For years, car owners have been using the "penny trick" to determine when they need new tires. This is important as worn tires can affect safety, performance and fuel efficiency. Keep reading for a step-by-step guide on how to perform the penny test.
Why Checking Your Tire Tread is Important
Safety Concerns
Your car’s tire tread is essential for its safety, providing traction between the car and the road’s surface. When this wears down, it reduces the grip on the road, making it dangerous in certain conditions, especially on wet roads and when there is snow and ice. It can also impact its braking performance and the ability to maintain consistent contact with the road, reducing the control you have over your car.
Worn tread can also increase the risk of tire blowouts as the tire will be more susceptible to damage from the road such as debris and potholes.
Impact on Fuel Efficiency and Performance
Worn tires reduce your car’s fuel efficiency because the rolling resistance increases, forcing the car’s engine to work harder. This decreases fuel efficiency and increases fuel consumption.
In addition, worn tires will also affect your car’s handling, making it unpredictable when driving at high speeds or in bad weather.
What is the Penny Test?
The penny test is a quick test to check the tread depth of your tires to determine whether they need to be replaced or not.
Understanding Tread Depth and Tire Wear
Tread depth is the measurement of the grooves and channels on the surface of your tires, which is measured in millimeters or 32nds of an inch. New tires typically have a tread depth of around 10/32” to 12/32”. The grooves in your tires help to channel water away from the tire’s contact patch, improving traction and grip. As tires wear down, the tread depth decreases, reducing the tire’s ability to grip the road, especially in wet weather.
Tire wear happens naturally over time as your tires come into contact with the road. You should make a note of how your tires are wearing down as excessive or uneven tire wear can signal underlying issues such as suspension issues, tire inflation problems or improper alignment.
Step-by-Step Guide to Performing the Penny Test
What You’ll Need
All you’ll need to perform the penny test is your car’s tires and a penny!
How to Measure Tread Depth Using a Penny
To check the tread depth, simply hold a penny with Abraham Lincoln’s head facing down into one of the tire’s tread grooves. You’ll be able to measure the tread depth by how much of Lincoln’s head is still visible. It’s important to measure multiple grooves around your tires as tread wear is not always consistent.
What the Results Mean (Pass or Fail)
If part of Lincoln’s head is covered by the tread, it means your tread depth is still at least 2/32” deep and your tire has passed the penny test.
If however, you can see the top of Lincoln’s head or most of his forehead, this means that your tread depth has worn to less than 2/32”. At this depth, your tires are considered unsafe and should be replaced.
Alternative Methods to Check Tire Tread Depth
Using a Tread Depth Gauge
If you prefer to use a more accurate tool to measure tread depth, then you could use a tread depth gauge. You can use this in the same way as a penny and it will give you a reading in millimetres or 32nds of an inch. As with the penny test, a reading less than 2/32” indicates that you’ll need to replace your tires.
The Quarter Test: Is It More Accurate?
You can also use a quarter to measure tread depth. You need to place the quarter into the tire’s tread grooves with George Washington’s head facing down. If the tread covers most of his head, it is at least 4/32”, however if his head is fully visible it means the tread depth is below 4/32” and you should replace your tires.
The quarter test uses a deeper coin so it provides a clearer indication of the tire’s tread depth than a penny. However, it is still not as precise as using a tread depth gauge.
Checking Wear Indicators on the Tires
Many modern tires have built-in tread wear indicators designed to monitor your tires’ condition. These are small, raised bars of rubber located in the grooves of the tires’ tread. Once the tread wears down to a certain level, these indicators make themselves visible and indicate that the tire needs replacing.
When to Replace Your Tires
Legal Tread Depth Requirements in Different States
US laws dictate the minimum allowable tread depth for tires, typically around 2/32”, as is the federal minimum tread depth. However, state-specific laws can differ. For instance, states like Michigan and Minnesota which have harsh winters, both recommend replacing tires when the tread depth is at 4/32”.This is because it will allow for better traction in snowy and icy conditions.
Signs of Uneven Wear and Other Issues
You should also pay attention to uneven wear as this affects your tires’ lifespan and makes them less safe. Look out for the following:
Uneven treadwear:
- Center wear: If your tires are more worn in the middle then this could signal overinflation as the tires have less contact with the road.
- Edge wear: This tends to mean that your tires are underinflated. Make sure your tires are properly inflated or replace them if they are significantly worn.
- Cupping or scalloping: If your tires have a wavy or bumpy surface it could be a sign of alignment issues, suspension problems or improper tire balancing. This can affect handling so should be replaced if significant.
- Patchy wear: If the tread wear is uneven, this may also signal alignment or suspension issues. These tires should be replaced and your car should be checked for alignment and suspension issues.
Tire damage:
- Sidewall: Cracks or punctures on the tire’s sidewall are often a sign of damage and should be replaced immediately. This compromises the tire's structural integrity and can lead to sudden tire failure or blowouts.
- Punctures and large cuts: Large punctures can’t be fixed. You should also look out for deep cuts or tears in the tire’s surface as these can lead to air loss or a dangerous blowout.
- Bulges: This is an indication of internal damage or weakened structural integrity, often after hitting a pothole or curb. It can cause a blowout at high speeds and should be replaced immediately.
Age and rubber cracking:
- Age: Even if the tread on your tires looks good, they should be replaced every 6 to 10 years, depending on the manufacturer’s guidelines. Tire rubber degrades over time, leading to reduced performance and increased risk of failure.
- Cracking: Cracks in your tires are a sign of aging and that they may not be as effective at gripping the road. They should be replaced, even if the tread appears to be in good condition.
Tips to Extend Tire Life
Proper Inflation and Rotation
Maintaining proper tire pressure is one of the most effective ways to extend the life of your tires. Both underinflated and overinflated tires can affect your tires’ wear, reducing their lifespan.
Use a tire pressure gauge to check your tire pressure regularly and before long trips. Your car’s owner manual should display your car’s recommended tire pressure. It’s important to ensure all four tires are inflated to this level. It’s especially important to check after weather changes as temperature can affect tire pressure. You should use a reliable air compressor if you need to add air to avoid overinflating your tires.
Tire rotation can also extend your tires’ life span. This is where you move the tires on your car to different positions to promote even wear. This is useful because the tires at the front of the car usually wear more quickly than those at the back.
When rotating your tires, follow the guidelines in your car’s owner manual. The usual rotation interval is around 6,000 to 8,000 miles and you should ensure that you are rotating your tires in the correct pattern. When you are rotating them, you should use the opportunity to inspect them for signs of wear or damage.
Avoiding Common Driving Habits that Wear Out Tires Faster
The way you drive can affect how quickly your tires wear out. Here are a few tips to help your tires last longer:
- Aggressive driving: Hard breaking, rapid acceleration and sharp cornering all increase friction on the tires, leading to faster wear.
- Excessive weight: Always check your car’s maximum load capacity as excessive weight can put strain on your tires and cause them to wear out more quickly.
- Unpaved roads: Rough or unpaved roads can cause your tires to wear uneasily. If it is unavoidable, it’s best to drive slowly to avoid damage. In addition, potholes and other road debris can also damage your tires.
- Misalignment: Misaligned wheels can cause uneven tire wear, especially on the edges. If your tires are wearing unevenly you should have your alignment checked.
- Suspension: Worn-out suspension can lead to uneven weight distribution and cause your tires to wear more quickly. Have your suspension system checked regularly, especially if you notice unusual tire wear.