Both edges worn, centre fine
This usually means the tire has been running underinflated. With too little air, the edges carry the load and the centre lifts. Cold weather makes it common in Ontario: pressure drops roughly 1 psi for every 5–6 °C the temperature falls. Check pressure monthly, cold, against the placard on the driver's door, not the maximum printed on the tire.
Centre worn, edges fine
The opposite: overinflation. The centre bulges slightly and carries most of the load. It often happens when tires are filled to the sidewall's maximum pressure. Set them to the door placard figure instead.
One edge worn: inner or outer
Wear on just one edge usually points to wheel alignment, typically camber (the wheel tilting in or out) or toe (the wheels not pointing straight ahead), or to worn suspension and steering parts. It's especially common after a hard pothole or curb hit.
Feathering
If you run your hand across the tread and the blocks feel smooth one way and sharp the other, that's feathering. It's a classic sign of a toe problem, which is an alignment issue.
Cupping or scalloping
Dips or scoops worn around the tread, often with a rhythmic hum that changes with speed, usually point to worn shocks or struts, or to a wheel that's out of balance. Tire balancing fixes the balance side; worn suspension parts need to be replaced for the wear to stop.
Front tires wearing faster than rear
On front-wheel-drive cars the front tires steer, brake and drive, so they wear faster. That's normal, and it's what regular rotation is for: moving tires between positions so the set wears evenly.
What to do about it
Work from the cheapest fix up:
- Set the pressure to the door placard and check it monthly.
- Rotate the tires at the interval in your owner's manual.
- Have the balance checked if there's a vibration or cupping.
- Have the alignment checked if one edge is wearing or the car pulls.
- Replace badly worn tires only after the cause is fixed.
