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Topic: center of gravity location on truck

Posted By: RV Jim on 08/09/10 07:27pm

Hey folks, I hate to be a pia, but, am I figuring correctly?
I have an 03 Chevy crew cab with a 6 1/2' bed, 4X4, sticker in glove box gives measurements of A = 38" B " 00"
This is telling me basically, from cener of axel to the tailgate is my location for center of gravity.Does anybody have an the same truck?
and am I figuring correctly?
I am loking at a Sunline TC with an eight foot floor on it. Waiting for a model name or number from owner.
Trying to figure if it will fit on my truck OK.
Thanks Again,

Jim


Posted By: MegaCamper on 08/09/10 08:27pm

the center of gravity of a camper has nothing to do with the truck. the center of gravity of the camper you chose should be right over or in front of the rear axle of your truck. measured as specd by the manufacturer of the camper.


Posted By: mkirsch on 08/09/10 08:50pm

I just went out and looked in my 2003 Silverado 1500.

Max camper weight: 582 lbs
A: 79" (!!!)
B: 0"

Technically, I could put a 582lb camper with a CG right at the back edge of my box with no adverse effect to steering or braking.

That makes sense, because weight is weight. Bagged concrete, truck camper, or a trailer tongue. The WC rating of the factory hitch is 500lbs. GM says it's perfectly fine to hitch 500lbs way back there. Loaded in the bed, hitched to the receiver... It's actually BETTER being in the bed!


2002 Chevy 3500 DRW/8.1/Allison & 2000 Palomino B1500 popup TC

-Yes, I haul a popup with a dually. No, I don't think I need a dually to haul a popup.


Posted By: mkirsch on 08/09/10 08:42pm

The "B" measurement of 0 applies to campers no heavier than what is listed on the glove compartment sticker.

If your max camper weight on the sticker is only 750lbs, you can't put a 1500lb camper right on the back edge of the box.

Basically, if you choose to ignore the maximum camper weight, the A and B measurements are invalid too. You're on your own.

No camper has a CG at 79" from the front, though. 8' campers tend to have CGs ahead of 48".


Posted By: kaydeejay on 08/09/10 10:16pm

Perhaps this will help?

But wait a minute - you plan to put an 8' camper in a truck with a 6'8" bed???? Don't you think that's going to be a little tail heavy?
And what's your Cargo Weight Rating (CWR) off the same label as you got the Dim-A and Dim-B numbers?


Keith J.
1999 Sunnybrook 27RKFS Fiver.
2005 GMC Sierra 2500HD CC/SB/DA 2WD, LLY with LBZ air cleaner, 52 gal Titan tank, Bilsteins, Line-X, Westin steps, Prodigy, Retrax cover, 16K Superglide, 5th-Airborne pin-box, Multi-vex mirrors, TST TPMS.



Posted By: BrandonR on 08/09/10 09:59pm

mkirsch wrote:

I just went out and looked in my 2003 Silverado 1500.

Max camper weight: 582 lbs
A: 79" (!!!)
B: 0"

Technically, I could put a 582lb camper with a CG right at the back edge of my box with no adverse effect to steering or braking.

That makes sense, because weight is weight. Bagged concrete, truck camper, or a trailer tongue. The WC rating of the factory hitch is 500lbs. GM says it's perfectly fine to hitch 500lbs way back there. Loaded in the bed, hitched to the receiver... It's actually BETTER being in the bed!


My '99 K1500 had a camper rating of 650lbs that was with the "camper" package. Somehow oddly enough it had no trouble with a camper that was more than triple the "rating" with only some extra spring capacity.


Brandon Reed
Albany, OR



Posted By: mkirsch on 08/10/10 05:01am

Loading a truck properly is a matter of physics and common sense, not some dumb A and B measurement.

Putting the CG of the camper directly above the axle is preferred, but ahead of the axle is much much better than behind. Ahead spreads the weight across both axles. Behind pulls weight off the front axle and could cause a dangerous reduction of braking and steering effectiveness.

The Northstar 850SC is designed for short (6'6") bed trucks. It will work fine on your truck.


Posted By: kaydeejay on 08/10/10 06:12am

mkirsch wrote:

Loading a truck properly is a matter of physics and common sense, not some dumb A and B measurement.
The "A" and "B" measurement is calculated by the truck engineers according to Federal regulations so that "physics and common sense" don't have to be called on!
All it does is provide a safe range for the Camper CG to fall. As long as the camper is not heavier than the available truck payload, it will be OK.
According to your theory, putting a deadweight on the hitch at the back of the bumper is also unsafe?


