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Cruisin' in Neutral - Actually a blast!

Discussion in 'Roadster' started by smorgasbord, Sep 14, 2011.

  1. smorgasbord

    smorgasbord Active Member

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    #1 smorgasbord, Sep 14, 2011
    Last edited: Sep 14, 2011
    If you haven't tried hitting the "N" button while driving your Roadster v2.5 - try it! Not accelerating never felt so fast!

    If you've read about how low friction the Roadster drivetrain is, but don't believe it, get onto an empty road and while moving at, say, 40MPH, shift into Neutral. It's pretty darn amazing. A Roadster in neutral just coasts and coasts and coasts.

    So, besides the non-rush rush, what's interesting about this? Hypermiling. A fellow Roadster owner pointed out to me that while regen is great, true hypermilers want to coast. The thinking being that regen only gets back around 66% (and that's on the generous side) of what you expended, but you'd get more back by letting your car pick up speed going downhill and then continue to coast until the speed drops too low, and then provide power. In other words, the power stored in the moving vehicle is more efficient than converting that power into battery juice which is subsequently used to make the car continue to move.

    While popping into Neutral is fun and easy, getting back into Drive can be a bit jarring. I need to play around some, but it doesn't appear that you can "rev the motor" by pressing the accelerator pedal while in neutral, but I need to see if pressing the pedal reduces the regen so the transition back into drive isn't so jarring. And, while this technique might save some watts, it surely seems like it would create more wear and tear on the drivetrain.

    Anyone else experiment with this?
     
  2. zack

    zack Member

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    Sounds fun! When my Tesla's back from Chicago I'll try it!
     
  3. Fabrizio

    Fabrizio Member

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    If you fully charge the Roadster in Range mode, you will not have Regen for the first few miles - you get the same effect. Someone posted that they lost traction control and regen going over a bump in a curve, the Roadster accelerated on it's own - they were actually feeling the coasting sensation rather than unexpected acceleration.
     
  4. Doug_G

    Doug_G Lead Moderator

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    First time I lost regen due to cold I thought my Roadster was trying to throw itself out of the parking lot. Of course it was just coasting with no regen braking. You're right... it really rolls!
     
  5. ChadS

    ChadS Petroleum is for sissies

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    #5 ChadS, Sep 14, 2011
    Last edited: Sep 14, 2011
    Yeah, that's fun. There's been a lot of enthusiast debate about the merits of coasting and regen.

    The RAV4-EV doesn't have any regen by default; when you let up on the accelerator, you are coasting. There are two levels of regen that you can apply: there's a button on the shifter for low regen, and a "B" mode on the shifter for high regen. When driving the RAV, I move between them a lot--alternating between coasting and giving it a little juice when cruising, and turning on regen when I have to slow down. Trying to extend the range by coasting is fun to do every now and then; I don't drive the RAV that often. (Why would I when I have a Roadster? Although the real reason is that my wife prefers the RAV, so I have to drive the Roadster. Pity me).

    Regen is indeed bad in that it wastes energy; it's only "good" when you compare it to braking which wastes more energy. If top efficiency is your goal, you never slow down unless you really have to, which is why coasting is a good efficiency default. Only when you "have to" slow down do you use regen (instead of braking). This is why some enthusiasts claim that the RAV's setup is better than the Roadster's.

    I agree that it would be nice to be able to turn regen on and off (better yet: dial in a level for when your foot is off the pedal). But that really just makes it easier to get top efficiency; you can achieve the same effect by carefully holding the go pedal in the right position, or using neutral. For everyday driving in traffic, where you "have to" speed up and slow down a lot more to avoid annoying other drivers, having sizable regen on by default is a great thing (again, note that being able to adjust it and/or turn it off would still be great! I'm just saying it's a good default). It makes for really easy one-pedal driving that keeps you at just the right speed, yet the regen still is only used when you "have to" slow down. You just "have to" slow down a lot more often (along with accelerating faster) when worried about other drivers.

    I figure the Roadster is already the most efficient car on the road, and I don't want ICE drivers to waste more energy than I'm saving to get around me, so I drive the Roadster using the go pedal to keep my speed where I want it to fit in traffic, and enjoy how simple it all is--it's the easiest car I've ever driven in traffic. I've tried neutral a few times, but just to test it out.

    Truth be told, I'm not going to win any efficiency awards anyway because the Roadster is so much fun to drive, and I have a lot of years of slow hybrid and diesel driving to make up for. Maybe that's the real reason I like high regen on all the time in the Roadster.
     
  6. AndrewBissell

    AndrewBissell Member

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    I tried this extensively early in my ownership, but couldn't find any appreciable range gain so stopped. Btw I agree with the theory that it should work
     
  7. suxxer

    suxxer ElektroVolt

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    One could also try this:

    Cruise at a speed >5 mph. Then shift into N. Floor the gas pedal (nothing will happen) and then shift into D (be sure the car is rolling otherwise you get a "gear shift not allowed error"). Now the car takes off instantly ;)
     
  8. JRod0802

    JRod0802 Member

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    #8 JRod0802, Sep 15, 2011
    Last edited: Sep 15, 2011
    I have a question about this. I read that the roadster has "creep" built into it, so at 0 mph it doesn't have a "neutral spot" in the pedal. As you speed up the "creep" diminishes and then regen fades in. Once you hit a certain speed (like 10 or 20), does the behavior of the go pedal stop changing such that the "neutral spot" stays in the same position, or does the "neutral spot" of the pedal always change based on how fast you're going?
     
