Home » Public Forums » GMCnet » Re: [GMCnet] New RV Buddies article
| Re: [GMCnet] New RV Buddies article [message #112730] |
Sun, 23 January 2011 09:59  |
Gary Casey
Messages: 448
Registered: September 2009
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Senior Member |
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Hardie,
I think you have the right general idea. I'll comment on your points below:
Previously posted: "With the new 6-wheel rear suspension
and disc brakes, you can now stop on a dime."
Hardie: Has anyone actually done any braking distance runs? 60-0 in how many
feet? And where are the two extra wheels mounted?
My comment: You must be confused about the "two extra wheels." No extra
wheels. I guess the 4-wheel rear suspension and the 2-wheel front suspension
make up the "6-wheel" suspension. "Stop on a dime?" I think the shorter
stopping distance that is usually quoted is a result of running out of pedal
force capability with the standard system. Once the rears lock, at about 0.6
G's the pedal force increases disproportionately and I assume it reaches a point
that the driver runs out of ability to push harder. My rough estimate is that
it might take 150% as much pedal force than "expected" to get all 6 to lock.
Even with the new system I doubt that the fronts will ever lock. There have
been stopping distance tests done, but I don't recall ever reading about what
the limit was: Is the stopping limited by pedal force? Which wheels lock
first? The standard system will lock the rears at about 06 G's, well below the
ultimate limit of about 0.9 G's. How close does the "new" system come to that
limit? I have no idea.
Previously posted: "The “Chuck Aulgur Rear Anti-Skid Kit” prevents the back
rear wheels from skidding and having
the rear of the RV move in front of you.
It also eliminates torque on the center bogie arms
which provides for more effective braking on
all four rear wheels. Translation: Your coach is safer
and you won’t end up with four bald spots on
your tires after a panic stop."
Hardie: Does this overstate the case?
My comment: Yes. The rear wheels skidding (locking) does NOT dramatically
reduce stability, since the middles still have plenty of downforce. It's not at
all like a 4-wheel vehicle where rear lockup dramatically reduces stability.
And of course, you don't end up with "four bald spots", only 2 :-).
Hardie: If the rear wheels cannot be locked up (isn't that what it means if
they do not skid?) has anything been improved?
My comment: Hopefully, they can still be locked up - after all, that's the
purpose of a braking system; to provide as much braking effort as the driver
commands. Yes, it has been improved - the "torque link" suspension lessens the
tendency for the rears to lock and better balances the braking between the
middles and rears. Definitely a good thing.
Hardie: Clearly this text describes the effect of some sort of ABS technology,
which I do not think it actually implements, does it?
My comment: You're right - as far as I know, a real anti-lock, or Adaptive
Braking System (ABS) has never been implented in our coaches.
Hardie: If one pair locks up then retarding force would be reduced, but if the
other pair would continue to roll that would reduce the tendency to skid. I
thought that was the behavior we have with the stock system?
My comment: You are exactly correct.
Hardie: Does it 'eliminate torque' as he writes, or just change the way the
reaction forces influence the chassis? Eliminating the torque from brake
reaction is of course impossible. Changing how it affects the chassis and the
wheels, maybe.
My comment: Again, exactly correct. The "torque" on the bogie pins has
nothing to do with braking. What it does is reduce (not eliminate) the lifting
effect from the fronts and the down load from the rears. During braking it
effective "lengthens" the swing arm, a very good thing.
Hardie: The new system may well be better, but it would be helpful if someone
actually quantified this.
Hardie: Certainly in the last 30 years a lot has been learned about suspension
action under braking and acceleration, anti-dive and anti-squat are common
considerations for geometry these days, and if anyone has stepped up to the
plate for our coaches it is Jim and Chuck.
My comment: Just a slight correction - I think all the things we talk about
today were known in 1973. The difference, I think, is in the priorities
attached to the several factors involved: Production cost, ride control, ease
of height control for campsite leveling, brake wear, and of course finally,
braking performance. It's my opinion that braking performance to a back seat to
some of the other factors. Today we have a different perspective and braking
performance would be higher in the rankings.
Hardie: I am not saying the system is an ineffective use of time, money, and
effort, just it seems the level of rhetoric about the advantages is escalating.
Numbers would help.
My comment: I agree completely.
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