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Can't cruise above 90 mph?

Discussion in 'Model S' started by MarcG, Mar 14, 2015.

  1. MarcG

    MarcG Active Member

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    #1 MarcG, Mar 14, 2015
    Last edited: Mar 14, 2015
    Anyone who has driven on I-5 in central California would know there are long boring streches of straight, flat freeway where speeding way above the limit is the norm.

    So I was cruising along at 80 mph (about 130 kph) when a series of cars passed me going significantly faster.
    As I had plenty of charge left to make it to the next supercharger, I figured "what the heck, let's see what this P85D can do".

    In order to follow the train of cars at a safe distance, I decided to increase my normal following distance of 1 to 4, and tried to set the cruise to a high speed so the TACC would keep up with the fast cars in front.

    To my great surprise, it unfortunately seems as though 90 mph (about 145 kph) is the maximum speed at which TACC can be set. Even if I set it at a lower speed and increase it manually, it will stop at 90 mph.

    image.jpg
     
  2. Saghost

    Saghost Active Member

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    Huh. I don't know if it's connected, but for the record, what's your Speed Limit Assist set to?
    Walter
     
  3. MarcG

    MarcG Active Member

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    +10 mph over the speed limit, which is 70 mph on most of I-5.

    I tried to set it to +25 mph so it would only warn me at 95 mph, but that didn't make a difference in terms of allowing a TACC speed over 90.
     
  4. Saghost

    Saghost Active Member

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    Well, phooey. That was my only theory, and it obviously isn't related. Maybe Tesla hard-coded a limitation.
     
  5. tomas

    tomas Traded in 9 rep bars for M3, used to be somebody!

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    C'mon this makes perfect sense. You want to go that much over the limit, you drive the car! Wheel and 2 pedals. I'm surprised it's not 80.
     
  6. marchyman

    marchyman Member

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    80? There are roads in the US with a posted speed limit of 85.
     
  7. tomas

    tomas Traded in 9 rep bars for M3, used to be somebody!

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    Fine. 85 then. 90 is generous.
     
  8. AmpedRealtor

    AmpedRealtor Active Member

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    Maybe TACC cannot properly decelerate in an emergency if the car is going above 90 MPH based upon stopping distance vs following distance?

    What if you set the following distance to 7?
     
  9. mgboyes

    mgboyes Member

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    If true this will give the Germans yet another reason not to buy Model S's.

    In an Audi A8 the adaptive cruise can be set at any speed from 30 - 155.
     
  10. gg_got_a_tesla

    gg_got_a_tesla Model S: VIN P65513, Model 3 Res Holder

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    This limit may be higher for Euro versions of the Model S. We'd need someone from your side of the pond to try it.
     
  11. BerTX

    BerTX Member

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    That was my thought, too. But I'd be surprised if it calculates stopping distance for each following distance and has a different max TACC setting for each.

    - - - Updated - - -

    There is only part of ONE road in the US that has an 85 MPH speed limit -- 41 miles of SH 130 in Texas (a toll road).
     
  12. ecarfan

    ecarfan Well-Known Member

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    I think that cruise control top speed makes sense for the U.S. It may well be higher for Euro spec cars.

    I know I5 well. I normally keep to 75 in the right hand lane. Sometimes cars whiz past me on the left.
     
  13. Lloyd

    Lloyd Active Member

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    My Mercedes has a 90 mph limit also on the ACC.
     
  14. AudubonB

    AudubonB Mild-mannered Moderator Lord Vetinari*

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    I'd like to see a show of hands of those who believe it's prudent to drive with cruise control at 90mph or above.
     
    • Helpful x 1
  15. ibcs

    ibcs Member

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    Many rural areas could support higher cruising speeds. Just drive through Kansas once.
     
  16. AudubonB

    AudubonB Mild-mannered Moderator Lord Vetinari*

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    I have driven many tens, possibly several hundreds of thousand of miles through the rural highways of the western US and Canada, and agree that one prudently can drive at 90, and in places slightly above, along good amounts of these roads. I vehemently disagree, however, that that should be done with cruise control. When you're moving at one mile every forty seconds, or 132 feet every second - or faster - then the lag in reaction when your go-foot has not been firmly attached to the go-pedal is, I will insist, irresponsible driving.
     
  17. Saghost

    Saghost Active Member

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    The car can see more clearly and react faster than you can. The Delphi radar that I think it the most likely candidate for the Model S tracks everything out to 600 feet in front of the car within a twenty degree arc twenty times per second, with exact position and speed on all of it. I haven't found an exact answer for the Model S, but 100 mph to 0 stopping distances at full panic seem to be in the 350-400 foot range for most cars.

    I'd hazard to say if it isn't safe for TACC to be driving at those speeds, it isn't safe for you to be, either. :)
    Walter
     
  18. Apoclyps

    Apoclyps Member

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    umm. isn't stopping distance at 90 mph 600 feet? So if the tracker can only see 600 feet....then it limits to 90 mph?

    edit: changed braking to stopping.
     
  19. Saghost

    Saghost Active Member

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    I don't know, for the Model S. However, I found a Car and Driver article about brake fade from a few years ago, in which they tested a bunch of cars from 100 mph to 0 over and over again. That's where the 350-400 feet I mentioned above came from. I really doubt the Model S had longer distances than all the compact cars and SUVs considering how short the 60 mph distance is.
    Walter
     
  20. Oil4AsphaultOnly

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    Not trying to start a fight here, but the problem with that line of thought is assuming that the human can only see down 600 feet as well. My eyes are pretty good, and during my younger speeding (statute of limitations have long passed) days, I would look about a mile down the I-5 for signs of cops. 1 mile - 5230 feet. Pretty significant difference in awareness vs. reaction time. Wouldn't try that again at my age, but just pointing out that TACC seems to be inferior for some stretches of highway (namely long straight ones).

    My guess is practicality. Tesla probably doesn't want to encourage high cruising speeds, because it'll drop the range down like a rock! No numbers available to back that up though.
     

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