Montana Department of Transportation

Bigge Crane Megaload Permit Issued

A permit has been issued for a megaload to travel from Idaho through Montana to Great Falls. The move, planned for seven stages, will travel at night to minimize travel disruptions to others along the route. MORE INFORMATION

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Tire Equipment and Towing Options

Snow Tire Options

Restrictions as to tire equipment -- particular tires, chains, or traction equipment

Because of the many different road and weather conditions throughout our state, MDT along with the local tire industry wants motorists to know there is a variety of snow and studded tire alternatives available so they can choose appropriately. Since different types of winter tires provide varied performance under different road conditions, tire dealers can assist motorists to select the best option for them. Visit your local tire dealer to find out more.

A tire on a vehicle moved on a highway may not have on its periphery a block, stud, flange, cleat, or spike, or other protuberance of a material other than rubber that projects beyond the tread of the traction surface of the tire, except that it is permissible to use farm machinery with tires having protuberances that will not injure the highway. It is also permissible to use tire chains of reasonable proportions or pneumatic tires (means a tire in which compressed air or nitrogen is designed to support the load.), studded tires, that may not protrude more than one-sixteenth of an inch beyond the tire tread or that are clearly marked by the manufacturer on the sidewall "all season mud and snow", upon a vehicle when required for safety because of snow, ice, or other conditions tending to cause a vehicle to skid.

The use of pneumatic tires embedded as provided in this section is permitted only between October 1 and May 31 of each year, except that one of those tires may be used for a spare in case of tire failure. School buses equipped with such embedded pneumatic tires may operate from August 15 through the following June 15.

If the department of transportation determines at any time that dangerous or unsafe conditions on a highway require particular tires, tire chains, or traction equipment for vehicles in addition to or beyond the ordinary pneumatic rubber tires, the department may establish the following recommendations or requirements with respect to the use of the equipment for all vehicles using the highway:

  1. chains or other approved traction devices recommended for driver wheels;
  2. chains or other approved traction devices required for driver wheels; or
  3. chains required for driver wheels

When the department of transportation determines that chains are required and that no other traction equipment will suffice, the requirement is applicable to tires on driver wheels of one axle, as defined in 61-10-104, of a vehicle, including embedded tires. The signs or traffic control devices may differentiate in recommendations or requirements for four-wheel-drive vehicles in gear.

Regular tire chains or cable chains are approved for use.

Allowable load per inch width of tire

With the exception of reduced weight for spring breakup, the allowable weight per inch width of tire (500 lbs.) is to be computed for "Wide Based" tires only. A wide based tire is a tire 14 or more inches in width as shown on the sidewall of the tire, or by using the metric conversion formula.

Single axles with singled out tires cannot exceed 11,000 lbs. unless equipped with wide based tires. Wide based tires cannot exceed 500 lbs. per inch width of tire.

Remember: Steering axles are exempt from this. Manufacturers rated capacity or bridge formula should be used to determine allowable weight on a steering axle.

A single axle with 4 tires can go up to 20,000 lbs. of statutory weight, regardless of the tire size; the 500 lbs. per inch width of tire IS NOT used, as tires not meeting the definition of "Wide-Based" do not fall under the 500 LB per inch width limitation.

Metric Tires

Vehicles which operate on radial tires, display a metric "Nominal Cross Section" on the side of the tire that can be converted to inches using the following formula: If the nominal width on the tire is in inches, use that figure.

To determine inch width on metric radial "Wide-Based" tires, you must divide the number (tire size) by 25.4 EXAMPLE: Tire size 385-65R 22.5 (Divide385 by 25.4) (385 divided by 25.4 = 15.16) (Tire width is 15.16 inches)

REMEMBER: The 500 lbs per inch width of tire is ONLY used for "Wide Based Tires". Providing an axle has 4 tires, it is allowed to carry 20,000 lbs.

Additional information

MCS Trucker's Handbook

Towing – Passenger Vehicle Combinations

Reference: 61-10-104 M.C.A.

A passenger vehicle or truck of less than 2,000 pounds "manufacturer's rated capacity" may not tow more than one trailer or semi-trailer. This combination may not exceed an overall length, inclusive of front and rear bumpers, in excess of 65 feet, except as provided in 61-10-124 M.C.A.

Passenger vehicles or trucks with a "manufacturer's rated capacity" of 2,000 pounds or more may tow 2 trailers. This combination may not have an overall length, inclusive of front and rear bumpers, in excess of 75 feet, except as provided in 61-10-124 M.C.A. Each trailer exceeding 3,000 pounds must be equipped with brakes and breakaway brakes, as required in 61-9-304 M.C.A. and 61-9-305 M.C.A. The total weight on and including the wheels of the trailer or trailers may not exceed 40% of the gross weight of the towing vehicle when connected to the trailer or trailers as per 61-9-304(1)(a) MCA.

Manufacturer's maximum GVW capacity can normally be found on a metal plate inside of the door or door post.

Manufacturer's rated capacity is determined as follows:
Manufacturer's Maximum GVW 6,500 lbs.
Shipping Weight of Truck -4,500 lbs.
Meets requirement of law 2,000 lbs.
Manufacturer's Maximum GVW 4,800 lbs.
Shipping Weight of Truck -3,000 lbs.
DOES NOT meet requirement of law 1,800 lbs.

Brakes are required on all wheels EXCEPT on trailers not exceeding 3,000 pounds provided that the total weight on and including the wheels of the trailer or trailers shall not exceed 40% of the gross weight of the towing unit, when connected to the trailer(s).

First Trailer 4,500 lbs.
Second Trailer 2,000 lbs.
Total, Both Trailers 6,500 lbs.
Weight of Towing Unit 4,500 lbs.

Montana Codes Annotated