By on July 18, 2011

It’s been 27 months since I wrote a check for $5,000 to Tesla Motors, my deposit on a Model S sedan. As owner number P717, I’ve gotten some modest bennies to keep me interested till the expected delivery date of mid-2012: a test drive in the Roadster, an invitation to the opening of the New York Tesla store, and some nice promotional swag (T-shirt, coffee mug, and, most recently, a cool little remote-control toy Roadster) .

Last week I was invited to an owners-only preview before a Model S promotional event in Greenwich, Ct. Set in the posh clothing store Richards, just across the street from an Apple store, the event featured a sinuous dark red early proof-of-concept prototype of the Model S. Unfortunately, we weren’t allowed to drive, sit in, or even touch the car (“It cost more than $2 million to build,” we were told). But the black-clad Tesla reps on hand offered some intriguing technical info about the car that, to my knowledge, had not been previously revealed. Among the more interesting tidbits:

  • The Model S will not have the blended regenerative/friction braking that is standard in the Nissan Leaf, Chevy Volt, Toyota Prius and virtually all other mainstream electric and hybrid cars. Like the Tesla Roadster, the brake pedal in the Model S will operate only standard friction brakes. Regen braking, which turns the electric motor into a generator and sends power back into the battery, will occur only when the driver backs off the accelerator. From the driver’s point of view, the feeling is precisely the same as engine braking in a standard car.The question is, how much regen? Hopefully not as much as the Roadster. Back off the gas pedal at 60 mph in that high-performance two-seater, and you’ll be thrown against your shoulder harness by the aprupt deceleration. The feeling is like driving a high-revving gas-powered sports car stuck in first gear. That may be fine for racing or high-performance driving on twisty roads, but in my opinion it’s highly annoying in normal everyday driving.Tesla is currently mulling over whether to include driver-adjustable trailing-throttle regen on the Model S, and if so, what form it should take. There’s currently no industry consensus about driver-adjustable regen. Nissan doesn’t include it on the Leaf, but the Volt has a simple and very effective system: the driver can increase regen by shifting to “Low” on the gear selector. (There’s no actual change of gear, of course; it just feels like it when you back off the gas pedal.) Volkswagen’s Golf Blue e-motion goes a step further with a paddle shifter on the steering wheel that offers three levels of trailing-throttle regen, plus a “coast” mode.

    According to a Tesla rep in Greenwich, the current Model S Alpha prototypes have infinitely adjustable driver regen. Perfect! I fervently hope production cars retain this feature. But I got the feeling that the company may be leaning toward no driver-adjustability at all for the Model S, along with jarringly strong built-in regen like that of the Roadster. “You’ll get used to it,” the rep told me.

    Bad move. Instead of telling us what we’ll have to get used to, Tesla should be asking us, “What would you prefer?” I , for one, would prefer blended pedal braking and infinitely adjustable trailing-throttle regen.

  • Longer-range versions of the Model S will have better battery chemistry, not just more cells. Tesla’s battery packs are arrays of thousands of standard Model 18650 laptop computer batteries. (The Roadster battery pack, for example, has about 6,800 18650 cells.) The Model S will come with three available battery packs offering nominal ranges of 160, 230, and 300 miles. But instead of merely adding more cells to increase capacity, the longer-range versions will also have more advanced cells being developed by Sanyo. As a result, the longer-range versions will weigh only a few pounds more than the basic 160-mile model. But each jump in battery capacity will cost an additional $10,000 or so. “The more advanced chemistry is expensive,” the Tesla rep said.Actual everyday range numbers will be about 20 percent less than the quoted numbers. According to the Tesla rep, the 160, 230, and 300-mile numbers assume the use of 100 percent of the battery capacity. In practice, however, the batteries will be charged only up to 90 percent. And when the battery charge drops to 10 percent, it will revert to a limited “limp-home” mode to conserve power. Thus for normal driving, the range options of the Model S will be 128, 184, and 240 miles, plus a small limp-home reserve..
  • Those killer 21-inch wheels that we’ve drooled over in all the Model S photos and displays will be extra-cost options. The standard car will come equipped with 19-inch wheels and low-rolling-resistance all-season tires.
  • Beta prototypes of the Model S, virtually identical to the production cars, will be available for test drives by owners (and presumably the press) beginning this fall. Where do I get in line?
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25 Comments on “Tesla Model S Customer Blog: Regenerative Braking And Its Discontents...”

