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Know when your current tires are due
Three ways to check, from quickest to most precise: the penny test, the built-in wear bars molded into the tire itself, and a tread depth gauge for an exact number.
✓ Correct — in a grooveInsert the penny or gauge into one of the channels between tread blocks, where the rubber is actually cut away.
✗ Wrong — on a tread blockResting it flat on top of solid rubber gives a false 0/32" reading every time — that's not wear, that's just the surface.
The penny test
Insert a penny into the tread, Lincoln's head down. If you can see all of his head, tread is at or below 2/32" — replace now.
2/32" replace4/32" plan ahead6/32"+ healthy
What it is
A tread depth gauge is a small handheld tool — usually a couple dollars at any auto parts store — with a probe on one end and a sliding numbered scale on the other. It gives you an exact number instead of a rough pass/fail like the penny test.
How to read it
Push the probe straight down into a tread groove until the flat shoulder plate sits flush against the tread surface. The slider gets pushed up as it goes in — wherever its edge lines up on the printed scale is your depth in 32nds of an inch. In the picture, the slider lines up at 6/32" — still healthy, but worth watching.
Where to check
Measure in the main grooves at a few spots — center, inner edge, and outer edge — on each tire. Tires often wear unevenly, so one low spot doesn't always show up if you only check the middle.
What the number means
New tires start around 10–11/32". Most states call it worn out at 2/32". Plenty of drivers start losing real wet-weather grip well before that — many mechanics suggest starting to shop once you hit 4/32", especially heading into a rainy or snowy season.
Two common styles — pull-slide (left) and plunger-style with a color-coded wear zone (right)
Pull-slide style (left)
Push the probe into the groove until the shoulder sits flush against the tread, then read the number where the sliding scale stops — that's your depth.
Plunger style (right)
Same idea — press it into the groove — but the fast read is the color band left showing: green/teal means healthy tread, yellow means start watching it, red means it's time to replace.
Both of these are manual gauges. Digital tread depth gauges are also out there and give you an exact readout on a small screen — no reading a scale by eye, if you'd rather go that route.
Built-in wear bars — no tool needed
Most tires have this built right in: small raised bars molded into the bottom of the main grooves. When the surrounding tread wears down to their level, the bar goes flush with the rest of the tread — that's the tire telling you it's done, without a penny or a gauge.
Healthy treadWear bar sits well below the tread surface — plenty of groove depth around it
Worn outTread has worn down to meet the bar — it's flush with the surface, time to replace
Between tread blocksNot every bar sits in a plain straight channel — it can bridge the groove right between two tread segments. Same rule: flush means it's worn
Where to find them
Look for a small arrow, triangle, or "TWI" mark on the tire's sidewall near the tread edge — that points to where a wear bar sits inside the nearest groove. Most tires have 6 to 9 of these spaced evenly around the circumference.
How to read them
Glance at the groove near one of those markers. If there's still a visible channel around the bar, you've got tread left. Once the bar is flush with the surrounding rubber — no more dip — that section has hit the legal wear limit.
Why check a few of them
Because tires can wear unevenly, one wear bar going flush before the others is a useful early flag — it can point to an alignment or pressure issue worth checking, on top of just needing new tires.