How much difference in tire size is acceptable on AWD?
On all‑wheel‑drive (AWD) vehicles, the drivetrain and handling are designed around tires with nearly identical size and circumference. In practice, the safest approach is to run four identical tires. If you cannot, aim to limit the difference in rolling circumference to about 2–3% across tires, and follow the vehicle maker’s guidance. This article explains the limits, why they matter, and how to handle tire changes on AWD systems.
What counts as a tire size difference on AWD?
When people talk about tire size differences, they are usually referring to two measurements: the nominal tire size printed on the sidewall (width:aspect ratio:Rim diameter) and the resulting overall diameter or rolling circumference once the tire is mounted and inflated. Even small differences in diameter between tires can translate into differences in rolling circumference, which AWD systems monitor and compensate for. The critical point is not just the label on the tire, but how the tire’s actual diameter compares with the others on the vehicle.
Manufacturers often set strict requirements because mismatched tires can cause the center differential, clutch packs, or torque-vectoring systems to work harder. That can lead to uneven wear, drivetrain binding, or reduced traction control effectiveness. As a result, most automakers and tire professionals recommend keeping all four tires the same size and, ideally, of the same model and tread pattern.
General guidelines from manufacturers and tire experts
Before listing common recommendations, note that exact tolerances vary by model and AWD system (center differential, viscous coupling, or electronically controlled multi‑plate couplings). The guidance below reflects typical industry standards and practical advice used by tire shops and manufacturers.
- Match all four tires in size, model, and tread pattern on AWD vehicles whenever possible.
- If you must replace only two tires, install them on the rear axle (or as advised by the vehicle’s manual) and choose tires with a circumference as close as possible to the existing tires—aim for roughly within a 2% difference.
- Avoid mixing tire brands or tread types on AWD unless the manufacturer explicitly allows it for your model.
- Replacing just one tire is not recommended for most AWD systems, as the imbalance can place extra load on the differential and drivetrain components.
Concluding guidance: following these recommendations helps minimize drivetrain stress, preserves handling balance, and reduces the risk of transmission or differential wear. If your vehicle’s owner manual provides a specific tolerance, always follow that value over general guidance.
Why the 2–3% figure matters
The 2–3% threshold translates to a small difference in the tire’s overall diameter and circumference. For example, a typical 25-inch overall diameter tire would tolerate about a half-inch difference in diameter at most, spread across all tires. Exceeding this can cause the center differential to work harder to equalize wheel speeds, potentially leading to uneven wear and drivetrain stress over time.
What to do if you already have mixed sizes on an AWD vehicle
If you’ve already mixed sizes or tread depths, consider the following steps to minimize risk and preserve drivetrain life.
- Measure and compare actual diameters or use the rolling circumference calculation to estimate the difference. If the largest and smallest tire differ by more than about 2–3%, plan a replacement to restore balance.
- Check your vehicle’s manual or consult the dealer for the official tolerance and recommended replacement strategy for your model.
- When possible, replace tires to restore a uniform set (ideally all four) rather than mixing sizes long‑term.
- Avoid aggressive driving or heavy torque loads while the mismatch persists, as this can accelerate wear on the AWD components.
Bottom line: mixed sizes on AWD are not ideal and should be corrected as soon as feasible to protect the drivetrain and maintain consistent handling.
Practical tips for maintaining AWD tire health
These practical tips help minimize risk when tire changes are unavoidable or you’re shopping for replacements.
- Use the same tire size on all four corners, and ensure the tires have similar tread depth and wear.
- When replacing two tires, place the new tires on the rear axle if your vehicle’s platform and manual permit it, and choose a matching size as close as possible to the existing tires.
- Consider all-season or dedicated winter tires in matching sizes for seasonal changes to keep consistent performance year‑round.
- Periodically rotate tires according to the vehicle’s maintenance schedule and maintain proper tire pressures to minimize rolling circumference differences due to wear or pressure changes.
If you’re unsure about the correct approach for your specific model, consult the owner’s manual or contact the manufacturer or a qualified tire technician. They can provide model‑specific tolerances and installation recommendations.
Summary
For AWD vehicles, the best practice is to run four identical tires in size, type, and wear. If that isn’t possible, limit the rolling circumference difference to roughly 2–3% across tires and follow the vehicle manufacturer’s guidance. Replacing in a way that minimizes drivetrain stress—typically by placing new tires on the rear axle and aiming for the closest possible match in diameter—is advisable. When in doubt, consult your owner’s manual or a trusted tire professional to ensure you protect your AWD system and maintain reliable handling.
Related note: the importance of OEM guidance
Because AWD systems vary (center differentials, transfer cases, torque-vectoring), always prioritize the guidance provided by your vehicle’s manufacturer for tolerance levels and replacement strategies. This ensures your AWD system operates as designed and preserves safety and performance across seasons.
