Ride height

I get major differences at the same pressure based on my load, mainly due to occasionally carrying a large-ish scooter on the rear bumper. I also vary quite a bit from empty to full of fuel and water.

In my case - I really need at least 3 or 4 pressures for various loads - but the Wireless Air only has two presets... Right now - I keep preset one at 70 PSI and preset two at 75 PSI - which lets me quickly get to any 5 or 10 PSI number...

Being able to quickly measure my rear height from inside would be great - but finding time to finish the project gets in the way of camping... Having an Raspberry Pi and two ultrasonic sensors is pretty simple - basically an electronic ruler...

Rob
Victoria, BC
76 Royale - Rear Twins/Dry Bath

>
> No need for an electronic way to measure ride height as the hysteresis in most GMC suspensions keeps it from changing all that much in use. Set your coach to proper ride height (block the rear at proper ride height, set the front and then drive the coach a few miles and recheck ride height front and rear until it is proper front and rear after your drive. Now, measure the air pressure in the rear air bags. When you are about to leave on a trip, put that much air in the rear bags and boogie on. You will find few coaches need anything more than that. KISS is very much your friend here.
>
> Jerry
>
> Jerry Work
> Kerby, OR
 
Keith:

The sensor I was testing with (JSN-SR04T) is rated for 2 mm (!) accuracy - but I think it's realistically closer to 5 or 10 mm.

The issue I had was the "minimum" distance that this waterproof sensor could read - it's about 20 cm (~8 inches). My initial search for a place to mount on the GMC wasn't successful and I didn't get back to the project - the breadboard is still sitting in my family room...

Rob
Victoria, BC
76 Royale - Rear Twins/Dry Bath

>
> Rob,
> How accurate is fairly accurate?
 
Redundancy is great in spacecraft. So not neccessary in 40 year old
coaches. Kinda like putting lipstick on a pig. Do what you will, it is
still a pig. But, what the heck, it's your money, spend it how you see fit.
Jim Hupy
Salem, Or

On Thu, Jul 25, 2019, 6:53 PM Rob via Gmclist
wrote:

> I get major differences at the same pressure based on my load, mainly due
> to occasionally carrying a large-ish scooter on the rear bumper. I also
> vary quite a bit from empty to full of fuel and water.
>
> In my case - I really need at least 3 or 4 pressures for various loads -
> but the Wireless Air only has two presets... Right now - I keep preset one
> at 70 PSI and preset two at 75 PSI - which lets me quickly get to any 5 or
> 10 PSI number...
>
> Being able to quickly measure my rear height from inside would be great -
> but finding time to finish the project gets in the way of camping... Having
> an Raspberry Pi and two ultrasonic sensors is pretty simple - basically an
> electronic ruler...
>
> Rob
> Victoria, BC
> 76 Royale - Rear Twins/Dry Bath
>
> > On Jul 25, 2019, at 6:07 PM, Gerald Work via Gmclist <

> >
> > No need for an electronic way to measure ride height as the hysteresis
> in most GMC suspensions keeps it from changing all that much in use. Set
> your coach to proper ride height (block the rear at proper ride height, set
> the front and then drive the coach a few miles and recheck ride height
> front and rear until it is proper front and rear after your drive. Now,
> measure the air pressure in the rear air bags. When you are about to leave
> on a trip, put that much air in the rear bags and boogie on. You will find
> few coaches need anything more than that. KISS is very much your friend
> here.
> >
> > Jerry
> >
> > Jerry Work
> > Kerby, OR
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
It's less about redundancy (for my calibrated height measurement stick) and more about convenience. $49 ($35 for a Raspberry Pi and $14 for two sensors) isn't really enough to get too worried about...

I guess $49 would buy a lot of rulers - but one instance of not having to measure the height outside in the rain would more than make up for the difference (IMO)...

Rob
Victoria, BC
76 Royale - Rear Twins/Dry Bath

>
> Redundancy is great in spacecraft. So not neccessary in 40 year old
> coaches. Kinda like putting lipstick on a pig. Do what you will, it is
> still a pig. But, what the heck, it's your money, spend it how you see fit.
> Jim Hupy
> Salem, Or
 
Rob,

8" minimum shouldn't be much of a problem when the rear clearance beneath
the frame should be 8-7/16" -- mounted on the floor at the top of the frame
there would give about 13" at normal ride height -- more up front.

