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  1. #1
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    Speed limiter / detection.

    I have a question.
    Does anyone know how the N54 detects your speed?
    Why am I asking? Well, this autumn I was near Germany, and couldnít resist to get a run to 250km/h which I hadnít done before with my 135i.
    Iím normally not a big fan for straight line speed (I think itís boring, and all you need is money, not skill to do it) caused by my go-karting past I presume. But even with a Go-kart is is fun to drive on a F1-circuit every now and then. 20sec. burst at 16000 rpm at a time (until it melts, happened a few timesClick here to enlargeÖ)

    So there I was, putting the cat in DS, and pulling the paddles on the steering wheel.
    Because I normally do not drive this fast I did a few runs to 250+ km/h and then I had to slow down for oncoming traffic. Anyways, I pulled 270km/h on the speedo (European speedoís go to 280km/h) in fifth gear, which my TomTom claimed being 253km/h. I do not have inboard navigation. I believe my TomTom with GPS detection more than my speedo.
    At that speed the rpms were 6500, and pretty much against redline.
    I reached my goal, actually got a little bored with it, and abandoned my detour of 70 km and turned around to be home in time to see F1.
    Never got around to use the 6th gear at top speedÖ
    And so forgot to test if the speed limiter would have prevented me from reaching the same speed in 6th gear, or if it would have continued. I was at the time more annoyed with the discrepancy between my actual speed and the speedometer.
    But it got me wondering how the engine detects what speed you are traveling with.
    Anyone knows the answer to that?

    Btw. On the way back I found that 220km/h in 6th the car is actually equally fuel efficient than in city traffic, 8km/liter. I found that to be pretty funny. I would take the autobahn over city traffic every day.
    In the Netherland you want to be carefull with excessive speed though. If you're caught doing 50 km/h over the limit, you lose your license...

  2. #2
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    1 out of 1 members liked this post. Yes Reputation No
    IIRC there is an error margin programmed into the speedo, so it may have claimed you were going 270 km/h, but in fact you were only going 250 (or maybe only 240.

    As long as the car hasn't been delimited, you wont have surpassed what the limiter is set at. I'm not sure what the error margin in a gps is, but I would trust that over your speedo.

  3. #3
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    So the speed limiter is controlled by the speedometer?
    Not on engine rpm/gear selection? Or even internal GPS, if you have navigation?
    Had I gone to 6th gear on those attempts the topspeed would have been exactly the same?
    GPS cannot really be wrong, technically speaking. Not at constant speeds. Or else speed on the map and the reading of the speed would fluctuate. Which I am sure it didn't. But that's not important here.
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  4. #4
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    Click here to enlarge Originally Posted by DavidV Click here to enlarge
    So the speed limiter is controlled by the speedometer?
    I think he is just saying that the speedometer is off. The ecu controls the limiter.

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