GPS Speed vs. Actual Speed

BBShark

BBShark

Garage Monkey
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I drove down to Tennessee a couple of weeks ago to pick up a Tahoe I bought. It was a rental that I turned in and drove the Tahoe back. The rental was a newish Toyota. I was using Google for directions. When I was on the expressway I noticed the Toyota speedo said 70mph and Google had my speed at 67mph. I thought it was strange that a new vehicle would have a speedometer error. So, is it the speedometer or the GPS?
 
Might be a common problem….


“If you're experiencing Google Maps GPS speed errors, ensure your speedometer is enabled under "Driving options," check for location permission issues, and try restarting your phone or clearing the Google Maps cache and data.

Here's a more detailed breakdown of potential causes and solutions:

1. Enable Speedometer in Google Maps:
  • Navigate to "Driving options" in Google Maps settings.
  • Make sure "Show speedometer" is turned on.

2. Check Location Permissions:
  • Ensure Google Maps has permission to access your location, even when the app is in the background.
  • Some phones have battery saver features that might turn off GPS when the phone is on low battery or in the background.

3. Troubleshoot GPS Signal Issues:
  • Restart your phone: A simple restart can resolve minor software glitches.

  • Clear cache and data: Go to your phone's settings, find Google Maps, and clear the cache and data.

  • Check for GPS signal interference: Certain car window films or obstructions can interfere with GPS signals.

  • Try a third-party GPS status app: If your device struggles to acquire a GPS signal, a third-party app might help diagnose the issue.

4. Update Google Maps:
  • Make sure you have the latest version of Google Maps installed.”
 
The Toyota rental had less than 15,000 miles on it so assuming the tires were original. I'm getting new tires on Tuesday (they are the same diameter as the OEM tires. I'll check again. I also need to figure out if this is a proportional (to speed) error or an offset error. Some (Google) people say that if it's an offset, you can re-attach the needle.
 
Got the new tires and checked the speedo again. At 70mph, the GPS says 64mph. At 35mph it's 32mph. So it's ~8% error. I have seen people on OBS truck forums talk about programmers that allow you to change the speedo reading but they are not available (for maybe 20 years). The "Speedometer Shop" here told me that a pre-96 can be reprogrammed with jumpers on a module. On 2000-up it can be reprogrammed with a very expensive scan tool that dealers use. For 97-8-9, there is apparently no way to do it.

What was suggested is a "ratio adapter" module that changes the VSS signal. $250-300
 
Let me get this. You can drive 70 (on the speedo) in a 65 zone.
And if you think the Highway Patrol will let you slide for 10-over, you can show 80-85 on the speedo and keep up with the other traffic!
Go any slower - better not be in the Left Lane. {BTW--we're straightening that out in Florida}
Seems better than spending the $250-300. Save it for a ticket.

Cheers - Jim
 
 
$15.00! I might just do that. One of the other things that is driving me nuts (short trip), is the Tahoe has factory tinted windows. In the full sun, you can't see the gauges. So it kind of useless what the speedometer says.
 
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