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Mountain Driver

Discussion in 'Model S' started by andrigtmiller, Jan 21, 2012.

  1. andrigtmiller

    andrigtmiller New Member

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    I live in Colorado, and thinking about driving in the Rockies brought up a question. How does the car's regenerative breaking deal with typical mountain driving without overheating the breaks?

    I always downshift my car to utilize engine breaking when decending steep grades when driving in the mountains to prevent the breaks from overheating, and to keep a safe speed. Sometimes, the people that scream down the descents at 80, 90 or faster miles per hour, and hit their breaks over and over again really scare me.

    With an EV, like the Model S, there doesn't seem to be an option for maintaining ones speed down a steep descent without using the breaks.
     
  2. rlawson4

    rlawson4 Member

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    The brakes on my Fusion Hybrid charge the battery until it is full. When considering the Volt there was an article about the brakes coming down Loveland Pass. According to the story, the Volt gained back 12 miles of battery life from braking all the way down Loveland Pass. So, I don't think brakes are the issue. I would be concerned with a rear wheel drive car in the rockies for obvious reasons. Maybe the Model X (reported to be 4 wheel drive) makes more sense.
     
  3. richkae

    richkae VIN587

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    The regenerative braking is all controlled by the throttle pedal. If you ease off the pedal completely you have full regen. That regen is powerful enough that you dont need to use the brakes for normal slowing and stopping. That regen lets you descend steep slopes without needing the friction brakes.
    In the Roadster I crossed a high mountain pass, with a 7 mile long 7% grade descent. I set the cruise control to 55mph and did not need to touch the friction brakes. The regenerative braking did everything to keep the car at the speed I wanted, and not only did I use no energy over those 7 miles - they returned 3 miles of range to the battery.
    If I had needed my friction brakes for a panic stop, they would have been cool and ready.
     
  4. efusco

    efusco Moderator - Model S & X forums

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    That is one of the beautiful things about regenerative braking...no or almost no friction brake wear, all the energy you're wasting braking with traditional friction brakes goes back into the battery for future use. You would not need or want to downshift, just back off the accelerator pedal a bit until you achieve your target speed...on those rare occasions that that isn't enough you can always ease on the brake pedal to regen and slow further.
     
  5. richkae

    richkae VIN587

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    With proper balance ( and the Model S has that ) and good traction control ( the Model S has that as well ) I don't think that rear wheel drive is any kind of penalty.
     
  6. andrigtmiller

    andrigtmiller New Member

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    Thanks for the clarification on regenerative breaking. I didn't understand that it wasn't actually using the friction breaks! That answers my question, and certainly alleviates any concern. I was wondering why no one seemed to ask about this, but it was just my misunderstanding. Thanks guys!
     
  7. rlawson4

    rlawson4 Member

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    I certainly agree about wear on the brakes. My Fusion has 31000 miles. As of my 30000 mile service there has been almost zero brake pad wear. I cannot imagine needing a brake job in less than 120000 miles. Of course I am selling the Fusion when my model S arrives.
     
  8. efusco

    efusco Moderator - Model S & X forums

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    I'm approaching 120k miles on my Prius with about 50% of my pads remaining.
     
  9. Andrew Wolfe

    Andrew Wolfe Roadster 472 - S 440

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    Yep. I sold my first Prius at 130K having never needed to replace a brake pad.
     
  10. strider

    strider Active Member

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    Yep. I used to drive a C6 Corvette (6.2L V-8 w/ 6-speed manual) and the regen in the Roadster is stronger than downshifting my Corvette. You'll be able to keep your brakes nice and cool and gain some range to boot.

    I have a 7% grade to descend ~500ft leaving my neighborhood every day. The Roadster's regen will slow the car down on that grade so you could go steeper and still not need the friction brakes. Wonder what the breakeven grade is for a Roadster where it would hold a steady speed?

    Lastly, the traction control on an EV is phenomenal. With an ICE car, even if the cut the spark, etc, they still have a ton of mechanical things whirling around. With an EV they can cut all the power in milliseconds (and switch it back on just as fast). IT's much more responsive than in an ICE vehicle. We have several Roadsters running around in the Great White North and everyone says that it handles quite well in snow.
     
  11. neroden

    neroden Happy Model S Owner

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    The bigger worries are:
    (1) brake calipers rusting and seizing up from disuse.
    (2) brake discs rusting from disuse.
    My family had both happen in cars (we're very gentle drivers who use a lot of engine braking).

    Any electric drivers have any experience with problems caused by brake underuse? I mean, it's easy enough to deal with (slam on the brakes repeatedly one day each month :wink:) but that's not easy to remember to do.
     
  12. brianman

    brianman Burrito Founder

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    If you buy the Performance package and you have "brake issues from underuse", that's just wrong. :wink:
     
  13. EV_de

    EV_de Model SP10/XP9 EU ZOE#47

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    "brake discs rusting" should not be a problem if TM use Mercedes's Brake System:

    http://500sec.com/sensotronic-brake-system-sbc/

    Tesla can modify the Software to activate this function once a week ...
     
  14. Robert.Boston

    Robert.Boston Model S VIN P01536

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    This brake-wear issue is a big plus for my decision to buy a Model S. Much of my driving is on highly congested roads, with lots of accelerate/brake/accelerate/brake "rubber banding". I go through a set of brake pads in about 25k miles.
     
  15. NigelM

    NigelM Recovering Member

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    Legend of Lightning Green thread has some of Dragon's experiences with mountain driving including this result from constant regen:

    DSC_0232.jpg
     
  16. VolkerP

    VolkerP EU Model S P-37

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    That's easy to calculate. Roadster mass is m=1250kg, max regen power is P=40kW (as indicated by the power gauge). Going downhill will release potential energy (m*g*h) at a rate of P=m*g*dh/dt. If we neglect* other energy dissipation (aero, rolling resistance), 40kW equals descending 3.2 meters per second in height = 10ft = 150ft run of 7% descent.
    In other words you have to run downhill 7% at 165kph=100mph or 14% at 80kph=50mph to max out regen. Insane.

    *) Ah yes the neglects that we physicists are often accused of. Going 100mph on a flat surface takes 50kW according to Roadster Efficiency and Range | Blog | Tesla Motors so you can't ever get 40kW of regen power on a 7% downhill. You need far steeper decline but I'll have that as an exercise for everybody interested to figure out.
     
  17. brianman

    brianman Burrito Founder

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    Sounds like a really fun ride under controlled conditions though. Maybe our stunt person from the other thread has some stories to share on this front.
     
  18. neroden

    neroden Happy Model S Owner

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    Hey, I know of a 41% grade in a town not so far away. I have a photo of the road sign warning!
     
  19. VolkerP

    VolkerP EU Model S P-37

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    Please post! Still not possible to predict if a Roadster would accelerate if you let go the pedal.
     
  20. neroden

    neroden Happy Model S Owner

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    I'll have to dig it up, it's actually my fiancee's photo...
     

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