- Mar 14, 2005
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With all due respect, the fact that a driver may have an articulated lorry HGV licence and experience is only part of the story.
HGV's do 'tow' at weight ratio's at well above 100% even as much as 400%, but the way the trailer is coupled is very different to that of a caravan and that affects the tractors ability to maintain control of the whole outfit.
Artics use a 'fifth wheel' to couple the outfit. Significantly this is located within the wheel base of the tractor unit. This means any down force created by the trailer on the hitch adds down load to all axles of the tractor unit. The typical arrangement of the trailers wheels also means that a significant proportion of the trailers weight is carried by the fifth wheel and thus the tractor. This means that as the trailer load increases so does the down force on all wheels of the tractor. Increased load on the tyres increases traction which is good for steerage and braking.
By comparison, the nose load of a caravan on a car, is carried by the tow ball which is behind the rear axel and outside the wheelbase. This means the car acts like a see saw, where any increase in the caravan nose load applies additional down force on the rear axel, but a reduced down force on the front steering axle. By design the nose load is typically limited to 75 to 100Kg, which is only a small proportion of the trailers weight. So regardless of the weight of the trailer, the actual down force on the cars wheels is relatively constant. So you do not get the same increase in tractive control that an artic achieves as the trailer load increases.
The skills of an HGV driver will be an advantage when it comes to position on the road, and negotiating bends and obstructions. They will probably be better at reversing the outfit than most car only drivers, and they will have an understanding of how loads can affect the dynamics and controllability of an outfit, but the actual effect that a caravan has on car is very different to that of a trailer on an artic. I am sure they will be quick learners, but it would be foolhardy to assume that HGV experience is going to make controlling a caravan easy especially on the first outing.
HGV's do 'tow' at weight ratio's at well above 100% even as much as 400%, but the way the trailer is coupled is very different to that of a caravan and that affects the tractors ability to maintain control of the whole outfit.
Artics use a 'fifth wheel' to couple the outfit. Significantly this is located within the wheel base of the tractor unit. This means any down force created by the trailer on the hitch adds down load to all axles of the tractor unit. The typical arrangement of the trailers wheels also means that a significant proportion of the trailers weight is carried by the fifth wheel and thus the tractor. This means that as the trailer load increases so does the down force on all wheels of the tractor. Increased load on the tyres increases traction which is good for steerage and braking.
By comparison, the nose load of a caravan on a car, is carried by the tow ball which is behind the rear axel and outside the wheelbase. This means the car acts like a see saw, where any increase in the caravan nose load applies additional down force on the rear axel, but a reduced down force on the front steering axle. By design the nose load is typically limited to 75 to 100Kg, which is only a small proportion of the trailers weight. So regardless of the weight of the trailer, the actual down force on the cars wheels is relatively constant. So you do not get the same increase in tractive control that an artic achieves as the trailer load increases.
The skills of an HGV driver will be an advantage when it comes to position on the road, and negotiating bends and obstructions. They will probably be better at reversing the outfit than most car only drivers, and they will have an understanding of how loads can affect the dynamics and controllability of an outfit, but the actual effect that a caravan has on car is very different to that of a trailer on an artic. I am sure they will be quick learners, but it would be foolhardy to assume that HGV experience is going to make controlling a caravan easy especially on the first outing.