Home » Public Forums » GMCnet » [GMCnet] Pneumatics question relating to the Quadra-bag
| [GMCnet] Pneumatics question relating to the Quadra-bag [message #105533] |
Tue, 09 November 2010 11:04  |
GMC_LES
Messages: 569
Registered: October 2009
Location: Montreal
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I woke up this morning with an idea in my head and it's been bugging me ever
since!
I've read several comments that indicate that the 4 bag rear suspension
upgrades (Harrison & Applied) give a slightly harsher ride than the original
single bag system. I may be wrong, but I think that the harsher ride may to be
due to the smaller internal volume of the new 4-bag components as compared to
the original single bag system.
My idea is this:
Why can't we add a small "ballast air" tank on each side, plumbed into the
tubing between the ride height valve and the bags so that it adds air volume to
the bags? This would increase the volume of air that can be compressed as
the suspension encounters bumps, resulting in a softer ride. It is the pressure
of the air in the bag that determines ride height. The volume of the compressed
air in the bag is one of the factors that determines the "spring rate" or ride
firmness.
The only negatives I can see with such a set-up would be:
- Compressor will run longer to raise coach due to the extra air needed to fill
the small ballast tanks.
- Coach handling may be affected slightly.
- Complexity of system is increased, more places for leaks to develop.
Comments anyone?
Thanks,
Les Burt
Montreal
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1975 Eleganza 26ft
A work in Progress
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| Re: [GMCnet] Pneumatics question relating to the Quadra-bag [message #105534 is a reply to message #105533] |
Tue, 09 November 2010 11:12  |
midlf
Messages: 2212
Registered: July 2007
Location: SE Wisc. (Palmyra)
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| Les Burt wrote on Tue, 09 November 2010 11:04 |
My idea is this:
Why can't we add a small "ballast air" tank on each side, plumbed into the
tubing between the ride height valve and the bags so that it adds air volume to
the bags?
<snip>
The only negatives I can see with such a set-up would be:
Les Burt
|
I suspect the small diameter tubing, as compared to the diameter of the bag, will limit any significant effect of this type of ride softing setup.
Steve Southworth
1974 Glacier TZE064V100150 (for workin on)
1975 Transmode TZE365V100394 (parts & spares)
Palmyra WI
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| Re: [GMCnet] Pneumatics question relating to the Quadra-bag [message #105536 is a reply to message #105534] |
Tue, 09 November 2010 11:50 |
GMC_LES
Messages: 569
Registered: October 2009
Location: Montreal
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I'm curious to know if my idea is even theoretically correct? Small technical details such as the tubing restriction could be overcome by increasing to 3/8" or 1/2" between the ballast tank & bags. The remaining tubing would work as is.
Les Burt
Sent from my iPhone
On 2010-11-09, at 12:12 PM, Steve Southworth <midlf@centurytel.net> wrote:
>
>
> Les Burt wrote on Tue, 09 November 2010 11:04
>> My idea is this:
>> Why can't we add a small "ballast air" tank on each side, plumbed into the
>> tubing between the ride height valve and the bags so that it adds air volume to
>> the bags?
>>
>> <snip>
>>
>>
>> The only negatives I can see with such a set-up would be:
>> Les Burt
>
>
> I suspect the small diameter tubing, as compared to the diameter of the bag, will limit any significant effect of this type of ride softing setup.
> --
> Steve Southworth
> 1974 Glacier TZE064V100150
> Palmyra WI
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1975 Eleganza 26ft
A work in Progress
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| Re: [GMCnet] Pneumatics question relating to the Quadra-bag [message #105537 is a reply to message #105536] |
Tue, 09 November 2010 12:01 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
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Burt,
I haven't studied the question and determined the relative figures for the 3
equipments, but logically, the difference in effective spring rate comes
from two factors: 1. Different "piston" areas for the air pressure to
operate upon. 2. Different lever arms from the suspension arm pin to the
effective center of force for the bag. From past statements of JimK, I
believe both are factors for the Quad Bag, with #2. even more important when
the available "bag extenders" are used.
In neither case is the volume of air a significant factor, IMHO. You might
be able to get an idea of how important is by attaching a pressure gauge
directly to a bag with plumbing to allow you to watch the gauge while
driving. If the pressure varies wildly over bumps, increased volume might
help; if it's fairly steady, probably not. I wouldn't put a lot of time or
money into a mod before such a test.
