I don’t remember reading a single post by the original poster arguing with what is being said in this thread. A lot of us understand that the real world is not a world of absolutes and they are not looking for an absolute yes or no answer but are instead seeking information so they can themselves make an informed decision.
Remember, the original poster was considering towing a 400 lbs motorcycle trailer behind a Prius, not a 4000 lb camper, not the Queen Mary, not even a small aluminum boat.
My opinion is that a small motorcycle trailer riding in the car’s wind shadow would stress the power train less than putting all that cargo on top of the roof, which is virtually guaranteed to convert one of the most aerodynamic cars on the road into the equivalent of a Jeep, not to mention making the car more top heavy, which can cause its own handling problems.
Who are you responding to? The OP never replied after the first post to argue the point.
I dont think anyone is thinking about towing 2000 lbs with a Prius. That is a Crazy BAD idea. And this is coming from a guy who towed with a prius.
The OP are talking about a 200lb motorcycle trailer with say 200lbs of stuff in it.
I towed maybe 450 lbs Max with my prius and it was fine. No issues. But I would say that was as much as I would pull with it. I have a small harbor freight trailer I have used to haul mulch with the trailer weighs maybe 100 lbs and is not much bigger than the yard cart I tow behind my mower, In fact the reason i use this trailer is I can load it at the depot, and then unhitch it from my car (van now) and hook it to the lawnmower and pull the mulch where I need it. That way i do not need to move the bags of mulch twice. When hauling mulch with the prius I didn’t even feel it back there.
And the Prius V come in at 3420lbs curb weight IIRC.
The Prius V is the Station wagon model of the prius, it has a different dash, center console, many small differences.
There is a regular Prius Level 5 which is a trim level.
You can get a Prius V in a level 2,3, or 5. IIRC
Are confused yet?
Its ok everyone, The prius V has 4 wheel disc brakes. It can handle it. lol…
Again, how is 400lbs of trailer and contents any harder on the brakes than 400lbs of people? Does not compute.
Depending on the weight and amount of people and cargo in the car, I would consider this reasonable.
You’re right about the original question, B.L.E.
The discussion did however wander far from that, including Circuitsmith’s photo for emphasis.
I’d still politely decline to install the hitch. It would be human nature to push the tow load a bit higher later, and then a bit higher, and on into loads that push the limit. One big rig with a good headwind could spell disaster. Even with a motorcycle trailer, I’m not sure how resistant the rear end of a Prius is to a good lateral shove. Theoretically it should be more stable than a motorcycle… at least a good sized one… but there are also a lot of motorcycles that get pushed around even without trailers .
How much a vehicle gets pushed around by crosswinds has as much to do with aerodynamic drag as it has to do with weight. I suspect that a Prius, with its 3000+ pound curb weight combined by a low coefficient of drag and a low effective frontal area is one of the more stable cars in a cross wind. Some of the most blown around by the wind vehicles I have driven were full sized vans. My wife’s Honda Element seems to get more blown around by crosswinds than my Toyota Yaris does, in spite of the fact that the Element is a larger and heavier vehicle.
B.L.E. you are right I went back and read all the posts. I had mistaken YOU for the OP.
It has to do with a lot of things. Not having a trailer attached is one.
The drag of a trailer can also stabilize a vehicle, like the tail on a kite. I have pulled a lot of small trailers with small cars. You notice the weight when accelerating and climbing hills, and it does increase your stopping distance, but turning the car into an unstable white-knuckle vehicle that gets blown off the road every time an 18-wheeler goes past, not so much. This assumes a properly loaded trailer.
Also, modern front wheel drive cars have the rear axles very close to the trailer hitch as opposed to the long trunks behind the rear axles of classic 1960’s rear wheel drive cars. The farther the trailer hitch is behind the rear axle, the more unstable it is.
Not to further this but I’ve never had a problem with cross winds or buffeting from a semi with the camper. If it got pushed at all the car just quickly pulled it back straight and that includes on ice and snow. I do remember running through a very heavy wind south of San Antonio once and the only problem was trying to get enough power out of that diesel to buck the wind.
As long as the tow vehicle is appropriate for the tow, there should be no problem. There are a whole lot of cars perfectly capable of towing loads, even substantial ones. The Prius manufacturer, however, recommends against towing. They know the capabilities of the powertrain, the braking system, and the vehicle better than any of us. Personally, I’d be inclined to follow their recommendation not to tow.
Can the OP tow a motorcycle with one? Sure, it’s a free country, and I wish him only the best.
Would I do so? Nope. But that’s my personal choice. 
On the other hand, some trailer makers are now, I believe, goading people into buying bigger and bigger trailers without buying enough truck.
My brother recently traded in his 23’ travel trailer for a new 28’ model. 28 feet. The tag on the trailer showed a dry, unloaded weight of 7600 lbs. I imagine that even without water in the tanks, outfitting the trailer with kitchen gear, clothes, food, other camping items will easily add another 1,000 lbs or more. That’s almost 4 1/2 tons. And the decal on the side of the trailer says “Half-ton Series. This trailer is towable with a 1/2 ton truck.”
My brother barely felt comfortable towing his 23 footer with a Dodge 1500, and picked up a 2500 Cummins to tow this trailer. But I wonder how many people will gleefully hitch up 9000 lbs to a half-ton truck and take off down the highway.
Seems unrealistic that a 3400# car would be unstable with a small trailer. I towed a car across country with my Plymouth Duster (3200#) and during the trip the vehicles were quite stable. My C10 pickup weighed 3990# and I towed many cars and trailers with that truck.
There’s more involved than just stability. There’s the capabilities of the powertrain and braking systems.
It comes down to laws. The UK assumes you will put the weight distribution farther back on the trailer, which will lower the tongue weight, which will allow the car to pull the trailer without overloading the vehicle. The US assumes you will put more weight to the front of the trailer, which will make the tongue weight heavier, which will overload most cars design. The manuals are written assuming the driver loads the trailer according to the law.
The UK way of doing things is inherently more dangerous at high speeds than our way of doing things, because with a lower tongue weight, as you increase speed the tendency of the trailer to sway goes up. The US way is safer because that trailer is going to stay stable even if you exceed the speed limit.
But with safety comes higher requirements - because the tongue weight is higher, you need a bigger vehicle to take the weight.
Bottom line is that your vehicle might be 100% identical (except for swapping where the steering wheel is) to a vehicle in the UK that’s rated to pull a 2700 pound camper, while yours isn’t rated to pull anything, or maybe 1,000 pounds at the most. This means that you technically could pull a trailer with your car, but if you load it properly according to US standards you will overload your car, and if you load it properly according to UK standards, you’d better keep the speed way down because your safety margin is going to be cut, at which point the best practice is to not tow at all.
I will NEVER tow a trailer with the weight loaded in the back. I’ve seen what happens when the weight loaded in back causes the trailer to unhitch itself. It’s nor pretty.
Just for fun I did a search for trailer regulations in the United Kingdom. Rules they do have plenty. As for loading the few sites I saw stated the load weights should be evenly distributed and since all the trailers for cars and trucks I have seen all have the wheels behind the center of the trailer. That means to me that the most weight would be at the front and not the rear.
To clarify, “farther back” does not mean “all the way back.”