Posted By: kaydeejay on 08/10/10 11:44am

mkirsch wrote:

Putting the CG of the camper directly above the axle is preferred, but ahead of the axle is much much better than behind. Ahead spreads the weight across both axles. Behind pulls weight off the front axle and could cause a dangerous reduction of braking and steering effectiveness.
Look at it this as a teeter-totter (using round numbers).
A 1200# weight on the bumper maybe 3' behind the axle will remove 1/4 of that (or 300#) from the front axle 12' ahead of the rear axle. I suggest it would need a LOT more than that to make the steering "go light"


Posted By: sleepywheel on 08/09/10 11:04pm

My truck is a 09 Chev 2500HD CC with the 6'5" box.
Dim A = 38" and B = 00" with a CWR of 2106 lbs.
I think I'm in the same frame of mind as RV Jim in that it's strange that the COG of the camper has to be between the middle of the rear axle and the tailgate. I would think that the A dimension would start from somewhere ahead of the rear axle.

Does that mean a popup camper would not be within legal specifications?
A Northstar 850SC has it's COG at 32" measured from the front of the camper. At 32", the COG would not reach the A measurement of 38". If that makes any sense................


2009 Chev CC 2500HD 6L 4x4
2007 Palomino Bronco 1251SB popup


Posted By: BrandonR on 08/09/10 10:46pm

kaydeejay wrote:

But wait a minute - you plan to put an 8' camper in a truck with a 6'8" bed???? Don't you think that's going to be a little tail heavy?


Actually it's pretty normal for short-bed campers to be 8'+ I have an 8'6" camper (you can see it in my sig) on a truck with a 6'6" bed. All that really matters is the center of gravity and total capacity of the truck, the camper could be 12 feet long if somehow you magically made the back half light enough to keep the COG in front of the axle the truck would handle fine.


Posted By: wnjj on 08/10/10 10:28am

mkirsch wrote:

Loading a truck properly is a matter of physics and common sense, not some dumb A and B measurement.

Putting the CG of the camper directly above the axle is preferred, but ahead of the axle is much much better than behind. Ahead spreads the weight across both axles. Behind pulls weight off the front axle and could cause a dangerous reduction of braking and steering effectiveness.

The Northstar 850SC is designed for short (6'6") bed trucks. It will work fine on your truck.


Behind the rear axle somewhat is just fine too. Like Kaydeejay pointed out, a trailer loads up to 500# considerably far behind the rear axle. This means a 3000# camper could be 1/6 of the way toward the hitch with the same effect.

I often see the concern about taking weight off the front axle affecting steering when the opposite is true as well. If the steering axle becomes overloaded the steering components may not work smoothly either.


Posted By: RV Jim on 08/10/10 09:11am

sleepywheel said:
"Does that mean a popup camper would not be within legal specifications?
A Northstar 850SC has it's COG at 32" measured from the front of the camper. At 32", the COG would not reach the A measurement of 38". If that makes any sense................"
kaydeejay's link:
"The longitudinal center of gravity zone has been determined for the full Cargo Weight Rating of this truck.

"If a slide-in camper has a total weight less than the Cargo Weight Rating (CWR), the permissible longitudinal zone of the center of gravity may be larger."

However, individual axle loads should not exceed either of the gross axle weight ratings (GAWR)."
I beleive this answers your question.
But, I am still not quite sure for me.
Sounds like, if the weight of TC is within specs, I should be fine?
Jim

* This post was edited 08/10/10 10:30am by RV Jim *


Posted By: Davis83 on 08/10/10 12:01pm

02 2500HD Ext Cab 6.5 bed

Sticker says max cargo load 1203kg/2653lbs A= 79in B= 25in thats a broad area for CG


Posted By: SoCalDesertRider on 08/10/10 07:34pm

Y'all are confusing each other.

The dimensions 79" and 25" means your camper's center of gravity can fall from between the front bed wall and 25" ahead of the rear of the bed.

What this means is, don't choose a camper where the center of gravity falls in the rear most 25 inches of the bed.

This means the center of gravity can be from all the way forward to slightly behind the axle center, but not in the rear two feet of the bed.


05E350 6.0PSD
97F350DRW 7.3PSD 4x4 4.10 11' flatbed
98Ranger
69Bronco ATC250R CR500
20' BigTex flatbed carhauler
Callen Camper

92F350 CrewCab 4x4 351/C6
B&W TurnoverBall, Curt Magnum V
HD Springs Bilsteins,
285/75-16E BFG AT on 16x8 Stocktons
4.56's & LockRite rear


Posted By: mkirsch on 08/11/10 06:59am

My owner's manual CLEARLY shows the "A" measurement being from the FRONT of the bed.

