tire, it can’t move the water out of the way and you start to hydroplane.
This is where the studies come in. We think you’ll be surprised. A section of a test track was flooded with a thin layer of water. If you laid a dime flat on the track, the water would be deep enough to surround the coin, but not enough to cover it.
A car and a full-sized pick-up truck were brought up to 70 mph and then made a hard stop in the wet test area. Stopping distance and time were measured for three different tire depths. First, they tested new tires. Then tires worn to legal limits. And finally, tires with 4/32” of tread were tested – this is the depth suggested by Consumer Reports
When the car with the legally worn tires had braked for the distance required to stop the car with new tires, it was still going 55 mph. The stopping distance was nearly doubled. That means if you barely have room to stop with new tires, then you would hit the car in front of you at 55 mph with the worn tires.
Now with the partially worn tires – at the depth recommended by Consumer Reports – the car was still going at 45 mph at the point where new tires brought the car to a halt. That’s a big improvement – you can see why Consumer Reports and others are calling for a new standard.
Now without going into all the details, let us tell you that stopping the truck with worn tires needed almost 1/10 of a mile of clear road ahead to come to a safe stop. Obviously this is really a big safety issue.
The tests were conducted with the same vehicles, but with different sets of tires. The brakes were the same, so the only variable, was the tires.
So, how do you know when your tires are at 4/32”? Well, it’s pretty easy. Just insert a quarter into the tread. Put it in upside down. If the tread doesn’t cover George Washington’s hairline, it’s time to replace your tires. With a Canadian quarter, the tread should cover the numbers in the year stamp.
Now you may remember doing that with pennies. But a penny gives you 2/32” of an inch to Abraham Lincoln’s head. The quarter is the new standard – 4/32”.
Tires are a big ticket item and most people want to get the most wear out of them that they can. But do you want that much more risk just to run your tires until they are legally worn out? For us, and we would guess for many, the answer is “no”.
Well, Mr. Washington, let’s go out and look at my tires.