  9. smorgasbord

    smorgasbord Active Member

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    Is this akin to the 0-60 times from a "rolling start?" If so, does anyone have a time to report?
     
  10. ChadS

    ChadS Petroleum is for sissies

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    Correct. I think that creep goes up to 3mph and then disappears suddenly, but I am not sure.

    Interesting question; I'm not positive. I could speculate, but I don't think it matters because there's not really a "dead" spot on the pedal. There's just a point at which you are neither doing any regen nor putting in any power. And whether or not that varies with speed, it will vary with inclines, wind, drafts from other cars...so there is some work involved to keep the power needle vertical to simulate coasting.
     
  11. jkirkebo

    jkirkebo Model S P85+ VIN 14420 EU

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    Regen can be better than coasting. Example: You are going down a long hill (several minutes of downhill). If you coast, terminal velocity is maybe 75mph since air resistance increases by the square of speed. If you instead set the cruice control to 50mph, you will regen down the whole hill and put a lot of energy back into the battery. At the foot of the hill you will be traveling 25mph slower than by coasting, but have a lot more energy in the battery. The coasting car will also slow to 50mph after a while, but the energy you use to keep the car at 50mph at level ground will only be a fraction of what you gained by using regen down the hill.
     
  12. Roger Reid

    Roger Reid Old but effective

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    Keep in mind that coasting in neutral will tax an already weak braking system. Driving with a fully charged battery in range mode (reduced regen braking) will also place extra demand on the brakes. I switched to a carbotech 6 compound and the brakes are much better.
     
  13. S-2000 Roadster

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    I don't see how this could possibly be any more wear and tear than flooring the pedal from a standstill. The Tesla Roadster is one of the most abused drive-trains under 'normal' conditions, and keep in mind that nothing physical is disengaged or engaged when shifting in or out of neutral - it's all magnetic.

    That said, the computer does hold back on the torque from a standstill to avoid spinning the tires. If this same torque limiter is thwarted by shifting from Neutral to Drive from a rolling start, then I can see how that might be more jarring that 'normal' driving.

    By the way, even if you leave it in Drive, the noise from the gears when transitioning from acceleration to deceleration or vice versa is maybe not jarring but certainly alarming.
     
  14. S-2000 Roadster

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    I don't find the brakes to be weak. The discs are larger diameter than usual for such a small car. I had to make a sudden stop on a steep downhill when I was already traveling quite fast, and the brakes did their job quite well without even triggering the anti-lock system. I was impressed.

    What sort of driving are you doing?
     
  15. zack

    zack Member

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    I find the brakes to be weak compared to my G55, which is roughly 3000 lbs heavier. The brakes are, as I understand it, designed for the original Lotus Elise, which is significantly lighter than the Roadster. I'd love to have better brakes. I'm used to stopping on a dime. I feel like I really have to stomp them to get a reaction.
     
  16. richkae

    richkae VIN587

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    The Roadster brakes are weak compared to other high performance cars - they are the same brakes that the Elise uses to slow down ~2000 pounds, but slowing down 2800 pounds instead.
    I went to a track day at PGP Motorsports Park ( short track ~20 turns over less than a mile - top speed 75 mph ) and drove both my Roadster and a friends Porsche Cayman. The Roadster and Cayman had very similar lap times, but I could brake much later in the Cayman at the end of the short straights every time - if the Roadster had Cayman brakes it would have shaved off a few seconds per lap.
     
  17. Fabrizio

    Fabrizio Member

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    Do you have a Roadster or a Roadster Sport? I noticed that the Roadster Sport I test drove had Brembo brakes and the Roadster I own does not. Could that be the difference in the braking experiences?
     
  18. zack

    zack Member

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    #18 zack, Sep 15, 2011
    Last edited: Sep 15, 2011
    I have a Roaster Sport 2.5 and my old '99 BMW Z3's brakes were notably better. I'm looking for a dramatic improvement even if that includes replacing the rotors. The biggest deficiency in the Roadster is the brakes, followed by charge time, followed by range, followed by storage space, which I've already fixed with a custom boot bag and cargo net. Also, it needs a 200A 240/120VAC inverter for powering my building in an emergency. Otherwise it's perfect. 8^D
     

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  19. richkae

    richkae VIN587

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    I am pretty sure there is no factory brake upgrade for the Sport - if somebody has upgraded their cars brakes it needs a post on this forum because I would love to hear the specifics.
     
  20. drees

    drees Active Member

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    Getting OT for this thread, but there could be a lot of reasons for "sub-par" braking performance. But a couple notes:

    1. If you are engaging ABS - the brakes are plenty strong. Since all cars can easily engage ABS with a good stab of the pedal let's assume that the brake hardware is sufficient for now.
    2. Now that you've got the tires nearly locked up - what you really need are stickier tires. As others have already mentioned, the Roadster is a lot heavier than the Elise, but the tires are the same width. Wider tires ought to reduce braking distances significantly. The Auto-X / track guys seem to like 195 width tires in the front
    3. The other problem with "weak" brakes could be brake fade - but I didn't hear anyone complain of that so I'll assume the stock brake equipment is sufficient. Perhaps after stickier tires you'll find that brake fade is an issue - looks like there are big-brake-kits for the Elise that might fit.
     

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