Calculator 11 / Tire Tread Life
Tire Tread Life Calculator
Remaining tyre life comes from your own wear rate, not from a mileage estimate — measure the tread twice and the rest is arithmetic. Project remaining tire life in miles from your current wear rate and a legal or safety minimum tread depth.
How this calculator works
Units below default automatically — Metric for non-English pages (or if your device's language is set to one we support), US customary otherwise — and convert automatically if you switch the toggle above the form. Changing language resets to that language's default unless you toggle again.
This projects tread wear as a straight line based on your wear so far — a reasonable estimate for steady highway driving, though actual wear rate can change with load, alignment, inflation pressure, and driving style over the life of the tire. The FMCSA minimum tread depths (4/32" on steer axles, 2/32" on all other axles) are federal minimums for commercial vehicles; some fleets and states set stricter internal or local standards.
Worked example: a drive tire at 40,000 miles
The calculator's defaults are a tire that started at 14/32 in and now measures 10/32 in after 40,000 miles, against the 2/32 in drive-axle minimum:
- Tread worn = 14 − 10 = 4/32 in
- Wear rate = 4 ÷ 40,000 = 0.1/32 in per 1,000 mi
- Tread left above the minimum = 10 − 2 = 8/32 in
- Remaining life = 8 ÷ 0.1 × 1,000 = 80,000 mi
Total life from new works out at 120,000 miles. Move the same tire to a steering axle, where the federal minimum is 4/32 in rather than 2/32 in, and the remaining life drops from 80,000 to 60,000 miles — a quarter of the tire's whole life disappears purely because of which axle it is fitted to.
Federal minimum tread depths
In the United States these come from 49 CFR 393.75 and apply to commercial motor vehicles. They are the point at which a vehicle is placed out of service — not a target to aim for, and not a depth at which the tire still performs.
| Position | Minimum | Metric | Rule |
|---|---|---|---|
| Steering axle | 4/32 in | 3.2 mm | Measured in a major tread groove, not at a wear bar or tie bar |
| All other axles | 2/32 in | 1.6 mm | Drive, trailer, tag and pusher axles |
| Passenger cars (most US states) | 2/32 in | 1.6 mm | State law, not federal; a few states differ |
| Cars in the EU and UK | — | 1.6 mm | Across the central three-quarters of the tread, all the way round |
1.6 mm and 2/32 in are the same depth expressed two ways, which is why the two regimes land on the same number. Where the measurement is taken matters as much as the reading. Federal rules specify a major groove and exclude wear bars, tie bars and the tread-depth indicators moulded into the rubber — measuring on one of those gives a shallow reading and a tire that fails an inspection it should have passed.
What tires start at
The calculator needs an original depth, and guessing it badly is the fastest way to a wrong answer. If you did not measure the tire when it was new, these are typical starting depths — but the specification for your exact tire is printed by its manufacturer, and deep-tread and regional variants of the same size differ substantially.
| Tire type | Typical new depth | Metric | Usable above its minimum |
|---|---|---|---|
| Passenger / touring | 10–11/32 in | 7.9–8.7 mm | 8–9/32 in |
| All-season light truck | 11–13/32 in | 8.7–10.3 mm | 9–11/32 in |
| All-terrain / mud-terrain | 15–19/32 in | 11.9–15.1 mm | 13–17/32 in |
| Commercial steer | 18–22/32 in | 14.3–17.5 mm | 14–18/32 in (to 4/32) |
| Commercial drive | 24–32/32 in | 19.0–25.4 mm | 22–30/32 in |
| Commercial trailer | 14–18/32 in | 11.1–14.3 mm | 12–16/32 in |
Note the last column. A commercial steer tire measured against the 4/32 in steer minimum has less usable tread than the raw depth suggests, and a drive tire has far more — which is why the same casing can be worth retreading off one axle and not the other.
Checking without a gauge
A tread depth gauge costs very little and is worth owning. Failing that, US coins give two useful thresholds, because both are pass/fail at exactly the depths the law cares about.
| Coin | Insert | If you can see the top of the head | Threshold |
|---|---|---|---|
| US penny | Lincoln head first, into a major groove | Tread is below the drive/trailer minimum | 2/32 in |
| US quarter | Washington head first, into a major groove | Tread is below the steer-axle minimum | 4/32 in |
Check several grooves and both shoulders of every tire, not one spot. Uneven wear across a single tire is itself the finding — it points at inflation, alignment or a mechanical fault, and it means the shallowest groove is the one that governs. A coin cannot give you the numbers this calculator needs; it only tells you whether you have already run out of time.
Why the projection is optimistic
This calculator draws a straight line: it takes the wear you have already recorded and assumes the rest of the tire wears at the same rate. Real tread does not oblige, and almost every deviation is in the direction of less life than projected.
- Wear accelerates as tread shallows. A shallower block flexes less and runs hotter, and there is less rubber to spread the load. The last few 32nds usually go faster than the first few.
- Under-inflation wears the shoulders and over-inflation wears the centre, and either can take a tire out of service while the groove you happen to measure still looks healthy.
- Position changes everything. Steer, drive and trailer positions wear at different rates and in different patterns, so a rotation invalidates the rate you measured before it.
- Load, route and season all move the rate. Heavy haul, mountain grades, high ambient temperature and stop-start city work all wear faster than steady highway miles.
- Age is a separate limit. Rubber degrades whether or not the vehicle moves, and many manufacturers and fleets retire tires on date code regardless of remaining tread. A trailer that sits still can time out with 14/32 left.
- Damage ends the projection instantly. A cut, a bulge, exposed belt or a sidewall injury retires the tire that day, and no amount of remaining tread changes that.
Where this goes wrong
- Guessing the original depth. It is the input the whole projection hangs on. Assume 12/32 on a tire that started at 18/32 and you will underestimate the wear rate badly, and overestimate the life left.
- Using the wrong minimum for the axle. The steer minimum is double the drive minimum. Choosing the wrong one moves the answer by tens of thousands of miles, which is why it is a dropdown and not a constant.
- Measuring on a wear bar. The raised bars in the groove are indicators, not tread. Measure the groove floor beside them.
- Measuring one groove on one tire. The shallowest point on the tire is the one an inspector will find, and the difference between grooves is diagnostic information you want.
- Treating the projection as a service interval. It is a planning figure for ordering and budgeting. Tires still need looking at.
- Forgetting the odometer counts the vehicle, not the tire. If the tires were fitted used, or moved from another position, the miles you enter have to be the miles those tires have run.
Where these numbers come from
Tread depth is a legal minimum with an inspection consequence, not a wear preference — and the minimum differs between steer tires and every other position.
- 49 CFR 393.75 — Tires — The federal minimum tread depth: 4/32 in on a steer axle, 2/32 in elsewhere, plus the conditions that put a tire out of service.
- U.S. Tire Manufacturers Association — Industry guidance on inflation, rotation, retreading and what actually drives wear rate.
Why is the steer axle minimum deeper than other axles?
Steer tires handle steering and the majority of braking traction, especially in wet conditions, so federal rules require more tread depth margin than drive or trailer axles.
My tires seem to be wearing faster than this predicts — why?
Underinflation, misalignment, aggressive braking, and heavier-than-average loads all accelerate wear beyond a simple straight-line projection — treat a widening gap between predicted and actual wear as a sign to check alignment and inflation.
Estimates only, based on a straight-line wear projection. Always measure tread depth directly with a gauge before making a run/no-run decision — don't rely on a mileage projection alone.