How to gauge the strength (or stupidity) of a custom car cargo carrier?

How to gauge the strength (or stupidity) of a custom car cargo carrier?

We spend summers travelling to music festivals in Fest Van, a 1995 Mazda MPV. One of the larger items—really important with a six-year-old—is our garden cart. It’s steel, very robust, and about 70 pounds empty.
We’d get a basic trailer hitch installed by U-Haul. I can’t link directly to their page, but its description is a “Heavy Duty 1¼" receiver; Max weight 3500 pounds Class 2 hitch.” Other than towing, it will also accept a commercially available cargo carrier (example).

Instead of going that route, we’d like to take the cart to our mechanic (a very good welder and mechanic, but not a structural engineer) to fabricate/weld onto it a male fitting.

Given the age and delicacy of FestVan, we wouldn’t load up the cart with anything extraordinary—we’d likely keep the bulky items in there and the max weight added to the carrier would unlikely be more than a couple hundred pounds (if that).

So assuming that the male end is securely welded and supported on the bottom of the cart and that it fits correctly into the female receiver, how do we gauge the stupidity of this idea? I’d be pretty confident on my own that the mere weight isn’t going to be a problem (again, bulky but not heavy items), but what about torque or other structural issues? Is 1¼" of steel (on the female side) strong enough to resist the cart wobbling as we drive?

Since no one has replied with facts…

I like the van.

However the garden cart is not made to go 55 MPH.

I would seriously doubt that the tires and axles would last 10 minutes at highway speeds.

There’s also such things like tail/brakelights, reflectors, etc.

I agree. I thought the OP was referring to putting some kind of carrier on top of the van for the cart. My guess is that a pothole or bump will get the thing bouncing and snap off the hitch if you go over maybe 10 or 15 mph.

OP is not going to drag the garden cart along on its wheels, he’s going to have a hitch welded onto the side of it so he can shove it sideways into the receiver, and it will dangle there behind the van with its wheels off the ground.

I think it’s a great idea, and I really wouldn’t worry about strength; seems to me that any decent welder will be able to make it strong enough. IANA mechanical engineer, though.

eta: If you’re worried about wobbling, you could always run ratchet straps from the outside corners of the cart to the roof, if you mounted some tie downs up there. That’s getting into permanent modifications to the van, though. Could you add roof rails? You may also want to have a female receiver welded onto the cart so you can remove the male part; otherwise you may be bashing shins as you roll around. Then you’d have to use a chunk of square stock as your adapter.

Here’s an example of someone doing this, but I’ll note that it appears to be an aluminum cart. Here’s a commercial product that allows you to crank up a cart.

Both are clearly Class 3 receivers, though. Is that an option? You may want the larger opening, it would resist twisting better.

eta: Seriously, this is such an awesome idea I’m going to steal it for my own camping trips.

Who said anything about towing it, the OP specifically called it a cargo carrier

They tend to be rated for 500 lbs. of cargo. If I had one, I wouldn’t hesitate to strap the cart on it.

Your idea sounds good in principle, but the bottom of the cart may need to be reinforced and braced like the ones in the link.

I think it would work, but on the other hand, the commercial cargo carrier linked to in the OP is only $122 and would carry more and offer more flexibility (such as when the garden cart is no longer needed). The mechanic is probably going to charge $50-100 for the welding.

I agree. Getting a carrier that the cart will fit on would be more cost-effective and more versatile with less worries about it not working as desired or having unforeseen drawbacks.

It’s a clever idea but I don’t think you’ll have much ground clearance with the cart wheels and it won’t take much to bend or snap them off. I have a cargo carrier for my CUV and it scrapes backing out of our slightly sloped driveway. You might look into modifying a bike carrier like this in some way to hold the cart. Maybe tubes welded to the bottom of the cart that would slide onto the carrier arms.

So the original idea was like the pictures steronz included, but reading through the idea of attaching the handle to the hitch, giving the boy a helmet and some snacks seems just so much more fun!

The thought of doing the cart rather than just a rack is to get it out of the van. It fits, but there is a lot of dead space, not to mention we have to take steps to secure it in case of an accident (though if it did crush the boy’s legs it would come in handy for longer than we anticipated).

We thought (and are still considering) a flat, side-less commercial carrier to attach the cart to, but so far having trouble finding something that fits within its wheelbase. But given SmellMyWort’s insight into they clearance issue, it my be the necessary way to go.

Do the sides remove from the cart? If so, it might mount upside down, or even on its side.

Perhaps I missed (or misunderstood) something in the various theories flying back and forth, but …

What’s the problem with buying a commercial cargo carrier rack big enough to take the kid’s wagon sitting in/on it as cargo? The kid wagon ends up outside the van and can be filled with whatever else, further emptying the van.

Those carrier platforms can hold a bunch of weight; many are used for elder folk’s power scooters that weight a hundred plus pounds.

are you worried about the weight of the total load (cart plus cargo carrier) with respect to your vehicle, and how it might affect performance? A common rule of thumb is that, when towing, you should aim for ~10% of the towed vehicle load as a vertical downward force on the hitch. Now, this isn’t the same situation, but with respect to that concern i think it approximates a maximum reasonable figure for dead weight onto your hitch point. So whats the total cart weight compared to the tow allowance of your vehicle? If its getting close to 10%, I might be looking more closely, if it is miles short of that, that feels good.

I fabricated a very similar thing to use for my trail bike. Here is an example link
My bike weighed around ~100kg = 220 pounds. My vehicle didn’t even notice it

what i did find is that the without being ‘grounded’ i.e. having a point of contact with the load like a trailer does through its wheels, is that anything plugged into the hitch wobbles like crazy. It sortof has to, otherwise you couldn’t feed the item into the hitch - you need clearance and that allows wobble.

I solved that issue by drilling a hole into my hitch, and then welding a nut outside of that hole. I would then insert my carrier into the hitch, use the factory pin like normal, then wind a bolt into the nut. It would press against the carrier in the hitch, and lock it up good, and it made me feel heaps better. No wobble after that. The same guy who welds your carrier up could easily drill and weld a nut into place for you.

You could also just ratchet strap it to your car - there is normally a tie down strap under your car at the back somewhere, for vehicle tie down during freight from the manufacturer.