You heard it from your Dad, and he heard it from his Dad… Use a penny to see if you need to replace your tires! It’s easy and simple to place a Lincoln penny in the tread groove of a worn tire and use Honest Abe’s likeness to help make your decision, today’s conditions may make the “Honest Abe” test less than honest. It’s not Abraham Lincoln’s fault! Times change, the Lincoln penny didn’t!
The Lincoln penny tread depth test has been used for many, many years as a supposedly accurate way of deciding whether it’s time for new tires. The idea behind the “Lincoln” test is you put a penny upside down into a groove in the tread of your tire, and you’re driving on legal tread depth (Not worn down enough) anytime the top of Lincoln’s head is hidden by the tire tread.
The idea behind using the “Penny Test” is the idea (mistaken) that a tire’s performance doesn’t really go down in bad driving conditions (rain, slush and snow) until the tread wears to around 2/32″ of remaining depth. So, if you can see the top of Lincoln’s head, you’re ready for new tires at 2/32″. (See Photo #1) Can it really be that simple? Unfortunately, NO. Here’s why…
But that’s only half of the calculation involved; tread depth also contributes to how well the tire design does its job. The air that fills the tires is less dense than a liquid, so at highway speeds it can be compressed and moved out of the way with relative ease. However the same isn’t true of liquids. When water collects on the road during rainstorms, the depth of the water on the road, your vehicle speed and weight, besides the tires’ tread designs and tread depths ALL determine when and if the tires will be forced to hydroplane (Float on top of the film of water, losing contact with the road) and then, how quickly they can stop or steer your vehicle.
The standard passenger car tire only has about twenty square inches of total footprint surface touching the road, and has about 1/3″ of tread depth when new. While most of this tire “footprint” surface is made up of the rubber that grips the road, the rest is the space of the grooves that make up the tread design. Tread wear affects how both the rubber tread and the grooves between them perform! The difference in tread depth performance might surprise you. Identical vehicles equipped with the 2/32″ minimum tire tread depth (Lincoln Penny Test) usually take about 100 more feet to stop than the vehicles equipped with the 4/32″ deep tires when stopping from 70 MPH. That’s a big difference, and on wet or slippery pavement, the difference goes up.
So waiting to replace your tires until “Honest Abe” tells you they are legally worn out may seem to be the most economical practice, but it is far more expensive to repair your car if it can’t stop in an emergency situation in less distance than the vehicle ahead of you! Not to mention risk to you and your passengers. Have our experts check your tires next time you stop in, we’re happy to do it!
The driver’s ability to keep in control the vehicle is entirely dependent on the traction between their tires and the road. It’s what “Holds” the car on the road. If you’ve ever watched an automobile race, you see that tires actually don’t require tread designs or even much tread depth to deliver traction under perfect conditions like dry roads, or a racetrack.
But, in less than perfect conditions, tires do require tread designs to generate traction. These conditions include wet, slushy or snow-covered roads. Liquids laying on the road can’t be compressed, and so require the tire to move them out of the way as it rolls through them. It takes time and energy to move liquids out of the way as the tires drive through them. Racing tires with no treads lose traction at amazingly slow speeds anytime something prevents them from maintaining perfect contact with the surface of the road.
So, in order for a car to be useful in all weather, a tread design is necessary in its tires, to direct water and slush from between the tire and the road, as well as provide edges that bite into snow.
