Sedan Rear Axle Weight Rating?

[Iplayfarmer]

I've been looking on the internet for typical rear axle weight ratings for a mid size sedan, but this information is surprisingly hard to find. Someone here must know.

The situation is that I have a rear axle out of an early 90's Pontiac Bonneville. I will eventually make some kind of light weight trailer out of it, but I want to know just how light weight it needs to be. The best I've been able to figure out is that these mid size sedans typically weight about 4500 pounds loaded, and the weight is spread roughly half and half between the front and back. If I can't find any other information, I'm going to go with 2250 as my axle capacity.

 

[Diamondpilot]

I think you are about right. Look at the tires for a rating also.

I know they do not allow for much tongue weight when towing. Average around 250# or so.

Chris

 

[Iplayfarmer]

The tires are long gone. All I have is the axle. I guess I could check someone else's Pontiac Bonneville.

Any trailer I made out of this axle would be intentionally light weight. I'm considering something to pull behind my fifth wheel trailer to haul a 4-wheeler, etc. I already have a double axle tilt 16' trailer. I wonder if I could build the trailer light enough to leave me with a one ton payload capacity.

 

[Renze]

I think you can count the same ratings for tires as for axles:
When they are rated for 1200kg at 180km/h (cars top speed) they can take 1600kg at 100km/h.
Car axles have a much higher safty margin (thus a lower rated weight) than a trailer axle.
I have a rear axle of an old fwd car, rated for 800kg but i think if a trailer manufacturer would use the same cartridge bearings and brakes, it might be rated for at least 50% more, when i compare it with the axles under my trailer...

 

[lostcause]

i'd say try to use a little deductive reasoning. look at the size of the spindle and the bearings and see what it looks comparable to. in the past i've used volkswagen rabbit rear spindles and hubs/drums to make light utility trailers out of. the spindle and bearing are fairly similar in size to what is used for standard 2000lb axles. i'd have to guess that a bonneville is going to be slightly larger than that, but probably not as large as a 3500lb axle/hub/spindle setup. maybe 2500-3000kb max?

depending on how your state is on trailer registrations and requirements, it might be easier to class it as a 2000lb trailer anyways. around here you get into brakes and other requirements when you get much past that point.

 

[Iplayfarmer]

Idaho's laws all pertain to the weight of the trailer itself, not how much the trailer can haul. If the trailer is under 2,000 lbs. it can be licensed without a VIN.

 

[brokenot]

Car axles have a much higher safty margin (thus a lower rated weight) than a trailer axle.

I'm not sure about that. Why would they? Yes, a car is capable of high speeds, but except for the occasional photo like this, when is the last time you saw a car severely overloaded? This photo shows what will happen if a car's soft and comfortable suspension is loaded beyond the few hundred extra pounds, (passengers and groceries), it was built to carry. The rear axle that normally carries ~1500 pounds probably isn't going to be built strong enough to carry a 2X or 3X or whatever weight "safety margin" because it doesn't have to. The bumper would be on the ground, and manufacturers cut weight everywhere they can for fuel economy reasons. That's why axles like this are basically spot-welded together bits of stamped light gauge steel....instead of heavier *real* tubing.

That's not to say I haven't used the odd FWD car's rear axle myself once or twice for a light-duty trailer project, but looking at the metal stampings used to create those assemblies leads me to believe they're not all that "over-built" for the application they're designed for. If you've got one laying around that's available for free, go ahead and use it. Otherwise, a set of *real* trailer stub spindles and hubs and some heavier tubing would be a wise investment....if you don't want to spend the $$ for a ready-made trailer axle.

 

[Redneck in training]

I have built a trailer using Renault Fuego torsion spring axle about 20 years ago. I am guessing it was rated about 1500 lb at most. I added cheap shocks and welded them such a way when overloaded the shocks would bottom out and support the load. The trailer took quite abuse for all those years hauling dirt, river rock etc way overloaded. Sometimes I worried that the wheel spindles would bent or break but so far it still works.

 

[Renze]

That's why axles like this are basically spot-welded together bits of stamped light gauge steel....instead of heavier *real* tubing.

Thats correct, the axle beam itself is usually light. But if you compare the size of bearings and brakes of an 800kg car axle, you'll find this size on a 1500kg trailer axle.
BPW of germany sells their 1800kg axles with the same 250x40 brakes as their 3 ton agricultural axles.

 

[brokenot]

Thats correct, the axle beam itself is usually light. But if you compare the size of bearings and brakes of an 800kg car axle, you'll find this size on a 1500kg trailer axle.

So where does the more conservative rating come from? Applying the age-old "a chain is only as strong as its weakest link" principle to this scenario, what sense does it make to install a larger set of bearings on a flimsier axle assembly?

If an increased load bearing "safety factor" was desired, the entire assembly from hub-to-hub would be beefed up. But it isn't. I'd have to guess that an upgrade in bearing size or quality would have more to do with increased service life and reliability with less maintenance....and very little to do with wanting to carry a larger payload safely.

Having said all that, I'd add that when my wife totaled her GM front-driver years ago, I dropped the 2.5 engine and transmission out and mounted it on the back of a frame to create a DIY dune buggy of sorts. I also kept the rear axle, (still have it here somewhere), for a light duty trailer project. Never got around to it though....didn't seem all that hefty. With one end clamped in a vise, I could twist it a bit by hand. I was cheating a bit though. With it out of the car it didn't have the plethora of linkages attached to it that kept it all nice and straight and square in the chassis.