What should I verify before using this information?

Use TireFitLab values as a sizing reference, then verify the vehicle handbook, tire placard, rim compatibility, load rating, and physical clearance before fitting.

Tyre wear indicators guide

What are tyre wear indicators and when should you replace your tyres?

Tyre wear indicators (TWIs) are raised rubber bars moulded into the base of the main tread grooves at a height of 1.6 mm — the legal minimum tread depth in Europe, UK, and most of the USA. They are located at intervals around the tyre (usually 6–8 positions per tyre) and are visible as small raised platforms inside the grooves. When the surrounding tread wears down to the level of the TWI bars, the tyre is at the legal limit and must be replaced. In practice, most safety experts recommend replacing tyres at 3–4 mm (well above the legal limit) because wet braking distance increases dramatically between 4 mm and 1.6 mm — the stopping difference from 80 km/h can be 10–15 metres longer on a wet road with 1.6 mm versus 4 mm of tread.

Tyre wear indicators (TWIs) are raised rubber bars moulded into the base of the main tread grooves at a height of 1.6 mm — the legal minimum tread depth in Europe, UK, and most of the USA.
They are located at intervals around the tyre (usually 6–8 positions per tyre) and are visible as small raised platforms inside the grooves.
When the surrounding tread wears down to the level of the TWI bars, the tyre is at the legal limit and must be replaced.

FAQ

What are tyre wear indicators and when should you replace your tyres?: Tyre wear indicators (TWIs) are raised rubber bars moulded into the base of the main tread grooves at a height of 1.6 mm — the legal minimum tread depth in Europe, UK, and most of the USA. They are located at intervals around the tyre (usually 6–8 positions per tyre) and are visible as small raised platforms inside the grooves. When the surrounding tread wears down to the level of the TWI bars, the tyre is at the legal limit and must be replaced. In practice, most safety experts recommend replacing tyres at 3–4 mm (well above the legal limit) because wet braking distance increases dramatically between 4 mm and 1.6 mm — the stopping difference from 80 km/h can be 10–15 metres longer on a wet road with 1.6 mm versus 4 mm of tread.
What should I verify before using this information?: Use TireFitLab values as a sizing reference, then verify the vehicle handbook, tire placard, rim compatibility, load rating, and physical clearance before fitting.

Tread depth reference: from new to bald

Depth	Condition	Wet braking impact	Recommendation
8 mm	New tyre (typical new tread depth for a passenger car tyre)	Baseline — optimum wet grip	Fit or continue use
4 mm	Half worn. Legal in all markets. Wet braking distance begins to increase noticeably.	~10–15% longer stopping distance vs new (80 km/h wet road)	Plan replacement. Required minimum for winter tyres (safety recommendation, not everywhere legal)
3 mm	Approaching wear limit. Safe for summer dry but wet performance is reduced.	~20–25% longer stopping distance vs new	Replace before winter or wet-weather driving season
1.6 mm	Legal minimum in EU, UK, and most USA states. TWI bars flush with tread surface.	~40–50% longer stopping distance vs new (80 km/h wet road)	Replace immediately — this is the legal limit, not the safety limit
0 mm (bald)	Tread below TWI bars. Illegal in all regulated markets. Aquaplaning begins at low speed.	Extremely poor — grip on wet is minimal; braking distance unpredictable	Do not drive. Immediate replacement required.

How to locate TWI bars on your tyre

Feature	Detail
TWI sidewall markings	Small raised triangle, arrow, or "TWI" text is moulded into the sidewall rubber at each indicator position. The marking points horizontally into the tread groove where the TWI bar is located.
Number of TWI positions	Most passenger car tyres have 6 TWI bars at equal intervals (every 60 degrees). Some have 8 (every 45 degrees). High-performance and winter tyres may have more frequent indicators.
TWI bar appearance	A flat rubber bridge moulded into the base of the groove. Colour is the same as surrounding rubber — it is flush with the groove base. It becomes visible at eye level when looking along the groove length.
Winter tyre secondary indicators	Many winter tyres include a secondary indicator (often marked "2") that signals the 4 mm winter safety threshold — when this marker becomes flush, winter performance is significantly degraded even though the legal limit is not yet reached.

Step-by-step: look along the sidewall for a small triangle or the letters "TWI" — they are moulded into the sidewall rubber. Trace horizontally inward to the groove. Crouch to look along the groove; the TWI bar is a flat platform slightly raised above the groove base. When the surrounding tread wears to the level of that platform, it becomes flush — the legal limit has been reached.

