It is where the weight is centered on a T/C from the front to the back. It is important to us as the further forward it is, the less the total weight of the camper will be carried by only the rear axle. Too far rearward and it will actually remove weight from the front axle. Typically it is compared as where it is relating to the center of the rear axle on the truck when the camper is loaded. Almost always campers with a considerable overhange past the rear bumper will have a more aft center of gravity as it relates to the trucks axle. Some manufactures measure it differently. Some will give a dimension from the front of the part that sits in the truck bed, others as a distance from the rear in inches. Mine came with an arrow on the camper marking the spot.
Truck Campers- Center of Gravity (COG)
The unique thing about a truck camper is that it sits in the back of a standard pickup as all cargo. Today’s typical truck campers typically weigh 3500 to 4000 lbs loaded for a weekend of fun. That’s a lot sitting back there. It’s a wonder your truck doesn’t flop over backwards with all of that weight (like that popular internet photo of a overloaded donkey cart lifting the donkey off the ground). What keeps this from happening? All makes of modern campers will list their Center of Gravity (COG). That number tells you the balance point of that camper. Ideally, the COG should be in front of the rear axel, in other words, that point should be between the center of the rear wheels and the cab of the truck. A minority of manufactures will measure their COG from the back of the camper towards the center, but most by far measure from the front of the camper (at the pass through window) back to the COG point.
First thing to do is go out to your truck and measure from the front of your truck bed (the wall behind the cab) to the center of the axle. Don’t trust that the center of your wheel well is the center of the axle. That distance will be your reference, usually 50 to 60 inches or more. Next check the camper manufacture’s listed COG. You want your camper’s COG to be 6” or shorter than the reference measurement you have for your truck, but no more than the distance you have measured.
Some people do drive around with the COG behind the axle (mostly not even knowing it). The weight of the cab and engine counterbalance, but this condition is inherently unsafe. To begin with, the rear axle is unduly overloaded. The front tires are also going to be lifted, loosing contact with the road. Steering and handling will be affected, and so on.
Also, you may have done the measurements and bought the proper camper and still end up with the COG behind the axle. That usually happens with improper loading. You will find this out when you go to the scales loaded. When you originally weighed the unloaded truck, the front axle was probably around 3500 lbs for a gas engine truck. If your loaded weight is less than 3500 lbs in front, you COG is off. You need to see if there is a way to reload the camper (take the bikes and chairs off of the ladder rack and install a front hitch and bike rack for example).
Now that all of that has been said, remember that some camper or truck manufacturers will figure their COG from the tailgate of the truck. The above principals are the same, all that changes is keeping track of where to take your measurements from and how to then apply that to the camper.
Also, Center of Gravity (COG) is referenced here and can more accurately be defined as the balance point from front to back of the camper, while a true (COG) may actually be located not just a certain distance measured along the bottom of the camper, but also up inside the camper. This figure could be helpful to know, but only if you know how to relate it to your specific truck. Most only know where the balance point is on their truck so COG has been generically used to refer to this dimension.
2005 Dodge 3500 SRW, Qcab long bed, NV-6500, diesel, 4WD, Helwig, 9000XL,
Nitto 285/70/17 Terra Grapplers, Honda eu3000Is, custom overload spring perch spacers.
2008 NorthStar Arrow short bed.
Tiger4x4RV wrote: When I brought up the term in another thread, I meant the center (front/back and up/down) of the mass of the entire rig (truck plus living quarters).
Remember, we have to think in three dimensions here.
If the COG is too high the rig can tip over when hard cornering.
Paul
Extra Class Ham Radio operator - K9ERG (since 1956)
Retired Electronics Engineer and Antenna Designer
Was a campground host at IBSP (2006-2010) - now retired.
Single - Full-timer
2005 Four Winds 29Q
1982 6.2L Diesel Suburban 1500
For the most part, it only matters for short bed trucks. For short bed trucks, you need to make sure that the camper you use was made for a short bed truck. Length is not the indicator.
However, if you put anything in the front of the bed, it will impact the COG for a long bed as well.
'06 F350 Lariat Supercab SRW, 6.0 PSD 4x4 Long Bed, Intake Elbow, Walker Big Truck Muffler. '06 Host Rainer 950 Double Slide, Fastguns. Firestone Air Bags, Rancho 9000s, Vision 19.5s with Hankook DH-01 245s, Energy Suspension bump stops.
Imagine a see-saw with two same-weight kids on each end. The board is perfectly balanced around the 'center pivot pin' and it will rock either way with no effort.
If one kid moves forward on the seat, the center of gravity (COG) moves towards the other kid and the see-saw tips to the then heavier side.
Your TC has a 'calculated' pivot point (COG), like a see-saw pin.
We want the COG ahead of the rear axle so it puts a little more weight on the front tires. If the COG is behind the rear axle, the rear-weighted load of the camper is trying to lift the front tires just a bit.
Here's a pic. Read more about it and see the pictures.
The center of gravity (front to back) can very greatly from when the camper is loaded to when it is empty. The old Avion campers had a slightly rearward center of gravity when empty. They balance great when they are loaded. They weigh about 2,550# wet. The original water tank was 30 gallons and it was all the way forward in the bed.
Ford F-350 4x4 Diesel
1988 Avion Triple Axle Trailer
1969 Avion C-11 Camper
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