JMHO,
Ken H.
On Tue, Nov 9, 2010 at 12:50 PM, Les Burt <burtco99@yahoo.com> wrote:
> I'm curious to know if my idea is even theoretically correct? Small
> technical details such as the tubing restriction could be overcome by
> increasing to 3/8" or 1/2" between the ballast tank & bags. The remaining
> tubing would work as is.
>
>
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Ken Henderson
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www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Pneumatics question relating to the Quadra-bag [message #105541 is a reply to message #105537] |
Tue, 09 November 2010 13:46 |
GMC_LES
Messages: 569
Registered: October 2009
Location: Montreal
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Ken,
I was just thinking about monitoring a pair of gauges to see exactly how much fluctuation there is in bag pressures while negotiating rough roads.
Hopefully there are a few members here that have installed gauges and can provide some input.
From what Jim Maher wrote, my idea appears to have some merit, so when my coach is back on the road, I'll tinker with the idea unless someone else has already done so by then :)
Les Burt
Sent from my iPhone
On 2010-11-09, at 1:01 PM, Ken Henderson <hend4800@bellsouth.net> wrote:
> Burt,
>
> I haven't studied the question and determined the relative figures for the 3
> equipments, but logically, the difference in effective spring rate comes
> from two factors: 1. Different "piston" areas for the air pressure to
> operate upon. 2. Different lever arms from the suspension arm pin to the
> effective center of force for the bag. From past statements of JimK, I
> believe both are factors for the Quad Bag, with #2. even more important when
> the available "bag extenders" are used.
>
> In neither case is the volume of air a significant factor, IMHO. You might
> be able to get an idea of how important is by attaching a pressure gauge
> directly to a bag with plumbing to allow you to watch the gauge while
> driving. If the pressure varies wildly over bumps, increased volume might
> help; if it's fairly steady, probably not. I wouldn't put a lot of time or
> money into a mod before such a test.
>
> JMHO,
>
> Ken H.
>
>
> On Tue, Nov 9, 2010 at 12:50 PM, Les Burt <burtco99@yahoo.com> wrote:
>
>> I'm curious to know if my idea is even theoretically correct? Small
>> technical details such as the tubing restriction could be overcome by
>> increasing to 3/8" or 1/2" between the ballast tank & bags. The remaining
>> tubing would work as is.
>>
>>
> _______________________________________________
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Les Burt
Montreal
1975 Eleganza 26ft
A work in Progress
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| Re: [GMCnet] Pneumatics question relating to the Quadra-bag [message #105545 is a reply to message #105533] |
Tue, 09 November 2010 14:29 |
Marsh Wilkes
Messages: 155
Registered: January 2004
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Hi Les,
Your idea is sound.
For it to work dynamically (over bumps in the road) the connection to the
tank would have to be quite large. You can take it a step further and make
an adjustable spring rate by using a bladder tank and adding or removing
uncompressible liquid on the other side of the bladder. There are also
relatively simple ways of turning sway bars on and off, for camp leveling or
a boulevard float ride with the reduced spring rate. The question is what's
your goal? The possibilities are wide open, but even I (you would have to
know me) don't think it would be worth the trouble. However if you have the
time money talent and interest why not...
Marsh Wilkes
Perry Florida
----- Original Message -----
From: "Les Burt" <burtco99@yahoo.com>
To: <gmclist@temp.gmcnet.org>
Sent: Tuesday, November 09, 2010 12:04 PM
Subject: [GMCnet] Pneumatics question relating to the Quadra-bag
I woke up this morning with an idea in my head and it's been bugging me ever
since!
I've read several comments that indicate that the 4 bag rear suspension
upgrades (Harrison & Applied) give a slightly harsher ride than the original
single bag system. I may be wrong, but I think that the harsher ride may to
be
due to the smaller internal volume of the new 4-bag components as compared
to
the original single bag system.
My idea is this:
Why can't we add a small "ballast air" tank on each side, plumbed into the
tubing between the ride height valve and the bags so that it adds air volume
to
the bags? This would increase the volume of air that can be compressed as
the suspension encounters bumps, resulting in a softer ride. It is the
pressure
of the air in the bag that determines ride height. The volume of the
compressed
air in the bag is one of the factors that determines the "spring rate" or
ride
firmness.
The only negatives I can see with such a set-up would be:
- Compressor will run longer to raise coach due to the extra air needed to
fill
the small ballast tanks.
