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You know those simple wooden train sets for kids? The kind with wooden
tracks and wooden cars connected with magnets? If you pull a train up
one of the hills all the cars stay on the track. But when you let the
train slide down the hill and hit a curve, many times the cars behind
the engine jump the track.
Why? The momentum of the cars cannot compensate for the change in
direction. They want to continue going straight, but the hitch is
telling them to turn.
I have seen more trailer accidents and near accidents than I care to
remember, most of which were caused by the trailer getting out of the
window of control of the vehicle that was towing it - the vehicle didn't
weight enough or was too short to re-stabilize the trailer after it
started moving.
The lever of side to side motion is far greater than the lever of the
distance from the hitch to the rear wheels. Think of how many
jackknifed rigs you've seen.
I've driven rigs with short trucks (Ford Ranger) and long trucks (Ford
F-250 SuperCab). There is no comparison in trailer stability. When a
big side gust of wind comes up, the F250 sits still, the Ranger moves a
lot. Part of it is the weight of the F250, part is the wheelbase.
I believe that the most important safety factor is the quality of the
braking system in the trailer. Just my opinion.
Mike
> -----Original Message-----
> From: Frank Mechelhoff [SMTP:fmechelh@c-s-k.de]
> Sent: Friday, May 09, 1997 9:33 AM
> To: Mike Sofen (Excell); ridecamp@endurance.net
> Subject: RE: Trailer Woes/ Stability
>
> Mike Sofen (Excell) wrote:
>
> > While Joe's points are completely valid, the issue of bumper-pull
> > trailer stability/safety is a completely different subject.
> > Gooseneck
> > rigs are inherently stable, bumper pulls are inherently instable...
>
> Hi Mike, I saw some American cars here in Europe with hitches
> fixed
> on the bumper. I also would be very careful to haul a
> 2-ton-trailer
> with these devices. In Europe we pay some 100 $ to get a stable,
> permissioned hitch out of 3" steel connected a specified car
> frame.
> With a (what we called) "middlesized" offroad-car (i.e. a
> LandRover, Mitsubishi, Nissan Patrol or Pathfinder or Mercedes G)
> you get permission to haul up to 3,5 tons (depends on the car).
> We
> very seldom use bigger cars to haul.
>
> Maybe you car overheat in the mountains when it's too weak, but
> the
> stability of the trailer or hitch is very seldom cause for
> trouble.
> The speed limit we have to respect is about 80-100 km/h (-65
> mph).
>
> > -
> > tongue weight (the weight of the trailer that is applied to the rear
> > end
> > of the vehicle at the hitch) presses the rear of the vehicle down
> > and
> > lifts the front end. If enough weight presses down on the rear, the
> > front wheels start losing their grip on the road...
>
> With a proper hitch and trailer, this don't happen. Usually, there is
> a
> weight limit for the weight that pulls on the hitch (for example 75 or
> 100 kgs). This limit should be roughly kept, neither crossed nor
> decreased. If the trailer goes too light on the hitch, this is worse
> for
> stability of the rig than to heavy.
>
> As far as stability of the rig is concerned, a strong single rear axle
> with leaf suspension is a big advantage. "old-fashioned" offroad-cars
> have this kind of chassis usually.
>
> >
> > What's not correctable is the ratio that Joe refers to - the trailer
> >
> > length (from hitch to trailer wheels) versus the vehicle wheelbase.
> > A
> > short vehicle wheelbase relative to the trailer length allows the
> > trailer to 'out muscle' the vehicle, because it can act like a
> > lever.
> > The longer the vehicle wheelbase, with a bumper pull trailer, the
> > safer
> > the rig. It's just physics.
>
> Right, in priniple. But even with a short-wheelbase car you can haul a
> heavy trailer safely and with enough speed, when weight distribution
> of
> car and trailer are correct and rear-axle and hitch are strong enough.
> And of course, you need good maintained brakes, tires and stuff like
> that. I always pass motorhomes and camping rigs easily with my 25 year
> old trailer. Advantage is, the horse trailer is much heavier than
> other
> ones and therefore runs much more calmly.
>
> There is a second variable which is more important than wheelbase: the
> distance between rear-wheel and hitch. This distance should be as
> short
> as possible, because every movement of the car will transmitted to the
> trailer (and vice versa) the more, the bigger this distance is. THIS
> is
> the actual lever.
>
> regards
> FRANK
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