My owner's manual CLEARLY shows the "B" measurement being from the REAR of the bed.

My bed is 79" long.

My "A" is 79"
My "B" is 0"

To me, that says the CG of the camper MUST fall at the rear edge of the bed.

Tell me how that makes sense.


Posted By: mkirsch on 08/10/10 03:56pm

kaydeejay wrote:

mkirsch wrote:

Loading a truck properly is a matter of physics and common sense, not some dumb A and B measurement.
The "A" and "B" measurement is calculated by the truck engineers according to Federal regulations so that "physics and common sense" don't have to be called on!
All it does is provide a safe range for the Camper CG to fall. As long as the camper is not heavier than the available truck payload, it will be OK.
According to your theory, putting a deadweight on the hitch at the back of the bumper is also unsafe?


Explain this to me, then:

My "A" measurement is 79".
My bed is 6'8" (i.e. 79") long!

Find me a camper with a CG of 79".

The CG spec doesn't make sense! If they know so much better than me, why did they publish such a ridiculous figure for the front of the CG range on my truck?


Posted By: kaydeejay on 08/10/10 06:43pm

mkirsch wrote:

Explain this to me, then:

My "A" measurement is 79".
My bed is 6'8" (i.e. 79") long!

Find me a camper with a CG of 79".

The CG spec doesn't make sense! If they know so much better than me, why did they publish such a ridiculous figure for the front of the CG range on my truck?
Nothing says your CG will be at 79" from the back of the box, those two dimensions together say the CG should be BETWEEN 79" and the "B" value of 25".
You say there is no camper with a CG that far forward? What about campers with the overhead section the full length of the cab roof. I'll be willing to bet their CG is not too far back from the front of the box.

The engineers have determined that it would be OK if it was right at the front. But it doesn't matter, as long as the camper weight is within the CWR and the CG is between the two values.

And you'd better believe those engineers make sure they know what they're talking about 'coz if they get it wrong, the Feds can throw 'em in jail!


Posted By: kaydeejay on 08/11/10 12:53pm

mkirsch wrote:

My owner's manual CLEARLY shows the "A" measurement being from the FRONT of the bed.

My owner's manual CLEARLY shows the "B" measurement being from the REAR of the bed.

My bed is 79" long.

My "A" is 79"
My "B" is 0"

To me, that says the CG of the camper MUST fall at the rear edge of the bed.

Tell me how that makes sense.
S'funny, the picture on Page 4-61 of my 2005 2500HD Manual CLEARLY shows both dimensions are taken from the tailgate end of the bed.
In fact the picture looks VERY similar to that on Page 3 of this 2003 document (that is the year of your truck, right?), which also says VERY CLEARLY:-
"Longitudinal Center of Gravity (CG) Zone for CWR ? The forward limit of the recommended CG Zone is determined by the application of dimension "A" measured in centimeters (inches) from the rear of the truck bed. The rearward limit of the recommended CG Zone is established by application of dimension "B", also measured in centimeters (inches) from the rear of the truck bed. The recommended CG Zone lies between these points."

(My emphasis).

If your manual really DOES say something different I would love to see a picture - you see the guy who wrote the Manual AND the Camper Loading Booklet worked for me before I retired. Mistakes were rare but the odd one did still slip through all the reviews that took place on this stuff. But the fact this section had not (and has not) changed for years just increases my doubt that it is wrong.

Perhaps you should go and read your manual again and hopefully it now makes sense and that will be the end of it


Posted By: cant spell on 08/11/10 08:08am

the sticker sead see ownwers manuel. so let see.
there must be a picture there.


Posted By: cant spell on 08/10/10 02:30pm

I would like to see that sticker.
I would think the number would be from the front of the bed.
Most, but not all camper cog measurements are from the front of the camper.


Posted By: RV Jim on 08/11/10 06:21am

Y'all are confusing each other.

The dimensions 79" and 25" means your camper's center of gravity can fall from between the front bed wall and 25" ahead of the rear of the bed.

"What this means is, don't choose a camper where the center of gravity falls in the rear most 25 inches of the bed.

This means the center of gravity can be from all the way forward to slightly behind the axle center, but not in the rear two feet of the bed. "

Some are talking CG on camper and others when measuring from rear of bed are talking Center of Gravity ZONE on truck, lets not confuse or mix the two.
The ZONE the sticker talks about is also at MAX Camper Weight


Posted By: Davis83 on 08/10/10 06:07pm



Your wish = my command.

My interpretation of this is: Any camper with a CG that would sit between 25 and 79 inches from the end of my bed would be safe to carry.


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