Prius Hitch Mounts Strength

I don't think it'd be realistic or practical to reinforce the body. There are tow hitches designed. They connect at the exhaust bracket on the right side, and at a tow lug on the left side. I think a small, well balanced trailer is best bet. Thought about it a bit, wouldn't do it myself, but others have.

 

I'm a chemical engineer by education, but mechanically inclined.

The Prius manual states to not tow with it, so we'll start there as the Toyota engineers warn against it.

1. Is anything possible: Yes
2. Could you make the Prius tow: Yes
3. Have others added a hitch to their Prius: Yes
4. Could you do more work to reinforce the area: Sure
5. What are the effects on the other components as a result of the extra weight added to the rear of the Prius: Not sure
6. Could you damage something in the process: Possibly
7. Is it worth the extra effort: Only you can answer that

That's my perspective. If I need to haul something, I usually pony up a small amount of cash that I've saved in fuel and rent a small pickup for the day. Or borrow the neighbors Taco as he doesn't mind .

 

I won't speak as an Engineer, but as a Licensed Mechanic and owner. Between my last 2010-II and current 2015-4 Prii I have towed more times over more miles than I care to remember...and big loads too. No damage has occured to anything other than MPG. Relax...you are over thinking this. Just mind your fluids better.

 

Good luck collecting your data and keep us posted.

 

Worst was about 25-26 mph doing 65 mpg front Denver to Dallas (the KS route) with open 6x9 hauling top and bottom roll-away and personal belongings. Use a 1-1/4 Curt Class 1 hitch with 2" ball high offset and harness.

 

I bent my Curt 1-1/4" hitch... The receiver used to almost touch the black trim at the bottom of the bumper cover and now there's a 3/4" inch gap. It happened because I needed to haul my wheelbarrow size wood chipper ~250 pounds on a round trip of 1,600 miles and didn't want to dismantle and put inside the car like I usually do because I needed that space for sleeping.

And because most hitch mounts stick out too far (longer lever = more force) I built a custom mount for my chipper that was as short as possible and dismantled and removed as much of the weight of the chipper as possible and mounted it so close to the rear bumper cover that I used some wet sponges to limit movement / prevent scratching and the whole thing was wrapped in a tarp, so it was a solid covered extension of the rear of the car so their was no noticeable loss in MPG. It did handle more sloppy, but I drive a Prius so it's all about driving slow and getting good MPG anyways so anything to encourage me to drive slower is great as far as I'm concerned!

Everything was going really well and no issues, then I got to the worst part of the drive on the 880 in SF Bay Area where people drive like lunatics on crazy worn out roads. There was a section that just to merge in the "slow" lanes you had to be going 75mph and that's when I hit a major slump in the road I knew that was going to be the max force on what I built. And sure enough the hitch bent... It still works fine and no signs of damage to the vehicle where it mounts or elsewhere. I tried jacking the car up from the hitch receiver to try to bend it back, but there's no way I could come near the force that bent it down in the first place and even if I could, it's would weaken the metal even more.

So if I were you, I'd find a way to rapidly dismantle the motorcycle so you keep the load of the tongue weight down and then I'd build an aerodynamic structure that the hypermile max-MPG folks use which will give you more room to store lighter stuff in the far back and hopefully find a to modify your rear hatch so you can get the majority of the motorcycles weight over the rear wheels of the car rather than hanging off the edge in a way that will bend your hitch, or cause unpredictable handling if you're ever trying to avoid getting in an accident at freeway speeds. That way you also don't have to waste a fortune of money and dozen of hours re-designing the suspension or reinforcing the hitch...

 

My Son hauled his Harley twice using the 2015-4 with the Curt 1-1/4 set up no problem. YMMV

 

A really important point that may explain some of the reactions that you may see as being overly cautious:

If you don't know what you're doing when you try BASE jumping, well, that could be a problem for you.

If you don't know what you're doing when doing something like this, that could really ruin someone else's day or life.

May be better to let the more knowledgeable people blaze the trail and follow them, if you really want to do something out of the ordinary. Many of your basic comments on this are fundamentally wrong and I don't think you know. This project is not a place to learn that.