- Coach handling may be affected slightly.
- Complexity of system is increased, more places for leaks to develop.
Comments anyone?
Thanks,
Les Burt
Montreal
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| Re: [GMCnet] Pneumatics question relating to the Quadra-bag [message #105548 is a reply to message #105545] |
Tue, 09 November 2010 15:17 |
 |
mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
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| Marsh Wilkes wrote on Tue, 09 November 2010 12:29 |
... There are also
relatively simple ways of turning sway bars on and off, for camp leveling or
a boulevard float ride with the reduced spring rate. ...
|
Due to the use of sway bars with the production version of the "Chuck Aulgur Rear Anti-Skid Kit." This might be interesting.
Please explain.
Thanks.
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
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| Re: [GMCnet] Pneumatics question relating to the Quadra-bag [message #105549 is a reply to message #105533] |
Tue, 09 November 2010 15:48 |
Steven Ferguson
Messages: 3447
Registered: May 2006
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Les,
I think you should try one before you decide it might need changes. I
sincerely doubt that you could tell the difference in ride quality.
On Tue, Nov 9, 2010 at 10:04 AM, Les Burt <burtco99@yahoo.com> wrote:
> I woke up this morning with an idea in my head and it's been bugging me
> ever
> since!
>
> I've read several comments that indicate that the 4 bag rear suspension
> upgrades (Harrison & Applied) give a slightly harsher ride than the
> original
> single bag system. I may be wrong, but I think that the harsher ride may to
> be
> due to the smaller internal volume of the new 4-bag components as compared
> to
> the original single bag system.
>
> My idea is this:
> Why can't we add a small "ballast air" tank on each side, plumbed into the
> tubing between the ride height valve and the bags so that it adds air
> volume to
> the bags? This would increase the volume of air that can be compressed as
> the suspension encounters bumps, resulting in a softer ride. It is the
> pressure
> of the air in the bag that determines ride height. The volume of the
> compressed
> air in the bag is one of the factors that determines the "spring rate" or
> ride
> firmness.
>
> The only negatives I can see with such a set-up would be:
> - Compressor will run longer to raise coach due to the extra air needed to
> fill
> the small ballast tanks.
> - Coach handling may be affected slightly.
> - Complexity of system is increased, more places for leaks to develop.
>
> Comments anyone?
> Thanks,
> Les Burt
> Montreal
>
>
>
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Steve Ferguson
Sierra Vista, AZ
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| Re: [GMCnet] Pneumatics question relating to the Quadra-bag [message #105550 is a reply to message #105548] |
Tue, 09 November 2010 16:01 |
GMC_LES
Messages: 569
Registered: October 2009
Location: Montreal
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I didn't have any specific goal in mind other than seeing a possible way to soften up the ride. This idea might become another one of those "because I can" mods.
Since you brought up the swaybar disconnect idea, please share a little more detail with us.
Les Burt
Sent from my iPhone
On 2010-11-09, at 4:17 PM, Mike Miller <m000035@gmail.com> wrote:
>
>
> Marsh Wilkes wrote on Tue, 09 November 2010 12:29
>> ... There are also
>> relatively simple ways of turning sway bars on and off, for camp leveling or
>> a boulevard float ride with the reduced spring rate. ...
>
>
> Due to the use of sway bars with the production version of the "Chuck Aulgur Rear Anti-Skid Kit." This might be interesting.
>
> Please explain.
>
> Thanks.
> --
> Mike Miller
>
> #01 - `73 26' X Painted D. "The Spare"
> #02 - `78 23' Birchaven Rear Bath "The User"
> #03 - `77 23' Birchaven Side Bath "The Keeper"
> Hillsboro, OR
> _______________________________________________
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Les Burt
Montreal
1975 Eleganza 26ft
A work in Progress
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| Re: [GMCnet] Pneumatics question relating to the Quadra-bag [message #105551 is a reply to message #105549] |
Tue, 09 November 2010 16:09 |
GMC_LES
Messages: 569
Registered: October 2009
Location: Montreal
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Steve,
I agree 100% with you. I am planning on buying both a quadrabag system & a reaction arm system once the rest of my chassis is well advanced.
I expect I'll be quite happy with these 2 improvements as they are, right out of the box but, as many of us enjoy tinkering with new ideas, this is one I might pursue.
