Car care guide · Elgin Auto Sales & Service Center · Elgin, IL
Tire Tread Depth: How Much Is Enough?
Tire tread depth is usually given in 32nds of an inch. This guide covers the minimum depth NHTSA gives, how to check your tires with the wear bars or a penny, and the tread rules in Illinois law.
2/32 inchNHTSA: replace tires worn down to this depth
MonthlyNHTSA: check tread when you check pressure
3/32 inchIllinois minimum for a tire on a vehicle sold or leased
3 spotsIllinois measures at three places around the tire
The short answer
NHTSA says tires are not safe and should be replaced when the tread is worn down to 2/32 of an inch, the same as 1/16 inch. Tires have built-in treadwear indicators that show when the tread reaches that point, and NHTSA also describes a quick penny test. Illinois law treats a tire with less than 2/32 inch of tread (other than on a motorcycle or truckster) as unsafe to drive on a highway.
The minimum tread depth
NHTSA says tires are not safe and should be replaced when the tread is worn down to 2/32 of an inch. Its tire safety booklet puts the same limit as 1/16 of an inch; 2/32 and 1/16 are the same depth.
Tread is measured in 32nds of an inch, so a reading of 4/32 means four thirty-seconds of an inch of tread left above the bottom of the groove. That is the depth this guide is talking about whenever it gives a fraction.
From NHTSA, Tire Safety Ratings and Awareness (nhtsa.gov) and the NHTSA tire safety booklet (DOT HS 809 361), read November 2, 2026.
How to check your tread depth
NHTSA recommends checking your tread at least once a month, when you check your tire pressure. Two simple ways to check it:
Look for the wear bars
Tires have built-in treadwear indicators: raised sections spaced in the bottom of the tread grooves. When the tread is worn down so it is level with those indicators, NHTSA says it is time to replace the tire.
Try the penny test
Place a penny in the tread with Lincoln's head upside down and facing you. If you can see the top of Lincoln's head, NHTSA says to replace your tires.
Check more than one spot
Tires do not always wear evenly. Illinois law measures tread in two or more adjacent grooves at three places spaced around the tire, including where the tread looks thinnest, and does not count a reading taken over a tread wear indicator.
Look for other damage
While you are there, NHTSA suggests checking for uneven wear, cracks, foreign objects or other signs of wear or trauma, and removing bits of glass or other objects wedged in the tread.
From NHTSA, Tire Safety Ratings and Awareness, the NHTSA tire safety booklet (DOT HS 809 361) and 625 ILCS 5/12-405, Illinois Vehicle Code (tires), read November 2, 2026.
What Illinois law says about tread depth
| Rule | Tread depth |
|---|---|
| Tire unsafe to drive on an Illinois highway | Less than 2/32 inch (1/32 inch on a motorcycle or truckster) |
| Front tire on a vehicle covered by Chapter 18B of the Vehicle Code (commercial vehicle safety rules) | Less than 4/32 inch at any one location |
| Tire, or a vehicle with a tire, sold or leased for highway use | Must have at least 3/32 inch (2/32 inch on a motorcycle or truckster) |
From 625 ILCS 5/12-405, Illinois Vehicle Code (tires), read November 2, 2026. The statute measures tread depth in two or more adjacent grooves at three roughly evenly spaced locations and excludes any measurement over a tie bar, tread wear indicator, hump or fillet. This is general information, not legal advice.
Why tread depth matters
NHTSA explains that tire tread provides the gripping action and traction that keep your car or truck from slipping and sliding, especially when the road is icy or wet. That is why worn tread is a safety issue, not just a cosmetic one.
How fast tread wears depends partly on the tire. NHTSA says treadwear grades indicate a tire's relative wear rate: the higher the number, the longer the tread should take to wear down, so a tire graded 400 should wear twice as long as one graded 200. Even with tread left, NHTSA notes that some vehicle and tire manufacturers recommend replacing tires that are six to 10 years old, regardless of treadwear. Our guide on when to replace tires covers tire age and the date code.
From NHTSA, Tire Safety Ratings and Awareness and the NHTSA tire safety booklet (DOT HS 809 361), read November 2, 2026.
Tire help at Elgin Auto Sales
We service all makes, and our tire service pages cover Toyota, Honda, Hyundai, Kia, GMC and Buick models. If you are not sure how much tread you have left, our service team can take a look.
Elgin Auto Sales & Service Center is at 1200 E. Chicago St. in Elgin. Our service department is open Monday to Friday 8 a.m. to 5 p.m. and Saturday 8 a.m. to 4 p.m., and is closed Sunday. Get directions.
Schedule service online or see our service specials.
Tire tread depth FAQ
What is the minimum safe tire tread depth?
NHTSA says tires are not safe and should be replaced when the tread is worn down to 2/32 of an inch (1/16 inch).
How do I do the penny test?
Place a penny in the tread with Lincoln's head upside down and facing you. If you can see the top of Lincoln's head, NHTSA says to replace your tires.
What are tread wear indicators?
Raised sections spaced in the bottom of the tread grooves. When the tread is worn down level with them, NHTSA says it is time to replace the tire.
What is the legal tread depth in Illinois?
Under 625 ILCS 5/12-405, a tire with less than 2/32 inch of tread (1/32 inch on a motorcycle or truckster) is unsafe to drive on an Illinois highway, and a tire or vehicle sold or leased for highway use must have at least 3/32 inch.
How often should I check my tire tread?
NHTSA recommends checking your tread at least once a month, when you check your tire pressure.
Is 4/32 tread depth OK?
4/32 inch is above the 2/32-inch point at which NHTSA says to replace tires, but it means the tread is getting closer to that limit. Keep checking monthly, and remember that some vehicle and tire makers also recommend replacing tires at six to 10 years old regardless of tread.
Tread looking thin?
Book a visit with our service department at 1200 E. Chicago St. in Elgin.
Sources
Tread depth limits, checking methods and treadwear information are from NHTSA's tire safety page and booklet; Illinois limits are from 625 ILCS 5/12-405. All were read on November 2, 2026. This page is general information, not legal advice. Our services, tire service pages, address and hours are from our own website, checked the same day. Photo is of our dealership.
- NHTSA, Tire Safety Ratings and Awareness, NHTSA
- NHTSA tire safety booklet (DOT HS 809 361), NHTSA
- 625 ILCS 5/12-405, Illinois Vehicle Code (tires), Illinois General Assembly
- Service department, online scheduling form and service hours, Elgin Auto Sales & Service Center
- Toyota tire service (and the Honda, Hyundai, Kia, GMC and Buick tire service pages), Elgin Auto Sales & Service Center
- Home page: address, sales hours and "we service all makes", Elgin Auto Sales & Service Center