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).
The COG on my Snowriver is not only forward of the rear axle, it is also about 6" further forward than the tire's forward most edge.
So even though I have a crewcab, the 3200#s of camper is divided 500# front, 2700# rear (with full water). I try to load the heaviest items as far forward as possible to keep as much weight forward as I can. It amazes me how well the truck handles even on wallowed roads having done nothing to the stock camper package that came with the truck in 1997 (still has original shocks).
INSAYN's 8' 10 Snowriver has the furthest forward COG of any truck camper I'm aware of, which makes it a good choice for a short bed truck especially. The 9'6 is a bit further forward than most (38 inches), but only by about an inch. Bob Mehrer told me that 40 inches from the front vertical is about average. My Adventurer 9'6 is about 39. More than that & you will likely be back of your rear axle.
Air bags would help with the 2 inch sag, but wouldn't do much for the porpoising. If you haven't upgraded the shocks, thats what I would do next. I brought my camper home on the stock shocks and the porpoising was noticeable. I went to the tire dealer the next day and had the shocks replaced and the porpoising was eliminated in a way I never imagined. I went with self adjusting shocks, which are much better with a load, but they don't self adjust down as much as I expected when the truck is unloaded. If you will be driving the truck a lot without a camper on, you will probably want to go the adjustable heavy duty shocks (Rancho 9000 for example).
I measured my Lance 1161 and compared it to my Dodge Ram 3500 Quad Cab dually yesterday, and discovered the COG is about 2" - 3" behind my rear axel. The camper has always had a noticeable, if gentle, porpoising over bumps, even on a relatively smooth road, so this was not entirely unexpected. The truck/camper combination drives and handles well, but I can see the Hapi-Jacks working over every irregularity on the road surface and the bobbing up and down is a little annoying. I am about 400 lab overloaded when full of water and with the wife and I aboard for a long weekend. Do you think there is anything I can do to alleviate this situation and do you have any recommendations? I have considered airbags to raise the rear, which drops about 2“ when fully loaded. Thanks.
The COG is not as you say the balance point, it is some point within the camper-Pu combination that determines how tippy the rig will be if the height of the total rig is exceeded. It will change with any change in height or weight of the rig. Except for the defination of COG, what you say about the balance point is corect.
1992. Silverado 2500HD Ext. cab long box 454CI with owner installed Banks Power Pack 4L80E AT. 1997 Sunnybrook 5th Wheel, 27-foot with slide.I used to have a 1971 C20 Chevy and 1972 11.5 Saturn PU Camper.
Hi! This is my first message on the forum. Glad to see all the wisdom you give us. Thanks! I've learned about campers by the seat of my pants and have made some decisions I need to change. One of the things that I didn't think about when I bought my camper (besides weight) was the fact that I have a crew cab. This pushes more of the camper weight over the rear axle than it would on a 2-door truck. I lost my weight-scale numbers, so will have to do it again, but it was scary. What is your opinion about camper length when dealing with a crew-cab pickup? Do I need to buy a shorter camper with an extended cabover to help move more of the weight forward? What about the weight-carrying capacity of the cabover portion of a camper? I wonder if the cantilevered cabover has its own cargo-carrying limits. Thanks again!
'85 F350 Crew Cab Dually, 6.9 diesel, 4WD Banks Turbo, stock 16" wheels and Uniroyal Laredos, 45 gal rear tank, add-on leafsprings, Firestone airbags, rear sway bar. 11ft.6in. Vacationeer camper (standard, not extended cabover)