Flat towing a Rivian

Discussion in 'Rivian General Discussions' started by CappyJax, Mar 4, 2019.

  1. CappyJax

    CappyJax Well-Known Member

    Vehicles:
    Subaru Forester
    Joined:
    Dec 26, 2018
    Messages:
    157
    Likes Received:
    41
    I hope Rivian is listening.

    I think they should consider making their vehicles flat towable by RV's. It would be like turning the RV into a hybrid. The Rivian could use power to reduce or eliminate its load on the RV, and maybe even assist in going up hills. Such a feature would allow for towing by just about any other vehicle since the actual load on the towing vehicle would be minimal.

    It could also provide for regenerative breaking going down hills and for stopping the RV. This alone would keep the Rivian batteries fairly well charged.

    These features would make the Rivian the perfect toad.
     
    fastwheels and ACDC like this.
  2. ACDC

    ACDC Member

    First Name:
    Michael
    Vehicles:
    2013 Outback, 2012 Tacoma
    Joined:
    Feb 27, 2019
    Location:
    Portland OR
    Messages:
    23
    Likes Received:
    6
    Great idea and would be an industry first for EVs, but Teslas and the Nissan Leaf can't be flat towed so I'm wondering if there's a reason EVs specifically can't be flat towed.
     
  3. CappyJax

    CappyJax Well-Known Member

    Vehicles:
    Subaru Forester
    Joined:
    Dec 26, 2018
    Messages:
    157
    Likes Received:
    41
    I think the issue is that they can't be towed with the power off. If you had a system whereby the power remained on, the EV would be driving itself with steering coming from the towing vehicle. I am sure this could easily be done with software. If the RV has a tow capacity of 3,500 pounds, then the Rivian would moderate the power to reduce the load on the RV. This wouldn't take as much energy as driving, and the range of the Rivian under such conditions would probably be double or triple its driving range. The return of energy from regenerative breaking could be substantial since it is slowing both vehicles.
     
  4. EyeOnRivian

    EyeOnRivian Well-Known Member

    Vehicles:
    Mitsubishi Endeavor, pre-ordered R1S but may change to R1T
    Joined:
    Feb 14, 2019
    Location:
    Chicagoland
    Messages:
    145
    Likes Received:
    96
    Yes, very innovative idea. I like it. However, this sounds like it would require a significant amount of system integration and of course safety testing. So, if Rivian is listening ;), I personally would rather see them consider it *after* they launch the initial version of their vehicles. Spend the time now refining and testing the reliability of their current options/features for the initial launch.

    RIvian has to be careful to not fall into the trap Tesla did with the Model X by putting in way too many features in the initial version. An admission by Elon himself. He even had a name for it that escapes me at this moment. All those additional bells and whistles drastically delayed the Model X production many times.

    I suspect some feel some of these "additional features" are worth waiting for - they're just too important to not have. I get it, but for me, I would rather have a few less features and a more reliable vehicle get launched in a timely manner than to be strung out over repeated delays. This also typically translates to less vehicle service problems. Plus, it seems a lot of new vehicle features/options for an EV can be added via OTA (over the air) software updates versus having to buy a whole new model year. So we can be enjoying the vehicle now/sooner while we wait for the new feature(s) to become available after sufficient vehicle testing.
     
  5. Kengrigg

    Kengrigg New Member

    First Name:
    Ken
    Vehicles:
    Honda Ridgeline
    Joined:
    Mar 13, 2019
    Location:
    Sacramento California
    Messages:
    1
    Likes Received:
    0
    Will this truck be towable? Behind my Motorhome.
     
  6. stank65

    stank65 Well-Known Member

    First Name:
    Rich
    Vehicles:
    Tesla Model 3, Chevy Tahoe, GMC Acadia
    Joined:
    Apr 2, 2019
    Location:
    Coopersburg, PA
    Messages:
    48
    Likes Received:
    17
    Per Rivian twitter, the Rivian will be able to be flat towed. I am going to the NYC event and will be asking them about this.

     
    Aurum and Administrator like this.
  7. CappyJax

    CappyJax Well-Known Member

    Vehicles:
    Subaru Forester
    Joined:
    Dec 26, 2018
    Messages:
    157
    Likes Received:
    41
    Please ask the curb weight of the 180 kWh battery vehicle. I am looking at RVs now, and would hate to get one that doesn’t have enough owing capality.
     
  8. godfodder0901

    godfodder0901 Active Member

    First Name:
    Jared
    Vehicles:
    Honda Civic
    Joined:
    Mar 12, 2019
    Location:
    Washington
    Messages:
    35
    Likes Received:
    31
    There is a chart on this site that list the curb weight as 2670kg for all battery options. Doesn't seem 100% correct, but will likely be in the ballpark.
     
