How Much Tread Difference Is Too Much for AWD?

Keep all four tires on an AWD vehicle as closely matched as possible: a tread depth difference greater than about 1–2/32 inch (≈0.8–1.6 mm) or a rolling circumference difference over roughly 1/4 inch (≈6 mm) is commonly considered too much and risks driveline stress. In practice, many automakers advise replacing or shaving tires to keep the set closely matched; always check your owner’s manual for your model’s exact limit.

Why tread mismatch matters on AWD

All-wheel-drive systems assume each tire rolls the same distance per revolution. When one or more tires are effectively larger (more tread) or smaller (less tread), their rolling circumference differs, forcing the center coupling or differential to slip constantly. That ongoing slip generates heat and wear, which can trigger binding, noise, or premature failure of transfer cases, center differentials, clutches, or couplers. It can also confuse ABS/ESC systems and reduce stability in emergencies.

Practical limits and what automakers recommend

Common industry rule of thumb

Across the industry, service departments and tire specialists typically aim to keep AWD tires extremely close in size and wear. The most conservative guidance you’ll hear is to maintain no more than 1–2/32 inch difference in tread depth across the set, or to ensure rolling circumference stays within about 0.25 inch (≈6 mm) tire-to-tire. As a percentage, that’s roughly around 1% (or less) difference in rolling radius for many vehicles.

Examples from automakers

Manufacturers vary in strictness. Subaru guidance, for instance, specifies that the difference in rolling circumference between tires should not exceed about 1/4 inch; they also caution that all four tires must be the same size, construction, and similar wear. Premium full-time systems (e.g., many Subaru and some Audi/older BMW arrangements with mechanical or clutch-based center differentials) tend to be most sensitive. On-demand AWD systems (electronically controlled couplers that engage the rear axle as needed) can be a bit more tolerant but still benefit from tight matching. Always defer to the number in your manual or a marque-specific service bulletin for your model year.

Translating tread depth to circumference

Every 1/32 inch of tread depth difference roughly equates to about 0.20 inch of circumference difference, though construction, inflation, and load can shift real-world results. That’s why a strict 0.25-inch circumference limit can translate to roughly 1–1.5/32 inch of allowable tread difference in some cases.

How to measure tread and rolling difference

You don’t need specialized shop tools to do a quick health check. The steps below show simple ways to measure tread and approximate circumference so you can decide whether you’re within safe limits.

1. Measure tread depth at three points (inner, center, outer) on each tire using a tread gauge; note the average per tire.
2. Compare the average tread depth of the most-worn tire to the least-worn tire to get your set’s spread.
3. Check tire maker data for “revolutions per mile” for your exact model/size; mismatched models can differ even when new.
4. Approximate rolling circumference difference by wrapping a flexible tape around the centerline of each inflated tire (vehicle on the ground), then compare lengths.
5. Confirm pressures are set to spec before measuring; underinflation can skew measurements and harm driveline parts.

If your measurements suggest a spread near or above your brand’s threshold, consider corrective steps before putting more miles on the car.

What to do if the difference is too large

If your AWD tires are outside acceptable limits, you have a few options to protect the drivetrain and restore handling balance.

• Replace all four tires to ensure a matched set in brand, model, size, and load rating.
• Tire shaving: have a new tire shaved to match the remaining tread on the other three, restoring circumference match.
• Replace two tires only if, after mounting, the rolling circumference of all four still falls within your manufacturer’s limit.
• Recalibrate alignment and confirm pressures; mismatches can accelerate uneven wear and re-create the problem.

While replacing all four is often the safest route, shaving or carefully matching two can be cost-effective when the other pair still has substantial life and measurements confirm you’re within spec.

When is replacing just two tires on AWD acceptable?

It can be acceptable on some AWD systems to replace just two tires, but only if stringent matching criteria are met and verified after installation.

• Brand/model match: use the same tire model and size already on the vehicle to minimize rev-per-mile variance.
• Post-install measurement: confirm tread depths and rolling circumference are within your vehicle’s stated limits.
• Positioning: mount the better (newer) pair on the rear axle for stability, unless your manufacturer specifies otherwise.
• System type: on-demand AWD may tolerate slightly more variance than permanent/mechanical AWD, but don’t rely on that; measure.

If you can’t meet these conditions—or measurements show you’re out of bounds—replace all four or shave the new pair to match.

Preventing future mismatches

Simple habits can keep your AWD system happy, prolong tire life, and reduce the chance you’ll face a costly full set replacement prematurely.

• Rotate tires on schedule (often every 5,000–7,500 miles or per the manual) to even out wear.
• Maintain proper inflation; check monthly and before long trips.
• Keep alignment in spec; misalignment accelerates uneven wear and increases circumference spread.
• Replace tires in matched sets (brand/model/size) and avoid mixing types (e.g., winter with all-season).
• Re-measure tread spread at each oil change and after any tire replacement or repair.

Staying ahead of maintenance keeps tread depths aligned and protects expensive AWD components from undue stress.

Notes for hybrids and EVs with dual-motor AWD

Even without a mechanical center differential, dual-motor AWD EVs and hybrids still rely on closely matched tire circumferences for accurate wheel-speed sensing, traction control, and stability systems. Overly mismatched tires can trigger warnings, reduce range, or impair handling. The same matching guidelines and rotation discipline apply.

Summary

AWD vehicles are sensitive to tire size and wear. As a safe rule, keep tread depth within about 1–2/32 inch across the set and rolling circumference within roughly 1/4 inch, with some brands (notably Subaru and certain full-time AWD systems) requiring especially tight matching. If you’re outside limits, replace or shave to match—and always verify with measurements and your owner’s manual. Proper rotation, inflation, and alignment will help you avoid the problem next time.

What tread difference is too much?

If you’re asking because you have an all wheel drive/4-wheel drive vehicle I’d keep it under 2/32 difference if at all possible. If you get up to 4/32 difference you will almost certainly have a problem if you drive that way very many miles.

What is the 7 7 rule for winter tires?

If you leave them on too late, your winter tires will degrade quickly. So, when is the right time to swap? The rule of thumb is 7-for-7: wait until there are seven consistent days at 7 degrees Celsius. The reverse is also true for transitioning to winter.

Do all tires need to match on AWD?

Equal Traction for Better AWD Performance
AWD systems send power to all four wheels to improve traction and control. To work efficiently, all four tires must have the same tread depth , size, and type. Mismatched tires can cause the wheels to rotate at different speeds, which can confuse your AWD system.

Can I just replace two tires in AWD?

Recap: Why You May Need to Replace All Four Tires on Your AWD Vehicle. Mismatched tires are often a primary factor in drivetrain damage. To minimize variances, ensure they all match (same brand, size and type). The tread depth difference between front, rear, left and right tires should be minimal.