| Re: Non-linear speedometer error [message #370674 is a reply to message #370652] |
Tue, 11 October 2022 08:37   |
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RF_Burns
Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada
Karma:
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Senior Member |
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So Paula and I went out for some tests yesterday afternoon. With a second set of eyes, it would seem the error is not as bad.
First, I'm in Canada so we are with 96% of the world that uses Metric. My coach is a 1977, so it has Km/Hr markings, but they are not accurate. So I made a chart using MPH from the speedometer and EBL's What's Up Display (WUD). I have my GPS set to KM/Hr so I put all the readings into a spreadsheet and had it convert the measurements, then give me the error factor compared to the GPS speed.
I drove to the indicated speeds on the speedometer and then Paula recorded the indicated speeds from the GPS and the WUD.
The change from 3.07 to 3.42 is a factor of 1.114 or 0.898 depending on which way you are looking at it.
So it appears that a gear reduction to 0.90 will put the Speedometer just about right on in the 55MPH (about 90Kmh) and above range which is hyway driving. The inaccurate Km/hr markings were taking me down a rabbit hole!
My WUD is reading a tad high, which I can fix in the EBL parameters for the Vehicle Speed Sensor (VSS).
First Pass (cMPH and cKPH are calculated MPH and KPH in the spreadsheet)
Speedo MPH |Speedo error factor | GPS (KPH) | GPS (cMPH)| EBL (MPH) | EBL (cKPH) | EBL error factor
15 1.08 26 16.2 17 27.4 1.05
25 0.97 39 24.2 25 40.2 1.03
35 0.94 53 32.9 33 53.1 1.00
45 0.93 67 41.6 43 69.2 1.03
55 0.90 80 49.7 52 83.7 1.05
65 0.89 93 57.8 63 101.4 1.09
Second pass
15 1.04 25 15.5 17 27.4 1.09
25 0.94 38 23.6 26 41.8 1.10
35 0.94 53 32.9 33 53.1 1.00
45 0.94 68 42.3 43 69.2 1.02
55 0.90 80 49.7 52 83.7 1.05
65 0.90 94 58.4 63 101.4 1.08
70 0.90 101 62.8 65 104.6 1.04
75 0.89 108 67.1 69 111.0 1.03
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
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