What I've been wondering about is the effectiveness on anything other than
a hard, smooth surface: What will soft dirt and/or grass do to your
accuracy?

I'd be offering to help if my MSEE wasn't so old & my brain so atrophied.
:-)

Ken H.

On Thu, Jul 25, 2019 at 10:14 PM Rob via Gmclist
wrote:

> Keith:
>
> The sensor I was testing with (JSN-SR04T) is rated for 2 mm (!) accuracy -
> but I think it's realistically closer to 5 or 10 mm.
>
> The issue I had was the "minimum" distance that this waterproof sensor
> could read - it's about 20 cm (~8 inches). My initial search for a place to
> mount on the GMC wasn't successful and I didn't get back to the project -
> the breadboard is still sitting in my family room...
>
> Rob
> Victoria, BC
> 76 Royale - Rear Twins/Dry Bath
>
> > On Jul 25, 2019, at 1:25 PM, Keith V via Gmclist <

> >
> > Rob,
> > How accurate is fairly accurate?
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
Just because we CAN build the great pyramids using forced slave labor,
notched sticks, knotted papyrus reeds crafted into string, and barges to
float the huge stones from the quarry to the job site, doesn't mean we have
to do it that way today.
Heavy lift cranes, laser measuring instruments, motorized moving
equipment, etc. all make the job much easier, particularly the forced slave
labor part. What is my point, you might ask?
Well, sometimes we get caught up in all the stuff available to us now,
and lose sight of the final task. Which is getting the front ride height
correct to prevent stuff like excessive nose deflection upon heavy braking,
unloading the rear most wheels and flat spotting the tires as a result.
Rear ride height changes while underway are difficult to tell much about
before they change again. Get the front absolutely correct, the rear? Good
luck.
Jim Hupy
Salem, Oregon

On Thu, Jul 25, 2019, 7:35 PM Rob via Gmclist
wrote:

> It's less about redundancy (for my calibrated height measurement stick)
> and more about convenience. $49 ($35 for a Raspberry Pi and $14 for two
> sensors) isn't really enough to get too worried about...
>
> I guess $49 would buy a lot of rulers - but one instance of not having to
> measure the height outside in the rain would more than make up for the
> difference (IMO)...
>
> Rob
> Victoria, BC
> 76 Royale - Rear Twins/Dry Bath
>
> > On Jul 25, 2019, at 7:19 PM, James Hupy via Gmclist <

> >
> > Redundancy is great in spacecraft. So not neccessary in 40 year old
> > coaches. Kinda like putting lipstick on a pig. Do what you will, it is
> > still a pig. But, what the heck, it's your money, spend it how you see
> fit.
> > Jim Hupy
> > Salem, Or
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
I'm not too worried about what my ride heights are underway - I have little control over that. But I do like *trying* to have my rear ride height semi-correct before I start driving. Since I have a Wireless Air and dramatically varying rear loads - I have to manually check my heights. I suppose I could just *hope* they're good - but I'd prefer to measure them and I don't see $49 being a big deal... Cheap compared to almost anything else that can be done to a GMC...

I don't have the tools to get the front heights adjusted - and my location means there are very few options for having it done for me... That may change at some point - but not before my next trip!

Rob
Victoria, BC
76 Royale - Rear Twins/Dry Bath

>
> Just because we CAN build the great pyramids using forced slave labor,
> notched sticks, knotted papyrus reeds crafted into string, and barges to
> float the huge stones from the quarry to the job site, doesn't mean we have
> to do it that way today.
> Heavy lift cranes, laser measuring instruments, motorized moving
> equipment, etc. all make the job much easier, particularly the forced slave
> labor part. What is my point, you might ask?
> Well, sometimes we get caught up in all the stuff available to us now,
> and lose sight of the final task. Which is getting the front ride height
> correct to prevent stuff like excessive nose deflection upon heavy braking,
> unloading the rear most wheels and flat spotting the tires as a result.
> Rear ride height changes while underway are difficult to tell much about
> before they change again. Get the front absolutely correct, the rear? Good
> luck.
> Jim Hupy
> Salem, Oregon
 
On the rears I always set them and drive it for 8 miles on 2 lane county roads and come back on 4 lane divided highway to where it settles down. Then
I readjust and drive it again. Usually it does not need a 3rd adjustment.

