How to Check Your Tire Tread

To check your tire tread, put a penny into a tread groove with Lincoln's head upside down and facing you. If the top of his head is visible, you are at or below 2/32 of an inch and the tire is legally worn out. A quarter gives you earlier warning: if you can see the top of Washington's head, you are at about 4/32. For an actual number, a tread depth gauge costs a few dollars and takes ten seconds per tire. Check several spots across each tire and a few places around it, because tread rarely wears evenly.

The Penny Test And The Quarter Test

Both coin tests work because of where the top of the head sits relative to the coin's edge. They are quick checks, not measurements. The penny test tells you one thing: whether the tire is done. Lincoln's head showing means 2/32 or less, which is the legal minimum in most states and the point at which the tire should already have been replaced.

Washington's head showing means roughly 4/32 left. By that point wet traction has dropped off noticeably and the tire is well into the back half of its life. For a Minnesota driver, the quarter test is the more useful of the two. Do either test in more than one groove. A tire can be fine in the center and bald on an inner edge.

Tread Wear Indicator Bars

Every passenger tire sold in the US has wear bars molded into the bottom of the main grooves. They are small raised strips running across the tread, and they sit at exactly 2/32 of an inch.

Look into a groove. If the bar sits clearly below the surrounding tread blocks, you have tread left. If the bar is flush with the tread and forms a smooth band across the tire, that tire is at the legal limit. If you cannot find the bars, look for small triangles on the sidewall shoulder. They point to them.

What The Fractions Actually Mean

Tread depth is measured in thirty-seconds of an inch. A gauge reads it directly.

• 10/32 to 11/32: where most new all-season passenger tires start. Winter tires and truck tires often start deeper.
• 6/32: the point where snow traction falls off. Deep tread is what packs and throws snow, and a tire below 6/32 stops doing that well even if it still handles dry pavement fine. This is the number that matters here.
• 4/32: wet traction is meaningfully reduced and the tire is more prone to hydroplaning. A good time to start pricing replacements.
• 2/32: the legal minimum in most states, including Minnesota.

Two of those deserve emphasis. First, 2/32 is a legal minimum, not a safe minimum. It is the point at which a tire is unfit to be on the road, not the point at which it stops being good. Second, if you drive through Minnesota winters, plan on replacing at 6/32 rather than running tread down to the coin test. The difference between 6/32 and 3/32 on an unplowed side street in January is not subtle.

Apply the same 6/32 rule to dedicated winter tires. A worn winter tire is the worst of both: it has lost the depth that made it good in snow and still has the soft compound that makes it vague on dry roads.

Good Versus Bad Tread: Reading Wear Patterns

Depth is only half the picture. How a tire has worn tells you what is wrong with the car.

• Worn in the center, good on both edges: chronic overinflation. The tire is bulging in the middle and carrying the load on a narrow strip.
• Worn on both shoulders, good in the center: chronic underinflation. The tire is flexing and riding on its edges. This is common in winter, because tire pressure drops with the temperature.
• Worn on one edge only: alignment. Camber or toe is off, and the tire is being dragged sideways every mile you drive.
• Cupping or scalloping: uneven high and low patches around the tire, with a wavy feel under your hand. Usually worn shocks or struts letting the tire bounce, sometimes with a balance problem behind it.
• Feathering: tread blocks worn sharp on one side and rounded on the other, so the tire feels smooth in one direction and rough in the other. That is a toe alignment problem.

Fixing the cause matters as much as replacing the tire. New tires on a car with a bad alignment will wear out the same way.

Check All Four, And Check The Inside Edge

People check the tire they can see and stop there. Front and rear tires wear at different rates, and left and right can differ too, so measure all four.

The inside edge is where alignment wear hides. It faces away from you, and a tire can look nearly new from the curb while the inner shoulder is down to the cords. Turn the steering wheel all the way to one side and the inner face of the front tire swings into view. Run a hand along it carefully and feel for a step in the tread or an exposed belt.

When To Get It Looked At

• Now: tread showing wire or belt, a bulge in the sidewall, or a tire at 2/32.
• Before winter: anything at or under 6/32. Salt, slush, and cold roads ask more of tread than dry pavement does.
• Soon: uneven wear of any kind. An alignment check now is cheaper than a set of tires later.
• Can wait: even wear in the 5/32 to 7/32 range in summer. Keep measuring.

If you would rather have someone measure all four and tell you what the wear pattern means, we can do that on a lift and check the alignment while the car is up. Stellar Autoworks is in Plymouth and serves the west metro, including Golden Valley, Minnetonka, St. Louis Park, Hopkins, and Wayzata. schedule service and we will take a look.