AWD Tire Size Tolerance Calculator
Verify if different tires or tread wear levels are within the strict circumference limits for All-Wheel Drive vehicles.
Quick Answer
Subaru requires all four tires to be within 0.25 inches (¼ inch) of rolling circumference of each other. If you have three tires with 6/32" tread remaining and try to replace one blown tire with a brand new 10/32" tire, the circumference difference is approximately 0.78 inches — resulting in a Fail verdict that could damage your AWD system.
Generic AWD (typical — 1.0%)
Examples:
Common Manufacturer AWD Tire Tolerances
| Vehicle Brand | Max Tread Depth Diff | Max Circumference Diff |
|---|---|---|
| Subaru (Symmetrical AWD) | 2/32 inch | ¼ inch |
| Audi (Quattro) | 4/32 inch | ½ inch |
| BMW (xDrive) | 2/32 inch (or 1% diameter) | ≈ ⅓ inch |
| Toyota (AWD models) | 3/32 inch | ⅜ inch |
| Honda (Real Time AWD) | 2/32 inch | ¼ inch |
| Porsche (Quattro / Haldex) | 30% treadwear max | Varies by model |
Formula
Circumference Difference (in) = (Diameter 1 × π) − (Diameter 2 × π)
- Diameter = overall tire diameter adjusted for tread loss (subtract tread depth loss × 2)
- π = 3.14159
- Example: A 0.25-inch diameter difference × 3.14159 = 0.78 inches circumference difference