The fronts are a different issue. We have found 1/4" off transfers 125 pounds between the front wheels (front left to right). So I set and block
the rear wheels at exactly correct, then adjust the fronts by weight (maximum 100 pounds difference). Then measure the front heights and they almost
always equal. So we adjust the front as a pair to get the correct height.

The problem with this coach design is the rears are a dynamic adjustment while the fronts are static. Unlike a car or truck with torsion bar
suspension, is a strange relationship.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
I did test it on carpet and some other surfaces - but not on grass. I'll
have to build a rig to test on grass and gravel to determine true accuracy.

I was testing with a "headless" Raspberry Pi and I wrote a small Python
program to display the measurements over an SSH connection. But I think
that a small 2-x16 char display would be good and cheap. All I'd need to
display is a left and right delta from the "calibrated" level position.
I'll poke around under the GMC again and see if I come across a viable
mounting spot...

All this talk has me interested in continuing... But my fall is already
mostly booked up! Another winter project?!?

Rob
Victoria, BC
76 Royale - Rear Twins/Dry Bath

On Thu, Jul 25, 2019 at 7:51 PM Ken Henderson
wrote:

> Rob,
>
> 8" minimum shouldn't be much of a problem when the rear clearance beneath
> the frame should be 8-7/16" -- mounted on the floor at the top of the frame
> there would give about 13" at normal ride height -- more up front.
>
> What I've been wondering about is the effectiveness on anything other than
> a hard, smooth surface: What will soft dirt and/or grass do to your
> accuracy?
>
> I'd be offering to help if my MSEE wasn't so old & my brain so atrophied.
> :-)
>
> Ken H.
>
 
I keep reading here that the elevation control (ride height) does not do much. I guess I don't care very much what others think and how much they can
feel. I do know two things as facts.

If we stop to take on fuel, that is typically ~300# (45~48gal), when we restart, the compressor usually runs.

When we had a bad cab control valve that leaked air into the system, it would not be long before one could feel the change in handling.

Admittedly, we have a much lighter coach than most and as a refugee from automotive testing and car racing, I am likely to be more sensitive. For as
little work as it takes to keep the system working as designed, I just don't think it is a good thing to ignore.

Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit
 
Ken,
Know that Friont present a problem as lot or the suspension parts will
cause severe histerrisid when taking height measurements .
Also the geometry is such that the wheels will also add to this .
We use the swivel plate that is built in on our lift to lessen that effect
and bounce it several times but we still need to drive it to where it
settles.

On Fri, Jul 26, 2019 at 2:23 AM Ken Burton via Gmclist <

> On the rears I always set them and drive it for 8 miles on 2 lane county
> roads and come back on 4 lane divided highway to where it settles down. Then
> I readjust and drive it again. Usually it does not need a 3rd adjustment.
>
> The fronts are a different issue. We have found 1/4" off transfers 125
> pounds between the front wheels (front left to right). So I set and block
> the rear wheels at exactly correct, then adjust the fronts by weight
> (maximum 100 pounds difference). Then measure the front heights and they
> almost
> always equal. So we adjust the front as a pair to get the correct height.
>
> The problem with this coach design is the rears are a dynamic adjustment
> while the fronts are static. Unlike a car or truck with torsion bar
> suspension, is a strange relationship.
> --
> Ken Burton - N9KB
> 76 Palm Beach
> Hebron, Indiana
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502
 
Those frequent adjustments of the stock system drove me crazy, they definitely do change the behavior of the coach.

