How Does Tire Tread Affect Braking Distance?

Tire tread helps give your car grip and control, but when tires go bald, you're not stopping, you're probably skidding to the sound of pure regret. Those grooves help channel away water, slush, debris, and whatever else is trying to sneak in between the rubber and the pavement, while the tread peaks allow your vehicle to grip the surface. As the tread wears down, you lose that grip in dry conditions, but things get worse under wet conditions. A study released by AAA revealed that driving with moderately bald tires on wet highways can cause stopping distances to increase by a scary 43%.

Tire Rack's wet-braking tests with a 2006 BMW 325i showed just how terrifyingly real tread depth differences can be. With brand-new tires, the car hauled itself down from 70 mph to a stop in 195.2 feet and 3.7 seconds. At 2/32 of an inch, the legal minimum for tire tread depth, the vehicle needed 378.8 feet and 5.9 seconds to come to a complete stop. Drivers in the test described the braking as noticeably delayed. Even with 4/32-inches of tread left, the car took 290 feet and 4.7 seconds to stop. It was the same car, the same brakes, and the same driver, showing how, when it comes to worn tread, the difference between a safe stop and a dangerous crash can be just a few millimeters of rubber. Mandated automated braking requirements may not be far away, but you still need ample tread depth for the tech to work properly.

Tire tread absolutely affects how well your car stops, but that simple statement doesn't even begin to cover the full picture. Tire tread comes in various styles, including directional, symmetrical, and asymmetrical, and the tread has a specific depth. Essentially, tread depth is the distance between the grooves that channel water and the raised peaks that grip pavement. Most new tires start out with around 10/32 to 11/32 inches of tread depth. As you rack up miles, heat, friction, and road grime slowly shave the tread down. Once you're under 4/32 inches, traction drops fast. By 2/32 inches, you're barely hanging on, especially in the rain.

Tests comparing different tread depths have found that stopping distances grow alarmingly longer as tires wear down. According to a study by Hunter Engineering Company, on average, a car with fresh tires and 10/32 inches of tread depth stops in 234 feet. Knock the tread depth down to 6/32 of an inch, and the vehicle stops at 253 feet. By the time you reach the minimum 2/32 of an inch, you're sliding 356 feet after applying the brakes.

Clearly, worn tire tread is dangerous. But what does a smart driver do? Monitor tread depth — and not just visually. Using a simple coin to test the tread or buying a measuring gauge can help you see the warning signs long before the tire is dead.

The old-school penny test is still one of the simplest ways to find out if your tires are toast. Flip a penny upside down and stick it into the tire's groove. If you can see the top of Lincoln's head, congrats because you've hit 2/32 inches of tread, and it's time to start shopping for new tires. If Lincoln's hairline is hiding, you've still got a little tire life left. But legal doesn't mean safe. Below 4/32 inches, your stopping distance spikes, and hydroplaning becomes way too easy. That's where the quarter test comes in handy. Drop in George Washington headfirst, and if you can see his scalp, you're below 4/32 inches and running on limited traction.

If you're penniless (it's understandable, as new cars are too expensive), check for tread wear bars — those little raised strips between the grooves. Once they're flush with the tread, your tires are done. For the most accurate reading, though, grab a tread depth gauge. Check often and in multiple spots. Tires wear unevenly, and your safety literally rides on those few millimeters of rubber.

Lastly, consider your tire choice. Some tires are built to maintain better traction on wet surfaces and come with specialized tread patterns. So, if you live in rainy climate, prioritize those traits when shopping. Consider all-season tires instead of all-terrain tires, as they hit a good sweet spot for all-round use.