Maximum Legal Weight Allowed
Maximum load limits may depend on the following:
- What type of highway you are operating on;
- The number of axles and the distance (spacing) between the axles or axle assemblies on which the vehicle or combination of vehicles is operated (spacing is the distance between axles, measured from the center of one axle to the center of another axle);
- The gross vehicle weight of the vehicle or combination of vehicles;
- Tire width (as published by the manufacturer).
Depending on the conditions listed, your vehicle may be subject to the maximums found under the bridge formula or the normal loading standards.
Bridge Gross Weight Formula
The bridge formula applies to vehicles operating on interstate highways and specially designated highways which:
- do not exceed 80,000 pounds gross weight;
- do not exceed the maximum allowed under the formula.
Normal Loading Maximum General Information
|Spacing Between Axles||Normal Exceeding when Seasonal Load Limitations are Not in Force||Seasonal Load Limitations (Speed Limit 35 mph)|
|Vehicles Exceeding 80,000 lbs. Gross Weight||Vehicles 80,000 lbs. (Or under) Bridge Formula Gross Weight||Rigid (25% Reduction)||Flexible (35% Reduction)|
|9′ or over *normal loading||18,000 pounds||20,000 pounds||13,500 pounds||11,700 pounds|
|3 1/2′ or more but less than 9′ *normal loading||13,000 pounds||13,000 pounds||9,750 pounds||8,450 pounds|
|When part of a tandem axle assembly *on designated routes only||*16,000 pounds||34,000 pounds on tandem||12,000 pounds||10,400 pounds|
|When less than 3 1/2′ *normal loading||9,000 pounds||9,000 pounds||6,750 pounds||5,850 pounds|
|Maximum load on any wheel shall not exceed (pounds per inch of tire width)||700 pounds||700 pounds||525 pounds||450 pounds|
*On any legal combination of vehicles, only 1 tandem axle assembly shall be permitted at the gross weight of 16,000 lbs. per axle and no other tandem axle assembly in such combination of vehicles should exceed a gross weight of 13,000 lbs. per axle. On a combination of truck tractor and semi-trailer not having more than 5 axles, load, 2 tandem axle assemblies shall be permitted at a gross weight of 16,000 lbs. per axle, if there is no other axle within 9′ feet of any axle of the assembly.
The Bridge Gross Weight Formula was developed to prevent stress to highway bridges caused by heavy trucks. The formula provides a standard to control the spacing of truck axles and weight on those axles. Vehicles with a gross weight of 80,000 pounds or less may be eligible for increased weights using the Bridge Gross Weight Formula. Vehicles exceeding a gross weight of 80,000 pounds or the gross weight calculated using the Bridge Weight Formula are not eligible for bridge weights.
The Bridge Gross Weight Formula allows:
20,000 pounds for a single axle;
34,000 pounds for a tandem axle group.
The weight of other axle groups would be determined using the Bridge Gross Weight Formula:
W = The maximum weight in pounds that can be carried on a group of two or more axles to the nearest 500 pounds;
L = The spacing in feet between the outer axles of any two or more consecutive axles;
N = The number of axles being considered.
The bridge formula allows up to 20,000 lbs. per single axle, if the vehicle is equipped with large enough tires. Steering axle weights will vary depending on the gross weight of the vehicle.
Maximum Permit Weight Allowed
In Michigan, it is not permitted more than 700 pounds per inch of tire width for a single axle.
Source of information: http://www.truckingsafety.org/Portals/0/GuideBooks/18th%20Ed%20TDGB.pdf