One other interesting thing about the ride height system is the sensors are on the drivers side rear and pass side front. this means of the ground isn't perfectly level when you are calibrating it will through the heights off a lot more than you expect as one wheel is lower and the the other is higher than you think

Microlevel has less hysteresis than the stock system, it also doesn't adjust as often so it doesn't change heights on a cloverleaf and then again afterwords so the coach feels more stable in turns and crosswinds.
Calibration is easier also as the height sensors have zero hysteresis and the controller knows the actual height of the coach. No need to drive around after setting height

Keith
________________________________
From: Gmclist on behalf of Matt Colie via Gmclist
Sent: Friday, July 26, 2019 7:41 AM
To: gmclist
Cc: Matt Colie
Subject: Re: [GMCnet] Ride Height

I keep reading here that the elevation control (ride height) does not do much. I guess I don't care very much what others think and how much they can
feel. I do know two things as facts.

If we stop to take on fuel, that is typically ~300# (45~48gal), when we restart, the compressor usually runs.

When we had a bad cab control valve that leaked air into the system, it would not be long before one could feel the change in handling.

Admittedly, we have a much lighter coach than most and as a refugee from automotive testing and car racing, I am likely to be more sensitive. For as
little work as it takes to keep the system working as designed, I just don't think it is a good thing to ignore.

Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit

_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
Yesterday, I was thinking about weight and balance while I was driving from
Petaluma, California to our home in Salem, Oregon. A distance of 597 miles.
Elapsed time? About 11 hours. Take stops every 2 hours for toilet needs, a
gas stop in Ashland, Or. and a 20 minute lunch break at the Weed, Ca
airport rest area, and you can tell that no grass was growing under my
tires. We drove through the summit of the Siskiyou's and lake Shasta, and
three lesser known summits all with 6% gradients both up and down with
sweeping right and left high speed curves posted at 50 mph, which I took at
70 plus. I was driving my 2006 Chevrolet Trailblazer 4 x 4.
In the back, I had a complete Manny T. 1 ton front end, a stripped TM
425 Transmission, 2 ViAir 480 c compressors, all our clothes for a week
stay, Oh yes, a number of bottles of lower cost (than Oregon) liquor, and
several bottles of hand made premium Merlot and Cabernet wine by some
friends in Calistoga. Didn't weigh all that stuff, rough guesstimate is
near 500 pounds. All positioned behind the rear wheels, and above wheel
centerline.
Not conducive to crisp handling, to say the least. Talk about the
tail wagging the dog!
That brings us to weight and balance for travel. Kinda like rigging a ship
for weather. Some of you have experience in that.
What's your point, you might ask. Well, my Chev 4 x 4 ain't no race
car, and neither is a GMC MOTORHOME. Best you can hope for is to get them
to go straight down the road, neither oversteering (pushing) in the sharp
curves, nor understeering, no bump steer in the rough stuff, and minimum
amount of rut wander and wind push. That won't happen if you are the least
bit sloppy in the joints and bushings. Keep it all in as new condition as
you can, and drive them within human and mechanical limits. Best it is
likely to get.
Jim Hupy
Salem, Or

On Fri, Jul 26, 2019, 6:34 AM Jim Kanomata via Gmclist <

> Ken,
> Know that Friont present a problem as lot or the suspension parts will
> cause severe histerrisid when taking height measurements .
> Also the geometry is such that the wheels will also add to this .
> We use the swivel plate that is built in on our lift to lessen that effect
> and bounce it several times but we still need to drive it to where it
> settles.
>
> On Fri, Jul 26, 2019 at 2:23 AM Ken Burton via Gmclist <

>
> > On the rears I always set them and drive it for 8 miles on 2 lane county
> > roads and come back on 4 lane divided highway to where it settles down.
> Then
> > I readjust and drive it again. Usually it does not need a 3rd adjustment.
> >
> > The fronts are a different issue. We have found 1/4" off transfers 125
> > pounds between the front wheels (front left to right). So I set and
> block
> > the rear wheels at exactly correct, then adjust the fronts by weight
> > (maximum 100 pounds difference). Then measure the front heights and they
> > almost
> > always equal. So we adjust the front as a pair to get the correct
> height.
> >
> > The problem with this coach design is the rears are a dynamic adjustment
> > while the fronts are static. Unlike a car or truck with torsion bar
> > suspension, is a strange relationship.
> > --
> > Ken Burton - N9KB
> > 76 Palm Beach
> > Hebron, Indiana
> >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >
> --
> Jim Kanomata
> Applied/GMC, Newark,CA
> jimk
> http://www.appliedgmc.com
> 1-800-752-7502
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
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