Buying a used car for Colorado winters

Ask ten people in Denver what makes a good winter car and most will say all-wheel drive. They are not wrong, but they are only partly right. The vehicle that gets you to the trailhead in February is the result of several things working together: what drives the wheels, what is on the wheels, how much room there is underneath, and whether the car has been looked after through the salt and slush of previous winters. If you are shopping used, each of those is something you can check.

Drivetrain and tires do different jobs

All-wheel drive and four-wheel drive help a vehicle accelerate on a slippery surface, because power goes to more than one axle. That is a real advantage when you are pulling away from a stop on an icy hill or climbing a snowy driveway. What a drivetrain does not do is help you stop or turn. Braking and steering depend almost entirely on the grip between the tires and the road, and every vehicle, AWD or not, brakes on four tires.

This is why a front-wheel-drive car on good winter tires can feel more secure in snow than an AWD SUV on worn all-seasons. The AWD vehicle gets moving easily and then takes longer to stop. For many Front Range drivers who mostly stay in the metro area, a well-shod front-wheel-drive car is a perfectly sensible winter vehicle. For people who head into the mountains regularly, AWD or 4WD combined with good tires is the stronger combination.

When you look at a used vehicle, look at its tires as carefully as its drivetrain. They are a significant part of what you are buying here.

The traction law

Colorado has a traction law that the Colorado Department of Transportation puts into effect when conditions require it, most often on the I-70 mountain corridor. When it is active, passenger vehicles generally need one of the following: four-wheel drive or all-wheel drive, tires marked M+S (mud and snow), tires with the mountain-snowflake symbol, or dedicated winter tires. In each case the tires need adequate tread depth. There is also a stricter chain law that can apply to commercial vehicles and, in severe conditions, to passenger vehicles.

The details, including the minimum tread depth, are set by the state and can change, so check CDOT's current guidance instead of trusting memory or a friend's advice. The practical point for a buyer is simple: if you plan to drive I-70 in winter, the tires on the vehicle you buy need to meet the requirement, or you need to budget for a set that does.

Ground clearance

Clearance matters more in Colorado than in many places, but for specific reasons. It helps with unplowed residential streets, deep ruts in a mountain driveway, the ridge of packed snow that plows leave at the end of a drive, and forest service roads. It matters much less on a plowed interstate.

Be honest about where you will actually drive. A crossover with modest extra clearance covers most metro and resort-town needs. If you live at the end of a long private road above 8,000 feet, more clearance and a proper 4WD system may be worth the trade-offs in fuel use and ride. Manufacturers publish clearance figures, but they are measured differently from brand to brand, so treat them as a rough guide. They aren't an exact ranking.

Tread depth: how to check it yourself

Tread depth is easy to measure and worth measuring on every used vehicle you consider. A tread depth gauge costs very little at any auto parts store and gives you a reading in 32nds of an inch. Measure across each tire (inside, middle and outside) and on all four tires. Uneven wear across a tire can point to alignment or suspension issues. Different readings from tire to tire can matter on AWD vehicles, where many manufacturers specify that all four tires be closely matched in size and wear to avoid straining the drivetrain. Check the owner's manual for the specific vehicle.

Also look at the tire's date code on the sidewall, a four-digit number showing the week and year it was made. Rubber hardens with age, and older tires can lose winter grip even when the tread looks fine. Look at the tread for the M+S marking or the mountain-snowflake symbol so you know what you are getting.

Rust and magnesium chloride

Colorado roads are treated with de-icers in winter, including magnesium chloride and salt brine. They work well for keeping roads clear, and they are hard on metal. Brine clings to the underside of a vehicle and can speed up corrosion of brake lines, fuel lines, exhaust components, suspension parts and the frame or subframe.

When you inspect a used vehicle, look underneath with a flashlight. Surface rust on cast parts and exhaust is common and often cosmetic. What deserves closer attention is flaking or scaling on the frame, rust on brake and fuel lines, bubbling paint along the rocker panels and the bottoms of doors, and corrosion around the rear wheel arches. If you are not comfortable judging what you see, a pre-purchase inspection on a lift is the best money you will spend. A good inspector will tell you whether the rust is ordinary for the vehicle's age or a warning sign.

A vehicle's history can also give clues. One that spent its life in a dry climate may show less underbody corrosion than one that has been through many treated winters, but there is no substitute for looking.

Other winter checks worth making

Test the battery or ask whether it has been tested. Cold weather is hard on weak batteries. Check that the heater and defrost blow hot and clear the windshield properly. Check the wipers and washer system, and make sure the washer fluid is rated for freezing temperatures. If the vehicle has heated seats, a heated steering wheel or heated mirrors, confirm they work. On an AWD or 4WD vehicle, ask about service history for the transfer case and differentials, since those fluids are sometimes overlooked.

Putting it together

A good Colorado winter vehicle is not one feature. It is a sensible drivetrain for where you drive, tires that suit the conditions and meet the traction law, enough clearance for your actual roads, and an underside that has not been eaten by years of brine. Every one of those can be checked before you buy.

You can browse vehicles currently available through ABC, where listings note drivetrain and any known condition issues. If you are not sure what kind of vehicle fits how you drive, tell us about your winter driving and get a recommendation, and we will explain the reasoning behind it.