Tyres are the only part of your car that actually touches the road. When tread gets low - or wears unevenly - wet grip drops, braking distances increase, and the risk of aquaplaning goes up significantly.
A quick tread check is one of the simplest, highest-impact safety habits you can build into your routine. This guide covers the UK legal minimum, the safer replacement threshold, and three methods for checking tread depth at home - including the one most drivers get wrong.
Why Tyre Tread Depth Matters
Tread isn't there for show. Its main job is to channel water away from the contact patch between tyre and road, so the tyre can maintain grip in wet conditions. As tread gets shallower, tyres become far less effective at dispersing water - increasing aquaplaning risk and reducing braking performance.
Good tread also helps with:
- Stability when cornering and changing lanes, particularly in rain
- Shorter braking distances on wet roads
- Predictable handling and reduced risk of skidding
In the UK, wet roads are normal - not rare. That's why tread depth matters here more than many drivers realise. Running near the legal limit in autumn or winter carries real risk.
UK Legal Minimum - and the Safer Replacement Threshold
For cars, light vans, and light trailers, the Highway Code states tyres must have a tread depth of at least 1.6mm across the central three-quarters of the tread, around the entire circumference. Driving with less than 1.6mm is illegal and can result in a fine of up to £2,500 per tyre and three penalty points.
However, 1.6mm is the legal minimum - not the point at which tyre performance is still considered adequate. TyreSafe notes that water-dispersing performance drops significantly below 3mm, and recommends considering replacement earlier.
Three Ways to Check Tread Depth at Home
Tread depth gauge
The most accurate method. A gauge gives you an exact reading in millimetres, so you know precisely whether you're above or below the 3mm and 1.6mm thresholds. Available cheaply from any motoring retailer.
Tread wear indicator bars
Most tyres have small raised bars moulded across the grooves. When the surrounding tread wears down to the level of the bars, the tyre is at or near the legal limit. Look for a "TWI" marker or triangle on the sidewall to find them.
The 20p test
Insert a 20p coin into the main tread groove. If the outer band of the coin is hidden, tread is generally above the legal limit. If the band is visible, measure properly or seek a professional check immediately.
The Right Way to Measure Tread
Most drivers check one spot on one tyre and call it done. The problem: tread often wears unevenly, particularly on the inner edge - and that inner edge is where the legal requirement applies too.
Step-by-step tread check - 2 minutes for all four tyres
| 1 | Check all four tyresFront and rear tyres wear differently depending on drivetrain and alignment - don't assume all four are the same. |
| 2 | Measure across three positions on each tyreInner edge (closest to the car), centre, and outer edge. The inner edge is often the first to wear and the easiest to miss. |
| 3 | Measure at three points around the circumferenceFront, back, and at least one other point. Wear isn't always uniform around the tyre. |
| 4 | Record the lowest reading you findThe lowest reading across all positions is what matters - this is the one that determines whether the tyre is legal and safe. |
Turn the steering wheel slightly to get a clear view of the inner shoulder on the front tyres - this is the position that most often shows early wear and is most commonly overlooked.
When to Replace Tyres - Beyond Tread Depth
Tread depth is one part of tyre safety. There are other conditions that require immediate action regardless of how much tread remains.
Replace immediately if you see...
- Bulges or blisters on the sidewall
- Cuts on the sidewall or deep cuts in the tread
- Exposed cords or wire visible through the rubber
- Significant cracking or perishing from age or UV damage
- Tread at or under 1.6mm anywhere across the central band
- Repeated pressure loss suggesting a slow puncture or rim leak
Replace soon if you notice...
- Uneven wear on the inner edge, outer edge, or centre
- Vibration through the steering wheel or seat that wasn't there before
- The car pulling to one side - possible alignment or wear issue
- Noticeably longer braking distances in wet conditions
- Tread below 3mm heading into autumn or winter
Common Wear Patterns - and What They Usually Mean
Uneven wear often points to a fixable underlying issue. Spot it early and you can address the cause before the tyre becomes unsafe.
Centre wear
More worn in the middle of the tread than at the edges. Often linked to over-inflation - the tyre bows outward under excess pressure, concentrating wear on the centre.
Both shoulders worn
Worn more on both outer edges than the centre. Often linked to under-inflation - the tyre flattens under the vehicle's weight, wearing the shoulders first.
Inner edge wear
Very common and easy to miss without deliberately checking the inner shoulder. Often linked to wheel alignment issues or suspension geometry - worth investigating promptly.
Scalloping or cupping
Wavy dips that appear at intervals around the tread. Often linked to wheel balancing issues or worn suspension components - causes vibration and accelerates wear.
One-sided wear
Significantly more worn on one side than the other. Typically indicates a wheel alignment problem - the tyre is running at an angle rather than sitting flat on the road.
Patchy or erratic wear
Irregular wear with no clear pattern. Can point to a combination of alignment, balancing, and pressure issues - a professional inspection is advisable.
If you're unsure what's causing an unusual wear pattern, get it inspected - particularly before a long motorway trip where wear-related handling changes are most hazardous.
Your Monthly Tread Check Routine
TyreSafe recommends a monthly check and a check before every long journey as the minimum routine. The A.C.T. check covers the three most important elements in under a minute.
A.C.T. check - Air, Condition, Tread
- Air - are pressures stable and at the correct level? Check when cold using the vehicle placard spec (door jamb or handbook) - not the maximum shown on the tyre sidewall.
- Condition - any bulges, deep cuts, obvious cracking, or embedded objects? Carry out a quick visual of all four tyres including the sidewalls.
- Tread - above 3mm for a healthy wet-weather margin? Definitely above 1.6mm legal minimum? Check at the inner edge where wear is often most advanced.
Not sure whether to repair or replace?
If your concern started with a puncture, use this quick decision guide.
- Sidewall damaged, bulging, or cords visible? Replace immediately - do not drive if the tyre is unsafe.
- Puncture in the repairable zone and the tyre otherwise healthy? Professional repair may be possible - arrange inspection.
- Tread low (especially under ~3mm) or wear already uneven? Replacement is often the smarter move even if a repair is technically possible.
Key points from this guide
- The UK legal minimum is 1.6mm across the central three-quarters of the tread - below this is illegal and dangerous.
- TyreSafe recommend considering replacement at 3mm because wet performance drops significantly below this threshold.
- Always check the inner edge of the tyre - this is where wear is often most advanced and most commonly missed.
- Uneven wear patterns often point to a fixable underlying issue - alignment, pressure, or balancing.
- A tread depth gauge is the most accurate check method - the 20p test is a prompt, not a verdict.
- Check tread and pressure monthly and before every long journey as a minimum routine.