Truck and trailer rules in California: licence classes, trailer brakes and size limits

This page reports what the official source says. It is not legal advice: ask the office named here. The sources are Vehicle Code sections 12804.9, 26454, 29004, 35250, 35400, 35401 and 35550 as printed on the state's legislative information site, the California DMV commercial driver license page and three Caltrans legal truck access pages, all read on October 10, 2026. The Caltrans pages call themselves paraphrases of the code. Federal background and the other places are on the parent page, trucks and trailers for tree work.

At a glance

Item	What the sources say
Class A	A combination whose towed vehicle is rated over 10,000 pounds, or a vehicle towing more than one vehicle
Class B	A single vehicle rated over 26,000 pounds, or with three or more axles
Class C	A two-axle vehicle of 26,000 pounds or less, with a trailer of 10,000 pounds or less
Brakes	Section 26454 sets stopping distances from 20 miles per hour: 20 to 40 feet by vehicle group
Safety chain	Section 29004: in addition to the drawbar, except a semitrailer on a fifth wheel
Length	40 feet for a vehicle; 65 feet for a combination, 75 feet in a listed case
Width, height	102 inches wide; 14 feet high
Weight	20,000 pounds on one axle; 80,000 pounds for a combination

Licence classes

Section 12804.9 sets the three classes, in the version effective June 27, 2025 that the site marks as repealed on January 1, 2029 and replaced by a later version. Class A covers a combination of vehicles if the vehicle being towed has a gross vehicle weight rating or gross vehicle weight of more than 10,000 pounds, a vehicle towing more than one vehicle, and a trailer bus. Class B covers a single vehicle rated at more than 26,000 pounds, a single vehicle with three or more axles other than a three-axle vehicle under 6,000 pounds, and such a vehicle towing another of 10,000 pounds or less. Class C covers a two-axle vehicle of 26,000 pounds or less, including one towing a trailer or semitrailer of 10,000 pounds or less. The section also lists a recreational towing endorsement on a class C licence. It covers a trailer coach or fifth-wheel travel trailer up to 10,000 pounds gross vehicle weight rating, and a fifth-wheel travel trailer over 10,000 and up to 15,000 pounds after a specialized written exam, in each case not for compensation. The section also requires a valid medical examination report, given within two years, on file before a class A or B licence is issued or renewed.

The DMV commercial driver license page lists what counts as a commercial motor vehicle: a single vehicle rated 26,001 pounds or more, a combination rated 26,001 pounds or more, a vehicle towing a vehicle or trailer rated 10,001 pounds or more, one towing two trailers, a vehicle carrying more than ten passengers, a placarded hazardous materials vehicle and a three-axle vehicle weighing more than 6,000 pounds. It says a driver must be at least 18 for cargo that starts and ends in the state and 21 for interstate or hazardous work, and that an original class A or B applicant must complete 15 hours of behind-the-wheel training under Vehicle Code section 15250.1(b).

Brakes and safety chains

Section 26454 requires the service brakes on every motor vehicle or combination to be adequate to control, stop and hold it under all loading. It then sets the maximum stopping distance from 20 miles per hour by group. Passenger cars seating 10 or fewer are held to 20 feet. Single-unit property carriers rated 10,000 pounds or less are held to 25 feet. Single-unit property carriers over 10,000 pounds, and combinations of a two-axle towing vehicle with a trailer rated 3,000 pounds or less, are held to 35 feet. All other property-carrying vehicles and combinations are held to 40 feet. The section also sets a braking force as a share of weight for each group, from 65.2 percent for the lightest group to 43.5 percent for the heavier ones.

Section 29004 requires a towed vehicle to be coupled by a safety chain, cable or equivalent device in addition to the regular drawbar, tongue or other connection. The connections must be strong enough to control the towed vehicle if the hitch fails and must have a positive means of staying in place. They may have no more slack than turning needs, and with a drawbar the chain must connect so the drawbar cannot drop to the ground. The rule does not apply to a semitrailer on a fifth wheel and kingpin. A vehicle towed by a tow truck needs at least two safety chains, and a vehicle carried on a trailer needs at least four tiedown chains or straps.

Size and weight

Limit	Figure as printed	Source
Length, single vehicle	40 feet, with listed exceptions	Section 35400
Length, combination	65 feet; 75 feet for a tractor and two semitrailers or a trailer each 28 feet 6 inches or less	Section 35401
Width	102 inches for a vehicle or its load	Caltrans, section 35100
Height	14 feet; above 13 feet 6 inches only on highways the owner deems safe	Section 35250
Weight on one axle	20,000 pounds	Section 35550
Weight on one wheel, or one end of an axle	10,500 pounds	Section 35550
Axle group, under 8 feet 6 inches between outer axles	34,000 pounds	Caltrans
Gross weight, combination	80,000 pounds	Caltrans

Section 35550 sets the wheel load at the lesser of the tire maker's sidewall limit or 620 pounds per lateral inch of rated tire width, and the steering axle goes by the maker's limit. On loads, the Caltrans overhang page paraphrases a rear limit of two-thirds of the wheelbase, a front limit of three feet beyond the front tires, and a flag at least 18 inches square when a load reaches four feet or more beyond the rear, with two red lights at night. It says boom and mast extensions on cranes carried on a motor vehicle have their own front conditions under section 35407. The page says the paraphrase is not guaranteed and may change.