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Old 12-24-2009, 08:00 AM   #17
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Default Tires Q&A: Winter tires or not

In our ongoing series of Q&A blog columns, we will highlight common and interesting questions posted to our Car forums, with answers from our automotive experts.

Question:I have been on the fence about getting winter tires this year. I just saw a commercial (from a tire store, of course) basically saying that even though it snows "occasionally" in Seattle, the temperatures will mostly stay below 45 º F this winter and we should have winter tires whether or not there is snow. They said that all-season tires do not perform as well below 45 º F and lose grip on the cold wet pavement-- that’s why we need winter tires. What is your take on this?

Answer: Winter tires, particularly the studless models, generally have a tread that stays pliable in extremely cold weather to grip snow and ice. It’s this compound feature that also compromises dry and wet grip compared to all-season tires in warmer temperatures (above freezing).
We did some testing a few years ago to see if the dry and wet grip improved in cold temperatures for winter tires; we found no conclusive improvement in grip.

All-season tires are designed to perform reasonably well in most conditions. In our testing, they generally have better dry and wet grip in cooler temperatures in the range of 40 º F to 50 º F, compared to warmer conditions, like 80 º F to 100 º F. Our all-weather testing at temperatures between 20 º F to 30º F show that a rare few all-season tires grip as well as some winter tires on ice and snow, but we do not have data that directly compares dry stops in extremely cold temperature (less than 25 º F) and, of course, wet surfaces turn into ice in these temperatures.

The bottom line is that a good set of all-season tires with 40 percent or more remaining tread depth would suffice in mild winter conditions (more tread depth the better). But certainly winter tires provide a measure of grip on snow and ice for drivers who want added peace of mind and need to drive in severe weather
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