Mismatched tire circumference, not brand loyalty, damages an all-wheel-drive drivetrain — so the safest buy is four identical tires that match the door placard exactly.
AWD systems constantly compare wheel speeds, and a tire rolling at a different rate makes the system compensate for a difference that never goes away. Subaru’s owner documentation warns that mismatched size, circumference, or construction can damage the drivetrain and throw off handling, braking, and your speedometer.
What follows is the matching standard, the replacement math, and the winter-tire rule AWD does not excuse you from.
The Matching Specs That Actually Matter
Every tire should match in size, construction, load index, speed rating, brand, model, and tread pattern — and the door placard plus owner’s manual outrank whatever is currently bolted on. Read the placard on the driver’s door jamb, cross-check the manual, and buy to those numbers, since a previous owner may have gone off-spec. Confirm four things:
- Front-to-rear fitment. Some vehicles use a staggered setup; don’t “correct” a factory arrangement.
- Load index and speed rating. Identical nominal size doesn’t mean identical ratings, and the wrong load range changes how the tire carries weight.
- Tire type. Michelin advises against mixing all-season, all-terrain, and winter tires on a four-wheel-drive vehicle.
- Rolling circumference. Two tires stamped 225/65R17 can still differ in revolutions per mile.
To start from vetted options, our roundup of tested all-wheel-drive tires narrows the field by vehicle type and duty.
How Many Tires Do You Actually Replace?
Replace all four whenever tread depths differ meaningfully or you’re switching models — one or two tires is a narrow exception, not a budget strategy. Measure tread depth on all four first:
- All four. The default for uneven wear or a brand/model change; Subaru recommends replacing all four together.
- One tire. Only if it exactly matches the other three, which must be nearly new.
- Two tires. Only if the manufacturer permits it — and the deeper-tread pair goes on the rear axle, even on AWD, to guard against oversteer on wet roads.
Most shops work from a circumference difference of about 1/4 inch, roughly 2/32 inch of tread depth. A stricter manufacturer’s number wins — some manuals call for matching rolling radius or hold tread depth within 4/32 inch. Michelin’s general four-wheel-drive guidance allows up to 1 inch of circumference difference absent vehicle-specific instructions, but that’s a ceiling, never a target.
Tire shaving closes the gap when one tire must go and the other three are half worn: a specialist grinds the new tire’s tread to match, typically $25–$35 per tire. Shaving fixes tread depth only — size, model, construction, load rating, and speed rating still must match.
Winter Tires On AWD: Where The Rules Get Missed
Four winter tires are required, not two — AWD helps you accelerate on snow and does nothing for stopping or turning. Subaru calls for four matching winter tires in the same size, construction, brand, and load range. Michelin recommends fitting them once temperatures settle below 45°F and replacing at the wear indicator or 2/32 inch, the US legal minimum. Two winter tires on the front of an AWD car produce exactly the imbalance the system corrects: longer stopping distances and instability in a slide.
The 2/32-inch legal threshold is not an AWD service limit — drivetrain matching can demand replacement earlier, the moment tires differ materially in tread depth or circumference.
Mounting Day: What To Check Before You Drive Off
- Record placard and manual specs before you leave.
- Measure all four tread depths and note them.
- Compare the new tires’ circumference or revolutions per mile against the ones staying on the car.
- Have the tires professionally mounted, balanced, and inflated to placard pressure.
- Recheck pressure and watch for AWD, ABS, traction-control, or tire-pressure-monitor warnings.
No warning light and even tread depth across all four confirms a matched set. A traction-control lamp that stays lit after a few miles means something is still off.
Common Questions
Can I replace just one tire on an AWD car?
Only if the new tire exactly matches the other three in size, brand, model, construction, load index, and speed rating, and the remaining tires are nearly new. Measure tread depth first. If the other three are worn, the circumference gap keeps the AWD system working against itself, and shaving the new tire to match is safer.
Does AWD mean I don’t need winter tires?
No. AWD helps you accelerate but doesn’t shorten stopping distance or improve cornering on ice and snow. Michelin and Subaru both call for four matching winter tires, fitted when temperatures stay below 45°F. Two winter tires on an AWD vehicle create handling imbalance rather than solving it.
What happens if my AWD tires are mismatched?
The system reads wheel-speed differences as slip and compensates continuously, wearing the drivetrain and potentially causing damage. Subaru warns that incorrect size, circumference, or construction affects handling, braking, clearance, and speedometer accuracy. Staying within about 1/4 inch of circumference across all four keeps the system out of that fight.
Sources
- Subaru. “Owner’s Manual” Specifies matching tire requirements, the 1/4-inch circumference limit, four-tire replacement, and four matching winter tires.
- Michelin. “Can Tires Be Mixed?” Covers mixing tire types on four-wheel-drive vehicles and the 1-inch circumference guidance.
- Michelin. “Winter Tire Safety” Supports the 45°F fitting threshold and 2/32-inch replacement point for winter tires.