Can You Run Different Size Tires on an AWD Car?

Generally, no, it is not recommended to run different size tires on an All-Wheel Drive (AWD) car. Doing so can cause significant damage to the vehicle's drivetrain components.

Why Tire Matching is Crucial for AWD Vehicles

AWD systems are designed to distribute power to all four wheels, often relying on precise rotational speed differences between the front and rear axles. When all tires are the same size and properly inflated, they rotate at very similar speeds (allowing for slight differences during turns). However, if tires of different diameters are used, they will inherently rotate at different speeds when traveling in a straight line.

This constant speed difference forces the differentials and transfer case—critical components that manage power distribution—to work overtime to compensate. While some AWD systems are more forgiving than others, this continuous stress generates excessive heat and accelerates wear on these expensive parts, potentially leading to premature failure.

The Risks of Mismatched Tires on AWD

Running different size tires on an AWD vehicle can lead to a variety of detrimental effects:

• Drivetrain Damage: The most significant risk is accelerated wear or outright failure of the transfer case, differentials, and potentially the transmission. These components are not designed for sustained internal slippage caused by inconsistent tire diameters.
• Reduced Fuel Economy: The drivetrain components constantly working to compensate for mismatched tire speeds will increase friction and heat, leading to reduced fuel efficiency.
• Compromised Handling: Mismatched tires can negatively affect the vehicle's handling characteristics, stability, and braking performance, particularly in adverse conditions.
• Voided Warranty: Many manufacturers explicitly state in their warranties that using mismatched tires on an AWD vehicle will void the drivetrain warranty.

Exceptions and Important Considerations

While the general rule is to always use the same size tires on all four wheels of an AWD vehicle, there are rare exceptions:

• Factory-Designed Staggered Setups: A very select few AWD vehicles, notably some performance models from manufacturers like BMW, come from the factory with "staggered" wheel and tire setups (e.g., wider tires on the rear axle than the front). In these specific cases, the vehicle's AWD system is specially engineered to accommodate the slight differences in the overall rolling circumference, or the tire manufacturers have meticulously matched the rolling circumference of the front and rear tires despite differing widths. It is crucial to understand that if your vehicle did not come with a staggered setup from the factory, you should not attempt to create one.
• Owner's Manual: Regardless of any general advice, the most definitive source of information for your specific vehicle is its owner's manual. It will outline the manufacturer's precise recommendations for tire sizing, rotation, and maintenance for your AWD system. Always consult it to be safe.

Understanding Tire Diameter and Wear

Even tires of the "same size" can have slightly different effective diameters due to variations in manufacturing, tire wear, and inflation pressure. For AWD vehicles, it's not just about the numbers printed on the sidewall; it's about the actual rolling circumference. Significant differences in tread depth between tires can also cause issues. For instance, putting two brand-new tires on one axle and two half-worn tires on the other axle of an AWD car can be as problematic as using physically different sized tires, due to the difference in overall rolling diameter.

Best Practices for AWD Tire Maintenance

To ensure the longevity and performance of your AWD vehicle, adhere to these tire maintenance guidelines:

1. Replace All Four Tires Simultaneously: When it's time for new tires, replace all four at once to ensure consistent diameter and tread depth across the vehicle.
2. Maintain Consistent Inflation: Properly inflate all tires to the manufacturer's recommended pressure. Under or over-inflated tires will have a different rolling diameter.
3. Regular Tire Rotation: Follow your owner's manual for regular tire rotations. This helps ensure even wear across all four tires, maintaining consistent rolling diameters.
4. Check Tread Depth: Monitor tire tread depth. If one tire is significantly more worn than the others (e.g., due to a non-repairable flat that required individual replacement), consider replacing all four if the difference is substantial.

Quick Guide: AWD Tire Do's and Don'ts

Following these guidelines will help protect your AWD system and ensure your vehicle operates safely and efficiently.