Les Burt
Sent from my iPhone
On 2010-11-09, at 4:48 PM, Steven Ferguson <botiemad11@gmail.com> wrote:
> Les,
> I think you should try one before you decide it might need changes. I
> sincerely doubt that you could tell the difference in ride quality.
>
> On Tue, Nov 9, 2010 at 10:04 AM, Les Burt <burtco99@yahoo.com> wrote:
>
>> I woke up this morning with an idea in my head and it's been bugging me
>> ever
>> since!
>>
>> I've read several comments that indicate that the 4 bag rear suspension
>> upgrades (Harrison & Applied) give a slightly harsher ride than the
>> original
>> single bag system. I may be wrong, but I think that the harsher ride may to
>> be
>> due to the smaller internal volume of the new 4-bag components as compared
>> to
>> the original single bag system.
>>
>> My idea is this:
>> Why can't we add a small "ballast air" tank on each side, plumbed into the
>> tubing between the ride height valve and the bags so that it adds air
>> volume to
>> the bags? This would increase the volume of air that can be compressed as
>> the suspension encounters bumps, resulting in a softer ride. It is the
>> pressure
>> of the air in the bag that determines ride height. The volume of the
>> compressed
>> air in the bag is one of the factors that determines the "spring rate" or
>> ride
>> firmness.
>>
>> The only negatives I can see with such a set-up would be:
>> - Compressor will run longer to raise coach due to the extra air needed to
>> fill
>> the small ballast tanks.
>> - Coach handling may be affected slightly.
>> - Complexity of system is increased, more places for leaks to develop.
>>
>> Comments anyone?
>> Thanks,
>> Les Burt
>> Montreal
>>
>>
>>
>> _______________________________________________
>> GMCnet mailing list
>> List Information and Subscription Options:
>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>>
>
>
>
> --
> Steve Ferguson
> Sierra Vista, AZ
> _______________________________________________
> GMCnet mailing list
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_______________________________________________
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Les Burt
Montreal
1975 Eleganza 26ft
A work in Progress
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| Re: [GMCnet] Pneumatics question relating to the Quadra-bag [message #105552 is a reply to message #105533] |
Tue, 09 November 2010 16:27 |
LYNN L
Messages: 140
Registered: March 2005
Location: Pearland TX.
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I have one of Jim"s quad systems and do not feel that the ride is harsher. If anything, it has improved the handling of my coach.It has cut down dramatically on the rear end wallow when struck by a strong sidewind and keeps the backend from rocking as bad when sudden inputs are made to the steering at higher speed. I go around sharp curves with renewed confidence. With the tremendous upgrade in handling it has been the best change I have made. Now I need to figure out how to put enough money aside for the Huebler front end modification.
Lynn L
76 Eleganza Cad.500
Pearland TX.
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| Re: [GMCnet] Pneumatics question relating to the Quadra-bag [message #105571 is a reply to message #105533] |
Tue, 09 November 2010 18:36 |
GMC_LES
Messages: 569
Registered: October 2009
Location: Montreal
Karma: 0
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I went back and re-read a few of the comments on ride harshness and found that most were referring to the Harrison 4 bag system. Sorry if I have mis-lead anyone into believing that the JimK Quadrabag system was also a harsh ride. Most comments I could find were to the contrary.
I am still curious to know if my idea might affect the ride and handling.
Les Burt
On 2010-11-09, at 12:04 PM, Les Burt <burtco99@yahoo.com> wrote:
> I woke up this morning with an idea in my head and it's been bugging me ever
> since!
>
> I've read several comments that indicate that the 4 bag rear suspension
> upgrades (Harrison & Applied) give a slightly harsher ride than the original
> single bag system. I may be wrong, but I think that the harsher ride may to be
> due to the smaller internal volume of the new 4-bag components as compared to
> the original single bag system.
>
> My idea is this:
> Why can't we add a small "ballast air" tank on each side, plumbed into the
> tubing between the ride height valve and the bags so that it adds air volume to
> the bags? This would increase the volume of air that can be compressed as
> the suspension encounters bumps, resulting in a softer ride. It is the pressure
> of the air in the bag that determines ride height. The volume of the compressed
> air in the bag is one of the factors that determines the "spring rate" or ride
> firmness.
>
> The only negatives I can see with such a set-up would be:
> - Compressor will run longer to raise coach due to the extra air needed to fill
> the small ballast tanks.
