One tire tread in a macro mode ** Note: Shallow depth of field

A Beginners Guide To Tires

Your tires are arguably one of the most important parts of your vehicle. They’re the only parts that touch the road and the condition of your tires can affect the comfort of the ride and the safety of those in the car. Even with a perfect brake system in place, the wrong tires can cause the vehicle to skid or not stop in a feasible amount of time. So how do you know your car is in need of a new set of tires? Do you know what to look for when you inspect them? How about when it comes time to buy new tires? Do you have the know how to pick the right set for your vehicle? Here’s a quick guide to get you up to speed on all things tires.


The tire tread is what gives your tires grip on the road. When they wear out from use, exposure to oxygen, or age, the tires won’t hug the road as well as they used to. But how can you tell when the tread has been worn down too far for safe driving? It’s not a good idea to eyeball it, though you can do it with practice. There is an easier, faster way, however. This method is called The Penny Test. Take any classic American penny and hold Abraham Lincoln’s body between your thumb and forefinger. Then, twist your hand so Abraham Lincoln is upside down and place the penny upright in the tire tread. If the tread covers any of Abraham Lincoln’s head, your tires are still good. But if you can see all of his hair cut, then the tread is less than 2/32 of an inch and is not safe to drive on. At this point, it’s time for a new set of tires. The only time this test shouldn’t be used is when the tires are more than ten years old. If you’ve reached this point, maybe because you don’t drive the vehicle often, you should replace the tires. The rubber does age from oxygen exposure and loses its grip, even if the tread looks fine.

FUN FACT: Inspecting your tire tread can tell you lot about the state of your tires and your vehicle as a whole. If the center tread is worn down more than the rest of the tread, your tires are overinflated. If the shoulder tread is more worn down, however, your tires are underinflated. And any uneven wear on the tire tread could signal that your wheels are poorly aligned. All three of these situations can be easily fixed and will extend the life of your tires. So be vigilant in inspecting on a regular basis.


If your Penny Test inspection has lead you to decide it’s time for a new set of tires, you should first read the sidewall markings on your old tires. This will be the strange string of numbers and letters on the side of the tire. Those numbers and letters have meanings to help you identify the size and capabilities of the tires. If you liked the handle and performance of your old tires, you can buy the same code again. If you’re not sure if you’re using the right tires, your car’s owner’s manual will have the manufacturer’s recommendation. But here’s a little deciphering guide to understand what those sidewall markings mean.

Here is an example sidewall marking: P210/65R 19 Z

  • The first letter, in this case, “P” stands for the purpose of the vehicle. The “P” means “Passenger”. You will probably only purchase a tire marked “P” as the only other common option is “LT” which means “Light Trucks”.
  • The three numbers that follows the letter is the width of the tire. This is in millimeters and is probably one of the more crucial parts of the sidewall marking. Follow your owner’s manual closely on this number to get the best fit for your vehicle.
  • The two numbers after that is the aspect ratio of the tire. This is the ratio of height to width. The shorter the sidewall is, the smaller this number will also be.
  • The “R” stands for “Radial Construction”. Unless you’re buying tires for an antique car, this letter will always be “R”.
  • The following number, 19 in this example, will designate what the diameter of the wheel this tire is meant to fit will be. So, this tire is meant for a 19 inch diameter wheel.
  • The last letter, “Z” here, is the speed rating. The letter corresponds to the maximum speed a properly installed and inflated tire can be run at. “Z” is the maximum speed, and most tires have a speed rating far above any normal speed limits you’ll encounter on any drive.

There will probably be other markings on the sidewall, but the ones mentioned above are the ones you should pay careful attention to. Other markings can include maximum inflation pressure and maximum load index. You may also find safety markings or something like “M/S”, which stands for mud and snow. This is the terrain the tire can handle and is the most common marking you’ll find. Don’t let sidewall markings confuse or overwhelm you. When in doubt, take your vehicle to the tire store and ask the attendant to help you understand the markings. They are professionals and will gladly find the right tire dimensions and performance capabilities to match your make and needs.


Once you have the right tires on your vehicle, it’s valuable to check their inflation at least once a month. Why is this important? Tires that aren’t inflated properly, whether too much or too little, will not handle their best. It could either make corners trickier, or braking more difficult. And unevenly inflated tires can lead to poor gas usage, which means less money in your wallet. Know your vehicle. The proper inflation levels can usually be found on a sticker in the driver’s side doorjamb. If you don’t find it there, check the owner’s manual for your car. These numbers will give you the best performance and gas mileage to equal one happy driver. To measure the current inflation on your tires, purchase a tire gauge from nearly any gas station or auto parts store. Remove the valve cap from the tire, press the gauge strongly onto the valve until you don’t hear hissing, and read. Digital gauges will show the number, while manual ones will have a bar slide out so you can read the pressure level. Once you know if you have to inflate your tires more to match the sticker’s recommended numbers, find a nearby gas station. Many will have a free air pump, just ask the attendant inside. At most, some places will only charge you fifty cents.

Filling your tires is the same process as testing them. Remove the valve caps, being sure to keep them safe in your pocket, and press the hose of the air compressor down tightly on the valve. Hold down the lever to fill the tire, and check the readings until they’re exactly where you want them to be.

You don’t need to be a trained mechanic to maintain your tires. It shouldn’t be a scary experience, and should simply be a part of the vehicle care routine you go through. As always, never be afraid to ask questions. If you get a flat or a blow out, and need to call a handy tow truck like us here at Tow Truck Henderson, ask the tech what went wrong and how to avoid it in the future. You may find you’re over inflating your tires by accident, or that your wheels are not aligned as they should be. Let us help you enjoy the safest, smoothest drive possible. And tires are the foundation of that drive.

If you found this guide helpful, share it with your friends on Facebook and Twitter! And if you have more tips, like other tests besides The Penny Test, comment below!

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