Good luck and keep everyone safe.

 

I disagree... I think the OP's approach is both thoughtful and thorough and way safer than many others who would attempt this. And I find your comments provide no specific details whatsoever, just a bunch of sweeping overgeneralizations hyping up the fear via false equivalencies.

 

I will agree with that one.^^^

That does not mean it will be safe enough to be driven in front of you or me.

I'm trying to be as diplomatic about this as I can, so yes, I'm speaking kind of non-specifically.

If you look at some people's posts on here, you will see a lot of enthusiasm and very little skill, knowledge, experience, or good results. That's just fine for upgrading interior lighting, putting on bumper stickers, converting the car to cold fusion power, or adding a nitrous kit. Nobody ELSE is going to get killed if those projects fail. The project discussed here is completely different. It becomes a danger to innocent people driving down the road, minding their own business, wearing their seatbelts, just trying to safely get where they need to go.

As a different example, again, trying to be nice, if somebody led a 10 page thread of bewilderment about the difficulties they were having in doing an oil change or filling the gas tank ... then proposed a plan to make the back half of the car easily removable from the front, for ease of loading ... but they were really serious about it, what would you think? (yes, greatly exaggerated hyperbolic scenario to make my point)

Here's a specific one, guessing at the design engineers' intentions: "Although, I think, if I were a car engineer I would mount the hitch on the strongest part of the car trying to make it as much "one" with the car (I don't think they would do anything less than that)."

The "car engineers" don't design a Prius to carry a hitch as a prime directive. Or even an afterthought. Toyota knows people will try anything, but recommend not to install a tow hitch. They design the car as efficiently as they can to do what it has to do.

Trucks and SUVs are designed differently, and will have strengthened structural members with hitch mounting locations designed in place. Even my mini-vans have had that. I have 3 degrees in mechanical engineering and would never consider home brewing a tow hitch, even for use on a vehicle with designed mounting points. Sure, I might see things differently if I lived in a post-apocalyptic Mad Max world where the other dangers of the world outweighed that from a failing hitch.

And BTW, I absolutely love crazy ambitious stuff like that Prius longtail photo above. But things like that (yes, it is putting innocent people at risk, if something were to fall off) need to be done by competent people, where their enthusiasm does not outrun their capabilities.

 

There's plenty of evidence of idiots, especially pickup truck drivers, who don't properly secure their load... There's also plenty of evidence of people who modify their vehicle in a way that puts other people's lives in danger.

But I'm not seeing much evidence at all of people who spend a long time researching and discussing car hauling modifications losing their load or putting other people's lives in danger.

I spent over a dozen hours researching & designing a way to haul my 250 pound wood chipper on a 1600 mile trip and I put so much effort into it because I don't want anyone to get hurt and if it damaged my Prius I likely couldn't afford to get my car fixed.

So the more people I could talk to about what I was rigging up, as well as the more I tested and redesigned to improve strength of it, the better off I and everyone else sharing the road with me was...

By providing information and assistance to the OP of this thread, I'm hopefully helping make their rig safer. That's not what you're doing. You're just telling them not to do it, which doesn't make what they're going to do safer.

 

You're not looking very hard then.
Here's one of the two videos I looked at. The most shocking thing is how unconcerned he is.

If the kids in your local high school had some ideas about using Propane tanks in lieu of fireworks for Independence Day celebrations, would you try to give them constructive advice on how to do it, or maybe just advise against it?

 

In the UK, the current Prius is rated to tow up to 725 kg. When Toyota GB issued their press release on this, it read in part:

"Prius's new-found ability is thanks to heat management measures that have been introduced in the hybrid system's main electric motor-generator and the differential. As a result, the car has a maximum towing capacity of 725kg for both braked and unbraked trailers."

No mention of frame strength; I suspect it's a non-issue, but if you're really worried you can draw the FBD, write up your equations of equilibrium and solve for the forces at the attachment points.

 

To be clear... you can screw the puuch with a semi if you don't know what you are doing. If you have not "learned" how to tow/haul, you probably don't want to learn with a Prius...which IS documented as acceptable by the mfg in other Countries.