Replace tires before the Ottawa winter

Tread that still works in slush

Snow and slush need open grooves. By about 4 mm remaining (close to 5/32 inch), a winter tire has lost the depth that clears slush on Highway 417. It can still be legal. Ontario treats a tire as unsafe when less than 1.5 mm of tread remains, and that floor is a bare-pavement limit, not a snow limit. Do not wait for 1.5 mm if the tire's job is January.

Measure the shallowest groove, not the best-looking one. A tire worn on one shoulder after a bent wheel or a missed alignment is done when that shoulder is done. See potholes and alignment if the wear is uneven.

Age matters in a cold compound

The week and year of manufacture are in the DOT code on the sidewall. Tires built more than about six years ago often feel hard on the first cold morning even when the grooves look deep. Ten years is a common outer limit regardless of tread. There is no Ottawa bylaw that impounds a six-year-old tire. There is also no grip left in a compound that has cured on a sunny balcony all summer.

• Replace before the October changeover, not after the first storm, when shops are booked.
• Replace in a full set of four when the tires are the same age. Mixing a new pair with a worn pair repeats the two-tire problem.
• Cracks in the sidewall, a bulge, or exposed cord are reasons to remove the tire now, in any season.
• An all-weather tire lives through summer too, so it can age out of a second winter sooner. Compare that choice in all-weather versus winter.