Calculating center of gravity for an overland build

[Greybeard415]

I'm converting a 1979 8ft F250 truck bed trailer into an over landing/ camp trailer. It has 33 inch 10 ply tires, a topper shell and a home made heavy duty contractor rack that fits over the topper shell but bolts to the truck bed. Currently has the OEM axle but no drive shaft. Also has conversion plates from 5x5.5 to 8 lug Chevy wheels to match my 2001 Silverado 2500 HD tow vehicle.

I'm researching 2-things and need input. 1- with no brakes on the trailer, I'm looking for a trailer axle with electric brakes, but can't figure out which size and weight capacity to look for. 2- since the truck bed trailer no longer has the truck cab and engine to keep the weight heavy enough to prevent it from flipping over, I am trying to figure out how to calculate a safe center of gravity so I can determine if I need to lower the trailer frame or add weight to the frame to be safer when off roading . I certainly don't want the trailer to roll over and try to take the truck with it. Bear in mind, I do NOT off road-rock crawl, just want to camp in some remote and sparsely populated scenic areas. Maybe find some good hunting and fishing spots too.

Appreciate the input...

 

[NatersXJ6]

1) The center of gravity will change dramatically with changes in load.

2) You are somewhere between highly unlikely and virtually impossible to get a full-size truck bed trailer to roll over on regular fire service roads at sane speeds. The vehicles the fire departments use are huge and top heavy in comparison to a pickup bed trailer.

3) Speed compounds everything. Hitting crazy whoops or bumps or off camber around corners at more than 25 or 30 mph is recipe for disaster. Reference various threads about bent frames.

4) when I did my calculations for my trailer lid tip angle, I assumed the cog for the trailer was at center of the geometric shape of the trailer box. This is probably a bit conservative/ high because of the weight in the frame and wheels. More so in a truck bed because of the very heavy frame. Then simply add the geometric centers of each mass plus their distance from the center. When the vertical line through the cog moves outside the wheels as you tip, that is the rollover point.

I tested mine by tipping with an overhead hoist until it got light, my calculations were conservative by maybe 6-8 degrees of angle.

 

[broncobowsher]

Something funny is going on. '79 F250 is a factory 8-lug wheel. If you are starting with 5-lug you have a half ton axle. Does the cast center section come out the front of the axle? You have a 9". Not that it really matters.

Looks at the springs, get out your tape measure. 2½" wide, you have an F150. 3" wide, you have a F250 or F350 set of springs. Spring hangers are different so you can't swap springs.

I owned a 70's F250 camper special. Heavy spring packs, beefy rear sway bar.
I also own an F150 truck bed trailer. Hauled heavy loads with a high CG (probably 5' in the air). Worst trailer I ever towed. Not slightly bad, really horrible. The soft springs made it very rolly. No rear sway bar. 10MPH was the fastest speed you could drive it. Seriously, it was that bad. 15MPH it started swaying, didn't stop until slowing below 5MPH. It was a long drive home, a lot of back roads. Those soft long travel springs were not a good for towing a high CG load. Look at most any trailer made as a trailer. Short springs, high spring rate, limited travel. They are built that way for a reason.

 

[Greybeard415]

Something funny is going on. '79 F250 is a factory 8-lug wheel. If you are starting with 5-lug you have a half ton axle. Does the cast center section come out the front of the axle? You have a 9". Not that it really matters.

Looks at the springs, get out your tape measure. 2½" wide, you have an F150. 3" wide, you have a F250 or F350 set of springs. Spring hangers are different so you can't swap springs.

I owned a 70's F250 camper special. Heavy spring packs, beefy rear sway bar.
I also own an F150 truck bed trailer. Hauled heavy loads with a high CG (probably 5' in the air). Worst trailer I ever towed. Not slightly bad, really horrible. The soft springs made it very rolly. No rear sway bar. 10MPH was the fastest speed you could drive it. Seriously, it was that bad. 15MPH it started swaying, didn't stop until slowing below 5MPH. It was a long drive home, a lot of back roads. Those soft long travel springs were not a good for towing a high CG load. Look at most any trailer made as a trailer. Short springs, high spring rate, limited travel. They are built that way for a reason.

I can totally see the confusion. Let's just say its a franken-trailer. It started life as a '79 F250. When the guy I got it from made it into a trailer, he wanted the drive train for a crawler he was building. He didn't need the truck bed or frame or springs. He swapped out the axle as well b/c he wanted the 9 inch. Fast forward a decade or so and I was looking for a Chevy 8-lug axle to match my 3/4 ton Silverado, to match tires to the trailer. Could not find an affordable option, so opted for wheel spacers that went from Ford 5-lug to Chevy 8-lug. Much more affordable and expedient. @ $150 for the spacers and $200 for a decent set of wheels and rims that matched my truck.

Not having brakes with an empty trailer wasn't a huge concern because the truck has disc brakes all the way around. Now that I'm adding a topper shell, roof rack, and talk the shtuff that makes a trailer into a camp trailer, I figure I'd better look closer at better axle options as well as potential load issues. Would not want unnecessary issues if they can be compensated for...