  • avatar

    19″ diameter LRR tires? Are these even available?

    I’m with the author as to the preference for regenerative braking. It’s counterintuitive to have to maintain accelerator pedal pressure in order to coast.

    • 0 avatar

      When I completely back off the throttle in the 5 speed mustang and GS500, I get significant engine braking. On the insight, when I back down below about 10% input, I also get a small amount of regen braking.

      In all these vehicles if I want to completely remove the engine from the drivetrain then I need to disengage the clutch. Obviously that’s not an option in the Model S, but I suspect drivers will quickly learn what level of accelerator input allows them to coast.

  • avatar

    Electric cars are different. They should drive differently. Just because we’ve gotten use to the way gasoline engines brake (or don’t, with a slush box transmission) doesn’t mean electric vehicles should behave the same.

    I have often wondered why my Prius DOESN’T act that way. If I am off the throttle it means SLOW DOWN, braking means decelerate harder. That is intuitive to me. But then again I enjoy manual transmissions.

    • 0 avatar

      Okay, but should you have to put the car in neutral if you want to coast without regen? As the former owner of a Civic Hybrid, I’d like to know how you would go about this in a safe manner with an automatic transmission. BTW, mine was a manual.

    • 0 avatar

      “Electric cars are different. They should drive differently.”

      Agreed. So why not give us a third pedal? From right to left: accelerator, friction brake, regen brake. That way, you can control the amount of regen by foot pressure like any other brake and stomp the friction brake if you need it. Maximum control. Maximum efficiency.

  • avatar
    Educator(of teachers)Dan

    For me it’s a simple matter of the fact that true regenerative braking should increase performance of the battery. If I’m going to own an electric or hybrid car I would expect it to feel differently and for the manufacturer to do everything in their power to extend the range and performance of the vehicle, but I am an enthusiast and know that I am in the minority.

    Sadly most Americans likely want all cars to behave like appliances.

    • 0 avatar
      DC Bruce

      +1: Regen braking as a method of recapturing otherwise wasted energy (dissipated as heat from the brakes) makes sense to me. It seems like the design parameters should optimize that, and secondarily focus on making it drive like a ICE-powered car. For that matter, there’s a world of difference between driving a conventional autobox car (i.e. with a torque converter) and one with a manual tranny. People have dealt with that pretty well. In fact, I noticed on my Saab autobox that it apparently is programmed to essentially disengage the engine at speeds below 30 mph. Take your foot off the gas at 25 mph and the engine rpms immediately drop to idle speed. Similarly, on most cars that I have owned with cruise control and autoboxes, the car will overspeed if the descent is steep enough to overcome available engine braking in top gear . . . but my Honda Pilot will actually downshift to lower gears for more engine braking if that is necessary to avoid overspeeding.

      It still seems to me that the most intuitive system would engage some regen with dropped throttle and progressively more with an application of the brake pedal, until friction braking is necessary to achieve the desire amount of deceleration. Failing that, then the “go pedal” should only be for going (or coasting) and the “stop pedal” should be for stopping.

  • avatar

    I’ve read that users of the electric Mini adapted to regen-braking quickly enough. Maybe Tesla buyers are less adaptable? (Just kidding).

    Given that I’ve never driven one, my opinion isn’t worth much, but I think that I’d be fine with this.

    • 0 avatar

      Most Roadster drivers adapted quickly and found that they enjoy the strong regen braking, as it allows for driving with one foot save for slowing to a complete stop and for emergency braking.

      Maybe sedan drivers will have different expectations or use cases?

  • avatar

    …Thus for normal driving, the range options of the Model S will be 128, 184, and 240 miles…

    And for those who don’t drive like an egg is under the accelerator with the heat off, no stereo, and only the parking lights in the dark the real world range across all drivers will probably be 15% below the theoretical maximum range (given Volt and Leaf numbers). That is around 109 miles, 156 miles and 204 miles.

