One on each corner - it's the law.
NO IT'S NOT
Only if the tractor/vehicle/heavy machinery is over 10,000lbs
under 10,000lbs all you need is 2.
§393.128 What are the rules for securing automobiles, light trucks and vans?
(a) Applicability. The rules in this section apply to the transportation of automobiles, light trucks, and vans which individually weigh 4,536 kg. (10,000 lb) or less. Vehicles which individually are heavier than 4,536 kg (10,000 lb) must be secured in accordance with the provisions of §393.130 of this part.
(b) Securement of automobiles, light trucks, and vans.
(b)(1) Automobiles, light trucks, and vans must be restrained at both the front and rear to prevent lateral, forward, rearward, and vertical movement using a minimum of
two tiedowns.
§393.130 What are the rules for securing heavy vehicles, equipment and machinery?
(a) Applicability. The rules in this section apply to the transportation of heavy vehicles, equipment and machinery which operate on wheels or tracks, such as front end loaders, bulldozers, tractors, and power shovels and which individually weigh 4,536 kg (10,000 lb.) or more. Vehicles, equipment and machinery which is lighter than 4,536 kg (10,000 lb.) may also be secured in accordance with the provisions of this section, with §393.128, or in accordance with the provisions of §§393.100 through 393.114.
(b) Preparation of equipment being transported. (1) Accessory equipment, such as hydraulic shovels, must be completely lowered and secured to the vehicle.
(b)(2) Articulated vehicles shall be restrained in a manner that prevents articulation while in transit.
(c) Securement of heavy vehicles, equipment or machinery with crawler tracks or wheels. (1) In addition to the requirements of paragraph (b) of this section, heavy equipment or machinery with crawler tracks or wheels must be restrained against movement in the lateral, forward, rearward, and vertical direction using a minimum of four tiedowns.
