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Most accurate way to gauge speed?
What is the most accurate way to measure my speed? Not the speedometer, obviously.
But is using the rev counter RPM times the top gear ratio (20.2 mph/1000rpm) in my car a more accurate figure than the speed reading on my sat nav? When doing an indicated 75 mph my rpm is 3,500, a difference of 5 mph so I presume I am doing 70 mph, but my sat nav shows another figure. Which one do I believe?
But is using the rev counter RPM times the top gear ratio (20.2 mph/1000rpm) in my car a more accurate figure than the speed reading on my sat nav? When doing an indicated 75 mph my rpm is 3,500, a difference of 5 mph so I presume I am doing 70 mph, but my sat nav shows another figure. Which one do I believe?
Asked on 25 May 2013 by frank123
Answered by
Honest John
The most accurate way is the satnav, such as a TomTom, but it needs a clear view of at least three satellites and takes a few seconds to stabilise. That said, of a flat straight road such as a motorway, it will give you the most accurate figure.
Tags:
sat nav
speedometer
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