321.466  Increased loading capacity — reregistration.
  1.   The owner of a motor truck, truck tractor, or road tractor, if the owner’s operation has not resulted in a conviction or action pending under this section, may increase the gross weight registration of the vehicle to a higher gross weight registration by payment of one-twelfth of the difference between the annual fee for the higher gross weight and the amount of the fee for the gross weight at which the vehicle is registered, multiplied by the number of unexpired months of the registration year. If the owner’s operation has resulted in a conviction or action pending under this section, any increase in the gross weight registration shall be obtained by payment of the difference between the annual fee for the higher gross weight and the amount of the fee for the gross weight at which the vehicle is registered.
  2.  Upon conversion of a truck to a truck tractor or a truck tractor to a truck, an increased gross weight registration of the proper type may be obtained for the vehicle by payment, except as provided in section 321.106, of one-twelfth of the difference between the annual fee for the higher gross weight and the amount of the annual fee for the gross weight at which the vehicle is registered, multiplied by the number of unexpired months of the registration year from the date of the conversion.
  3.  The registered gross weight of a vehicle or combination of vehicles may also be increased by installing and using an auxiliary axle or axles, and the combined registered gross weight of the vehicle and auxiliary axle or axles shall determine the total registered gross weight. An auxiliary axle shall not be used to convert a single axle to a tandem axle unless equipped with a device to equalize the load carried by the single axle and the auxiliary axle when in tandem and when in motion or when standing, and the load transmitted to the highway by either the single axle or the auxiliary axle shall not exceed that permitted for a single axle, nor shall the load transmitted to the highway when in tandem and when in motion or when standing, exceed that permitted for a tandem axle.
  4.  A person shall not operate a motor truck, trailer, truck tractor, road tractor, semitrailer, or combination thereof, or any such vehicle equipped with a transferable auxiliary axle or axles, on the public highways with a gross weight exceeding the gross weight for which it is registered by more than five percent; provided, however, that any vehicle or vehicle combination referred to in this subsection, while carrying a load of raw farm products, soil fertilizers including ground limestone, raw dairy products, livestock, live poultry, or eggs, or a special truck, while carrying a load of distillers grains, may be operated with a gross weight of twenty-five percent in excess of the gross weight for which it is registered. However, this subsection shall not be construed to allow the operation of a special truck on the public highways with a gross weight exceeding the maximum gross weight allowed under section 321.463, subsection 6.
  5.  For the purposes of this section cracked or ground soybeans, sorgo, corn, wheat, rye, oats, or other grain shall be deemed to be raw farm products, provided that such products are being directly delivered to a farm, from the place where the whole grain had been delivered from a farm for the purpose of cracking or grinding and immediate delivery to the farm to which such cracked or ground products are being delivered.
  6.  The truck operator shall have in the truck operator’s possession a receipt showing place of processing on the return trip.
[C24, 27, §4921; C31, 35, §4921-c1, -c2; C39, §5035.15; C46, 50, 54, 58, 62, 66, 71, 73, 75, 77, 79, 81, §321.466; 81 Acts, ch 110, §2]
82 Acts, ch 1062, §31, 32, 38; 90 Acts, ch 1233, §18; 2009 Acts, ch 113, §1; 2012 Acts, ch 1093, §14; 2013 Acts, ch 103, §13, 14; 2019 Acts, ch 138, §4
Referred to in §321.123, 321.460, 321E.2, 805.8A(12)(d)
Vehicles carrying farm products, see also §321.460 
For applicable scheduled fines, see §805.8A, subsection 12, paragraph d