When to replace tires: Mileage, Age, or Wear?

Understanding when it’s time to replace tires

Knowing when to replace your tires can prevent accidents, improve handling, and save you money in the long run. This guide will help you understand the key tire replacement indicators and provide tips for maintaining tire health.

Key Indicators for Tire Replacement

Several factors indicate when it’s time to change your tires. These include tread wear, age, damage, and changes in vehicle performance.

• Tread Depth—  The legal minimum tread depth in most states

This illustration shows where the tread wear indicator bars are located on a tire

is 2/32 of an inch. However, you lose a significant amount of traction once your tires wear down to 4/32″. More on that below.

• Tire Age— Even if your tires have plenty of tread left, they can still be unsafe due to aging. Rubber deteriorates over time, leading to cracks and a loss of structural integrity. Many carmakers recommend replacing tires every six years. Many tire manufacturers disagree, stating that tires last ten years.

Cracks from heat and ozone

• Visible Damage— Uneven tire wear due to improper tire pressure or alignment issues is the #1 cause of early tire replacement. However, you should replace tires if you see visible signs of damage, such as cuts, cracks, bulges, or blisters. These can weaken the tire’s structure and increase the risk of a blowout.

• Changes in Vehicle Performance— You can’t always see internal tire damage, but it shows up as vibration, pulling to one side, or increased stopping distances. If you notice a change in how your car handles, it might be caused by your tires.

Understanding the effects of tread depth on stopping power

Safety studies show a dramatic decrease in stopping power once you wear down to 4/32″ and below.

When the wear bars are even with the tread blocks, you’re at 2/32″

Independent tests done by Tirerack.com and other consumer testing organizations prove that once tires wear to 4/32” it takes an additional 125-feet to stop on wet pavement than a new tire.

That statistic alone should convince you that you need to keep an eye on tread depth.

Worse yet, once your tires wear down to the legal limit of 2/32” your stopping distance increases by up to 250 additional feet on wet pavement than a new tire. Watch this video from Tirerack.com to see the test results.

Forget about the penny test; get a real tread depth gauge

The best way to determine the remaining tread depth on your tires is to buy an inexpensive tread depth gauge. Find one at any auto parts store for less than $10. Keep it in your glove box. Then, use it a few times a year to track how well your tires are wearing and to stop inflation and alignment problems.

How to use a tread depth gauge

Wipe dirt off the top of the tire. Extend the tread depth gauge probe and insert it into the groove in the middle of the tire. Read the depth and write it down on a notepad. Repeat the test on the outermost and innermost grooves. If the tire is wearing evenly and the vehicle is in alignment, all three readings should be within 1/32” of each other. If they’re not, refer to the images below to find out what’s going on. Repeat this test on all four tires.

How to check your tire’s age

Check the tire’s age using the DOT’s “born on” date. Find the DOT stamp on the tire and read the last four digits in the code. The last two digits indicate the year it was manufactured, and the preceding two digits indicate the week it was manufactured.

This DOT indicates that the tire was built in the 50th week of 2008 DOTB9YRUJNX5008

Tires have a maximum useful life of just ten years, regardless of the remaining tread—even if the tire shows no signs of cracking. After five years, tires should be inspected at least once a year for signs of deterioration.

How to tell what’s wrong by checking the tire wear pattern

Other tire wear photos that indicate problems

Cupping caused by worn shock absorbers or struts

The shock/strut’s job is to dampen spring rebound. When they wear, the tire bounces off the ground and slows while in the air. When it hits the ground, the pavement scrubs off the tread. Once that starts, the tire becomes unbalanced, and the tire will hit in the same spot on every bump. Eventually, the pattern becomes visible, and the tire is ruined.

Heat cracks are caused by running the tire when it’s low on air
When you drive on a tire that’s under inflated, you create excessive flex at the tire’s shoulders. The heat buildup causes the rubber to deteriorate and crack, eventually causing it to fail. I just hope that doesn’t happen in turn.

©, 2016 Rick Muscoplat

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