| Re: [GMCnet] Gary Bovee [message #115533] |
Fri, 18 February 2011 14:13  |
Gary Casey
Messages: 448
Registered: September 2009
Karma:
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Senior Member |
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Maybe a bit of clarification is in order. The standard system can certainly be
called "automatic leveling", but to call it an "active" system would be a
stretch. The leveling capability is far too slow to respond to any normal road
inputs unless they are present for a long time, like a minute. Things like
gusts and normal curves, etc are not present for long enough to allow a
response. I suppose a continuous crosswind or road camber might be the
exception. Most coaches that I've seen, including mine, have a working leveling
system. With regard to other comments, the aerodynamic drag will generally be
lower if the rear is slightly higher than the front. This is because the air
velocity under the coach, a non-streamlined area will be reduced. A reduced
turning radius with a higher rear end?? I can't come up with a logical
explanation for that. As for "push" from other vehicles, the same comment as
above applies - for most vehicles, adverse response to a crosswind or gust is
reduced with a positive "rake." (front lower than the back). Sorry, but I just
can't make any of that make sense. Others have stated that lowering the rear
will increase the castor angle of the front wheels, but it would take a lot of
height change to make a difference. For a short-wheelbase coach a 1 inch change
in height will change the castor angle by only 0.4 degrees, Is that enough to
make a difference? I don't think so.
Gary Casey
'73 23'
However, I think it is important to expand on what JimK said. The GMC was
designed to have an ACTIVE rear air suspension. That means that as driving
conditions change, the system stays level without the driver having to adjust
the air system. I've never actually driven a GMC that had a working active
system, but that was the intent 30+ years ago. The wireless system is a STATIC
air system, meaning it will not automatically adust for shifts in weight,
crosswinds?, or sweeping turns to relevel the coach automatically.
I'd imagine that a working active system is a real treat to drive, but I wonder
how often it actually makes a difference. I find that I raise and lower my bags
depending on what kind of driving I'm doing. The bags go up when I'm doing local
or windy road driving to cantor the coach forward and improve the turning radius
(and yes it does help as I've proved in my driveway. I can't k-turn around at
the top with the bags at the "correct" height, but bags most of the way up and I
can make it around in a few k-turns), they go down when I'm on the highway and
tracking a straight line as a low back end relieves a large amount of steering
movement and push from other vehicles.
I've often thought the "correct" height was a happy medium GM engineers made up
because they were afraid people would not understand the advantages of raising
and lowering the rear end manually. Of course, if I'm right I always kind of
wondered why they just didn't add a "town" and "highway" setting to the
controls.
--
Thanks,
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