Tyre Tread Life Calculator (How Many Kilometres Until the Legal Limit)
Distance and time left before your tyres — or brake pads — reach the legal minimum or the depth where you want to change them, from two measurements.
Results
What this tool does
Measure the tread in the same groove at two points in time and note the kilometres in between: the wear rate follows, and so does the distance until the limit. The legal minimum is 1.6 mm in the UK and most of Europe, and in most US states the limit is 2/32 inch, almost the same. Many tyre makers and road-safety bodies advise changing earlier, often around 3 mm, because wet grip and aquaplaning resistance fall off well before the legal limit. Wear is only roughly linear and varies by axle, so measure again every few thousand kilometres.
Formula
wear rate = (t₁ − t₂) ÷ km · distance left = (t₂ − limit) ÷ wear rate (also works for brake pads and discs)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
t1 | Tread depth at the first measurement | mm |
t2 | Tread depth now | mm |
d | Distance driven between the two measurements | km |
lm | Legal minimum depth | mm |
ad | Depth at which you want to replace them | mm |
ky | Distance you drive in a year | km |
KL | Distance left to the legal minimum | km |
KA | Distance left to your replacement depth | km |
WR | Wear rate | mm/1000 km |
ML | Time left to the legal minimum at your yearly distance | months |
Worked example
- Tread depth at the first measurement8 mm
- Tread depth now6.4 mm
- Distance driven between the two measurements8000 km
- Legal minimum depth1.6 mm
- Depth at which you want to replace them3 mm
- Distance you drive in a year12,000 km
- Distance left to the legal minimum24,000 km
- Distance left to your replacement depth17,000 km
- Wear rate0.20 mm/1000 km
- Time left to the legal minimum at your yearly distance24.0 months
Limitations
- For work that must comply with a standard or be signed off, check the result against the applicable code and have it reviewed by a qualified engineer.
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.