Do You Need To Replace All 4 Tires On Awd
The age-old question for owners of all-wheel drive (AWD) vehicles: do you really need to replace all four tires at once? The short answer, frustratingly, is: it depends. However, understanding why it depends is crucial to preserving your AWD system and avoiding potentially expensive repairs down the line.
Why All Four Tires Matter on AWD Vehicles
Unlike two-wheel drive (2WD) vehicles where tire wear differences primarily affect handling and braking performance, on an AWD system, mismatched tire circumferences can create significant mechanical stress. AWD systems are designed to distribute power to all four wheels, but they do so based on the assumption that all wheels are rotating at roughly the same speed. When one or more tires are significantly more worn than the others, their rolling circumference decreases. This means they have to rotate faster to cover the same distance as the newer, larger tires.
This difference in rotational speed tricks the AWD system into thinking that one axle is slipping relative to the other. In response, the system constantly engages its clutches and differentials, attempting to compensate for a perceived traction difference that doesn't actually exist. Over time, this constant engagement leads to premature wear and tear on the AWD components, including the transfer case, differentials, and even the transmission itself. Think of it like forcing a team of horses to run at the pace of the slowest one – it strains the entire team.
Acceptable Tire Wear Differences: The 3/32nds Rule and Beyond
The generally accepted guideline is that the difference in tread depth between the tires on an AWD vehicle should not exceed 3/32 of an inch. This is a conservative estimate, but it's a good rule of thumb to follow. Some manufacturers are even stricter. Consult your owner's manual for specific recommendations regarding tire replacement and wear limits for your particular vehicle model. For instance, Subaru, known for their symmetrical AWD systems, are particularly sensitive to tire diameter variations. Ignoring this can lead to shuddering, vibration, and ultimately, damage to the center differential.
How do you measure the difference? A simple tire tread depth gauge is an inexpensive and essential tool for any AWD owner. Measure the tread depth of each tire in multiple locations (inner, center, and outer) and compare the measurements. If the difference exceeds 3/32”, it's time to consider replacing all four tires.
When You *Might* Get Away with Replacing Only Two
There are very few situations where replacing only two tires on an AWD vehicle is acceptable. These situations require extremely careful consideration and measurement. First, if your tires are relatively new and only one tire is damaged beyond repair (e.g., a sidewall puncture), you *might* be able to shave down a new tire to match the tread depth of the remaining tires. This is a specialized service offered by some tire shops. However, it's crucial that the shaved tire matches the exact tread depth of the others, within that critical 3/32” tolerance. Second, some shops use a tire shaver. Never try this on your own.
Another option, although less ideal, is to find a used tire with the matching tread depth and tire specifications (size, load rating, speed rating) as your existing tires. This is a risky proposition, as you have no guarantee of the tire's history or internal condition.
Alternatives to Full Replacement: Rotating and Maintaining
Proactive tire maintenance is key to minimizing the risk of needing to replace all four tires prematurely. Regular tire rotations, every 5,000-8,000 miles, help ensure even wear across all four tires. Proper inflation pressure is also crucial, as under-inflated tires wear faster on the edges, while over-inflated tires wear faster in the center. Check your tire pressure regularly, especially with changes in temperature.
Furthermore, addressing any suspension or alignment issues promptly is essential. Misaligned wheels can cause uneven tire wear, leading to the need for premature replacement. A simple wheel alignment check can save you money in the long run by maximizing tire life.
The Cost of Neglect vs. The Cost of Prevention
While the cost of replacing four tires can seem daunting, it pales in comparison to the cost of repairing or replacing a damaged transfer case or differential. A new set of tires, properly maintained, is an investment in the longevity and reliability of your AWD system. Neglecting tire wear differences can lead to thousands of dollars in repairs. In the long run, paying attention to your tires is the most cost-effective approach to maintaining your AWD vehicle.