  9. CappyJax

    CappyJax Well-Known Member

    Vehicles:
    Subaru Forester
    Joined:
    Dec 26, 2018
    Messages:
    157
    Likes Received:
    41
    Yea, at roughly 4.5kg per kWh, the different between the 105 and 180 is around 340kg.
     
  10. stank65

    stank65 Well-Known Member

    First Name:
    Rich
    Vehicles:
    Tesla Model 3, Chevy Tahoe, GMC Acadia
    Joined:
    Apr 2, 2019
    Location:
    Coopersburg, PA
    Messages:
    48
    Likes Received:
    17
    Confirmed flat towing from RJ himself at the NY event. He said the four motors will be able to decouple which will allow for the flat tow. It sound like this decoupling ability (which Tesla doesn’t have) will be a key design feature that will help in extending the range of the trucks as well. With the motors being able to decouple, in some instances energy won’t be needed to spin up a pair of the motors and that will be a significant energy savings. Today dual motor model 3s get worse efficiency than single motor because they aren’t capable of decoupling one of the motors.
     
    krcossin likes this.
  11. CappyJax

    CappyJax Well-Known Member

    Vehicles:
    Subaru Forester
    Joined:
    Dec 26, 2018
    Messages:
    157
    Likes Received:
    41
    So no regenerative braking then. That stinks. You could literally charge the entire battery going through Colorado and using regenerative braking to slow the RV.
     
  12. EyeOnRivian

    EyeOnRivian Well-Known Member

    Vehicles:
    Mitsubishi Endeavor, pre-ordered R1S but may change to R1T
    Joined:
    Feb 14, 2019
    Location:
    Chicagoland
    Messages:
    145
    Likes Received:
    96
    @CappyJax - Have some good news about regen during flat tow. I found a recent article (posted yesterday!) stating regen IS possible during flat tow.

    "Many people like to use their motor home or a 5th-wheel to tow a vehicle behind it. Rivian says that the R1T will be capable of charging its batteries while being flat towed behind an RV or another vehicle. This is an innovative idea, but it could and would add an extra burden on the vehicle that is towing it." ​

    Source - TFLTruck: "Now the Rivian R1T Electric Pickup Truck Comes with a Kitchen Sink and Can Be Charged While Being Towed Behind an RV" - May 20th, 2019
     
  13. stank65

    stank65 Well-Known Member

    First Name:
    Rich
    Vehicles:
    Tesla Model 3, Chevy Tahoe, GMC Acadia
    Joined:
    Apr 2, 2019
    Location:
    Coopersburg, PA
    Messages:
    48
    Likes Received:
    17
    Man, this would be great news. Haha you can tell whoever said that doesn’t understand that you use the flat tow vehicle to help you slow down. If done right it shouldn’t be a “burden”.
     
    CappyJax likes this.
  14. CappyJax

    CappyJax Well-Known Member

    Vehicles:
    Subaru Forester
    Joined:
    Dec 26, 2018
    Messages:
    157
    Likes Received:
    41
    That is pretty cool! However, I am now leaning towards building a lightweight, aerodynamic tiny home and pull it with the Rivian. I think I can get over 200 miles of range with the right design.
     
  15. Hmp10

    Hmp10 Well-Known Member

    Vehicles:
    2015 Tesla Model S P90D; 2018 Honda Odyssey
    Joined:
    Mar 7, 2019
    Location:
    Naples, FL
    Messages:
    273
    Likes Received:
    136
    The only way that you could recharge the batteries while flat towing is for the wheel motors to be acting as generators. For wheel motors to act as generators, they have to have an external source of energy. In the case of regenerative braking, it's the recovered kinetic energy from scrubbing vehicle speed. In the case of flat towing, it's the pulling force of the tow vehicle against the resistance of the EV's motor spin when acting as a generator. There is no "free energy" that becomes available to store in the batteries from flat towing an EV. In effect, the energy being stored in the towed EV's batteries is coming from the combustion engine in the towing vehicle. The tow vehicle is not just towing the weight of another vehicle whose transmission is put in neutral with its wheels rotating freely. It's towing that weight plus overcoming the resistance of the EV's motors when they're behaving as generators. This most definitely creates an added load on the tow vehicle and in some cases could exceed its tow rating.
     
  16. CappyJax

    CappyJax Well-Known Member

    Vehicles:
    Subaru Forester
    Joined:
    Dec 26, 2018
    Messages:
    157
    Likes Received:
    41

    You are not grasping the concept. You don't have the regenerative breaking applied when you are accelerating or cruising (That would be really stupid), you only apply it when you are braking. Therefore, it IS free energy, because instead of heating up the break pads of the RV, you are putting energy back into the battery of the EV.
     
