04-03-2016, 11:00 PM | #1 |
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How's this possible (from Top Gear's F10 M5 clip)
I was catching up on DVR for the Bahrain F1 Grand Prix (awesome race btw) and then clicked into my Top Gear recording. I paused at this. If you remember, this is Hammond driving the car in a drag race vs. E60 M5. Notice the digital speedo at 38 mph and analog speedo at roughly 45 mph. How's that possible? I haven't noticed this in my car. Perhaps I'm missing something? Or is this just off?
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04-03-2016, 11:04 PM | #2 |
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And here's a screenshot of a few seconds later into the drag race. Looks like Hammond switched the driving programs! Here the analog and digital speedo's tie out.
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04-03-2016, 11:09 PM | #4 | |
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04-03-2016, 11:18 PM | #5 |
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The analog odometer is connected to the gearbox and catching the speed at real time speed. The digital odometer has a specific update rate and is always behind. Meanwhile, at higher speeds since the acceleration is slow, the digital odometer can almost catch up the analog odometer. You can take a video for 10 seconds from dig to 100+ mph to see what I said...
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04-04-2016, 07:54 AM | #6 | |
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But I doubt that they a re connected to different sensors.
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04-04-2016, 08:17 AM | #7 |
F10 1/4 WR: 9.9s / 142.5mph 1/2 WR: 175.5mph
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I doubt each comes from a different sensor - possibly digital moves in certain increments during quick accel (low speeds) and the camera happened to catch it before??
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04-04-2016, 08:43 AM | #8 | |
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04-04-2016, 10:10 AM | #9 | |
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04-04-2016, 06:10 PM | #10 |
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Top Gear is notorious for using filler shots on their show. I remember once when Clarkson tested the Veyron. Every time they showed the tachometer the car had the exact same number of miles on the odometer.
My guess is that those shots had absolutely nothing to do with the actual drag race.
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04-05-2016, 12:19 AM | #11 | ||
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And both readouts are processed by the ECU. On a side note, the digital readouts can be coded for accuracy and show exact speed. From the factory it's coded to show a certain percentage higher than real speed (for legal reasons and also in order to give you some tolerance in relation to public speed limits). AFAIK it's not possible to code the tolerance in the analog speedo, only the digital display. |
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04-05-2016, 08:44 AM | #12 | |
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04-05-2016, 11:51 AM | #14 | ||
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The internals of a old school eddy current speedo which is used on cars with a speedometer cable: Today the DME receives signals from the VSS and processes them into an output signal sendt to the speedometer. This signal is then converted to a movement on the needle, by similar means as the rpm counter or other dials in the dashboard. For instance, the needle sweep test demonstrated in the video below wouldn't be possible in a electro-mechanical system driven by a wire from the transmission, like in the example above. Today it's a purely electronic system that receives it's speed signals from the VSS via the DME. Last edited by Boss330; 04-05-2016 at 12:02 PM.. |
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