What Happens to Performance When Tires Are Worn?

Consumer Reports' tests compare tire performance of full and reduced tread depth

Tests show how worn tires perform

We know exactly how new tires perform, based on our extensive tire test program. But those results are a best-case scenario and, of course, tires are brand-new for only a short time. So that raises questions: How do tires perform when worn down, and when should they be replaced?

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The National Highway Traffic Safety Administration (NHTSA) has found that by the time a tire's tread is down to 4⁄32", which may take years, tire wear plays a measurable role in accidents. (You can find instructions below on how to gauge your tire's treadwear level.) At this point, a tire is approaching the end of its service life and Consumer Reports recommends drivers begin shopping for replacements.

To quantify how wear changes tire performance, the CR tire team measured the wet stopping performance and hydroplaning resistance of 23 performance all-season tires with full tread, which typically measures between 9⁄32" and 11⁄32", when new, and compared it against the same model tires shaved to 4⁄32". Hydroplaning happens when water gets between the tire and the pavement.

What You Should Do as Tires Wear

  • Determine if it’s time to begin shopping for new tires by placing a quarter, with George Washington’s head facing down, into a tread groove. The top of his head to the edge of a quarter is 4⁄32". If the top of his head can be seen, it’s time to start shopping in anticipation of upcoming tire replacement. 
  • Check our tire buying guide for maintenance tips to keep your tires running optimally. As tires lose tread depth, our testing shows that they'll lose grip on wet surfaces and are more likely to hydroplane. The United States Tire Manufacturers Association agrees: “Tread equals traction—giving your tires a grip on the road, especially in bad weather. Lose too much tread and you could lose control.” 
  • CR tire ratings can guide you to good-gripping and long-lasting tires. If you experience loss of grip on wet pavement, or even hydroplaning, it may be time to replace the tires even if they have not reached the worn-out (2⁄32" tread) depth.

No matter how worn your tires are, it’s prudent to slow down in foul weather. Even the best tires will yield traction to water and the laws of physics.

Test Highlights

Our testing demonstrates the range of tire performance an owner would typically experience during the overall life of their tires. While it makes sense that the loss of tread results in the loss of grip on wet surfaces, our testing shows just how significant the loss of grip can be. It's important to note, too, that some tire models better retain their performance as they wear.

The complete results from our tests, including braking distance by model and advice based on our analysis can be found below. Shorter braking distances are better, as they help drivers avoid crashes.

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