When should tires be replaced?

The condition of your tires is vital for staying safe on the road. Tires make a huge difference in the way the vehicle handles. Worn-out tires have less grip in turns and on wet surfaces, which means, for example, the vehicle is more likely to slide or hydroplane in the rain. The braking distance increases too. All-wheel drive, Vehicle Stability Control and Automatic Emergency Braking systems become less effective when tires are bald.

Working with cars we deal with tires almost every day. To illustrate what we mean 'bald' or 'worn out' tire, we took this photo of a new tire and the tire that is worn out beyond safety limit. So, when should tires be replaced? There are several common reasons to replace tires:

1. Worn out tread material.
2. Punctures that cannot be repaired safely.
3. Cracks, cuts or other damages that make tires unsafe.
4. Out-of-round shape or other tire defects that cause excessive vibration.
5. Uneven wear or "cupping."
6. Age. Tire should be replaced if it's more than 6-10 years old regardless of wear.

Let's look at each reason in detail and see the examples:

1. Worn out tread

Over time the tire tread wears out. Tires are considered unsafe when the tread is worn down to 2/32nds of an inch or 1.5 millimeters, like in this photo.

Of course, you don't want to wait until your tires become unsafe. It's a good idea to start looking for new tires when the tread is worn out to about 4/32nds of an inch or close to the tread wear indicator bar. This will give you some time to compare ratings and reviews of different tires and shop around.

Tread wear indicators are rubber bars built into the tread across the main grooves. Most tires have them. As the tire wears out, tread wear indicators become clearly visible. In a new tire, you can barely see them inside the grooves. In a worn-out tire like this one, the wear indicator bar is almost flush with the remaining tread material.

Another way to tell if the tire tread is worn out is to measure the tread depth. The tire tread depth is typically measured in 32nds of an inch. New tires have from 9/32" to 11/32" of tread material. When you take your car for a regular service to a reputable shop, the mechanic working on your car, checks your tires and measures the tire tread depth. You will typically see it marked on your vehicle inspection report. If you want to measure the remaining tire tread yourself, here are two ways to do it:

How to measure the tire tread depth

With the tire tread gauge: You can purchase a basic tire tread gauge in any parts store. Measure the tread depth in the most worn-out area of the tire.

Hold the gauge over one of the major grooves, with the foot of the gauge placed across the groove. Push the scale down lightly.
These two tires in the photo are the same two tires from the photo above. The new tire shows 9/32", while the tire on the right photo shows 4/32".

Using the Washington quarter: With the quarter placed upside down inside one of the major grooves, look at George Washington's head. If the head is covered by the tread, you have more than 4/32" of tread material left.

If the top of the head is even with the remaining tread surface, as in the right photo, you have about 4/32" of the tread material left.

Winter tires should be changed even earlier. With 4/32" of the tread remaining, winter tires are pretty much useless in snowy or icy conditions. Being in Canada, we often see cars damaged from hitting the curb during winter and many of them have either summer tires or winter tires with low tread.

2. Punctures that cannot be repaired safely

If your tire has picked up a small screw or nail, in most cases it's easy to repair the puncture. However, not all punctures can be repaired. if the puncture is too big to repair or is in the sidewall or your mechanic cannot repair it safely for other reasons, the tire will have to be replaced. For example, this tire that we came across recently, got punctured by a small wrench and cannot be repaired.

3. Cracks, cuts or other damages that make the tire unsafe

The tire needs to be replaced if it's damaged and deemed unsafe. For example, if the tire has deep cracks, a cut, a bulge or damaged bead, it is considered unsafe. We also often see tires become damaged after being driven flat. These are photos of the tires that we have seen over the years, from left to right:

1. Sidewall bulge.
2. The tread is completely worn out.
3. Cut into the sidewall.
4. Puncture in the sidewall (sidewall puncture cannot be repaired).
5. Rubber shavings inside after the tire was driven flat.
6. Sidewall damage after being driven flat. Photo.
7. Uneven wear: the tire worn on one side. Photo.
8. The cord is showing.
9. Damage to the sidewall.
10. Deep cracks in the sidewall.
11. Deep cracks in the tread groves.
12. The nail in the sidewall.

