Reading a winter tire size

How to read 225/65R17

• 225 is the tread width in millimetres.
• 65 is the sidewall height as a percentage of that width. A 65-series sidewall is 65 percent of 225 mm tall.
• R means radial construction.
• 17 is the wheel diameter in inches, not the tire's overall height.

The overall diameter is two sidewalls plus the wheel. That is the number the speedometer and the ground clearance depend on. A winter package often steps down an inch of wheel and raises the aspect ratio so the overall diameter barely moves. The tire size calculator shows both diameters, the difference, and what the speedometer does at an indicated 60 km/h.

Why the winter size should stay close

A much taller tire raises the car and makes the speedometer read slower than you are travelling. A much shorter tire does the opposite, and it can rub a liner or sit too close to a strut. Neither change is a Kanata-specific trick. The local reason to get it right is Highway 417: you want the stability system and the speedometer working from the size the car was designed around, in slush, at highway speed.

A slightly taller sidewall is the useful part of a smaller winter wheel. It puts more rubber between a March pothole and the rim. Compare the two sizes before you buy the wheels. The load index and speed rating on the new tire still need to meet or beat the placard.

The door jamb, not a forum post, is the list of sizes the vehicle maker approved. Start there, then check any alternate in the calculator.