How to Check Your Tires for the Colorado Traction Law

What the Law Asks of Your Car

The Passenger Vehicle Traction Law covers cars, SUVs and pickups under 16,001 pounds. The Colorado State Patrol says it runs on I 70 from Dotsero at mile 133 to Morrison at mile 259. That stretch is on the list every year from September 1 to May 31. The law only bites when CDOT turns it on with the overhead signs.

CDOT can also turn it on for any state highway when a storm calls for it. So it is not only a ski trip rule.

When it is on, your car needs one of three things. Good tires. Chains on two or more drive tires. Or an approved traction device on two or more drive tires. CDOT and the State Patrol both list the same three.

What is on the car	Does it pass
Winter tire with the mountain snowflake symbol and 3/16 inch of tread	Yes
Tire marked M+S, M/S or M&S with 3/16 inch of tread	Yes
Tire the maker rates all weather, with 3/16 inch of tread	Yes
Any of those tires worn below 3/16 inch	No. Add chains or a device.
Summer tire with no mark	No. Add chains or a device.
Chains or a CDOT approved sock on two or more drive tires	Yes

CDOT names four approved devices on its traction law page. Those are Alpha Trax, AutoSock, EasySox and the ISSE Tire Sock. The full list sits on the CDOT Approved Products List.

The 2026 Fix for Two Wheel Drive

The rule changed twice in two years. That is why the pages you find online disagree.

In 2025 the state passed SB25-069. It was signed May 15, 2025. The goal was to close a gap in the tire rule. The Aspen Times reported that the new wording left out two wheel drive cars by mistake. On paper, a front wheel drive sedan needed chains or a sock even with good snow tires. The State Patrol later said it would let those cars pass on good snow tires.

Lawmakers fixed it in 2026. HB26-1237 was signed May 5, 2026. The legislature lists August 12, 2026 as the day it took effect. It takes the words four wheel drive and all wheel drive out of the tire rule. The Post Independent reported in September that the rule now covers every car, no matter which wheels drive it.

One page has not caught up. The State Patrol chain law page still describes the 2025 rule. It says a two wheel drive car has no tire only option.

The safe play covers you under both readings. Run tires with the right mark and 6/32 or more. Then keep an approved sock in the trunk from September to May.

How to Check Your Tires at Home

1. Read the sidewall. Look for M+S, M/S or M&S. Look for a three peak mountain with a snowflake inside. Or look for the words all weather. Check all four tires. A mixed set fails if one tire has no mark.
2. Get a tread gauge. Any parts counter sells one. It reads in 32nds of an inch, which is what you need.
3. Measure the main grooves. Push the pin into a groove and slide the sleeve down flat on the tread. Skip the raised bars that sit inside the grooves. Those are wear bars.
4. Measure three spots across each tire. Outside, center and inside. Write down the lowest number.
5. Compare to the line. The law wants 6/32 or more on every tire.
6. Look at the pattern. One edge much lower than the other often points to alignment or worn front end parts. Get that looked at before new tires go on.

Lowest gauge reading	What it means for the law
7/32 or more	Passes with a little room
6/32	Passes, right at the line
5/32	Fails. Carry chains or a sock.
4/32	Covers the quarter but still fails

The math is simple. One sixteenth of an inch is two 32nds. So 3/16 inch is 6/32.

When the Law Turns On Near Frederick

Frederick sits on I 25, well east of the fixed I 70 stretch. You can drive the Carbon Valley all winter and never pass a traction law sign. The day you head for the ski areas, you will.

CDOT posts the law on overhead signs and on COtrip.org. You can sign up for text and email alerts at subscription.cotrip.org. Check before you leave the house, not at the Morrison exit.

There is a stricter step called the Chain Law. It means chains or a device on every passenger car, good tires or not. CDOT says it comes right before a road closes. The Post Independent reported that CDOT last used it in March 2019, during the bomb cyclone.

Common Misreads

The quarter test proves you pass. It does not anymore. CDOT taught the quarter test in 2018. Back then, covering the top of the head meant 1/8 inch, the old minimum. The line is now 3/16 inch. A tire can hide the whole head and still fail by 2/32.

All wheel drive gets a pass. It never did under the current law. The November 2025 CDOT release says the tire rule applies to all four wheel and all wheel drive cars. Extra driven wheels help you go. They do not help you stop.

All season tires count. Sometimes. CDOT and the State Patrol list M+S, all weather and the snowflake symbol. Some all season tires carry an M+S mark as well. Find that mark on the sidewall and you are covered.

The fine is $133. The official pages disagree. CDOT's November 2025 release says $50 plus a $17 surcharge. The Post Independent printed the same in September 2026. CDOT's own traction law page still lists $100 plus $33, and $500 plus $157 when a car blocks a lane. Plan for the higher one.

Before You Head Up the Hill

Tires get you a pass at the sign. The rest of the car gets you home.

• A battery that starts fine in town can quit on a cold morning at a trailhead.
• Long downhill grades work the brakes hard. Thin pads show it first.
• Wipers and washer fluid matter more than you think when trucks throw slush.
• Brine from the plows sits under the car. Rinse it off after the trip.

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