> - Coach handling may be affected slightly.
> - Complexity of system is increased, more places for leaks to develop.
>
> Comments anyone?
> Thanks,
> Les Burt
> Montreal
>
>
>
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
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List Information and Subscription Options:
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Les Burt
Montreal
1975 Eleganza 26ft
A work in Progress
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| Re: [GMCnet] Pneumatics question relating to the Quadra-bag [message #105592 is a reply to message #105533] |
Tue, 09 November 2010 22:32 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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On the Q Bag, it rides like the standard.
Only the Harrison is harsh.
We rin with80-85psi, Harrison 90-100 psi.
Apparently, you have not ridden in the back of a Q Bag.
Do not brand the Q Bag with the other.
Our bags are larger also.
We will be introducing very soon a copy of the SILVER MOTOR COACH rear
air bag system from 1991. It will be called the MONO Bag.
On Tue, Nov 9, 2010 at 9:04 AM, Les Burt <burtco99@yahoo.com> wrote:
> I woke up this morning with an idea in my head and it's been bugging me ever
> since!
>
> I've read several comments that indicate that the 4 bag rear suspension
> upgrades (Harrison & Applied) give a slightly harsher ride than the original
> single bag system. I may be wrong, but I think that the harsher ride may to be
> due to the smaller internal volume of the new 4-bag components as compared to
> the original single bag system.
>
> My idea is this:
> Why can't we add a small "ballast air" tank on each side, plumbed into the
> tubing between the ride height valve and the bags so that it adds air volume to
> the bags? This would increase the volume of air that can be compressed as
> the suspension encounters bumps, resulting in a softer ride. It is the pressure
> of the air in the bag that determines ride height. The volume of the compressed
> air in the bag is one of the factors that determines the "spring rate" or ride
> firmness.
>
> The only negatives I can see with such a set-up would be:
> - Compressor will run longer to raise coach due to the extra air needed to fill
> the small ballast tanks.
> - Coach handling may be affected slightly.
> - Complexity of system is increased, more places for leaks to develop.
>
> Comments anyone?
> Thanks,
> Les Burt
> Montreal
>
>
>
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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| Re: [GMCnet] Pneumatics question relating to the Quadra-bag [message #105594 is a reply to message #105592] |
Tue, 09 November 2010 22:37 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Senior Member |
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Les,
The additional volume will not only give a softer ride, byt cause a
change in the spring rate that will negate the intender design of
giving the rear better control.
On Tue, Nov 9, 2010 at 8:32 PM, Jim Kanomata <jimkanomata@gmail.com> wrote:
> On the Q Bag, it rides like the standard.
> Only the Harrison is harsh.
> We rin with80-85psi, Harrison 90-100 psi.
> Apparently, you have not ridden in the back of a Q Bag.
> Do not brand the Q Bag with the other.
> Our bags are larger also.
> We will be introducing very soon a copy of the SILVER MOTOR COACH rear
> air bag system from 1991. It will be called the MONO Bag.
>
> On Tue, Nov 9, 2010 at 9:04 AM, Les Burt <burtco99@yahoo.com> wrote:
>> I woke up this morning with an idea in my head and it's been bugging me ever
>> since!
>>
>> I've read several comments that indicate that the 4 bag rear suspension
>> upgrades (Harrison & Applied) give a slightly harsher ride than the original
>> single bag system. I may be wrong, but I think that the harsher ride may to be
>> due to the smaller internal volume of the new 4-bag components as compared to
>> the original single bag system.
>>
>> My idea is this:
>> Why can't we add a small "ballast air" tank on each side, plumbed into the
>> tubing between the ride height valve and the bags so that it adds air volume to
>> the bags? This would increase the volume of air that can be compressed as
>> the suspension encounters bumps, resulting in a softer ride. It is the pressure
>> of the air in the bag that determines ride height. The volume of the compressed
>> air in the bag is one of the factors that determines the "spring rate" or ride
>> firmness.
>>
>> The only negatives I can see with such a set-up would be:
>> - Compressor will run longer to raise coach due to the extra air needed to fill
>> the small ballast tanks.
>> - Coach handling may be affected slightly.
>> - Complexity of system is increased, more places for leaks to develop.
>>
>> Comments anyone?
