Tyre Wear Indicators — The Bars in Your Tread
A practical guide to tyre wear indicators for UK drivers, from the CarPal mobile tyre team.
What they are
Tread wear indicators, often abbreviated TWI, are small raised bars moulded into the bottom of the main tread grooves. They sit at exactly 1.6mm — the UK legal minimum.
Every road tyre sold in the UK has them. They are a built-in legal gauge that never needs calibrating.
How to find them
Look at the tyre shoulder for a small marker — usually a triangle, the letters TWI, or the manufacturer’s logo. That marker points to where an indicator bar sits in the groove alongside it.
Follow it inward and you will see the raised bar bridging the bottom of the groove. There are typically six to eight of them spaced around the tyre.
How to read them
Compare the height of the surrounding tread blocks against the bar. If the tread is clearly higher than the bar, you have legal tread. If the tread has worn down level with the bar, the tyre is at 1.6mm and legally worn out.
If the bar is flush with the tread across a continuous band, the tyre must be replaced.
Their limitation
They tell you when you have reached the legal limit and nothing before that. They cannot tell you that you are at 3mm and should start budgeting for tyres.
They also only measure at the specific points where the bars are. If the tyre is wearing unevenly elsewhere, the bars may not reflect the worst area. That is why a gauge, used in several places, remains the better tool for planning.
Frequently asked questions
What are the bars in my tyre tread?
Tread wear indicators, set at 1.6mm — the UK legal minimum tread depth.
How do I know where to look?
Find the small triangle, TWI marking or manufacturer’s logo on the tyre shoulder. It points to an indicator bar in the adjacent groove.
What if the tread is level with the bar?
The tyre is at the legal limit and needs replacing.
Are wear indicators enough on their own?
They are a reliable legal check but only at the points where the bars sit. A gauge used in several places is better for planning replacement.
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