  17. Hmp10

    Hmp10 Well-Known Member

    Vehicles:
    2015 Tesla Model S P90D; 2018 Honda Odyssey
    Joined:
    Mar 7, 2019
    Location:
    Naples, FL
    Messages:
    273
    Likes Received:
    136
    I do grasp the concept. I did not mean "free" in an economic sense. I meant "free" in terms of the laws of thermodynamics, which hold that energy cannot be created out of thin air. During regenerative braking, the energy of the car's forward momentum is converted from potential energy to kinetic energy to turn the motors which are switched to generator mode. It's not energy for which the driver pays anything at that point -- and therefore is "free" in that sense -- but it is energy in the system that was created when electricity flowed from the batteries to turn the motors and is recaptured to turn the generators -- and therefore not free in the thermodynamic sense.

    And I was responding to the comment that the author of the cited article was wrong in stating that charging an EV by flat towing would increase the burden on the tow vehicle. The author was, in fact, correct. When an EV's motors are switched to generator mode, they create a resistance to rotation, which is the very reason regenerative braking works. It is that resistance to rotation that brakes the vehicle. To charge an EV with flat towing, the tow vehicle has to generate the pull not only to move the weight of the towed vehicle and overcome its aerodynamic drag, but also to overcome the resistance to rotation in the towed car's motors. And that increases the burden on the tow vehicle beyond what conventional flat towing would require, as the energy to drive the generators has to come from some place. In a utility generator, the energy comes from coal, natural gas, nuclear-generated steam, or hydroelectric force. In a towed EV, it comes from the towing vehicle's pull.
     
    Ninja911 likes this.
  18. cllc

    cllc Member

    First Name:
    Craig
    Vehicles:
    Tesla model 3, Subaru Forrester, Ford F250 Superduty
    Joined:
    May 16, 2019
    Location:
    wisconsin
    Messages:
    20
    Likes Received:
    13
    Occupation:
    Electrician
    I thought they were referring to the energy they would be recovering when they would be going down hill and when they would be using the tow vehicle to slow down the vehicle that was doing the pulling.
     
  19. CappyJax

    CappyJax Well-Known Member

    Vehicles:
    Subaru Forester
    Joined:
    Dec 26, 2018
    Messages:
    157
    Likes Received:
    41
    Exactly. They wouldn't have the motors charging the batteries in cruise, that would make zero sense. They would use the EVs regenerative braking only to slow down the tow vehicle during braking or downhill. This would recharge the batteries significantly. Instead of garnering regenerative breaking from a 6,000 pound vehicle, you are now getting it from 20,000+ pound vehicle. If you were in the mountains and using it a lot, you could recharge the batteries to full in a couple hours of driving pretty easily.
     
  20. Hmp10

    Hmp10 Well-Known Member

    Vehicles:
    2015 Tesla Model S P90D; 2018 Honda Odyssey
    Joined:
    Mar 7, 2019
    Location:
    Naples, FL
    Messages:
    273
    Likes Received:
    136
    #20 Hmp10, May 23, 2019
    Last edited: May 24, 2019
    The article in question read thus:

    "Rivian says that the R1T will be capable of charging its batteries while being flat towed behind an RV or another vehicle. This is an innovative idea, but it could and would add an extra burden on the vehicle that is towing it."

    There is no reference in the article to charging only while going downhill.

    Are you saying that the Rivian being towed would switch from neutral into regenerative mode when it encountered a downhill slope and then back into neutral when the road flattened out? Exactly how would it to do so? When being driven, the motors don't just go into and out of regenerative mode on their own. They are switched into and out of regenerative mode by an electrical relay based on accelerator and brake pedal inputs from the driver.

    In order to switch between neutral and regen when those inputs from the driver are missing, the vehicle being towed would have to be able to detect when it was slowing or entering or leaving a downward incline.

    I could see Rivian having a tow recharge feature that a driver could select for towing, although that would significantly increase the fuel consumption of the tow vehicle. However, for the feature to work only when the tow vehicle is braking or going downhill, there would have to be some means for the car to detect those conditions without any driver input, such as inertia or mercury switches and associated computer programming . . . and I've never seen any mention of such a setup in a Rivian.

    I have been driving a car with regenerative braking for four years. While I really like the one-pedal driving it offers, it doesn't put as much energy back into the batteries as many people imagine. (One of the reasons Tesla is exploring adding capacitors to its battery pack is the low efficiency of regenerative energy capture using just batteries.)

    And let's get real. Regarding the benefits of a 20,000+ pound arrangement, how often are you going to be towing your Rivian (when loaded to its max gross weight of 7,650 pounds) downhill behind a 12,000+ pound vehicle? This is a fantasy exercise more than a realistic way to charge an EV in real-world situations.
     
    Ninja911 likes this.

Share This Page