How to measure tread depth accurately

Method	Accuracy	Cost	Procedure	Limitation
Dedicated tread depth gauge	±0.1 mm	EUR 3–10	Insert probe into tread groove, press gauge flat against tread surface, read displayed depth. Measure at three points across the tread width and three positions around circumference (9 measurements minimum per tyre).	Most accurate method. Recommended for pre-winter checks and purchase decisions.
Penny test (UK 20p coin)	±0.5 mm (approximate go/no-go)	20p (coin)	Insert the 20p coin into the main groove. If the outer band of the coin is hidden by the tread, depth exceeds ~3 mm. If the band is visible, depth is below ~3 mm — replace soon.	Only indicates approximate 3 mm threshold. Does not show exact depth.
Quarter test (USA 25 cent coin)	±0.5 mm (approximate)	Coin	Insert the quarter into the groove with Washington facing down. If the top of his head disappears, tread exceeds ~4 mm. If visible, tread is below ~4 mm.	USA-specific. Also check with a Lincoln penny: if Lincoln head fully visible, depth is below ~1.6 mm — replace immediately.
Wear indicator bars (TWI)	Binary — at 1.6 mm or not	Free (built-in)	Locate the TWI triangle, arrow, or "TWI" lettering on the sidewall. These point to the position of the raised bar in the tread groove. If bar is flush with surrounding tread, depth is at 1.6 mm.	Only indicates the legal minimum. Does not tell you depth above 1.6 mm.

Always measure at the shallowest groove, not the deepest. Measure across the full tread width (inner, centre, outer) and at three positions around the circumference — wear is rarely uniform. The legal limit applies to the main grooves; secondary grooves (between major channels) may be deeper but are not counted for legal compliance.

Legal tread depth limits by region

Region	Summer minimum	Winter minimum	Penalty
EU (all member states)	1.6 mm	1.6 mm (legal) / 4 mm (recommended)	Varies by country. Germany: fine up to €75 + 1 penalty point per defective tyre. UK: up to £2,500 + 3 penalty points per tyre.
United Kingdom	1.6 mm across central 3/4 of tread width around full circumference	1.6 mm (no legal winter minimum)	Up to £2,500 + 3 penalty points per tyre. Vehicle may fail MOT.
USA (federal)	2/32 inch (1.6 mm) for rear; some states require 4/32 inch (3.2 mm) for front	No federal winter minimum. Some states may require winter tyres in winter conditions.	State-level enforcement; insurance may be affected in accident.
Canada	1.6 mm (federal)	Quebec: 2 mm minimum for winter tyres Dec–Mar. Other provinces vary.	Provincial enforcement; insurance impact in accident possible.

The 1.6 mm legal limit is not a safe limit. It is the lowest threshold below which the tyre must not be used. Safety organisations including TÜV, ADAC, and the British Tyre Manufacturers Association recommend replacing tyres at 3 mm in summer and at the 4 mm winter secondary indicator for winter tyres.

Wear patterns: what uneven wear tells you

Wear pattern	Likely cause	Action
Centre wear (faster than edges)	Over-inflation — excessive pressure causes the tyre to ride on the centre crown, wearing the centre faster than the shoulders.	Reduce pressure to recommended level. Check door sticker or owner manual.
Edge wear (both shoulders worn faster than centre)	Under-inflation — low pressure causes the tyre to ride on its outer edges, wearing shoulders first.	Inflate to recommended pressure. Check for slow leak if pressure drops repeatedly.
One-sided shoulder wear (inner or outer)	Camber misalignment — excessive positive or negative camber tilts the tyre contact patch, loading one edge disproportionately.	Wheel alignment check and correction. See our wheel alignment guide.
Feathering (sawtooth pattern — smooth on one side, sharp on other)	Toe misalignment — tyres pointing inward (toe-in) or outward (toe-out) relative to direction of travel create a scrubbing wear pattern.	Toe alignment correction required.
Cupping / scalloping (random patches of deep wear around circumference)	Worn shock absorbers or unbalanced wheel — tyre bounces rather than maintaining constant contact with road, creating irregular wear patches.	Check and replace shock absorbers. Dynamic wheel balancing.
Flat spot (single localised wear patch)	Emergency braking with locked wheels on a vehicle without ABS; or prolonged stationary parking on wet road surface (flat spotting from deformation).	Minor flat spots may reduce after driving. Severe flat spots require tyre replacement.

Tread wear patterns are diagnostic: they tell you not just when to replace but why the tyre wore unevenly. Replacing the tyre without addressing the root cause (pressure, alignment, shock absorbers) will result in the same wear pattern on the new tyre. Always check pressure and inspect suspension before fitting new tyres.

When to check tread depth

Monthly visual check — look at the TWI bars during regular tyre pressure check. Takes 30 seconds per tyre.
Pre-winter measurement — measure accurately before the season change. If below 4 mm, do not fit winter tyres on them — winter tyre performance degrades sharply below 4 mm.
Before long trips — check all four tyres including spare (if present).
After any wheel alignment — alignment issues accelerate uneven wear; check depth and wear pattern after correction to establish a new baseline.
When purchasing a used vehicle — measure at the inner edge (the most frequently neglected position) using a gauge. Do not rely on a seller saying "good tread" without independent measurement.

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Last reviewed: 2026-06-21

Last reviewed: 2026-06-28

What changed

Reviewed deterministic geometry, load/speed references, sitemap inclusion and localized page shell.