THE BASIC PRINCIPLES OF TOWING FOR BICYCLE TRAILERS
When a bicycle is connected to a bicycle trailer it becomes an articulated vehicle and subject to the principles of towing, and so if you intend to use a bicycle trailer it can be useful to have an understanding of the basic principles of towing.
To explain the effects of towing bicycle trailers we shall look at two examples which highlight the basic principles. The first example will be a car towing a caravan and the second, an articulated lorry. For a car towing a caravan the general recommendation is that the car must be heavier than the caravan. However an articulated lorry consists of a tractor cab weighing approximately 10 tons with the ability to tow a trailer weighing thirty tons i.e. 3 times heavier than the tractor cab. This is possible because of weight distribution.
So firstly we shall consider weight and it s distribution.
The caravan's axel is almost centrally placed. It is recommended that a caravan should have a nose weight of 30 - 50 kg. This is the weight the caravan exerts on the cars towing hitch. So when the car is connected to the caravan the weight bearing down on the axels varies only slightly compared to the articulated lorry. Because the axels of the lorry trailer are placed to the rear of the trailer, when connected to the tractor cab approximately half of the trailer weight bears down on the axels of the tractor cab. So when connected to the trailer, the weight bearing on the tractor cabs axels increases dramatically i.e. the tractor effectively increases in weight. So it is of huge benefit if the cycle trailer can disperse half it s weight onto the cycle. This is achieved by placing the bicycle trailers wheel behind the load to increase the trailers nose weight.
Next we shall consider leverage. This is the force that can cause an articulated vehicle to jackknife. This usually occurs when the towing vehicle is trying to slow down and change direction. The trailer is trying to continue in the direction it is traveling. The force of the trailer combined with leverage can overwhelm the towing vehicle causing it to jackknife. Leverage is force x distance where distance is the measurement from the rear axel to the towing hitch. The greater the distance (the further back the towing hitch is) the greater the leverage. So because the tractor cabs towing hitch is never behind the rear axel the leverage applied by the trailer is minimum and the tractor cab can tow 3 x it s weight. Because the cars towing hitch is quite some distance behind the cars rear axle the car can tow nothing heavier than itself. So like the articulated lorry it is of huge benefit if the point at which the bicycle and trailer pivot is in front of the bicycles rear axle.
The other force of leverage to consider is center of gravity (c. of g.). The lower the c. of g. the lower the force trying to pull the bicycle from the upright position. The bicycle alone starts with a c. of g. because the cyclist is considerably heavier than the bicycle, when the cyclist sits on the bicycle the c. of g. is raised. Because the trailer load is considerably closer to the ground than the cyclist the addition of a cycle trailer can lower the c. of g. and add stability. The lower the trailer can carry its load, the greater the stability it can add.
Finally if your cycle has rear suspension it should also be considered that the bicycle trailer should not be connected to the cycles rear axle. When connected to the rear axel the weight of the trailer will restrict the cycle's rear suspension action. It is more ideal if the trailer can benefit from the cycles suspension, not hinder its action.