What does 'M+S' marking mean on your vehicle's tires?

Cold weather driving tires

Every year, starting on Oct. 1, B.C.'s highways are posted with signs saying the use of winter tires for light vehicles is required.

The signs show both the mountain and snowflake symbol and the “M+S” acronym. While both types of tire meet the requirements, it is very important to understand what “M+S” really means.

One would expect the marking “M+S” or the words “mud and snow” on a tire would mean it was designed for proper winter traction in all conditions. You might be surprised to find out it only defines a tire that’s tread:

• Has multiple pockets or slots in at least one tread edge that extends toward the tread centre at least 1/2 inch from the footprint edge

• Is measured perpendicularly to the tread centre line and has a minimum cross-sectional width of 1/16 inch

• Has edges of pockets or slots at angled between 35 and 90 degrees from the direction of travel

• Has a contact surface void area a minimum of 25% based on mould dimensions

It says nothing about the tire's rubber compound and its ability to stick to compact snow and ice.

Tire sipes may provide up to 40% of the traction on packed and icy snow. They are not required in order to meet the “M+S” designation.

Uniroyal's website gives the following advice concerning “M+S”, or all-season, tires:

“All Season tires should be replaced by winter tires on all-wheel positions during severe winter conditions (when temperatures are consistently below the freezing point and/or there are regular winter precipitations such as snow or freezing rain).”

Most B.C. residents would not think of this as being severe at all.

“M+S” generally means a rubber compound that stays hard and does a poorer job of sticking to highway surfaces at temperatures below 7 C.

Tires with the mountain and snowflake design are rated for their ability to provide traction in winter conditions, where the temperature is below 7 C.

Think of them as low temperature tires and choose them over all-season tires or M&S tires when you drive in B.C.’s winter road environment.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.

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About the Author

Tim Schewe is a retired constable with many years of traffic law enforcement experience. He has been writing his column for most of the 20 years of his service in the RCMP.

The column was 'The Beat Goes On' in Fort St. John, 'Traffic Tips' in the South Okanagan and now 'Behind the Wheel' on Vancouver Island and here on Castanet.net.

Schewe retired from the force in January of 2006, but the column has become a habit, and continues.

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The views expressed are strictly those of the author and not necessarily those of Castanet. Castanet does not warrant the contents.

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