Because the Toadmobile was supplied without a hitch receiver, I'm going to talk about the after-market variety. There are lots of vehicles that come with a factory fitted item which may or may not be up to the task. Factory fitted or after market, though, they all need inspecting by an expert and nothing should be taken for granted as they all have their pros and cons. Our hitch receiver was chosen, and modified, by Can Am RV; we most certainly would not be towing without their knowledge and assistance.
This is what our after market hitch receiver looked like before modification and before installation. The brackets at the end bolt onto the rear of the Sienna's body, some distance from the rear axle but at the maximum width of the car. The receiver box in the centre, the bit where the hitch head is fitted, has a 2" opening and is rated at Class III/IV.
Here's how it looks, installed on the Toadmobile; complete with humorous insert in the receiver box!
I mentioned before that the hitch receiver had been modified; the standard item isn't sufficiently robust to take a very heavy load, nor does it transfer sufficient weight forward when the weight distribution system is fitted. This is where the experts at Can Am RV come into play and it is they that have welded two three foot long L section steel bars onto a plate behind the receiver box. These bits of steel are then bolted to a point on the car just behind the rear axle.
Here is the modification as installed on the car. The bolting point can be seen on the left of the picture and the welding, with an additional plate, can be seen on the right, just behind the receiver box.
This modification adds rigidity to the device to counter the upward and forward forces exerted by the weight distribution system, adds an additional bolting point to the car as a fulcrum, and helps to transfer the weight on the hitch forward down the length of the car. Without the modification, it's unlikely that this particular hitch would do the work required of it, for our trailer at least.
One point worth mentioning here is that the receiver box is tucked under the car. The closer it can get to the rear axle, the better, as the distance from hitch to rear axle is critical; the shorter the better.
A quick look at the hitch head under tension (above) will show how close it is to the back of the car, so much so that the folks at Can Am RV have cut away sections of the head to allow it to be so close; these are the areas within the circles.
Going back to the factory fitted receivers, sometimes even they need similar modifications and for all the same reasons. Just because it's factory fitted doesn't mean that it will work particularly well; auto manufacturers are rarely experts in towing.
I hear a lot of people say that using a car that is of "Unibody" construction, that it is pressed steel and having no main frame or chassis, for towing is asking for trouble. Unibodies are said to twist and flex and fail to provide sound mounting points for hitch receivers. Well, this unibodied car is plenty rigid and does, with the receiver modification, provide robust mounting points. Indeed, the chassis on a pick up truck is really a very narrow frame that is more prone to twisting than the wider unibody. Receiver mounting points are necessarily narrower on a truck and whilst a chassis will transfer weight, it's all done down a narrow spine and not spread as widely across the vehicle as it is with the unibody. I know that I won't convince the traditionalists who like their chassis, but the unibody works for us.
We've run this set up for two seasons now and the hitch receiver has proven to be reliable and effective; clearly the receiver is doing its job and everything works as it should.
In the next instalment I'll be looking at what's been done to counter sway, a very real issue when towing anything...
I'm by no means an expert but the unibody vs. body on frame principle difference is that the unibody will take all the torsion from the engine and cause the body to twist, kind of a metal fatique thing. This will cause all the doors and other body parts to develop more movement, poor fitting, squeaks, etc. Body on frame is excluded from this since all the torsion is on the frame. Still, there are plenty of unibody SUVs out there, like the Toyota Highlander. I think you have addressed the principle concern, handling; starting, steering and (most importantly) stopping. The only other one is the transmission. Our '99 Sienna says it was designed to carry and not for towing, which is what aroused my curiosity about your rig. Looking forward to that blog entry :-)
ReplyDeleteNice set up on the hitch with the extra support, but how did you get the trailer to the Can Am RV folks or did you buy it there?
Hi Rich,
ReplyDeleteThanks for taking the time to read and comment.
I'm no expert on Unibody construction, either, but I have had some experience of the improvement in these structures over the years. My first car, in England, was an old style Mini, the first mass produced Unibody in the UK. That car has two steel subframes to support the wheels and in the front, the engine as well. Even with the short length, those cars twisted badly and mine leaked around the windscreen (because it no longer fitted)and the doors were struggling to close properly. That design and manufacture was from the 1950s, though, and needed some improvement. Fast forward to today, and taking the Sienna as an example, the structure of the unibody is so strong that it doesn't even need subframes; the suspension is mounted straight onto the body as is the engine. It also has a ten foot wheelbase and yet maintains its rigidity throughout. If you think about the overall structure of a car with a unibody, it has a wheel on each corner and the entire weight is sprung on those wheels. A car (or truck) frame is sprung on the wheels but the body is sprung on the frame, which allows some considerable lateral movement that adversely affects the handling of the vehicle. The narrowness of the frame also allows some considerable flex, even in the strongest construction, something that a rigid unibody simply doesn't allow.
I did say in the blog, though, that it's difficult to convince people of the advantages of the modern unibody against the traditional frame construction. I'd point to modern race cars, though, like F1 or Indycar; they are the ultimate in unibody construction, albeit that they use slightly tougher materials than pressed steel!
On the transmission issue, Can Am keep an eye on what happens to their customers cars over the long term and they have had no reports of transmission issues. Of course, if you're going to pull a 7000 lb monster behind you it will impact on the transmission and its components but so far, no one has had a major problem. What Toyota may or may not say about towing will be rooted in their desire to sell their cars to their intended markets. There is no advantage to Toyota to recommend Siennas for towing because they sell other vehicles that are perceived to be better for the task. I'm not knocking Toyota, they will do what's best for their business. Real-world experience shows, though, that the modern minivan is a competent tow vehicle, regardless of what Toyota might tell you.
We did buy the trailer at Can Am and the hitch and modifications were part of the deal. Had we not bought there I doubt we'd be towing with this combo.
I certainly enjoy reading this blog, in particular how it was done.
ReplyDeleteOne thing I have noticed is that Mr. Toad must get a bit of flak for towing with a car, as there is a peppering of comments about it.
And as in this post, it boils down to body on frame, vs unibody.
But times have changed. An important example of this is the Freightliner Sprinter (designed by Mercedes), which was deliberately designed as unibody for the versatility of outfitting it for whatever needs a company might have. It has a towing capacity of 7500 lbs - unibody construction!
Really things have come a long ways.
Hi Shapechanger, thanks for taking the time to comment.
ReplyDeleteI think it's difficult to persuade people away from Frame and Body construction as it's viewed as being being traditional and stronger. Unibody development has moved forward, though, and the rigidity that can be achieved in a modern Unibody actually betters the old frames. The proof, of course, is in real-world use and the Unibodies appear to be thriving.