Flat towing i3 "4 wheels down" behind rv

[Joff]

I know that it manual says the I3 can not be towed with it's drive wheels turning. I understand that the motor turns whenever the drive wheels turn. Does it also say you can't shift it into neutral and coast down a hill? Because I don't see a big difference, except that you can tow farther than you can coast downhill. What if you installed a switch that could disconnect the motor from the controller? Another possible issue is the steering lock. When you tow "4 wheels down" it is important that the front wheels can freely steer into the direction that the RV is pulling it. My Yugo with no power steering does that easily, but I don't know how well that works on a car with electrically assisted power steering. I don't own a I3 yet, but it is my current favorite of cars I am looking at. Figuring out how I could tow it would be a big plus. Thanks for any insight!

 

[PBNB]

You may be able to shift into neutral (haven't tried it) going down a hill but you need to be stopped with your foot on the brake to put the car back into "D" so that may not be very efficient.

Also you would not capture the energy from a descent to put back into your batteries if you are coasting.

Perhaps a dolly could be used with the i3 back wheels on the dolly and the steering locked?

 

[Anonymous]

From: THE BMW i3 RESCUE GUIDELINES manual.

Section 6 - BREAKDOWN ASSISTANCE AND MINOR ACCIDENTS.

• The vehicle may not be towed by the axles, as the electric motor could supply current to the high-voltage system. The car may only be transported on a flatbed vehicle.

• To bring the vehicle out of a danger zone, you may pull it extremely slowly over a short distance of no more than 500 m. If possible, make it rollable first by switching the selector lever to N.

I assume the electric motor could supply current to the high-voltage system means that this will cause damage to the high-voltage system by supplying more/higher voltage than the system can take. In other words, tow the car four wheels down, more than 500 meters, at more than a crawl, and you can fry the car.

If I was going to tow behind an RV, I'd invest in a small car-haul trailer.

 

[alohart]

Does it also say you can't shift it into neutral and coast down a hill? Because I don't see a big difference, except that you can tow farther than you can coast downhill.

Neutral is an electronic state possible only when the car is in drive readiness state. To stay in drive readiness state for towing, you'd need to exit the passenger door because opening the driver door causes the car to exit drive readiness state which shifts the car into Park locking the drivetrain. Drive readiness state involves all controllers being on which requires enough power to slowly discharge the Li-ion battery pack, so I wouldn't want to try to keep an i3 in drive readiness state for hours while towing.

What if you installed a switch that could disconnect the motor from the controller?

That might require 3 high-amperage switches because the motor is a 3-phase AC motor. Even isolated from the motor controller, a spinning motor would still produce heat that might overheat the motor.

Another possible issue is the steering lock.

The i3 has no steering lock, so that's not an issue.

When you tow "4 wheels down" it is important that the front wheels can freely steer into the direction that the RV is pulling it. My Yugo with no power steering does that easily, but I don't know how well that works on a car with electrically assisted power steering.

I don't know how much resistance to steering the i3's electric power steering motor creates. Our 2000 Honda Insight had electric power steering, and I was able to manually move its front wheels side-to-side when the front wheels were lifted off the ground. So electric power steering wouldn't necessarily prevent the front wheels from steering while towing.

 

[jadnashuanh]

Locking the steering generally requires straps. On cars with a steering wheel lock, it often only engages with the wheel slightly turned, so that would be problematic if they were on the ground.

 

[Joff]

Thanks for the replies. If the car can coast freely in neutral, I would reason the motor can't be producing a lot of heat or current, as the energy can't be produced without some resistance to movement. Maybe it would make too high a voltage if there was no load on it? If there is a chance it would drop out of "readiness" mode and lock up the wheels while towing, that might be a good reason for them to forbid it. I would think staying in readiness mode should take very little power compared to moving the car. BMW is warning against rolling a non functioning i3, which makes sense.

 

[jag932]

This discussion prompts a question. Am I to infer from what has been written so far that an i3 should not go through a carwash?

 

[CharonPDX]

This discussion prompts a question. Am I to infer from what has been written so far that an i3 should not go through a carwash?

Per the manual a carwash is fine - shift in to neutral, then power the car to "standby" (Push the power button once.) When it's time to get moving again, hold the brake while pressing power again to return to "on" status, shift in to drive, and go.

 

[TheMK]

If I understand correctly, the motor is permanently connected to the drive wheels (i.e. there is no clutch). There is a procedure you can use to engage neutral for an extended period of time, which would allow the i3 to roll behind your RV indefinitely. Honestly, I think the biggest issue with towing the car would be the lack of coolant flow through the motor. I'm not sure how hot it would get without any electrical current flowing through it, but the motion of turning it will create some. BMW likely was also concerned about high voltage generation, which is definitely possible with the wheels turning the motor, but I would expect the electronic management to be sophisticated enough that this wouldn't cause a problem. I just don't know what to say other than, it's probably best to not tow on the ground for an extended time. The high voltage charge generation shouldn't be a big issue, at least in my mind, as the contactors should prevent power from reaching the battery. The cooling though may be the biggest issue to work out. If you left the car in drive-readiness and in neutral, the coolant pump would still run, but you'd be draining the battery.

 

[keehn]

If I understand correctly, the motor is permanently connected to the drive wheels (i.e. there is no clutch). There is a procedure you can use to engage neutral for an extended period of time, which would allow the i3 to roll behind your RV indefinitely. Honestly, I think the biggest issue with towing the car would be the lack of coolant flow through the motor. I'm not sure how hot it would get without any electrical current flowing through it, but the motion of turning it will create some. BMW likely was also concerned about high voltage generation, which is definitely possible with the wheels turning the motor, but I would expect the electronic management to be sophisticated enough that this wouldn't cause a problem. I just don't know what to say other than, it's probably best to not tow on the ground for an extended time. The high voltage charge generation shouldn't be a big issue, at least in my mind, as the contactors should prevent power from reaching the battery. The cooling though may be the biggest issue to work out. If you left the car in drive-readiness and in neutral, the coolant pump would still run, but you'd be draining the battery.

Apologies for bringing up an old topic, but we recently purchased a 2015 i3 REX and would also like to use her as a "toad" behind our diesel pusher. Do you or anyone know specifically how to engage neutral for an extended period of time?

Also, wouldn't the HV disconnect plug in the frunk also negate any charging that a flat-towed motor might attempt (drive in neutral, of course)?

Again, thanks!

 

[alohart]

Do you or anyone know specifically how to engage neutral for an extended period of time?

As was written, drive ready state would be the only way to remain in neutral. That's certainly not ideal but probably not the biggest problem.

Also, wouldn't the HV disconnect plug in the frunk also negate any charging that a flat-towed motor might attempt (drive in neutral, of course)?

Drive ready state can't be entered with the HV disconnected. If the HV disconnect were disconnected while in drive ready state, an i3 would almost certainly exit drive ready state and shift to Park. BMW recommends not disconnecting the HV disconnect while the HV system is on because certain processes in HV electronic modules would suddenly be stopped, maybe leaving hardware in a bad state.