Updated October 19, 2026
Why the light comes on in January
Air pressure tracks temperature. A set filled to the placard in a 10°C shop bay will be several psi low after a night at −15°C in a Kanata driveway. The tire-pressure light is often that drop, not a nail. Confirm with a gauge anyway. A real leak keeps falling after the weather has levelled off.
The number on the sidewall is the most the tire may hold, not the pressure the car wants. The car's figure is on the placard, and it can differ front to rear. Use that placard for the winter set too, unless the winter tire size is so different that the vehicle maker publishes a second pressure. When in doubt, use the placard for the original size.
Highway runs hide a low tire
Heat from a 417 commute brings pressure back up, so a tire that was low in the driveway can look fine at a gas station after 20 minutes. That is why the morning, cold, reading is the one to trust. Low pressure on slush makes the car wander and builds heat in the sidewall.
- Keep a gauge in the car. The light is a warning, not a measurement.
- Add air outdoors in the cold. A warm reading overstates the cold pressure.
- Recheck the morning after a sharp drop, and again a day after any changeover.
How to set winter tire pressure in Ottawa
Measure cold, use the door placard, and check again after a deeper freeze.
- 01
Measure before the car moves. Check pressure in the morning after the car has sat outside, before a drive. A trip across Kanata warms the tires and raises the reading.
- 02
Read the door placard. Use the front and rear pressures printed on the driver's door jamb. Ignore the maximum pressure molded on the sidewall.
- 03
Add air until the cold reading matches. Fill to the placard figure. A loss of about 1 psi for every 5 to 6°C since the last fill is a normal cold-weather drop, not a puncture by itself.
- 04
Set front and rear separately. If the placard lists two pressures, set each axle to its own number. Do not copy the front pressure onto the rear.
- 05
Measure again after a harder freeze. When a January night is much colder than the day you last filled the tires, check again the next morning before leaving for Highway 417.
Questions
How much does tire pressure drop in an Ottawa cold snap?
About 1 psi, or 7 kPa, for every 5 to 6°C of temperature drop. A fall from 10°C to −15°C is several psi.
Should I use the pressure printed on the tire?
No. That sidewall number is a maximum. Set the pressure on the driver's door placard.
When is the right time to check winter tire pressure?
In the morning, before driving, while the tires are still cold.
Does a pressure light in January always mean a leak?
No. A uniform drop on all four tires after a freeze is often just cold air. A single tire that keeps falling after the weather settles needs a leak check.