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Old 04-27-2018, 10:10 PM   #1
Senior Member
DenverTransplant's Avatar
Brand: Thor Motor Coach
Model: ACE 30.1
State: Colorado
Posts: 388
THOR #5190
Garmin RV760RV speed vs F-53 speedometer

I'm pulling out all the stuff we took out of the coach for the winter. While I was updating my Garmin 760RV I recalled some behavior that I find a bit strange. The Garmin tells you your speed and it agrees with the coach speedometer up until you reach about 55 MPG. Then the two diverge, with the Garmin reading 2-3 MPH more than the coach speedometer. At 65 MPH on the Garmin, the coach is reading about 67 MPH. Once you get to about 70 MPH, the two start agreeing with one another again.

I'm thinking that for some reason the coach speedometer isn't linear in the 55-70 MPH range, but can't think of a reason why it would be. I'm running under the assumption that the GPS is more accurate as it its measuring actual rate of change in your coordinates and doesn't care about things like tire OD, but that's just an assumption.

Does anyone else with a Garmin see this type of behavior?

2017 Thor ACE 30.1
2017 Jeep Cherokee Trailhawk
Roadmaster Falcon All Terrain
RVi Brake 3
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Old 04-27-2018, 10:43 PM   #2
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mountainsam's Avatar
Brand: Thor Motor Coach
Model: Gemini 23TR
State: California
Posts: 981
THOR #6701
I have used a Garmin in three differant vehicles and now a 2639LMT in the motor home and I have never noticed a differant reading than that of the speedometer. I did once use a TomTom in a 57 Ford I had and they differed by many mph, of course the 57 didn't have anything factory on it so that was expected.
2017 Gemini 23TR Ford chassis w/ power stroke 3.2
DW, Daughter and 2 dogs, Sofie (black lab/boxer) and Phoebe (schnoodle)
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Old 04-27-2018, 10:44 PM   #3
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Bob Denman's Avatar
Brand: Still Looking
Model: Tiffin Wayfarer 24 BW
State: New York
Posts: 22,059
THOR #8860
I would imagine that the Garmin units are more accurate, since they use satellite triangulation in order to sort things out...
Having said that: if your Coach's speedometer is only off in one range of the dial... I'd say that you're pretty lucky!
1 or 2 mph isn't going to cause any issue at those speeds anyway...
"What: me worry?"
Good Sam Member 843599689
Current coach: Tiffin Wayfarer 24 BW
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