2012 Toyota Prius C: Can You Tow It Behind a Motorhome?
June 5, 2013
You can tow any car behind a motorhome if you strap it on a trailer. But motorhome aficionados rightly consider trailers to be a pain in the butt because they represent extra towed weight and a storage problem. They'd much rather tow the car on its on wheels with a simple tow bar in so-called four-down or "dingy" fashion.
Easy is the keyword here. This is, after all, a recreational activity. Upon arrival, a dinghy can be quickly unhooked and driven around on side trips while the motorhome sits parked with its awnings unfurled and its sliders popped out in full relaxation mode.
Of course there are mechanical implications for the car involved.
Can the 2012 Toyota Prius C join this club? Can you tow a Prius C behind a motorhome?
In a word, no. And the manual makes no bones about it. The hybrid drivetrain of the Prius C — or any other Prius — cannot tolerate being dragged about for any length of time.
As you can see, they don't go into details. But the reason has to do with the way a Toyota hybrid planetary transmission works.
The main electric drive motor is directly connected to the transmission's outer ring gear, the big one that encircles all the others with inward-facing teeth. The ring gear housing directly drives the differential and front wheels. Tow the car with the front tires on the ground and you spin the shaft of the electric motor. The "N" position on the shifter doesn't work like it does in a normal transmission.
But there's more to it than that. Any rotation of the ring gear will set the planet gears that mesh with it in motion, too. Unless the computer is fully awake and engaged, the orbit speed of the planet gears, and the engine's crankshaft which is connected to them, will be unregulated. That's because in normal use the central sun gear is the director that controls the whole works via a second motor/generator that's connected to it. The transmission doesn't work, even when being passively towed behind a motorhome, without the sun gear's full active participation.
A Prius "Hybrid Synergy Drive" planetary transmission is highly-optimized to carry out its high-mpg mission. Mechanically, it's simpler and has fewer parts than most other transmissions, but its control software is amazingly complex. On either front the needs of flat-towing would stand in the way of a drivetrain design capable of 50+ mpg.
Dan Edmunds, Director of Vehicle Testing @15,901 miles