Which maintenance principle is indicated by the 3/8 inch tolerance for dual tires?

• A. Tires on an axle should not differ by more than 3/8 inch in diameter
• B. You can mix tires of different diameters
• C. Only tread depth matters
• D. Only front tires matter

Answer: (A)

Keeping dual tires on the same axle within a small size difference is crucial because those two tires must rotate together and share the load evenly. The 3/8 inch tolerance tells you how close their diameters need to be. When the difference exceeds this limit, one tire will travel farther per rotation than its mate, causing uneven load distribution, extra heat, and vibration. That can lead to accelerated wear, tire damage, and even safety issues like reduced braking effectiveness or steering stability. Staying within the 3/8 inch limit helps ensure both tires grip and wear evenly, protecting the tire, the axle, and the suspension during all driving conditions.

Mixing tires of different diameters would force the pair to rotate at different speeds, which is unsafe and causes uneven wear. Tread depth alone doesn’t capture diameter differences that affect rotation and load sharing. This principle applies to any axle with dual tires, not just a specific position like the front.