You can predict when a truck tire needs replacing from three numbers: where its tread started, where it is now, and how far it has run. Fleets that track truck tire tread depth and wear rate plan replacements instead of handling emergencies.
In my years working with tires, the fleets with the lowest tire costs were rarely the ones with the best tires. They were the ones that measured. Tread depth is the simplest measurement you can take, and with a little arithmetic it tells you when each tire will need replacing. Here is how I do it.
Step 1: find the original tread depth (OTD)
OTD is the tread depth of a new tire, as published by the manufacturer. It depends on the brand, size and pattern, so a size alone is not enough: one size can come in several patterns with different depths. Look it up in the Original Tread Depth Database by choosing the brand, size and pattern. Values are often published in 32nds of an inch, so convert: 1/32 in = 0.79375 mm, which makes 20/32 in about 15.9 mm.
Step 2: measure today’s tread depth
Measure the remaining tread depth (RTD) with a depth gauge at the same positions each time, and write down the odometer reading. Compare readings from the same tire over time rather than across different tires.
Step 3: do the math
wear rate (km per mm) = distance run ÷ (OTD − RTD)
remaining km = (RTD − replacement depth) × wear rate
A worked example (illustrative numbers)
A steer tire started at 15.9 mm, now measures 8.0 mm and has run 60,000 km. Your policy replaces tires at 3.0 mm.
| Item | Value |
|---|---|
| Tread used (15.9 − 8.0) | 7.9 mm |
| Wear rate (60,000 ÷ 7.9) | about 7,600 km per mm |
| Usable tread left (8.0 − 3.0) | 5.0 mm |
| Remaining distance (5.0 × 7,600) | about 38,000 km |
| Estimated total life (60,000 + 38,000) | about 98,000 km |
Read the result with care
This method assumes the tire keeps wearing at the same rate. Wear usually changes with load, tire pressure, alignment, axle position and road conditions, so treat the answer as an estimate and re-measure every few weeks. A tire that wears much faster than its twin on the same axle points to a mechanical problem to fix, not just a replacement to schedule. Always follow your own replacement policy and the local legal minimum tread depth.
Let the tool do it
Enter both depths and the mileage into the Tire Performance tool and compare two tires side by side by axle position. Then use the expected total life in the Tire CPK Equalizer to see which tire really costs less per kilometer.
Why Tracking Tread Depth Pays Off
A tire that is replaced too early wastes usable rubber, and one that is replaced too late risks safety, fines and casing damage. Tracking depth over time lets you plan purchases, schedule replacements during planned service, and spot problems on a single tire before they become expensive. It also gives you your own mileage data, which is far more reliable than a brochure figure when you compare tires with the cost per kilometer method described in our guide to truck tire cost per km.
How to Measure Tread Depth Correctly
- Check pressure first. A tire at the wrong pressure can wear unevenly, and a gauge reading is only useful when you know the tire was in its normal condition.
- Use a proper depth gauge. Press the base flat across the tread and push the pin to the bottom of a main groove.
- Measure several points. Take readings across the tread width (inner, center and outer grooves) and at three or more points around the circumference.
- Record the lowest and the average. The lowest reading decides when the tire must be removed. The average is better for calculating wear rate.
- Write down the odometer reading with every measurement, so distance and depth stay linked.
What the Wear Rate Tells You
Wear rate in kilometers per millimeter is the number I trust most. A high figure means the tire lasts longer per millimeter of tread. Compare it between tires on the same axle and between axle positions. Steer, drive and trailer tires wear at different rates, because they work differently, so compare like with like.
If one tire wears much faster than its neighbor, look for a mechanical cause. Low pressure, misalignment, worn suspension parts and a bent wheel can all show up as fast or uneven wear. Our article on wheel alignment savings explains what to check.
Reading Irregular Wear
- Wear on both shoulders: usually underinflation.
- Wear in the center: usually overinflation.
- One-sided shoulder wear or feathering: often alignment, toe or camber problems.
- Cupping or scalloping: often worn suspension parts, out-of-balance wheels or loose components.
When the pattern is irregular, a single average depth hides the problem. This is why I measure at several points and write the readings down.
Choosing the Replacement Depth
Your replacement depth should never be below the legal minimum, and many fleets set a higher limit for safety and for casing protection. Legal minimums vary by country and by axle position. For example, many regions use 1.6 mm, and some rules in the United States require at least 4/32 in (about 3.2 mm) on steer tires. Always check the rules that apply to your vehicles and follow your own replacement policy.
If you plan to retread, remove the tire earlier, while the casing is still protected by tread. A casing worn down to the belts is much less likely to qualify.
A Simple Tread Depth Log
A spreadsheet is enough. I suggest these columns:
- Tire ID and brand, size and pattern
- Vehicle and axle position
- Date and odometer reading
- Tread depth readings (inner, center, outer)
- Tire pressure at the time of the reading
- Notes on damage, repairs or irregular wear
After three or four readings per tire, your wear rate becomes more reliable, and you can forecast how many tires you will need over the next quarter.
How I Use the Forecast
With remaining distance estimates for each tire, I group vehicles by when their tires will reach the replacement depth. This lets the fleet buy in planned batches, negotiate better prices and fit tires during scheduled service instead of emergency stops. A truck that is due in 10,000 km can be scheduled for the next maintenance window rather than discovered at the roadside. Treat each forecast as an estimate and update it after every new measurement.
Comparing Two Tires With Tread Depth Data
Here is how I use measurements to compare brands. These numbers are illustrative. Tire A is the steer tire from the worked example: it started at 15.9 mm, is now at 8.0 mm after 60,000 km, and has an estimated total life of about 98,000 km. Tire B, from a different brand, started at 16.5 mm and is now at 9.0 mm after the same 60,000 km, which is 7.5 mm used and a wear rate of 8,000 km per mm. With a replacement depth of 3.0 mm, its usable tread is 13.5 mm, so its estimated total life is about 108,000 km.
If Tire A costs 420 USD and Tire B costs 470 USD, the cost per 1,000 km is about 4.29 for Tire A and 4.35 for Tire B. The longer-lasting tire is not automatically cheaper once its higher price is included. This is the kind of insight you only get when you measure, and the Tire CPK Equalizer lets you run the comparison with your own numbers.
Common Mistakes to Avoid
- Measuring only one point on the tire and assuming the rest is the same.
- Forgetting to record the odometer, which makes the wear rate impossible to calculate.
- Comparing steer tires with drive or trailer tires.
- Ignoring uneven wear and replacing the tire without fixing the cause.
- Using a measurement taken once and never updating the forecast.
FAQ
What is original tread depth?
It is the tread depth of a new, unworn tire as published by the manufacturer for that brand, size and pattern.
How often should I measure truck tire tread depth?
Often enough to see a trend. Many fleets measure at every service interval and whenever a tire looks unusual.
Is tire wear always linear?
No. This method assumes a constant rate, so re-measure regularly and treat the result as an estimate, not a guarantee.