>> Thanks,
>> Les Burt
>> Montreal
>>
>>
>>
>> _______________________________________________
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>
>
>
> --
> Jim Kanomata
> Applied/GMC, Fremont,CA
> jimk@appliedairfilters.com
> http://www.appliedgmc.com
> 1-800-752-7502
>
--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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| Re: [GMCnet] Pneumatics question relating to the Quadra-bag [message #105597 is a reply to message #105533] |
Wed, 10 November 2010 03:04 |
George Beckman
Messages: 1085
Registered: October 2008
Location: Colfax, CA
Karma: 11
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Senior Member |
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| Les Burt wrote on Tue, 09 November 2010 09:04 |
I've read several comments that indicate that the 4 bag rear suspension
upgrades (Harrison & Applied) give a slightly harsher ride than the original
single bag system.
Thanks,
Les Burt
Montreal
|
There is an old article written near the beginning of the GMC Motorhome. It involved a test, comparing a GMC with a "lesser motorhome". They drove each coach over rail road ties. They said the GMC "stepped over" the ties while the traditional coach bounced. I assumed that this was because the actual bag, in the original design, can move front to rear. As lead wheel goes down off the tie, pressure is reduced and the second bogie can flex over it easily. It would appear the the Quad Bag, with the divider in the middle, reduces the bags give and take effect.
I could be all wet.
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George
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| Re: [GMCnet] Pneumatics question relating to the Quadra-bag [message #105606 is a reply to message #105533] |
Wed, 10 November 2010 07:31 |
Gary Casey
Messages: 448
Registered: September 2009
Karma: 0
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Senior Member |
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Les,
You are entirely correct in your thinking. I haven't referenced all the
comments, but here are mine:
First you have to clarify the term "harshness". That word implies an irritating
impulse or similar effect. The vertical movement of the wheels transmit force
to the body through both the springs and the shock "transmitters." The term
"shock" implies a rapid movement, like an impact, and the shock absorber does
little to absorb it - mostly it transmits it to the body. The spring,
regardless of type, does little or nothing to transmit that type of motion to
the body. The reason is that a change in spring force requires movement and a
rapid movement of the wheel is almost by definition very small in amplitude
(unless it was caused by a curb or chuckhole!). Take the shocks off and drive a
vehicle and the harshness will go away - of course only to be replaced by
undamped body motion. So the shock "absorber" should be simply called a
"damper." I digress.
The ride quality that can be changed by changing spring rate is the
low-frequency body motion due to road undulations and cornering. A too-stiff
spring will create what I call a "springy" ride. Lots of oscillations, bounces
etc. A too-soft spring will result in lots of body lean and sway as well as
excessive movement up and down. To damp the vertical body motion a stiffer
spring needs a stiffer shock. Are the springs in the Quadrabag and other
replacements stiffer than the original? Just by looking I would think so, and
that is probably somewhat desirable - when I drive mine with the originals I
conclude that the rear suspension is softer than what might be optimum. To be
sure, there is no correct answer - spring rate is a compromise and what is good
for one person might be bad for another. You said your truck rode poorly when
empty and well when loaded. This implies that the spring rate is too high when
empty - what I would call a "springy" ride.
What determines the spring rate for an air spring? The rate (stiffness) as it
relates to ride is a measure of what change in vertical movement is caused by a
given percentage in weight change of the body. Note I said "percentage" change
not just weight - that's the difference between a steel spring and an air
spring, and that's a entirely different discussion. The rate goes up in direct
proportion the effective area of the "piston", which is not exactly the diameter
of the piston itself. It goes up in direct proportion to the length of the
lever arm - the distance from the pivot to the air bag. AND - this is important
- it goes DOWN in direct proportion to the VOLUME of air in the bag. The
pressure in the spring has no effect on rate. So yes indeed, you can make the
spring softer by adding an external volume. But the air bag would have to be
well connected by a large diameter tube so that air can be exchanged rapidly.
What diameter? I would guess a half-inch tube would be okay, but a 1/4
diameter would not. You need the pressure to essentially equalize during normal
body movement - not during rapid, small displacement wheel movement. Of course,
the two types of movement blend, so again, it's another compromise. When I look
at any of the aftermarket springs it appears that they have a relatively smaller
internal volume than the original, so I suspect the ride will be "stiffer" and
somewhat less damped than on the original springs. I have no data to support
that observation.
And Jim thought his dissertation was too long....