    Not hating on electrics, I really don’t want to be a Tesla hater but the what the S will deliver keeps getting snipped back bit by bit as it gets closer to launch. I’ll still be shocked if the S goes to mass production. I suspect before it is all said and done, Toyota will come in and buy the gasping remains of the Tesla balance sheet, along with of course the patents, while dumping NUMMI and most of Tesla’s staff.

  • avatar

    Is the regenerative braking in a roadster gradual as you let off the accelerator, or is it just on/off?

    If it’s on/off I could see that being very annoying.

    If it is gradual I would say just let it off less if you want less “braking”, sort of like applying more braking pressure but in reverse. That should be very easy to get used to, since it’s even simpler that driving an ICE car. I wonder if there is a sweet spot where the car is truly coasting.

  • avatar

    I would think blended regenerative/friction braking would be a major marketing feature. It gives hybrids and pure electrics something that conventional cars can’t touch.

    That said, how much electricity is actually regenerated? Do you reclaim 1/2 of the energy used in acceleration? Obviously, if I brake hard enough, most of the speed is scrubbed with the friction brakes.

    My Prius experience with braking from 65 MPH is that it’s very easy to exceed the regenerative capabilities. I assume regenerative braking can’t do any more than electric-only acceleration for changing speed. In that case, the Tesla would be at a major advantage since its acceleration is fantastic.

  • avatar

    I think it may be time to ask for your $5k deposit back. Because….having to adapt to new technology is part of the deal and I applaud Telsa for pushing the boundaries in this case given the vehicle’s very focused market segment.

    To put it another way, what if Apple had decided that a traditional mouse control was the best way to navigate a “smart phone” when they were developing the iPhone, just because “that’s what everyone’s comfortable with using”? Instead, now we have innovative multi-gesture finger control. It take most people a little time to master it, but I don’t think many of them would want to give it up now that the benefits are obvious.

  • avatar

    I want maximum range, so that means I want maximum regen. If this were my car, I’d expect to only need the friction brakes for emergencies, and for holding the car in place while stopped on a hill.

    Instead of max regen when you lift off the throttle though, perhaps there should be a detent at ~10* of accelerator-pedal sweep. That detent would indicate zero power and zero regen- pure coasting. The further you relaxed the pedal from that detent, the more regen you get. Fulling taking your foot off the pedal results in max regen.

    If they want to make it more traditional, maybe they can have a little paddle shifter that simulates engine braking. In my 3-series, the ZF 6-spd auto downshifts at ~1000 rpm. If there’s nobody behind me, I just coast until about 20 mph until I hit the brakes. Sometimes, if I need just a bit more braking I’ll just paddle downshift at 2k rpm (also helps the car warm up faster in the morning, and gives the AC a little boost).

    Anyway, a little “shifter” to dial in varying increments of regen until you hit the accelerator the next time might be a good conventional-type approach, although I think many people prefer to be more passive than that.

    • 0 avatar

      I think the ability to dial-in braking characteristics is a bit iffy for most drivers. if there is one area of a vehicle that demands absolute, certain predictability then it is in the braking system.

      yes, i’m sure all the “enthusiasts” on here that believe they could out-drive any professional race car driver would not agree but if they were putting the sustainability of their business vis-a-vis potential lawsuits i suspect they would think differently.

  • avatar

    the car looks hot! throw a sweet bmw 2.0 diesel in it and call it acura…now we are talking!

  • avatar

    Unfortunately, the first thought that comes to mind is can Tesla be sued if the sudden slowdown causes accidents behind since the deceleration is not caused by brake input and seems to be so outside of normal parameters? Yes, I know that the driver behind a vehicle is always responsible for ensuring there is enough distance between them to stop safely, but it’s litigious America, after all.

    Nominal range = real range + inflation?

    Actually, are most Model S customers thought to drive it as sporty as the Roadster and the range numbers are derived from that type of driving?

