How to Really Tell When Tires are Worn Out
See why using the penny trick is not the best way to measure tread depth. Learn about critical information to consider during the decision making process. Discover how to sidestep unnecessary tire replacement.
Don’t Use the Penny Trick
I never liked the penny trick for gauging tread depth, because it’s a haphazard measurement open to interpretation. Tires are expensive and should be evaluated with pinpoint accuracy. When you use President Abraham Lincoln’s head to make the decision, you could be selling yourself short. When inserting the penny into the tread, it might land on top of a wear indicator. These lumps are 2/32 higher than the rest of the tire. Since the copper coin is round, orientation is another problem. I mean no disrespect to the U.S. Mint, but the penny was not designed to be a precision measuring device.
Measuring Tread Depth
There is a precision measuring device designed specifically to get a reading of how much tread is remaining on your tires. A tread depth indicator is an inexpensive tool that stores easily in the glove box. The measurement scale slides in and out of a metal tube and read just like a tire pressure gauge. Here in the United States, we use the thirty-second scale and our friends around the world will use the metric scale. Both are included on the tool.The measuring pin attached to the scale has a flat spot on the bottom where it’s pushed between the rows of tread lugs. The outside tube has two flat wings at a 90 degree angle to rest against the top of the tread. The depth indicator is measuring the difference between these two points. You can slide the tool up and back to feel the high and low points of the wear indicator bumps to assure the tool is in the lowest spot.
Evaluating The Remaining Tread
It’s recommended to take measurements in three spots across the tire. Obtain readings from the outside, center and inside portions of the road contact area. You can write these numbers down for each tire so you can carefully evaluate the numbers and what they might mean. Drastic differences between the outside measurement and the inside is a sign the car needs an alignment. A tread depth reading that is lower in the center can be an indication of over inflated tires. In the inverse, center tread that is deeper than both sides can indicate under inflated tires.
The Decision Making Process
When we decide to replace tires we’re making a large financial commitment. Rubber is not getting any cheaper. On some high line luxury cars replacing the tires can cost over $1000. A general rule of thumb held up as the standard by many leasing companies is to replace a tire when it’s below 4/32 of tread remaining. Many lease contracts state customers will pay a penalty if the automobile comes in with tires measuring below this reading. Although the 4/32 rule is a good one there may be situations where you can get more or less out of those tires.
It Depends on Operating Conditions
The tread of the tire is important to providing efficient traction. This is important on wet roads. It’s even more important when the vehicle is trying to gain traction in winter weather situations. They design the tread, channels and footprint of the tire to push away water, ice and snow as it rotates. The deeper the tread the more efficient the process is. Therefore, when making the decision on when to replace tires, driver experience and operational conditions are just as important as the amount of tread remaining.
Drivers that operate in the Arizona desert can probably get away with running their tires down to the 2/32 mark. This is considered by most tire companies as low as you can go. Although these drivers should be extra cautious or not drive should a rainstorm pop-up. On the other side of the spectrum would be drivers located in northern sections of the United States. If these car owners measured their tread at 4/32 with winter approaching it might be a wise decision to replace those tires before the first snowstorm. Use the measurements from the tread depth indicator to decide if an alignment is needed with those new tires.