Gary Casey
On 2010-11-09, at 12:04 PM, Les Burt <burtco99@yahoo.com> wrote:
> I woke up this morning with an idea in my head and it's been bugging me ever
> since!
>
> I've read several comments that indicate that the 4 bag rear suspension
> upgrades (Harrison & Applied) give a slightly harsher ride than the original
> single bag system. I may be wrong, but I think that the harsher ride may to
be
> due to the smaller internal volume of the new 4-bag components as compared to
> the original single bag system.
>
> My idea is this:
> Why can't we add a small "ballast air" tank on each side, plumbed into the
> tubing between the ride height valve and the bags so that it adds air volume
>to
> the bags? This would increase the volume of air that can be compressed as
> the suspension encounters bumps, resulting in a softer ride. It is the
>pressure
> of the air in the bag that determines ride height. The volume of the
>compressed
> air in the bag is one of the factors that determines the "spring rate" or
ride
> firmness.
> Comments anyone?
> Thanks,
> Les Burt
And a reply from Jim:
From: Jim Maher <hasbeen24@msn.com>
Les, My other ride is a 2006 Kodiac with a Monroe Toter body. It has a Link Air
Ride System which is what I had speced out before purchase figuring I would get
a softer ride when not towing the 32' Alpenlite fifth wheel which has a 14K
GVWR. Not the case. The truck was meant to have weight on it and it is very
comfortable when loaded. I complained to Link Systems and their first fix was to
send me larger air springs to soften the ride. This helped some. After further
contact I find that they have a Ride Enhancement Kit. This kit uses 2 additional
ping tanks plumbed to the bags with larger tubing and other extra valves and
stuff. Price was prohibitive to me so I now live with the harsh ride. The point
here being both you and Steve are correct in your thoughts. Sorry for the long
disertation, Jim
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| Re: [GMCnet] Pneumatics question relating to the Quadra-b [message #105621 is a reply to message #105533] |
Wed, 10 November 2010 11:13 |
Gary Casey
Messages: 448
Registered: September 2009
Karma: 0
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Senior Member |
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I agree with Jim, but the statements in his two posts below are a little
contradictory. Yes, if you add volume the spring rate will go down, but will
that "negate the intended design (philosphy?)of giving better control"? If the
design intent was to give better control, the only way it can do that is by
increasing the spring rate. After all, that's all the spring can do. And then
the second post says the Q-bag "rides like the standard", which says the spring
rate did NOT increase. Which is it? I suspect, although no data has been
presented to substantiate it, that the Q-bag has a higher rate, which improves
handling, but not so high as to instigate complaints of a rough ride. I gather
that users of the "Harrison" system complain about the stiff ride, but I don't
know. The higher pressure required in the Harrison unit is an indication that
the piston has a smaller area, and does not indicate a higher spring rate.
Without actual numbers it remains speculation and is open to disagreement.
Gary casey
Les,
The additional volume will not only give a softer ride, byt cause a
change in the spring rate that will negate the intender design of
giving the rear better control.
On Tue, Nov 9, 2010 at 8:32 PM, Jim Kanomata <jimkanomata@gmail.com> wrote:
> On the Q Bag, it rides like the standard.
> Only the Harrison is harsh.
> We rin with80-85psi, Harrison 90-100 psi.
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| Re: [GMCnet] Pneumatics question relating to the Quadra-bag [message #105622 is a reply to message #105548] |
Wed, 10 November 2010 11:20 |
Marsh Wilkes
Messages: 155
Registered: January 2004
Karma: -3
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Senior Member |
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Hi Mike,
In 1974 I had a Gulf service station, I Built up a first generation
econoline van with large tires, incredible shocks, very heavy sway bars
front and rear, I later put a Buick 350 in it...
That's when I came up with the idea of variable spring rate air suspension
and a means to turn off the sway bars(never built them). The sway bars were
so stiff that you could hang a wheel off of a curb without touching the
pavement below, but the van handled like a go cart! On a test run I had a
friend following me in my very well setup 1970 GTO, upon returning I asked
why he dropped so far back on the curves (although the car would easily do
it) he was afraid to take curves at the speed I was doing them, even in the
GTO! I had another friend that was going to show me up one night with his
914 so he headed for the same curvy road, but the 914 just didn't have
enough power to hit speeds above the GTO's cornering ability.