  • avatar

    It’s likely that the regen method chosen was because of the easier controls required. There is much more to manage during a split regen architecture. Also batteries can only take a certain amount of power depending on many conditions that change (SOC, temp). So to manage breaking with all the changing limitations takes a bunch of smart people, algorithms, calibrations and time.

    Actually allowing a neutral point in the pedal travel, and allowing the driver to control regen by reduction in pedal works well and is easy to get use to… been there done that…

    But not all think it is the right thing to do.

  • avatar

    Those with deposits will take whatever Tesla gives them. “Now take your made in China travel mug and ski hat and shut up.” You’ll get your car when we’re good and ready!

  • avatar

    Think of the benefit of having the Tesla behave like a radio control toy car: by getting rid of the steering wheel and brake pedal and controlling the car with the RC remote, you could instantly make a left or right hand drive car just by changing seating positions. Heck, you can drive from the rear seat or even outside the car, just like on Mythbusters!

    Just think of the cost savings from having to homologize the car to different markets. And the plastic remote would even be rechargeable and ultimately recyclable to channel the Eco sensibility of this product. Tesla could pair up with Vertu to offer a magnesium and diamond encrusted remote for, oh, the price of the car. If Tesla ever makes a pick up truck, they could cross market with Smith & Wesson to make the remote double as a gun (for US and Middle East markets only).

    But if a Tesla has a remote, then it’s not really a vehicle but rather a toy. That means no need for vehicle registration fees, and it opens the Teslas market to 3 to 16 year olds. Make that 3 to 16 year old millionaires, a rather exclusive market. But I don’t see Nissan’s Leaf marketing to broad swaths of people do you? They won’t even sell to you if you don’t have a garage. Nissan is old school, Tesla is innovative new school in the Silicon Valley sort of way. Except California is broke and would find a way of banning the Tesla in their own back yard for avoiding registration fees. Perhaps they can find a way to tax remote controls.

    I’ll take my Model S in 49MHz and red please.

  • avatar

    It’s true that “Electric cars are different” and if a person does not like the way they feel they should buy something else.
    Tesla would do well to heed that observation and try to make them feel more like gasoline cars. I think the pre-ordering and hype has created a certain amount of hubris over what customers should get used to.
    range anxiety is to be expected, poor driving dynamics that grades on you constantly is not.

    But hey, we are supposed to view this as a luxury car, or a green car, or a game changer, or…..

  • avatar

    Having driven many EVs (including volts, leafs, iMiEVs, and Tesla Roadsters), I like the way Tesla manages regen. However there is a problem with having regen on the throttle pedal which is amplified on a tail heavy car like the Tesla. If you lift suddenly in a corner on a reduced friction surface the car will exhibit severe oversteer much like early Porsches. More regen = more oversteer so making it driver settable creates a potentially dangerous situation. For experienced standard transmission drivers modulating the regen with the throttle pedal is fairly natural. Having the car freewheel when lifting the throttle feels out of control so a balance is needed for a sedan like the S. My guess is that Tesla will put a relatively small amount of regen on the throttle and stay with the standard friction brakes on the brake pedal. That gives the best overall driving feel and, to be honest, you don’t really get much back with regen anyway.

  • avatar

    I like reading all the ideas in this blog. Has anyone considered this simple and intuitive idea for a 2-pedal control system:

    Accelerator: Press foot on it whenever acceleration is needed. The amount of pressure applied (or depression distance) is proportional to the amount of acceleration desired.

    (no foot contact) Active constant velocity coast – a constant speed is maintained (active cruise control which adjusts engine torque as needed to overcome drag, fight uphill gravity, or regen for downhill negative gravity).

    Decellerator: Press foot on it whenever decelleration is needed. The amount of pressure applied (or depression distance) is proportional to the amount of decelleration desired.

    This is a simple, intuitive approach, since the 2 foot controls have exactly symmetric roles, and adhere to Newtonian mechanics governing motion.

    I like the idea of “no foot contact” equating to constant velocity cruise control, as I use my cruise control all the time in freeway driving, and on surface streets, I drive the speed limit between stops.
    Constant speed driving is safe, as the vehicle is predictable for other drivers.

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