Tread Wear Diameter Calculator
Estimate how tire diameter shrinks as tread wears. Enter new and current tread depths to compare diameter loss in mm, inches and percent.
Estimate diameter reduction from tread loss.
Tread Wear Diameter Calculator: Tire Size Inputs
Compare two tire sizes here. Use the formulas and reference tables below for this tool's specific calculation.
How Tread Wear Diameter Calculator Works?
The Tread Wear Diameter Calculator works by doubling the tread depth lost and subtracting the result from the new tire's diameter. The tool uses 3 steps.
Enter the size
Type the size, for example 225/45 R17, for a new diameter of 634.3 mm (24.97 in).
Enter new and current tread
Type the new depth (10/32 in) and the current depth (4/32 in).
Read the worn diameter
The calculator returns a 9.5 mm (0.38 in) loss and a worn diameter of 624.8 mm (24.60 in), −1.50%.
Tread Wear Diameter Calculator Formula
The Tread Wear Diameter Calculator formula is OD_worn = OD_new − 2 × (TD_new − TD_now).
ΔTD = TD_new − TD_nowOD_worn = OD_new − 2 × ΔTDΔ% = −2 × ΔTD ÷ OD_new × 100- TD_new
- New tread depth (mm)
- TD_now
- Current tread depth (mm)
- OD_new
- New diameter (mm)
Worked example
A 265/70 R17 truck tire starts at 802.8 mm with 15/32 in (11.9 mm) of tread. At 5/32 in (4.0 mm), the tire has lost 7.9 mm of tread and 15.9 mm (0.63 in) of diameter, a 1.98% drop.
Tread Wear Diameter Calculator Conversion Table
The Tread Wear Diameter Calculator conversion table shows the diameter of a 225/45 R17 tire at 5 stages of wear.
| Tread state | Diameter (mm) | Diameter (in) | Loss | Change |
|---|---|---|---|---|
| 10/32 in remaining (0/32 worn) | 634.3 mm | 24.97 in | −0.0 mm | -0.00% |
| 8/32 in remaining (2/32 worn) | 631.1 mm | 24.85 in | −3.2 mm | -0.50% |
| 6/32 in remaining (4/32 worn) | 627.9 mm | 24.72 in | −6.3 mm | -1.00% |
| 4/32 in remaining (6/32 worn) | 624.8 mm | 24.60 in | −9.5 mm | -1.50% |
| 2/32 in remaining (8/32 worn) | 621.6 mm | 24.47 in | −12.7 mm | -2.00% |
What is Tread Wear Diameter Calculator?
A Tread Wear Diameter Calculator is a tool that predicts how much shorter a tire becomes as tread wears. A tire loses tread on both the top and the bottom of its circle, so diameter falls by twice the tread lost.
A passenger tire worn from new to the legal limit loses 1.5% to 2% of diameter. A deep-tread truck tire loses 2% to 3%.
The worn diameter explains why speedometer accuracy improves slightly as taller-than-stock tires wear down.
What are the uses of Tread Wear Diameter Calculator?
There are 4 main uses of the Tread Wear Diameter Calculator, including mixed-wear matching and speedometer drift.
Mixed-wear matching
Compare a new tire with a worn tire's real diameter.
Speedometer drift
Track speedometer change over a tire's life.
Clearance planning
Size tires that rub when new and clear when worn.
Ground clearance
Estimate the height lost to tread wear.
Related Tread Wear & Tire Life Tools
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