Getting to your question: The key word here is RELATIVELY simple. Compared
to modifying the air suspension it would be very simple. What I am
presenting here is a concept and one possible way of executing it, without
necessarily addressing all the subtleties. There may be other better ways, I
don't have time to explore them now. The idea is to cut the sway bar
(between the frame rails) into 2 pieces that can move independently,
effectively turning the sway bar off. This could be done by sleeving the
sway bar with a snug fitting larger tube that spans the cut in the sway bar,
this tubing is solidly welded to the sway bar on one side of the GMC. The
sway bar on the other side of the GMC has a separate sleeve tube welded to
it also. The two sleeves are situated to abut each other, at the abutment
point each sleeve has a lever arm welded to it. One arm has a hole in it
that serves as a striker plate, the other arm has a tapered latch pin that
is driven by a small linear actuator. When the latch pin is engaged the sway
bar acts like any standard sway bar. When the latch pin is withdrawn, the
two sides of the sway bar can rotate independently, effectively turning off
the sway bar just like it isn't there! I believe the geometry is such that
there would be no effect on the Reaction Arm Braking System. Since the sway
bars are used with the Breaking System, WHICH IS THE GREATEST GMC
IMPROVEMENT, and there are some complaints about campsite leveling with 2
sway bars Jim and Chuck may want to look into this.
Marsh Wilkes
Perry Fl
----- Original Message -----
From: "Mike Miller" <m000035@gmail.com>
To: <gmclist@temp.gmcnet.org>
Sent: Tuesday, November 09, 2010 4:17 PM
Subject: Re: [GMCnet] Pneumatics question relating to the Quadra-bag
>
>
> Marsh Wilkes wrote on Tue, 09 November 2010 12:29
>> ... There are also
>> relatively simple ways of turning sway bars on and off, for camp leveling
>> or
>> a boulevard float ride with the reduced spring rate. ...
>
>
> Due to the use of sway bars with the production version of the "Chuck
> Aulgur Rear Anti-Skid Kit." This might be interesting.
>
> Please explain.
>
> Thanks.
> --
> Mike Miller
>
> #01 - `73 26' X Painted D. "The Spare"
> #02 - `78 23' Birchaven Rear Bath "The User"
> #03 - `77 23' Birchaven Side Bath "The Keeper"
> Hillsboro, OR
> _______________________________________________
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> List Information and Subscription Options:
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| Re: [GMCnet] Pneumatics question relating to the Quadra-b [message #105623 is a reply to message #105621] |
Wed, 10 November 2010 11:24 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
|
Senior Member |
|
|
Just what is meant by "better control"? Steering accuracy, tires in more
intimate contact with the road surface under all conditions like
acceleration, cornering, stopping, reaction to raised bumps in the pavement
surface, or holes below the surface? Or is it some arbitrary impression like
it "just feels better" or more closely resembles one's opinion of what is
good or right? I am not critisizing any comments offered here but rather am
curious as to what is being described. We can all learn from exact
descriptions of the forces at work here.
Jim Hupy
Salem, Or
78 Royale 403
On Wed, Nov 10, 2010 at 9:13 AM, Gary Casey <casey.gary@yahoo.com> wrote:
> I agree with Jim, but the statements in his two posts below are a little
> contradictory. Yes, if you add volume the spring rate will go down, but
> will
> that "negate the intended design (philosphy?)of giving better control"? If
> the
> design intent was to give better control, the only way it can do that is by
> increasing the spring rate. After all, that's all the spring can do. And
> then
> the second post says the Q-bag "rides like the standard", which says the
> spring
> rate did NOT increase. Which is it? I suspect, although no data has been
> presented to substantiate it, that the Q-bag has a higher rate, which
> improves
> handling, but not so high as to instigate complaints of a rough ride. I
> gather
> that users of the "Harrison" system complain about the stiff ride, but I
> don't
> know. The higher pressure required in the Harrison unit is an indication
> that
> the piston has a smaller area, and does not indicate a higher spring rate.
> Without actual numbers it remains speculation and is open to disagreement.
> Gary casey
>
> Les,
> The additional volume will not only give a softer ride, byt cause a
> change in the spring rate that will negate the intender design of
> giving the rear better control.
>
> On Tue, Nov 9, 2010 at 8:32 PM, Jim Kanomata <jimkanomata@gmail.com>
> wrote:
> > On the Q Bag, it rides like the standard.
> > Only the Harrison is harsh.
> > We rin with80-85psi, Harrison 90-100 psi.
>
>
>
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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