Winter is coming, and the first significant snowstorm of the season is often the one that catches drivers off guard. 

Before you head for the mountains, spend 30 seconds checking the part of your car that touches the road: your tires.

The quarter test for tires

Here's a quick way to spot worn tires. Turn a quarter upside down and slide it into a groove of your tire tread, with George Washington's head going in first.

If you can see the top of his head, your tread is worn below about 1/8 inch, and it's time to replace the tire. Test several spots across the tire, because wear is often uneven.

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Colorado specifically

Passing this test doesn't mean your tires are ready for snow.

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According to the Colorado Department of Transportation (CDOT), your vehicle needs one of these:

- Four-wheel or all-wheel drive with tires that have at least 3/16 inch of tread

- Mud and snow, winter or all-weather-rated tires with at least 3/16 inch of tread

- Chains or an approved traction device

(MORE: 9 bad winter habits that could ruin your car)

On Colorado's Interstate 70 specifically, between Morrison and Dotsero, if your vehicle causes a lane closure, the penalty can reach $500 plus a $157 surcharge. CDOT can activate the law during winter storms or when conditions require it, but generally, it's in place from Sept. 1 to May 1.

A tire can pass the quarter test and still fall short of the requirements. A tread depth gauge will tell you for sure.

Also, read up on any laws similar to the Colorado law mentioned earlier, as fines can vary. You can check with CDOT (https://www.codot.gov/) or the departments of transportation for Western states (Utah Department of Transportation’s website is udottraffic.utah.gov).

Why is the first snow the worst?

The first snow of the season often causes more trouble than the 10th. Roads that are still warm can melt the first flakes, which then refreeze.

Oils that build up on pavement during dry spells can make surfaces slicker.

Also, many drivers haven’t practiced a snow-safe following distance since the spring.

(MORE: Follow these extreme weather driving safety tips)

Snow is on the way for millions, and a quarter could give you a heads-up if you need new tires.