Tyre tread depth: meaning and examples
Tyre tread depth is how deep the grooves in a tyre are, measured from the top of the tread to the bottom of the groove. As tread wears, grip on wet roads falls, which is why tyres have a minimum depth.
How it works
Tread depth is how deep the grooves are on a tyre. New tyres start deeper, and the grooves wear shallower with use. Deep grooves clear water from under the tyre, so shallow tread grips less on wet roads.
The US National Highway Traffic Safety Administration says to replace tyres when the tread has worn to 2/32 of an inch (about 1.6 mm), and to check tread monthly along with tyre pressure. Its penny test is to put a penny in the groove with Lincoln's head upside down: if you can see the top of his head, the tread is too low. Rules differ by country, so check your local minimum.
Tread is only part of tyre health. Age, damage and pressure matter as well.
A monthly check
Illustration: you measure 3 mm in the main grooves in January and 2.4 mm in April. Two dated log entries show the rate of wear and give you an early warning before it reaches the minimum.
How to track it in Loggy
Record each tyre check or replacement as a log entry with the date, reading and receipt, and add the tread you measured to the notes.
- Measure or check tread at least monthly.
- Add a log entry with the date, reading and your tread figure in the notes.
- When you replace tyres, log the date, cost and receipt.
Loggy is a free maintenance logbook app for iOS and Android. The free plan has unlimited vehicles, reminders, PDF export and vehicle transfer, and no ads.
Frequently asked questions
What is the minimum tread depth?
NHTSA says 2/32 of an inch (about 1.6 mm) in the US. Other countries set their own limits.
How often should I check tread?
NHTSA suggests monthly, along with pressure.
Does Loggy measure tread?
No. You measure it and note the figure in a log entry.