Tyre Tread Depth: Legal Limit, Checking Guide & When to Replace

# Tyre Tread Depth: Legal Limit, Checking Guide & When to Replace

Tyre tread depth is one of the most safety-critical factors on your vehicle — and one of the most commonly neglected. For Scottish drivers dealing with wet roads for much of the year, understanding tread depth matters more than almost anywhere else in the UK.

What Is the Legal Minimum Tyre Tread Depth in the UK?

The UK legal minimum tyre tread depth is 1.6mm across the central three-quarters of the tyre, around the full circumference.

Driving on tyres below 1.6mm tread depth is a criminal offence. The penalty is up to a £2,500 fine and 3 penalty points per tyre. Four bald tyres can cost you up to £10,000 in fines and 12 points — an automatic driving ban.

Is 1.6mm Safe Enough for Scotland?

The legal minimum is not a safety recommendation — it is a legal floor. Independent testing by TyreSafe and the MIRA research institute consistently shows that tyre performance degrades significantly before you reach 1.6mm.

Wet stopping distance comparison (at 50mph):

Tread Depth	Wet Stopping Distance
8mm (new)	Baseline
3mm	+27% longer
1.6mm	+44% longer

On Scotland's wet roads, a tyre at 1.6mm takes nearly half as long again to stop as a new tyre. At 50mph on a wet Glasgow road, that difference is approximately 12 metres — enough to hit a pedestrian or the vehicle in front.

Tyre Rescue recommendation: Replace tyres when tread reaches 3mm on Scottish roads. This is the threshold used by many professional fleet operators and endorsed by road safety charities.

How to Check Your Tyre Tread Depth

Method 1: The 20p Coin Test

Insert a 20p coin into the tread groove. If you can see the outer rim of the coin (the raised band), your tread is below 3mm and approaching replacement territory. If the entire outer rim is hidden, you have more than 3mm of tread.

Method 2: Tread Wear Indicators (TWI)

All tyres have small rubber bars moulded into the tread grooves. These bars sit at exactly 1.6mm. If the tread surface is level with these bars, the tyre is at the legal minimum and must be replaced immediately. Look for a small triangle or 'TWI' marking on the tyre shoulder to locate where these bars are in each tread groove.

Method 3: Tread Depth Gauge

A simple tread depth gauge costs from £3 at a garage or online. Insert the probe into the tread groove and read the depth in millimetres. Check at least three points across the tyre width in each of four positions around the circumference (12, 3, 6, and 9 o'clock positions).

What to Check For

Beyond depth, inspect tyres for:

• Uneven wear across the width (may indicate alignment or inflation problems)
• Feathering — tread blocks worn on one edge only (alignment issue)
• Centre wear — excessive wear in the middle (over-inflation)
• Edge wear — worn on both outer edges (under-inflation)
• Cracks or bulges in the sidewall (tyre must be replaced immediately)

How Often Should You Check Tread Depth?

Check tyre tread depth at least once a month and before any long journey. In Scotland, check after periods of particularly bad weather, after driving on gravel roads or farm tracks, and after any kerbing incident.

When to Replace Tyres in Scotland

Replace immediately if:

• Tread depth is at or below 1.6mm (legal minimum)
• Sidewall cracks, cuts, or bulges are visible
• Tyre age exceeds 10 years (tyres degrade regardless of tread)
• The tyre has been run flat (even briefly)

Replace soon if:

• Tread depth is at or below 3mm (Scottish road safety threshold)
• Tyre age is 5–7 years (rubber compound begins to harden)
• Uneven wear indicates alignment or suspension issues

Tyre Replacement in Scotland

Need new tyres fitted? Tyre Rescue brings the tyres and fitting equipment to your location — home, work, or roadside — across all of Scotland.

• Call 0141 266 0690 to check tyre availability and get a quote
• [Book online](/book) to schedule a fitting at your convenience
• [Emergency callout](/emergency-tyre-fitting-near-me) if you need immediate assistance

[Best tyres for Scottish roads](/blog/best-tyres-scottish-roads-guide) | [Mobile tyre fitting Scotland](/mobile-tyre-fitting) | [Signs you need new tyres](/blog/signs-you-need-new-tyres)