Mmmm... I got a strange feeling after reading that explanation... I think I
feel smarter : )
> No flames in this message, Bruce. Only the facts, sir, just the facts.
> The difference in ride height on the GMC motorhome has a very distinct
> reason for it's existence. Appearance has absolutely NOTHING to do with
> it. And alignment is always performed AFTER ride height has been correctly
> set. So, camber, caster, and toe in/out, are not the reason, either.
> The remaining consideration after the before mentioned specs, staring
> you RIGHT IN THE EYE, WITHOUT BLINKING, is anti-dive. Weight transfer.
> Unloading the rear/rear bogies to the point where they unload with the
> pavement and skid the tires during moderate to heavy braking.
> That's it, pure and simple and uncomplicated. Vehicles with tandem
> rear tires are all subject to this. From 18 wheelers, dump trucks, and yes,
> GMC motorhomes.
> Heavily laden vehicles with high percentages of weight concentrated on
> the front axle are ESPECIALLY affected, particularly with front wheel
> drive.
> Sound familiar yet? Again, simple math applies here. A triangle, with
> level ground as the base (A). A 90° angle at the front spindle intersection
> (B), then back towards the rear of the coach until it terminates with the
> base (C). The difference in height, combined with the right angle at the
> front spindle makes the front end less likely to "nose dive" and unload the
> rear/rear tires.
> Jim Hupy
> Salem, Oregon
>
>
> > I posted this about a year ago. This is my updated thoughts on the rear
> > ride height specs.
> >
> > My thoughts on the GMC ride height.
> >
> > The GMC specified ride heights are set so the rear sits about an inch
> > lower than the front. This is my take on why this is so.
> >
> > I don't believe it has anything to do with getting more caster or the
> > “proper caster setting” The distance from the front wheel to the rear
> > ride-height slots is 214.5” An inch change in the rear height only
> changes
> > the front caster by 1/4 degree. This isn't up for debate, its simple
> > trigonomtric math.
> >
> > Caster recommendations are all over the place, but most agree more caster
> > the better up to about 4 degrees or so. So going from 2 degrees at level
> > ride height to 2.25 degrees at proper ride height isn’t going to
> magically
> > make the caster perfect any more than setting the caster to 2.25 degrees
> > at level ride height. What about the guy with 2.25 degrees at level, his
> > magically becomes perfect ride height at 2.5 degrees by lowering the
> rear?
> > What makes adding 1/4 degree of additional caster to any caster setting
> > suddenly make that caster setting perfect??
> >
> > My thoughts on the rear height specifications has to do with stability of
> > the rear bogie arms. When the rear is set to the recommended ride height,
> > the rear axles (if I am allowed to call them axles), sit about an inch
> > higher than the bogie pins. I'm thinking with the bogie pins sitting
> lower
> > than
> > the wheel axles, the bogie arms are more directionally stable, like
> laying
> > in a hammock. The bogie pins carry the rear weight of the coach. My
> senses
> > tell me that the rear suspension is more stable when the bogie pins are
> > below the wheel axles.
> >
> > When you raise the rear, the bogie pins become level or above the wheel
> > axles. Once the bogie pins are close to level or above the wheel axles,
> the
> > bogie arms (especially the front arm) become directionally unstable which
> > makes the rear of the coach squirrelly. The higher the bogie pins are
> above
> > the wheel axles, the more directionally unstable the bogie arms become
> (to
> > a certain point).
> >
> > If one was to mount the bogies lower on the frame (with the necessary
> > frame work), you could raise the rear of the coach while maintaining the
> > lower
> > bogie pin configuration and maintain the desired stability.
> >
> > Just my farmboy mechanic way of seeing things.
> >
> > Flame away if you must!
> >
> > --
> > Bruce Hislop
> > ON Canada
> > 77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
> >
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
> > My Staff says I never listen to them, or something like that
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