I’ve Always Wondered How Well These Monowheel Trailers Worked

So tomorrow I need to return that Polaris Ranger XD press loaner I had (story coming soon!) and that means I need to hook up a trailer to my old F-150 to return it. I’m not really looking forward to this errand because trailers are an ass-pain. I’ve pulled plenty of trailers over my driving life, in a variety of vehicles, but I’ve always hated backing them up, the geometry of which tends to make my brain hurt, and they always just seem sort of, I don’t know, janky.

It’s the pivot point between the towing vehicle and the trailer, of course, that gives these feelings. You’re adding a hinge to the middle of your combined vehicle, and we’re just not generally used to driving vehicles that bend in the middle there.

Sure, you can get good at it – real big-rig truckers tend to be incredible at it, having re-wired their brains over time with lots and lots of practice. I once tried it myself, and discovered that I have a surprising amount of hidden complete lack of talent at doing it! Look, you can watch me try!

Yeah, I was terrible at it. It’s not easy!

I think all of this is why I’m so taken by this peculiar little trailer from the 1960s, this one designed specifically for Volkswagen Beetles, and known as an Efes Auto-Porter:

The Auto-Porter would certainly have significantly increased the cargo capacity of your Beetle, sort of turning it into a little pick-up truck. But what I think is most interesting about this trailer is the way it mounts to the car. Oh, and the fact that it has just one wheel, on a caster, like a colossal shopping cart wheel.

First, let’s talk about the mounting; it’s not connected via a conventional trailer hitch, instead it mounts to the Beetle’s rear bumper brackets, which are in turn mounted to the bod, behind the fenders. The Beetle is a sort of semi-unibody design, where the body is self-supporting, but it’s still mounted to a separate chassis. I mention this because those bumper brackets aren’t just screwed into a bit of sheet metal, they can take at least a bit of load.

So, the result here is that the trailer acts as an extension of the car, with no pivot, which means that reversing should be easier, provided you remember that your Beetle is now about, what three feet longer? So that should be easier to drive and deal with. Of course, you’re also increasing the weight at the rear of an already rear-biased car prone to oversteer, so have fun with that.

You know what also may make for, um, interesting handling? That one caster wheel. Being a swiveling caster means that maneuvering is likely quite good, but I am a bit concerned about something I just learned is called “caster flutter.”

You know how sometimes you’ll be pushing a shopping cart in a nice straight path but one wheel decides it wants to go all crazy and wobbles all around? That’s what caster flutter is.

So what causes this? Happily, caster experts exist, and not just exist, they make videos! Like this one:

So, according to that video, caster flutter is caused by the caster hitting some resonant frequency of vibration, which makes it go nuts. One of the factors there is something called “swivel lead,” which seems to be the distance between the pivot of the caster and the axle of the wheel:

It seems a longer swivel lead can reduce flutter. The Auto-Porter wheel seems to have a bit of swivel lead there, but is it enough? Maybe!

I’d love to find one to test! Which seems pretty difficult, as these appear to be quite rare. Still, I’ve learned more about casters just now than I have in decades, so I’ll just enjoy that little victory.