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Speedometer Reading After Crash



 
 
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  #11  
Old May 14th 07, 02:32 AM posted to rec.autos.tech
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Default Speedometer Reading After Crash

On Apr 26, 10:09 am, panabiker > wrote:
> Over the weekend, I had a conversation with some friends on a recent
> accident involving NJ governor. It was reported by news media that the
> SUV was going at 91 MPH prior to the crash. My question was how they
> found out the speed, and one answer was that a speedometer would stuck
> at the speed the moment of the impact. I find it very hard to believe
> that any speedometer would stuck at the correct reading considering
> the violent nature of the collisions, unless the speedometers are very
> specially designed to record speeds and to sense the crash. Can anyone
> shed some lights on how accident investigators figure out the crash
> speeds?


WHEN ON IMPACT THE NEEDLE SLAPS THE GAUGE AND LEAVES A A MARK ON IT
THE SAME COLOR AS THE POINTER

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  #12  
Old May 16th 17, 12:27 PM posted to rec.autos.tech
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Default Speedometer Reading After Crash

The comments above have been interesting to read. We, however, need to remember that modern vehicles no longer have speedometers that work by attaching a cable to a vehicle wheel and the amount of revolutions that a wheel turns is transfer to the speedometer that works with internal weights that measure how far the separate the higher the revs.
Modern speedometers are electronic that receive a signal from a sensor on the vehicles gearbox and the analog needle moves to the speed that the vehicle is moving. There are small electromagnets in a servo that move the needle around. If the power to the vehicle is shut off due to a violent crash there is no residual power left to return the needle to its resting place. That is why the speedometer can give a good indication of what the vehicles speed on impact was. This method is accepted by Police in USA, Canada, UK and Australia. I hope this explains why this method is used. Black boxes are not fitted in all vehicles in other countries.

  #13  
Old April 15th 18, 01:58 AM posted to rec.autos.tech
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Default Speedometer Reading After Crash

i mostly agree with the above but will point out " no longer have speedometers that work by attaching a cable to a vehicle wheel " // was only true for bicycles and motorcycles. Car speedometers have always read thru a cable that attaches to the transmission, the modern difference is the magnets and sensors, the originals were simply spun by a gear in the transmission.
 




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