Do you really need to replace all four tires on an AWD?

Often yes—AWD systems generally perform best and last longest with four matching tires—but it isn’t always mandatory to replace all four. If the remaining tires are nearly new and the difference in tread depth or rolling circumference stays within your vehicle maker’s limits, you can sometimes replace just one or two tires (or shave a new tire to match). The right choice depends on the specific AWD system, the wear on your current tires, and the manufacturer’s tolerances.

Why AWD systems care about matching tires

All-wheel-drive vehicles distribute power to all four wheels, and even small differences in tire size cause the system to work harder. That added workload can translate into heat, wear, and eventual damage to components like the center differential or clutch packs.

• Rolling circumference mismatches make one wheel effectively “longer” or “shorter,” forcing the AWD system to slip or bind constantly to compensate.
• Center differentials, transfer cases, and on-demand clutch packs can overheat or wear prematurely when correcting continuous speed differences.
• ABS and stability control are calibrated for matching tire sizes; mismatched tires can degrade braking and handling behavior.
• Warranty concerns: some manufacturers warn that significant tire-size differences can void coverage for related drivetrain components.

Because AWD systems are sensitive to size differences, keeping tires closely matched reduces stress on expensive hardware and preserves predictable handling.

How much difference is acceptable?

Automakers and tire makers usually specify limits for tread-depth or circumference differences. While exact thresholds vary by brand and model, several common guidelines appear across owner’s manuals and service bulletins.

• Tread depth difference: commonly no more than 2/32 to 3/32 inch between any two tires.
• Rolling circumference or diameter: often within about 1% of each other; Subaru has historically cited approximately 1/4 inch allowable difference in circumference among tires.
• Brand/model consistency: many manufacturers require the same size, load index, and speed rating, and strongly recommend the same brand and model across all four positions.

Always check your owner’s manual or a dealership service department for the exact specification for your vehicle, since some systems (e.g., on-demand AWD vs. full-time AWD) have different tolerances.

When you can replace fewer than four tires

If the existing tires have minimal wear and are evenly matched, you may not need a full set. In specific situations, a single or pair replacement—sometimes with tire shaving—can be safe and manufacturer-compliant.

• Remaining tires are nearly new: if they’re within 2/32 inch of a new tire, replacing one or two may be fine.
• Tire shaving: a shop can shave a new tire’s tread to match the worn ones, bringing all four into spec without buying a full set.
• Exact match: the replacement tire should be the same brand, model, size, load index, and speed rating to keep rolling circumference and performance characteristics aligned.
• Even wear: if the three old tires are evenly worn (e.g., all at 7/32 inch) and within spec of the shaved new tire, the AWD system won’t be forced to compensate.

If measurements or brand/model mismatches put you outside the manufacturer’s limits, replacing all four is the safest choice to prevent driveline stress and uneven handling.

Practical decision steps

Use these steps to decide whether you can replace fewer than four tires without risking AWD damage or safety issues.

1. Measure tread depth on all current tires at multiple points across the tread using a gauge.
2. Compare the deepest and shallowest readings; note the gap versus a new tire’s typical 10/32 to 12/32 inch depth (varies by tire).
3. Check your owner’s manual or dealer for allowable tread-depth or circumference differences for your AWD system.
4. If within spec, replace one or two tires with the exact same model; if slightly outside spec, ask a tire shop about shaving the new tire(s) to match.
5. If clearly outside spec—or if tires are mixed brands/models—replace all four to protect the drivetrain and maintain handling.
6. Get an alignment and resume regular rotations (typically every 5,000–7,500 miles) to keep wear even.

Following a measurement-first approach ensures your decision is grounded in your vehicle’s limits rather than guesswork or one-size-fits-all advice.

Cost, safety, and warranty considerations

Beyond the technical limits, weigh the financial and safety implications before deciding.

• Cost trade-off: shaving a new tire and replacing one or two can be cheaper than a full set, especially if the other tires have plenty of life left.
• Safety: mixing brands or models can alter grip and wet-weather performance; even if sizes match on paper, compounds and tread patterns may not.
• Warranty exposure: if a drivetrain issue arises and tires were outside spec, manufacturers may deny related claims.
• Future rotation: four matching tires simplify rotations and keep wear even, extending tire life overall.

If you plan to keep the vehicle long term, four matching tires often pay for themselves in reduced drivetrain risk and consistent handling.

What about advice you see on Reddit?

Discussions on Reddit often split into two camps: replace all four to be safe, or replace fewer if the wear difference is tiny or if you shave new tires to match. While many anecdotes are useful, your best guide is your vehicle’s documented tolerance and a trusted tire shop that can measure tread depth precisely and advise on shaving. Treat online threads as starting points, not definitive policy.

Bottom line

AWD systems need closely matched tires. Replace all four if your tread-depth or circumference differences exceed the manufacturer’s limit or if you can’t match brand/model. If the remaining tires are nearly new and within spec, replacing one or two—ideally with tire shaving—can be acceptable. When in doubt, measure and consult your manual or dealer.

Summary

You don’t always have to replace all four tires on an AWD, but you do need all four to be closely matched. If tread-depth or circumference differences are minimal (commonly within 2/32–3/32 inch or around 1% circumference) and you can use the same tire model, you may replace fewer than four or shave a new tire to match. Outside those limits, a full set is the safest, most reliable choice.