Driving a Subaru in a Colorado winter

Most of the Subaru lineup comes with all-wheel drive, which is a big part of why you see so many of them on I-70 in January. But the car is only half of it. Colorado's Traction Law is about your tires, and it applies to all-wheel-drive vehicles too.

The Traction Law, in plain terms

• When: every year from September 1 through May 31 on the I-70 Mountain Corridor between Dotsero and Morrison. CDOT can also turn it on for other state highways when the weather calls for it.
• Tires that qualify: winter tires (the mountain-snowflake symbol), all-weather rated tires, or mud-and-snow (M+S) tires, with at least 3/16 inch of tread.
• All-wheel drive doesn't exempt you. An AWD or 4WD vehicle needs qualifying tires too, or chains or an approved traction device on at least two drive tires.
• The fine for not complying is $50 plus a $17 surcharge, according to CDOT.

Check your tread before the first storm, not at the Eisenhower Tunnel. A tire can carry the M+S marking and still fall short of 3/16 inch.

What all-wheel drive does, and what it doesn't

Subaru's Symmetrical All-Wheel Drive sends power to all four wheels, which helps you pull away and keep moving on snow and ice. It doesn't help you stop or turn any better. That's the tires' job, which is why good tires matter as much as the drivetrain.

• All-wheel drive is standard on the Crosstrek, Forester, Outback, Ascent, Impreza, WRX, Solterra and Trailseeker.
• Two exceptions: the BRZ is rear-wheel drive, and the Uncharted Premium is front-wheel drive. The Uncharted Sport and GT have dual-motor all-wheel drive.
• X-MODE, Subaru's low-traction mode, is standard on the Crosstrek and available on the Forester and Outback. The Forester Wilderness adds Snow/Dirt and Deep Snow/Mud settings.

Ground clearance by model

Clearance matters for unplowed side streets, deep ruts and trailhead roads. Subaru's published figures:

Electric Subarus in the cold

Cold weather reduces any electric vehicle's range, and fast charging is slower on a cold battery. The Uncharted, for one, can precondition its battery before a DC fast-charging stop. If you're considering an EV and drive the mountains often, ask me about real-world range for your routes before you decide.

Before winter: a short checklist

• Measure tread depth (at least 3/16 inch for the Traction Law).
• Decide between dedicated winter tires and all-weather tires based on how often you head up I-70.
• Keep a scraper, a blanket and water in the car. Mountain closures can run for hours.
• Check the CDOT road conditions site, COtrip.org, before heading west.