Which speed reading to trust – GPS or car’s speedometer?
April 16th, 2010 | by admin |For example: My GPS shows my 2005 VW Passat traveling at 65 mph. Looking at the actual speedometer in the car, where in my case there is a notch for the 10s and 5s (i.e. 60, 65, 70) the needle on the speedo is just under the notch for 70 mph, clearly not anywhere near the notch for 65.
Which should I trust? And if the speedometer in my car has now been proved inaccurate, how would it be recalibrated to display the correct speed?
Some details:
- Speed was measured using cruise control on a flat, straight highway
- wheels are OEM size with nearly-new tires inflated to VW recommended pressure for the Passat
Go with the speedometer. If everything is stock, it is within spec.
GPS does not measure actual distance travelled.
It measures distance between points.
Like looking at a map, there is no compensation for up and down which also figure into actual ground distance travelled.
There’s also the question of how accurate is the GPS.
For a long time, accuracy was purposely limited.
4 Responses to “Which speed reading to trust – GPS or car’s speedometer?”
By w61earl on Apr 17, 2010 | Reply
Go with the speedo. If you don’t trust it, go to the yellow pages under "speedometers", and get it calibrated.
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By monkees19 on Apr 17, 2010 | Reply
The speedometer would be right, or at least trusted more. I wouldn’t trust the reading of a GPS for speed anyway.
References :
By JetDoc on Apr 17, 2010 | Reply
Most car speedometers tend to be a bit optimistic, and will read 2-3 MPH faster than the car is actually going. If you are maintaining a steady speed on the highway, your GPS is probably more accurate, but for in-town driving or with frequent starts and stops, you should rely on your car’s speedometer, as the GPS speed indication will lag behind a bit while the car is accelerating.
References :
By Firecracker . on Apr 17, 2010 | Reply
Go with the speedometer. If everything is stock, it is within spec.
GPS does not measure actual distance travelled.
It measures distance between points.
Like looking at a map, there is no compensation for up and down which also figure into actual ground distance travelled.
There’s also the question of how accurate is the GPS.
For a long time, accuracy was purposely limited.
References :