In wet and wintry weather, all-season tires begin losing traction long before they appear worn-out, according to Consumer Reports’ testing. Tread depth is essential to disperse rainwater and slush, and claw at snow. As tires wear, this ability to hold the road confidently fades.
In CR’s tire tests, we started to see a decline in the performance of tires with half their tread depth still left—well before most drivers would consider replacement.
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This had the largest impact on snow traction, where acceleration fell about 14 percent, and on wet stopping distances, which increased by about 7 percent, compared with new versions of the same tires with full tread depth. All of the tires tested worked well in dry and temperate conditions.
The findings reinforce our recommendation that drivers use winter/snow tires if driving a lot in snow. These are specially formulated and constructed to provide maximum grip in snowy and icy conditions. Drivers should also be aware that tread depth has an impact on traction for these tires as well.
“Drivers in the snow belt should inspect their tires in the fall,” says Ryan Pszczolkowski, who runs the CR tire testing program. “We typically advise that shopping should begin when tires are down to 4/32 of an inch, but with snow, you want to make sure you have at least that tread depth in the middle of winter, even if that means replacing tires a bit earlier than you would during milder seasons.”
As part of a broader testing program, Consumer Reports also assesses about 50 tire models every year, numbering hundreds of individual tires. We put them through a dozen tests to come up with detailed ratings across many categories. These tests include not only track testing but also extensive tread wear testing. (See the latest tire ratings.)
To assess the impact of tread depth on winter traction, we compared the performance of three popular all-season tires—one set with a full tread and one with only half the tread left.
We shaved tires to about a half-tread depth to simulate a used tire with a lot of life left in it. We tested by accelerating on snow and braking on wet surfaces to assess traction.
We also tracked the speeds at which the tires started to skim or hydroplane on standing water on a road at our Auto Test Center. And we went to a local ice rink to measure stopping distance on ice.
The results show a decline in performance that consumers may experience before the tires are worn-out.
A tire with a half-tread depth usually has 5/32 to 6/32 of an inch remaining. Tires are worn-out when they reach 2/32 of an inch, but you don’t need to go that low to see a substantial decline in performance on slick (wet, snowy, or icy) surfaces.
On average with the half-tread tires, there was:
- A 14 percent decline in snow traction (based on the measured distance that it takes a vehicle to get up to speed).
- An 8 percent loss in hydroplaning resistance (based on the observed speed at which hydroplaning first occurred driving through standing water at our test track in Connecticut).
- A 7 percent loss in wet braking (based on the stopping distance from 60 mph on a wet surface, measured at our test track).
- A small loss in braking ability on ice (based on the stopping distance from 10 mph on the surface of a Connecticut ice rink).
To monitor your tire’s tread depth, buy a tread-depth gauge from an auto parts store, or simply use a quarter to judge whether the tires need replacing. If the top of George Washington’s head is just visible when placed head first in a tread groove, the tread has about 4/32 of an inch depth. That’s enough to offer some all-weather grip, but you’ll want to start shopping for replacements. Certainly when any tire groove is at 2/32 of an inch, it’s worn-out and needs immediate replacement. You can check by using a penny; the distance between the top of Abraham Lincoln’s head is 2/32 of an inch.
All-season tires perform well for more modest snow conditions. But as the test results show, if the tires are more than half-worn, you may want to wait out the snow storm until the roads have been cleared.
Knowing that winter is coming, even if the tires are at 5/32 in the fall, you should start shopping. Winter-friendly tires tend to get harder to find as the year winds down, and we have seen supplies disrupted during the pandemic. This means a tire store may need to order the tires for you, and deals may be harder to come by.
See our tire buying guide and ratings
