Minimum Tread Depth in California – Here are the rules

In California, the minimum depth for tire treads on any two adjacent grooves is 1/32nd of an inch. For major grooves, the minimum depth for tires on the vehicle’s steering axle is 1/8th of an inch. For all other tires the minimum depth is 1/16th of an inch.

Driving on tires with shallower tread can be ticketed under California Vehicle Code 27465(b) VC.

What is the minimum tire tread depth in California?

California state law mandates a minimum tire tread depth for inflatable tires on all vehicles. The minimum depth of the treads depends on the tire and the groove:

• the minimum tread required at all points in all major grooves is:
  • 4/32nd (or 1/8th) of an inch in all tires on the steering axle (usually the front tires), and
  • 2/32nd (or 1/16th) of an inch in all of the other tires; and
• the minimum tread depth for any 2 adjacent grooves, whether major or minor, is 1/32nd of an inch.¹

Snow tires must have a tread depth of at least 6/32nd (or 3/16th) of an inch at all points in all major grooves.²

For non-motor vehicles, tread depth has to be at least 1/32nd of an inch.³

This is shallower than the legal limit for tread depth in many other states. 42 other states require at least 2/32nd of an inch of tread depth. California and Idaho are the only states that require 1/32nd of an inch. 6 other states, including Montana and New Mexico, do not have minimums. There is also no federal law that requires a minimum inch tread depth in tires.

There are 2 types of grooves in a tire:

1. circumferential grooves, which are cut vertically around the tire’s outside to create an uninterrupted tread, and
2. lateral grooves, which cut across the outside of the tire from one side of the wheel to the other.

In California, a major groove is a circumferential groove.⁴ These often have tread wear indicators in them. These indicators are shallower sections of the tread groove. They can be used to visually determine how worn the tire has become.

Tread depth measurements can be made anywhere except on a:

• tie bar,
• hump, or
• fillet.⁵

Are there any exceptions?

There are 3 exceptions to California’s minimum tire tread depth law:

1. spare tires that have been temporarily installed,
2. farming equipment, and
3. non-inflatable tires.

Spare tires that have been temporarily installed on a disabled vehicle do not need to comply with the minimum tread depth requirements.⁶ However, these tires cannot be used as a permanent solution. If they are used for too long, they may become subject to California’s minimum tread laws.

California Vehicle Code 27465 VC says that the law does not apply to “implements of husbandry.” These are vehicles that are used exclusively as farming equipment.⁷

Finally, the tread depth laws in California only apply to pneumatic tires. These are tires that are inflated or are capable of being inflated with air.⁸ If the tire is non-inflatable, like a wooden wheel on a horse-drawn carriage, it is exempted from the tread depth requirements.

What are the penalties of a violation?

Driving a vehicle with less than the required tread depth is an infraction. This means that it is not a criminal offense, like a misdemeanor or a felony. Instead, it is punished with a traffic ticket. The ticket carries a fine of $25. That fine can increase when assessments get added to it.

Violating California’s tread depth law does not add a point to the person’s driving record.

Ignoring the traffic ticket can make the penalties worse. When drivers get ticketed in California, they sign a written promise to appear in court. Willfully failing to appear violates California Vehicle Code 40508 VC. Even though the underlying offense was only an infraction, failure to appear is a crime. It is a misdemeanor. A conviction carries up to:

• 6 months in county jail, and/or
• $1,000 in fines.⁹

It will also lead to a blemish on the driver’s criminal background.

If the violation led to a car accident, the ticket can also be used in a subsequent personal injury case against the driver. The violation can be used to show that the driver was being negligent per se.

Is it unsafe to drive on bald tires?

Yes, it is unsafe to drive on worn tires. Bald tires, or those that have very little or no tread depth, have a longer stopping distance. They are also more likely to:

• slide,
• skid,
• puncture,
• hydroplane,
• lose traction of the roadway,
• lose air pressure, or
• blowout.

All of these problems increase the risk of a car accident. They are even more dangerous on large vehicles, like pick-up trucks, especially when they are hauling cargo or a semitrailer. On wet roads, the dangers of driving on bald tires becomes even more pronounced.

How can I check my tire tread?

Drivers can check the depth of their tire tread by sliding a coin into the tire’s circumferential groove. Checking tread depth on an average passenger vehicle can take as little as thirty seconds.

In California, this major groove has to be at least:

• 4/32nd of an inch deep on the steering axle, and
• 2/32nd of an inch deep on the other axles.

To test the depth of the tire treads on the steering axle – usually the front wheels – drivers can use the quarter test. This test uses a 25 cent piece. Drivers can orient the coin so that they are looking at George Washington’s head. Gripping the coin at George Washington’s neck, drivers can slide the coin into one of the tire’s circumferential grooves. The distance from the rim of the coin to the top of George Washington’s head is 4/32nd of an inch. If his entire head is sticking up above the sides of the groove, then the groove is too shallow. The tire is not compliant with Vehicle Code 27465(b).

The process for testing the treads of tires on other axles is similar. However, it uses the penny test, instead. Drivers can grip a penny at Abraham Lincoln’s torso and slide his head into a circumferential groove. The distance between the rim of the penny to the top of Lincoln’s head is 2/32nd of an inch. If his entire head sticks up above the sides of the tire’s groove, then the tread has become too worn. The tire’s tread depth is too shallow for Vehicle Code 27465(b).

These are the minimum legal tread depths under California laws. Getting new tires before there is so little tread left is safer and can prevent an accident and potential liability.

Additional Resources

For tire safety tips, refer to the following:

• U.S. Tires Manufacturers Association – Information about safety, repairs, and recalls.
• AAA – Article on tire safety and maintenance.
• National Highway Traffic Safety Administration – Overview on tire safety.
• Consumer Reports – Tire Safety Checklist: What to Do Before Your Next Road Trip.
• Caltrans – Information on Chain Controls / Chain Installation.

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