"AWD" and "4WD" get thrown around interchangeably in car yards and forums, but the two drivetrains behave very differently when it comes to tyre wear, and mixing that up is one of the fastest ways to damage a transfer case or a diff. If you drive a soft-roader SUV or a genuine off-road 4x4, the tyre rules that apply to your vehicle are not the same, and getting them wrong is expensive.
How AWD systems use tyres differently
All-wheel drive systems in most crossovers and SUVs, think Toyota RAV4, Subaru Outback, Mazda CX-5, are designed to run continuously with tiny, constant differences in rotational speed between the front and rear axles. The system tolerates a small amount of speed variance, but that tolerance is narrow. A difference in overall tyre diameter of more than a few millimetres between axles, caused by mismatched tread depth or different tyre models front to rear, can put the AWD coupling under load it wasn't designed for.
Over time this shows up as premature wear on the viscous coupling or clutch pack, and in bad cases a seized transfer case. This is why AWD vehicle manufacturers are strict about replacing tyres in full sets of four, or at minimum in matched pairs with less than 5mm of tread depth difference between them.
How 4WD systems are different
Genuine 4WD systems, utes and wagons like the Hilux, Ranger, Prado and Patrol, use a part-time transfer case that is usually disengaged in everyday driving. In 2WD mode, tyre diameter mismatch is far less critical because the front and rear axles aren't locked together. It's only when 4H or 4L is engaged that mismatched diameters become a problem, because the transfer case then forces the axles to rotate at the same speed regardless of tyre size.
This is why 4x4 owners can often get away with replacing tyres in pairs rather than full sets, provided they're not doing serious low-range 4WD work, but it's still good practice to keep tread depth reasonably close across all four positions, especially if you tackle sand, mud or rock regularly.
What this means for your next tyre purchase
- AWD passenger vehicles: replace in sets of four wherever possible.
- 4WD utes and wagons doing highway and light off-road work: pairs are usually fine.
- 4WD vehicles doing serious 4-low touring or rock work: keep all four as close to matched as you can.
- Always check your tread depth difference: 5mm is the rule of thumb ceiling for AWD systems.
Not sure which category your vehicle falls into, or what tread depth you're currently running? Send us your rego or model details through our quote form and we'll tell you exactly what we'd recommend before you spend a cent.
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