"Dan G" wrote in message
ups.com...
On Oct 16, 4:46 am, Eric Greenwell wrote:
Dan G wrote:
On Oct 12, 3:57 pm, "01-- Zero One" wrote:
So to say that "Towing is simple. Follow these rules, and your rig
will
be stable in all conditions and not need stabiliser hitch." is in my
experience a gross oversimplification.

Think we'll have to agree to disagree - but I'd like to know of
examples where these guidelines were met, but the rig was still
unstable.

My '89 Dodge Caravan and ASH 26 E trailer meets all your rules and is
stable at 60 mph. At 70 mph, it's starting to quiver, and I've never
dared go faster. So, is the rig "stable" or "unstable"?

What's the speed limit for a towing vehicle in the US? In the UK it's
60, so your rig would be "stable", though of course it would be
preferable to have a higher safety margin in the event of cross-winds
etc.

Let me try and explain this another way:

*if your trailer is trying to lift the rear of your tow vehicle when
hitched, it will have reduced stability than if it's pressing down.

*If your trailer has a heavy mass at the far end, it will have reduced
stability compared to if it had that mass in low down over the axle.

*If your trailer has underinflated tyres, it will have reduced
stability compared to if it had correctly inflated tyres (and they
might go "bang", too)

*If your trailer weighs more than your towcar, it will have reduced
stability compared to if the towcar was heavier than the trailer.

I hope that's clearer. The Bath University guidelines were also
developed using average Euro cars - I would not expect an tall,
unstable American SUV or pickup with ancient suspension to be
particularly stable in many circumstances, even when not towing. More
recent models with relatively modern suspension should, of course,
fare better.


Dan


On our USA Interstate Highways, speeds tend to average 75mph. Speed limits
are lower, but not usually enforced until above 80 mph or more. Even the
Semi trailers (18 Wheel trucks) are doing 70-75 or more. If you drive 65,
you are continually passed by these trucks, each producing "bow waves" that
induce more sway. So stability up to 80 mph is highly desirable.

The above noted points all contribute to stability, but I tried them all,
and then some, one at a time, and in combinations. There was no dramatic
improvement until I changed vehicles. The Tahoe and the Avalanche weigh
about the same. The Avalanche has a longer wheelbase. They both have live
rear axles and use the same tires.

IMO the best way to improve a tow vehichle is with "helper springs" to
stiffen the rear, and if needed, the front, suspension. These are easy to
add, relatively inexpensive, and can improve the handling even without the
trailer. Of course, this is after bringing the suspension up to "specs"
first. Shortening the distance between the hitch and the rear axle, where
possible, helps too. Two inches can make a difference.


Hartley Falbaum
"KF" USA