By on November 29, 2011

TTAC has long held that GM should have initially sold the Volt as a Cadillac, putting its newest, most high-tech drivetrain in a luxury car that could support its high list price. Of course the bailout made a CadiVolt a touch too elitist, which led to GM canceling production plans for its Converj Concept coupe. But with plans back on to sell a Converj-inspired ELR coupe, a new question arises: can Cadillac really charge significantly more than the Volt’s $40k-ish MSRP without doing more than simply rebodying the Volt in Cadillac’s Art & Science styling? Automotive News [sub]‘s Rick Kranz reckons Cadillac could do more, and thinks that the ELR could end up with rear-wheel drive.

Kranz writes:

GM has a new rwd platform that will be shared by the Cadillac ATS, a compact sedan that goes on sale next year. That could be the game changer for the ELR.

But there’s a potential packaging issue with a rwd platform: Can the battery pack be modified so the driveshaft can be positioned below it? I don’t know. The Volt’s T-shaped battery pack is below the rear seats and center console.

Certainly the battery pack could be raised, eating up some space in the passenger compartment. The trade-off would be rear seat comfort, especially headroom, aggravated by the slope of the roof as it approaches the rear of the vehicle.

I find it interesting that the ELR is being touted as a 2+2 instead of a true four-passenger sedan. A 2+2 generally limits rear-seat space to kiddies and grocery bags. There’s no room for adults.

Maybe that’s a signal that the battery pack will be eating up some of the rear-passenger space so the ELR can be offered as a rear-drive coupe.

Kranz is right about one thing: with the Volt as expensive as it is, a CadiVolt needs to be distinctive to sell. But if the battery pack needs to be raised to fit a driveshaft underneath it, the ELR’s handling will certainly be compromised. The Volt is a surprisingly fine-handling car, largely because its huge weight is kept low and central in the body. Raising that huge weight upwards could ruin any handling benefits obtained by rear-drive, making the distinction between the two cars largely academic.

On the other hand, a DOE EV stimulus from 2009 allocated $105m for

Construction of U.S. manufacturing capabilities to produce the second-generation GM global rear-wheel electric drive system.

At the time, that expenditure was something of a mystery, and we still don’t know what it means. But if GM has developed a rear-drive EV platform, that could underpin a rear-drive ELR without the downsides of using the ATS platform. But that’s one Wild-Ass Rumor to be sure…

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14 Comments on “Wild-Ass Rumor Of The Day: “CadiVolt” ELR To Be Rear-Wheel Drive?...”


  • avatar

    When I read the piece, my main takeaway was that Krantz is clueless.

    1. No driveshaft would be involved in creating a RWD electric vehicle. You’d have the motor(s) in the rear, like in the Tesla, Karma, etc. Which would probably require a different platform, and a far larger investment than could be justified.

    2. For RWD to make sense in an electric vehicle, you’d want a much different torque curve than in the Volt. This is doable, but probably not desirable. One of the neatest things about the Volt is the smooth surge delivered by its powertrain–like on a subway or high-speed elevator. This wouldn’t be optimal for kicking the tail out.

    • 0 avatar
      mike978

      So it sounds like the Volt was almost too good in some key aspects like handling and powertrain refinement! The suggestion of making it a Cadillac in the first place has merit, but too late now.

    • 0 avatar
      sitting@home

      But the Volt didn’t turn out to be a pure Electric Vehicle, there is a mode where the ICE directly drives the wheels. So either they’d need to move the whole powertrain to the rear or have a driveshaft.

      But then why does the battery need to be T-shaped ? Surely, like a gas tank, it could be almost any shape … even split into two L’s with the drive shaft running down the center.

      • 0 avatar
        protomech

        They could easily have the engine/generator pair up front and the traction motors in the rear. The “driveshaft” would be the high-voltage cables running nose to tail.

        The Volt reportedly powers the wheels directly in certain modes where the “electric transmission” (generator -> motor) is less efficient than the mechanical transmission. The revelation was late enough in the model reveal that it may have been a choice Chevy made when they weren’t able to get the powertrain efficiencies they were looking for. Perhaps for voltec mk 2 the transmission will be solely electric.

        EV drive and energy storage systems do allow for significantly more varied packaging configurations. The battery packs can be shaped in whatever configuration design and safety considerations dictate.

      • 0 avatar
        sitting@home

        Sorry I don’t buy that. The packaging required to get the ICE to feed through to the drive shaft HAD to be in the design spec from day one. It makes much more sense to totally disassociate the motors from the generator otherwise.

        Maybe now they’ve got some beta testers (aka. customers) to add millions more miles of real world driving they can figure out exactly when and if the direct link is required and version 2 could do without it.

    • 0 avatar

      In the Voltec drivetrain the ICE and the two electric motors are all hooked up to the same planetary set so it’d be a chore to physically isolate the electric traction motors from the ICE. I suppose you could do it with a torque tube and rear transaxle like in the Corvette and some other cars, with the electric motors and planetary set in the transaxle.

  • avatar
    gslippy

    The Converj wasn’t killed because it was ‘too elitist\'; it was killed because its battery could only go 20 miles and the thing would cost around $60k.

    It should not be resurrected, particularly in light of the Volt’s slowish sales trend and today’s fire scare.

  • avatar
    tikki50

    I say make the car flexible as possible. Electric, standard gas, heck even a diesel turbo. Why only offer one form of engine type. The car looks great and will sell. Just make it a green car in some way and keep it Cadillac. I really think the generation of ugly green machines is about over (at least I hope so) and Cadillac should be the brand to demonstrate this. One vehicle, multiple proplusion types available. It only makes sense let the consumer decided which propulsion type they need for the car they want. Of course with it being a Cadillac can we expect a ELR-V in the future? LOL

  • avatar

    Given the huge investment in the Volt’s architecture, and how the whole engine/generator/transmission/motor are so highly integrated, it profoundly unlikely that the Caddy version would be substantially any different, under the skin.

    • 0 avatar
      Herm

      +1

      What he said..

      “Given the huge investment in the Volt’s architecture, and how the whole engine/generator/transmission/motor are so highly integrated, it profoundly unlikely that the Caddy version would be substantially any different, under the skin.”

  • avatar
    Dynasty

    Maybe the propulsion system could be located in the back, and the battery up front (with ample crash protection added).

    I don’t know. I think with some creativity, the vehicle could be packaged many ways. Eventually batteries will be able to packaged better and not necessarily all have to be physically congruent, but just electrically connected (if not already thought of.)

    Nice looking car though.

  • avatar

    COULD end up as RWD? You know, maybe? It might happen?

  • avatar
    FromaBuick6

    A rear-drive plug-in hybrid and a front-drive flagship sedan. That’s some solid thinking right there, Cadillac.

  • avatar
    toplessFC3Sman

    As interesting of an idea as it may be, there is one major problem with having the electric motors on the rear wheels (and not the front); stability. You can’t recapture as much of the braking energy, which really is responsible for the hybrid’s greater efficiency, because the rear tires do much less of the work when slowing a car down in the best of situations, and almost nothing (without skidding the rear end around) when it gets slick. Therefore you get much, much less regen energy back into the batteries from braking, and potentially at the risk of vehicle stability. The Lexus RX hybrid had some of these problems, especially when it was wet or snowy, where the rear wheels would lock up from regen as if the parking brake was pulled, or, conversely, be overpowered by the electric torque when starting off.

    This is besides the whole “cost of a new platform” argument, when they’re still trying to pay off the original. The whole powertrain could move to the back, Corvair-style (which def would be possible with such a huge rear end), but that limits the utility of the hatchback since the front hood height is still limited by driver sight-lines.


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