Trucks with trailers

Author
Discussion

drivin_me_nuts

Original Poster:

17,949 posts

218 months

Wednesday 17th December 2014
quotequote all
Is there a difference in the driving dynamics between a truck pulling a trailer with wheels mounted on twin central axles and those with a single turning axle at one end?

Is there a reason why a haulage company would prefer one over the other?

Cheers,

DMN

Nickyboy

6,704 posts

241 months

Wednesday 17th December 2014
quotequote all
Unsure exacty what you mean but i'm guessing you mean a normal trailer compared to one with an urban rear axle? If so then it makes it more maneuverable

StuntmanMike

11,671 posts

158 months

Thursday 18th December 2014
quotequote all
I think the OP means A - frame drawbar as opposed to the caravan type.
Both are very similar going forward, the A - frame is much much harder to reverse, owing to the swivel front axle.
The A - frame used to be extremely close coupled, which meant the trailers could be much closer together, so potentially carry more cargo, this was achieved by having a cam and piston on the front axle, this would extend the gap between the trailer and prime mover when cornering.
This however was outlawed in the late nineties ( I could be wrong about this bit ) as it took the total length over 60 feet when turning.
This effectively wiped out any advantage the A - frame had, and hauliers stuck with the mush easier to reverse and much easier to maintain ( fewer mechanical bits ) caravan type.
Both types of drawbar will carry more volume than an artic, but are less versatile.

drivin_me_nuts

Original Poster:

17,949 posts

218 months

Thursday 18th December 2014
quotequote all
Thank you, that is what I meant.

I've often wondered, are the A frame type ones more of a liability when braking - as in the potential to jack-knife the vehicle?

bigwheel

1,625 posts

221 months

Thursday 18th December 2014
quotequote all
StuntmanMike said:
I think the OP means A - frame drawbar as opposed to the caravan type.
Both are very similar going forward, the A - frame is much much harder to reverse, owing to the swivel front axle.
The A - frame used to be extremely close coupled, which meant the trailers could be much closer together, so potentially carry more cargo, this was achieved by having a cam and piston on the front axle, this would extend the gap between the trailer and prime mover when cornering.
This however was outlawed in the late nineties ( I could be wrong about this bit ) as it took the total length over 60 feet when turning.
This effectively wiped out any advantage the A - frame had, and hauliers stuck with the mush easier to reverse and much easier to maintain ( fewer mechanical bits ) caravan type.
Both types of drawbar will carry more volume than an artic, but are less versatile.
It was the caravan type (centre axles) trailer that experimented with a shortening system. This was a piston on the simple, single drawbar hitch.
Continental operators preferred A-frame, maybe because they're very easy/stable to leave un-hitched?

Humper

946 posts

169 months

Thursday 18th December 2014
quotequote all
StuntmanMike said:
Both are very similar going forward, the A - frame is much much much much much much much harder to reverse, owing to the swivel front axle
Sorted that bit wink


StuntmanMike

11,671 posts

158 months

Thursday 18th December 2014
quotequote all
bigwheel said:
StuntmanMike said:
I think the OP means A - frame drawbar as opposed to the caravan type.
Both are very similar going forward, the A - frame is much much harder to reverse, owing to the swivel front axle.
The A - frame used to be extremely close coupled, which meant the trailers could be much closer together, so potentially carry more cargo, this was achieved by having a cam and piston on the front axle, this would extend the gap between the trailer and prime mover when cornering.
This however was outlawed in the late nineties ( I could be wrong about this bit ) as it took the total length over 60 feet when turning.
This effectively wiped out any advantage the A - frame had, and hauliers stuck with the mush easier to reverse and much easier to maintain ( fewer mechanical bits ) caravan type.
Both types of drawbar will carry more volume than an artic, but are less versatile.
It was the caravan type (centre axles) trailer that experimented with a shortening system. This was a piston on the simple, single drawbar hitch.
Continental operators preferred A-frame, maybe because they're very easy/stable to leave un-hitched?
A - frames also had them, United carriers used them, my first driving job was in one of these, the piston broke on me one day, the trailer repeatedly hit the prime mover until it had stopped, frigging scary.driving

Upatdawn

2,187 posts

155 months

Thursday 1st January 2015
quotequote all
StuntmanMike said:
A - frames also had them, United carriers used them, my first driving job was in one of these, the piston broke on me one day, the trailer repeatedly hit the prime mover until it had stopped, frigging scary.driving
I worked for York trailers, Utd was part of the same group, most of the drawbars were sliding poles, awful things but good commission for me as we sold the parts....

The continental drawbars are close coupled, in a straight line the truck and trailer are about 3" apart, when turning a cam and gear move the trailer apart, opening the gap