Winter Tire Sizing Guide

1. Start With What the Vehicle Manufacturer Says

• Ford (2024 F-150 owner's manual): if you install snow tires, they must be the same size, construction and load range as the original tires listed on the tire placard, and installed on all four wheels. Ford also says wheels and tires must be the same size, load index and speed rating as those originally fitted.
• Jeep (2023 Wrangler owner's manual): snow tires can be identified by a mountain/snowflake symbol on the sidewall; select tires equivalent in size and type to the original equipment tires, and use snow tires only in sets of four. Jeep adds that snow tires generally have lower speed ratings than the original tires and should not be operated at sustained speeds over 75 mph (120 km/h).
• Michelin: replace tires with the same size designation, or approved options, recommended by the vehicle manufacturer, never with a tire that has less load-carrying capacity. Michelin says a lower speed rating is not recommended unless the tires are winter-capable (3-Peak Mountain Snowflake), in which case the vehicle must not be operated above the tire's maximum rated speed.

Because manuals differ, your own owner's manual and tire placard decide which winter sizes are approved. Load index and speed rating codes can be looked up on the load index chart and the speed rating chart.

2. Minus Sizing: Smaller Wheel, Taller Sidewall

Minus sizing means choosing a smaller wheel diameter (for example 17" instead of 18") and a tire with a taller sidewall (higher aspect ratio) so the overall tire diameter stays close to the original. Only do this if your manual or vehicle manufacturer approves the size, and check that the smaller wheel still clears the brakes.

Calculated examples (overall diameter = wheel diameter + 2 × width × aspect ratio):

• 225/45R17 (about 24.97 in.) to 205/55R16 (about 24.88 in.): about 0.4% smaller.
• 235/55R18 (about 28.18 in.) to 215/65R17 (about 28.00 in.): about 0.6% smaller.

These are calculated values, not manufacturer approvals. Check that the load index and speed rating of the winter size are still acceptable for your vehicle, as in point 1.

3. Matching Overall Diameter

The new winter tire's overall diameter should be very close to your original tires. Continental advises keeping rolling circumference within 3% of the original; this is not a manufacturer specification. For all-wheel-drive and four-wheel-drive vehicles, Michelin says that when the owner's manual gives no instructions, all four tires must be the same size, and the outside circumferences of all four must be within 1 inch (2.5 cm) of each other. Use the tire size comparison calculator to see the exact difference, the tire size difference check for AWD for the percentage, and the speedometer error calculator for the gauge effect.