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Graham Griffiths
Experienced User
Username: cineprojectorman

Post Number: 12
Registered: 5-2017
Posted on Sunday, 21 April, 2019 - 03:27:   Edit PostDelete PostView Post/Check IP

I noted when the car was traveling at 70 MPH my Garmin SatNav said 62 MPH a nearly 13% error.
Members may be interested in the latest update to my web site of how to calibrate the speedometer of a SZ spirit [not sure which other models use this speedo?]

http://35de8ignitionrepair.eu5.net/rolls-royce-silver-spirit-repairs-and-fixes.html#Calibration

http://35de8ignitionrepair.eu5.net/rolls-royce-silver-spirit-repairs-and-fixes-mobile-view.html#Calibration

Regards
Graham
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Kevin Deasy
Experienced User
Username: kevin1946

Post Number: 38
Registered: 1-2017
Posted on Sunday, 21 April, 2019 - 05:28:   Edit PostDelete PostView Post/Check IP

All that was very interesting to read,thanks for sharing it
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Robert J. Sprauer
Grand Master
Username: wraithman

Post Number: 302
Registered: 11-2017
Posted on Sunday, 21 April, 2019 - 06:40:   Edit PostDelete PostView Post/Check IP

Do you have the original "profile" tyres on the car?
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richard george yeaman
Grand Master
Username: richyrich

Post Number: 1070
Registered: 4-2012
Posted on Sunday, 21 April, 2019 - 07:03:   Edit PostDelete PostView Post/Check IP

I wonder what the Police speed trap cameras digital read out would be, I think I would trust my cars
speedo,

Richard.
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Graham Griffiths
Experienced User
Username: cineprojectorman

Post Number: 13
Registered: 5-2017
Posted on Monday, 22 April, 2019 - 02:58:   Edit PostDelete PostView Post/Check IP

My tyres are 235/70HR/15, which I believe are standard equipment. Since I've recalibrated the speedo on the bench, as they would do in the Smiths/Jaeger factory, my speedo and satnav GPS MPH tally. Badly worn tyres may make a difference, for example if the car speedo says 70MPH the satnav would show a slightly lower reading because the tyres are not travelling so far/fast and the odometer would read slightly more. Conversely larger tyres would produce the opposite effect I.E. the satnav would show a higher speed to that of the car speedo. [Would anybody fit larger wheels to a SZ Rolls Royce?]
Such a lot of talk on the internet of wheel size, final drive gear ratio, transducer etc. I see this as irrelevant because the electronic speedo has been bench calibrated. For 1 MPH, 8000 pulses mile * 1 mile hr/3600 sec = 2.222 Hz. E.G 8000*70/3600 = 155.5Hz
I could be wrong of course
Regards
Graham
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michael vass
Grand Master
Username: mikebentleyturbo2

Post Number: 552
Registered: 7-2015
Posted on Monday, 22 April, 2019 - 03:54:   Edit PostDelete PostView Post/Check IP

Good work Graham!
No wonder everybody was passing me lol
Cheers
Mike

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