How to check tire tread

We sell 17 tire brands at our Tyler and Longview shops and check tread on every vehicle that comes through. A set of new tires goes on in about an hour.

How to check tire tread with a penny or a quarter

Use a penny for the legal limit and a quarter for the "start shopping" point. Push the coin head-first into the deepest groove near the center of the tire, then check three spots around each tire, because tires rarely wear evenly.

1. The penny test. Lincoln's head goes in upside down, facing you. NHTSA's rule: if you can see the top of Lincoln's head, replace your tires. That's 2/32 inch.
2. The quarter test. Same move with Washington. If his whole head shows, you're near 4/32 inch, which is where wet stopping starts to slip.
3. Check inside and outside edges too. A tire that's fine in the middle and bald on one edge is telling you about your alignment.

It takes about a minute. Most people spend longer picking a gas pump, then stand there wondering whether it's the one that's always slow.

Tire tread depth, explained

Tire tread depth is measured in 32nds of an inch, from the top of the tread to the bottom of the main grooves. The deeper the grooves, the more water the tire can push out of the way, which is what keeps it gripping on a wet road.

The numbers that matter are 4/32 and 2/32. Tire Review reported Tire Rack's wet braking test from 70 mph: new tires stopped in 195 feet, tires at 4/32 needed 290 feet, and tires at 2/32 needed 379 feet. That's nearly double, or roughly the length of a football field plus the end zone you didn't plan on visiting.

Minimum tire tread depth in Texas

The minimum legal tire tread depth in Texas is 2/32 inch. The Texas Department of Public Safety inspection rules require "proper tread depth of at least 2/32 of an inch" on every tire, so a tire at the penny line fails inspection.

Legal and smart aren't the same number, though. At 2/32 the tire is technically allowed on the road the way a gas station hot dog is technically allowed to be food. Plan to replace at 4/32 if you drive in rain, which in East Texas is roughly every other Tuesday.

Tread wear indicators

Tread wear indicators are small raised bars molded into the grooves of every tire at 2/32 inch. When the tread wears down level with those bars, the tire is at its legal limit and needs replacing.

Look across the tread for a flat bar that runs sideways through a groove. If the tread is flush with it in two or more spots, the tire is done. Think of the bar as the tire tapping its watch at you.

Wear bars are most useful when they show up unevenly. Bars showing on the inside edge only usually point to alignment, and bars showing in the middle only usually point to overinflation. Either way, new tires on the same problem will wear the same way, so we check the cause before the new set goes on.

When to replace tires

Replace your tires when the tread reaches 2/32 inch, or sooner at 4/32 if you drive in rain. Replace them right away if you see a bulge, a cut or a cord showing in the sidewall, no matter how much tread is left.

• Tread at 2/32 inch, or wear bars flush with the tread
• A bulge or bubble on the sidewall, which means the inside of the tire is damaged
• Cracks in the sidewall from age and Texas sun
• A slow leak that keeps coming back after a repair
• Uneven wear so bad one edge is bald while the rest looks fine

Christy Johnson brought her tires to me at the Longview shop and wrote about it afterward: "He assessed my vehicle and balanced my tires - removing the vibrating!" Sometimes the tire's fine and the fix is cheaper than you feared. Sometimes the penny wins. We tell you which.

Tread questions