4. Out-of-round or defective tires that cause vibration

This type of damage is not too common, but once in a while we come across a tire that causes a vibration that cannot be solved without replacing the tire. Check out this video, this tire is simply out of round and even after balancing it was still causing a vibration at highway speeds. The tire has enough tread material but the owner of the vehicle opted to replace it due to consistent vibration.

5. Uneven wear or "cupping"

In some cars, tires become unevenly worn or "cupped." Cupping is a wear pattern where the tread material wears unevenly, with alternating low and high spots. Cupped tires might still have enough tread material and be considered safe, but they often produce a loud rumbling/humming noise, especially if a cupped tire is placed in the front of the vehicle.

If the noise is a concern, cupped tires will need to be replaced. However, it would make sense to eliminate the issue that caused tires to become cupped in the first place. This could happen due to problems with the suspension, incorrect alignment or a lack of tire rotations.

6. The tire should be replaced if it's more than 6-10 years old regardless of wear.

Even if the tread is in good condition, the tire material degrades over time. NHTSA recommends replacing tires that are more than 6-10 years old, regardless of wear. How can you tell how old the tire is? Check the DOT or Tire Identification Number.

On tires produced after the year 2000, the last four digits of the Tire Identification Number indicate the week and the year the tire was manufactured. For example, the tire in this photo was produced on the 34-th week (August) of 2008.

Do you have to replace tires with the same brand that was originally installed on your vehicle?

No, you can opt for any tires that fall within the car manufacturer's specifications (size, speed rating, etc.). In fact, by switching to different tires you can adjust your vehicle's handling to your preferences. If you enjoy spirited driving, you may want to switch to tires with better handling characteristics. If you like a quieter ride, you can select tires that provide better ride comfort. For example, one of our colleagues was looking to replace the original tires on his Mazda 3. He switched to Michelin Defender tires and reported a much quieter ride.

Sites like tirerack.com and consumerreports.org offer comparisons of different tires on tread life, fuel economy, ride comfort, noise level, handling in snow and other ratings. If you are looking for a better fuel economy, look for low rolling resistance tires. If you need more grip on wet roads, look for wet traction or wet braking scores. Replacing all four tires is not cheap, but it's an investment in your safety and a better driving experience.

How long do tires last? In an average car, tires last from 50,000 to 60,000 miles. Of course there are many reasons why tires can wear out sooner. We have seen tires that were completely worn out at 15,000 miles. It depends on the vehicle's mechanical condition, tire quality, driving habits, whether or not tires are rotated regularly and other factors.

Why do tires need to be rotated? Tires are rotated between the front and rear axles to even up the tire wear. Most cars on the road today have front-wheel drive. Many all-wheel drive SUVs and crossovers are also built on a front-wheel drive platform. Since the heavier components of the vehicle, such as the engine, transmission and the battery are placed in the front, front tires wear faster than the rear ones.

For example, see the photo above. This car came from a car rental company. It has only 20K miles, but without regular tire rotations its front tires are worn out, while the rear tires still have plenty of tread material left.

The other reason to rotate tires is that most modern cars have an independent rear suspension, which often causes the rear tires to wear more on the inside. In some cars, rear tires may wear unevenly or become cupped if not rotated regularly.

What can you do to make your tires last longer?

1. Opt for tires with a better tread life rating.
2. Keep the tire pressure up to specs and have the tire rotation done regularly
3. If you notice that the steering wheel is off-center when driving straight or the vehicle pulls to one side when driving on a level road, have the wheel alignment checked and adjusted.
4. Have your vehicle inspected regularly so problems with steering or suspension can be caught early.