Know when Car Tires Need Replacing

Ever wonder when to replace your worn car tires? The performance of your car tires is critical to the safety, performance and efficiency of your vehicle; the N.H.T.S.A. estimates that about 200 fatalities annually may have been caused by tire failures.[1] Most tires are designed to provide similar performance throughout their lives. However, at some point they start to lose performance in terms of their traction and braking ability. Here are a few tips that should help you decide if it is time to start shopping for a new set of tires and avoid spending more than necessary.


  1. Understand that the primary function of tread on a tire is to divert water from beneath the tire to improve traction and avoid hydroplaning on wet roads.[2] Tires become unsafe when they're worn, and once the tread is down to 1/16th of an inch (1.6mm), the tire is no longer safe.
  2. Look at the tread pattern. All tires sold in the United States and other countries have what are called "tread wear bars." These are small bridges that form between your treads. Look at the tread pattern and you'll see the beginnings of these bars start to form between the treads, or running across the tires. As the tires wear, these bars will become flush (level or even) with the tire's tread. At this point, it's time to replace the tires.
  3. Check the tread by using the "penny test." Take a penny and place it upside down with Lincoln facing you in the center of the tread (at the thickest part of the tire).
    • If you can see the very top of Lincoln's head or the copper above it, replace the tires immediately.
    • If Lincoln's hair on the top of his head is partially visible, it is time to go shopping for tires.
    • If you cannot see the hair on the top of his head (if the coin is inserted enough that the tire tread is at least as deep as Lincoln's forehead), your tires do not need replacing yet.
  4. Use a tread depth indicator or gauge. You can use a special tread depth indicator or gauge tool to measure your tire's tread. If you don't already own one, the gauge is cheap to purchase from an auto parts dealer and it's easy to use.
    • You may be able to find a downloadable tread depth gauge by searching online.
    • Alternatively, it might be easier to pop in to your regular tire place and ask them to check it for you; likely they'll do this for free if you're regular customer.
  5. Know the legal requirements. Worn tires should be replaced as a matter of common sense to assure safety, but in some jurisdictions, there are also legal requirements to replace worn tires. In many US States, tires are considered to be legally worn out when they have worn down to 1/16" (1.6mm) of their remaining tread depth.[3] In the UK, the minimum depth of the tread on tires (tyres) is 1.6 millimeters across the central ¾ of the tread around the whole tire (tyre).[4]
  6. Make note of any irregular tread wear. This could indicate a wheel misalignment, the need for a tire rotation, or both. Uneven tread wear is a sign that you need to take your car in for servicing.
    • If uneven tire wear is extreme or if tires wear out much faster than expected, have a competent tire workshop check your suspension and correct it as necessary before replacing tires. Improper alignment or worn suspension parts can dramatically shorten a tire's life.
    • It is a good idea to rotate your tires from front to rear in pairs. Take both front tires and move them to the rear and vice versa.
  7. Check for any abnormal bulges or "bubbles" in the sidewall. A sidewall bulge indicates that the rigid internal frame of the tire has been damaged and cracked, allowing air pressure to reach the flexible outer layers of the tire. Such damage could be caused by driving through a large pothole or over a curb, or by driving with low tire pressure. Continuing to drive on a tire that has a sidewall bulge is dangerous. The structural integrity of the tire has been significantly reduced, greatly increasing the likelihood of a sudden failure or blowout at highway speeds, which could cause a serious accident. Any tires with sidewall bulges should be replaced immediately, regardless of the tread status.
  8. Replace the tires at least every 6 years. If you're not sure, the minimum replacement time that is recommended by the NHTSA is six years regardless of use, with 10 years being the maximum service life for tires. Check your owner's manual for specific recommendations related to your car. And always err on the side of caution if you suspect your vehicle has tires that are over six years of age.
  9. Notice a vibration in the steering wheel. If your tires are worn unevenly, you may feel a vibration in the steering wheel when you are driving. Your tires probably need to be rebalanced. If that doesn't stop the vibration, more than likely the tire is damaged.
    • Vibrations may also be caused by tires that are "cupped," meaning they have a cupped or scalloped appearance around the tire. This occurs when tires haven't been rotated regularly.
  10. Check for dry rot. If you see little cracks all over your tires, it means that the rubber is breaking down. Tires with dry rot can fall apart, separating from the steel belt causing damage to the exterior of the car.


  • Keep your tires properly inflated.
  • Tire age is dated from the date of manufacture, not sale, as tires deteriorate even in storage
  • Test all of your tires and if possible, replace them all at the same time. Mismatched tires will not provide the same safety, performance and efficiency as a matched pair will.
  • On 4-wheel-drive or all-wheel-drive cars you should replace all four tires if it is recommended in your service manual. Differences in tire diameter, even due to different states of tread wear, can permanently damage differentials.
  • Treadwear grades are an indication of a tire's relative wear rate. The higher the treadwear number is, the longer it should take for the tread to wear down.
  • Tires do not wear perfectly evenly, so be sure to insert the coin at several points from the outside to the inside of your tires. Tires generally wear more on the inside but over-inflated tires will wear more in the middle.
  • Tires age faster in warmer climates.
  • If you see uneven wear on a front tire, chances are that the front end is out of alignment. You should have this checked and rotate the tires to the rear if possible (some vehicles have different sizes on front than the rear). The tires from the back should be fine and the uneven tires moved to the rear will start to correct themselves.
  • A quarter can be substituted for a penny; just use Washington's head as the point instead of Lincoln's.
  • A good practice is to rotate the tires by replacing the front tires with the back ones, especially on a two-wheel drive vehicle.


  • Tires should never rub against your fenders or any other part of your car. If your new tires rub during turns or when going over bumps, they don't fit, no matter how cool they look. Fix this before you suffer a blowout and crash.
  • Hydroplaning is an increased possibility with bare tires. The risk of hydroplaning increases as the tire wears. This is true even if the tire is not fully worn out. A tire with 50% tread life may hydroplane in conditions where a tire with 90% tread life may not.
  • If you happen to see wires on your tread or notice wear on the sidewalls of the tire, don't even bother with the penny – just get the tire replaced. The wire thing is rare, and even if Abe says the tread is still good, the wires indicate an immediate need for replacement. It happens and it's better to replace the tire than get the blowout as you're speeding along the road.
  • Be careful to buy tires that are the right size and type for your vehicle and rims (wheels). Changing to low-profile tires may require you to buy larger rims so that the outer circumference of the tire remains unchanged. Incorrect tire size or mismatched tread can also cause a low tire pressure warning to come on if the vehicle is equipped with a Tire Pressure Monitoring System (TPMS).
  • Be careful when rotating tires, and especially when moving tires to different rims. Many modern tires have a specific rotational direction and corresponding rotation method. Refer to your tire manufacturer or dealer for details. However, some sports cars have different size wheels on the front than on the back and can not be rotated. Make sure the wheels are the same size.

Things You'll Need

  • Penny
  • Tread depth indicator

Related Articles

Sources and Citations

  3. Tirerack, Measuring tire tread depth with a coin,
  4. KwikFit, What do I need to know about UK tire law?, tire law