Do You Have To Replace All 4 Tires On Awd
One of the most frequently debated topics among All-Wheel Drive (AWD) vehicle owners and mechanics is whether you always need to replace all four tires at once. The short answer is: it depends, but generally, yes, it's highly recommended. This article dives into the reasons why, common scenarios, troubleshooting, and best practices to keep your AWD system healthy and prevent expensive repairs.
The AWD System's Sensitivity to Tire Wear
AWD systems are designed to distribute power to all four wheels, improving traction and handling. However, they are also incredibly sensitive to differences in tire circumference. Even slight variations in tire size, caused by uneven wear, can put undue stress on the drivetrain. This stress can lead to premature wear or even failure of expensive components like the transfer case, differentials, and axles.
Problem: Hear a humming or whining noise coming from the center or rear of your AWD vehicle, especially at higher speeds? This could indicate stress or damage within the drivetrain due to mismatched tire sizes.
Cause: The most common cause is replacing only one or two tires, leading to a significant difference in rolling circumference compared to the older tires. Consider a Subaru Outback: its symmetrical AWD system is exceptionally sensitive. Replacing only two tires on an Outback with significant wear on the other two is practically guaranteed to lead to issues. Similarly, even on more forgiving systems like those found in some Honda CR-V models, prolonged differences can still cause problems.
Solution: The ideal solution is to replace all four tires with the same make, model, and size. If you absolutely must replace only one or two tires, there are a few strategies you can try (though they aren't ideal):
- Shaving Tires: Some tire shops offer a service to shave down a new tire to match the remaining tread depth of your existing tires. This is a relatively expensive option but can be cheaper than replacing all four.
- Used Tires: Finding used tires with a similar tread depth and wear pattern to your existing tires can be a temporary solution. Ensure they are the exact same size and load rating as your originals. This option requires careful inspection to ensure the used tires are in good condition and don't have hidden damage.
- AWD Disable: Some older or simpler AWD systems have a fuse or switch that can temporarily disable the AWD function, allowing you to drive in front-wheel or rear-wheel drive until you can replace all four tires. Consult your owner's manual *before* attempting this, as it's not always possible or safe.
Measuring Tire Circumference and Tread Depth
The acceptable difference in tire circumference or tread depth varies depending on the vehicle manufacturer and the type of AWD system. However, a general rule of thumb is to stay within 2/32nds of an inch (approximately 1.6mm) of tread depth between all four tires. Some manufacturers, like Subaru, specify an even tighter tolerance.
Problem: Your AWD warning light illuminates on your dashboard, possibly accompanied by reduced performance or unusual handling.
Cause: Many modern AWD systems are equipped with sensors that monitor wheel speed. Significant differences in wheel speed, caused by mismatched tires, can trigger the warning light and put the system into a protective limp mode. For example, some Audi Quattro systems are notorious for being picky about tire circumference. Even a small difference can trigger an error.
Solution: Start by checking the tread depth of all four tires using a tread depth gauge. If the difference exceeds the recommended tolerance (refer to your owner's manual), replacing all four tires is the safest and most reliable solution. After replacing the tires, the warning light may reset automatically. If not, you may need to use a scan tool to clear the fault codes.
Maintenance and Prevention
Proactive maintenance is key to preventing tire wear issues and protecting your AWD system.
- Regular Tire Rotations: Rotate your tires every 5,000-8,000 miles, following the rotation pattern recommended in your owner's manual. This helps ensure even wear across all four tires.
- Proper Tire Inflation: Maintain the correct tire pressure as specified on the sticker located on your driver's side doorjamb. Underinflated tires wear unevenly and can negatively impact fuel economy and handling.
- Wheel Alignments: Get a wheel alignment check at least once a year, or whenever you notice uneven tire wear or handling problems. Misalignment can cause rapid and uneven tire wear.
- Regular Inspections: Visually inspect your tires regularly for signs of damage, such as cuts, bulges, or embedded objects. Address any issues promptly.
Real-World Considerations
While replacing all four tires is the ideal scenario, budgetary constraints can sometimes make it difficult. In such cases, prioritize addressing the issue as soon as possible and consider the less-than-ideal solutions mentioned above. Driving an AWD vehicle with mismatched tires is like running a marathon with different shoes on each foot – it might work for a while, but eventually, something will break down.
Consider this scenario: You have a Jeep Grand Cherokee with the Quadra-Trac II AWD system. You get a flat tire that's unrepairable. If the other three tires have significant wear (say, less than 6/32nds of tread depth remaining), replacing all four is almost mandatory to avoid potential drivetrain issues. Ignoring this advice could lead to a costly repair bill for the transfer case down the road.
Keeping Your Car in Top Condition
Taking care of your AWD vehicle’s tires is a crucial aspect of overall vehicle maintenance. By following the guidelines outlined in this article, you can minimize the risk of premature wear on your drivetrain components and ensure your AWD system functions optimally for years to come. Remember, regular maintenance, careful attention to tire wear, and prompt attention to any unusual noises or warning lights are the keys to keeping your AWD vehicle in top condition and avoiding expensive repairs. Always consult your vehicle's owner's manual for specific recommendations regarding tire replacement and AWD system maintenance.