Google Maps/Phone GPS speed accuracy

[roaniecowpony]

Anyone know how accurate Google Maps GPS is? I used it to check against my speedometer.

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[Rhinebeck01]

I have always felt it is prudent to test with something other then a diddy that is paired up/synced/tied to the vehicle. Sure I do on occasion spot check with my navigation apps but... but to be really sure I use GPS Plus.

Consider getting the app GPS Plus or a similar app for your smart phone.
https://play.google.com/store/apps/details?id=com.chartcross.gpstestplus&hl=en_US&gl=US

 

[GATORB8]

I've found that when connected to the vehicle, the vehicle's speed is communicated to the phone and overrides GPS speed (at least with Iphone on carplay). So it has to be disconnected to use the GPS.

I use a simple speedo app to adjust.

 

[roaniecowpony]

I also have a garmin Alpha 200 GPS dog tracker with a trip function that gives speed. I'll try that this morning on the way to running the dog.

 

[Powelligator]

I have an ancient handheld GPS, no maps, no routing, nothing like we have now. But it does work well for displaying speed, so I use that to check against the speedo. As above, there are apps on your phone that can work also.

 

[roaniecowpony]

FYI, I thought I noticed that the Ucconnect showed the speedo error on the way home from the shop after installing 37s/4.88s. (based on the speedo showing 7 mph low, I believe the speedo uses wheel speed sensors rather than transmission rotation sensors.)

 

[roaniecowpony]

My Garmin Alpha matched the speedo at speeds up to 45mph. I'll have to get out on the freeways to see how it does at 70 ish. But I used the published tire diameter, which is validating my hunch that the "squat diameter" is not the correct value to enter.

 

[Rhinebeck01]

My Garmin Alpha matched the speedo at speeds up to 45mph. I'll have to get out on the freeways to see how it does at 70 ish. But I used the published tire diameter, which is validating my hunch that the "squat diameter" is not the correct value to enter.

I believe you are aware... but do check out your speedo at varying speeds and not just at say one or two speeds.

 

[Ratbert]

My Garmin Alpha matched the speedo at speeds up to 45mph. I'll have to get out on the freeways to see how it does at 70 ish. But I used the published tire diameter, which is validating my hunch that the "squat diameter" is not the correct value to enter.

I remember reading that Tazer assumes that we're idiots and adjusts the entered diameter down (5%?). You entered the new axle ratios too, right?

 

[roaniecowpony]

I remember reading that Tazer assumes that we're idiots and adjusts the entered diameter down (5%?). You entered the new axle ratios too, right?

Yes, I put in the axle ratios and the tires at the published specs. IIRC, the JSCAN has a tire value every half inch.

 

[roaniecowpony]

Back from a test drive. Tracked steady state, straight line at 60, 70, and 80, set with the cruise control using the driver's center display digital speed indicator. Depending on the speed the analog needle was between 1 mph low or dead on. There's parallax with a needle/dial, so it's really moot at that level.

All 3 speeds matched my Garmin. The Garmin reads to one decimal place. It was showing between .0 to .2 higher than the digital speed/cruise setting. Probably as accurate as I could expect or better actually. This also matched the phone with google maps running.

 

[Ratbert]

I'm not sure why some people are suggesting using special apps to determine your speed. They all getting their data from the GPS chipset.

And yes, I wrote the code that's interacting with similar GPS chipsets to track what's in orbit around the planet for the DoD.

 

[roaniecowpony]

I'm not sure why some people are suggesting using special apps to determine your speed. They all getting their data from the GPS chipset.

And yes, I wrote the code that's interacting with similar GPS chipsets to track what's in orbit around the planet for the DoD.

Possibly those apps have readouts one decimal place to the right? The google maps readout is to one mph.

 

[ChuckQue]

I use a Garmin Glo 2, I find it much more quick to update my position when out of cell tower range so I’d imagine it’s more accurate than the GPS in my phone

 

[GATORB8]

Possibly those apps have readouts one decimal place to the right? The google maps readout is to one mph.

I use a basic one so its just a large font number on a screen. I only downloaded it because I hadn't figured out wireless carplay was effecting the Waze speedo and was showing no change after a tire upsize.

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