AWD Tire Matching Comparator
Compare tread depth and circumference of AWD tires against vehicle-specific limits. Convert 32nds to mm and check circumference gap.
Compare measurements against vehicle-specific limits.
AWD Tire Matching Comparator: Tire Size Inputs
Compare two tire sizes here. Use the formulas and reference tables below for this tool's specific calculation.
How AWD Tire Matching Comparator Works?
The AWD Tire Matching Comparator works by converting each tire's tread depth into a circumference value and testing the largest gap against the vehicle maker's limit. The comparison has 4 steps.
Enter the maker's limit
Type the limit from the owner's manual, for example 2/32 in (1.6 mm) tread depth or 6 mm (1/4 in) circumference.
Enter 4 tread readings
Type the tread depth of each tire, or measured circumferences.
Convert tread to circumference
The comparator multiplies the tread gap by 2 and by π.
Check the gap
The comparator reports the largest gap between any 2 tires and a pass or fail against the limit.
AWD Tire Matching Comparator Formula
The AWD Tire Matching Comparator formula is ΔC = 2 × π × ΔTD, where ΔTD is the tread depth gap between 2 tires.
ΔOD = 2 × ΔTDΔC = π × ΔOD = 2π × ΔTDTD_mm = n ÷ 32 × 25.4- ΔTD
- Tread depth gap (mm)
- n
- Tread depth in 32nds of an inch
- ΔC
- Circumference gap (mm)
Worked example
A new tire at 10/32 in (7.9 mm) next to a worn tire at 7/32 in (5.6 mm) gives a 3/32 in (2.4 mm) gap. The circumference gap is 2 × π × 2.4 = 15.0 mm (0.59 in), more than double a 6 mm limit.
AWD Tire Matching Comparator Conversion Table
The AWD Tire Matching Comparator conversion table converts 7 tread depth gaps into the circumference gap an AWD system sees.
| Tread gap | Diameter gap | Circumference gap | Share of a 225/55 R18 circumference | 6 mm limit |
|---|---|---|---|---|
| 0/32 in (0.0 mm) | 0.0 mm | 0.0 mm (0.00 in) | 0.00% | Within 6 mm |
| 1/32 in (0.8 mm) | 1.6 mm | 5.0 mm (0.20 in) | 0.23% | Within 6 mm |
| 2/32 in (1.6 mm) | 3.2 mm | 10.0 mm (0.39 in) | 0.45% | Over 6 mm |
| 3/32 in (2.4 mm) | 4.8 mm | 15.0 mm (0.59 in) | 0.68% | Over 6 mm |
| 4/32 in (3.2 mm) | 6.3 mm | 19.9 mm (0.79 in) | 0.90% | Over 6 mm |
| 6/32 in (4.8 mm) | 9.5 mm | 29.9 mm (1.18 in) | 1.35% | Over 6 mm |
| 8/32 in (6.3 mm) | 12.7 mm | 39.9 mm (1.57 in) | 1.80% | Over 6 mm |
What is AWD Tire Matching Comparator?
An AWD Tire Matching Comparator is a tool that checks whether 4 tires on an all-wheel-drive vehicle are close enough in size to protect the drivetrain. AWD systems with a viscous coupling, center differential or clutch pack heat up when tires roll at different speeds.
Vehicle makers state limits in different units. Some list a tread depth gap in 32nds of an inch, some list a circumference gap in mm, and some list a percent. The comparator converts between all 3.
A single damaged tire on an AWD car often forces a 4-tire purchase or tire shaving. The comparator shows which option meets the limit.
What are the uses of AWD Tire Matching Comparator?
There are 4 main uses of the AWD Tire Matching Comparator, including single-tire replacement and tire shaving decisions.
Single-tire replacement
Decide whether 1 new tire fits with 3 worn tires.
Tire shaving decisions
Find the tread depth a new tire must be shaved to.
Rotation scheduling
Keep wear even across 4 tires.
Warranty records
Document compliance with the AWD maker's limit.
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