Tread Wear Diameter Calculator
See how worn tread makes the tire shorter. Use the calculator below. Results update as you type.
Overall Diameter = (Rim Diameter × 25.4) + 2 × (Width × Aspect Ratio / 100)How the Tread Wear Diameter Calculator Works
This calculator works by doubling the tread depth lost and subtracting it from the new tire's diameter. Tread wears from both the top and bottom of the tire's circle.
- Enter the tire size, for example 265/70R17 (31.61 in new).
- Enter the new tread depth, for example 12/32 in.
- Enter the current tread depth, for example 4/32 in.
- Read the worn diameter: 31.11 in, a change of −1.58%.
The Formula
The formula is Worn Diameter = New Diameter − 2 × Tread Lost.
Tread Lost = Depth_new − Depth_now Worn Diameter = D_new − 2 × Tread Lost Change (%) = −2 × Tread Lost ÷ D_new × 100 Overall Diameter = (Rim Diameter × 25.4) + 2 × (Width × Aspect Ratio / 100)Worked example: an 18/32 in to 4/32 in wear loses 14/32 in (11.1 mm) of tread and 0.88 in of diameter, or −2.77%.
Conversion Table
The conversion table shows diameter loss for 9 wear stages on a 265/70R17. Losses run from 0.12 in (−0.40%) to 0.88 in (−2.77%).
Mud-terrain tires that start at 18/32 in lose the most diameter over their life. A tire worn from new to 2/32 in can lose 2% of its diameter.
| Tread Change | Depth Lost (mm) | Diameter Lost (in) | Worn Diameter (in) | Change |
|---|---|---|---|---|
| 12/32 → 10/32 | 1.6 | 0.12 | 31.48 | -0.40% |
| 12/32 → 8/32 | 3.2 | 0.25 | 31.36 | -0.79% |
| 12/32 → 6/32 | 4.8 | 0.38 | 31.23 | -1.19% |
| 12/32 → 4/32 | 6.3 | 0.50 | 31.11 | -1.58% |
| 12/32 → 2/32 | 7.9 | 0.62 | 30.98 | -1.98% |
| 10/32 → 6/32 | 3.2 | 0.25 | 31.36 | -0.79% |
| 10/32 → 2/32 | 6.3 | 0.50 | 31.11 | -1.58% |
| 18/32 → 10/32 | 6.3 | 0.50 | 31.11 | -1.58% |
| 18/32 → 4/32 | 11.1 | 0.88 | 30.73 | -2.77% |
What Is the Tread Wear Diameter Calculator?
The Tread Wear Diameter Calculator is a tool that estimates how much smaller a tire gets as the tread wears. A worn tire has a smaller diameter and turns more times per mile.
Worn tires make the speedometer read slightly high, and a mix of worn and new tires creates an axle mismatch on AWD vehicles.
Common Uses
This calculator has 4 uses: AWD replacement checks, speedometer checks, clearance checks and lifetime planning.
- Check AWD replacements: Compare worn and new diameters.
- Check speedometers: Estimate the effect of wear.
- Check clearance: Know a new tire is taller than the worn one.
- Plan tire life: Track diameter over the tire's life.