Not the normal question. My car has always shown 3 mph over the actual speed when compared to radar-enabled signs. I know that is typical and I know why it's that way. Today I took a trip and the Waze app (based on GPS) mirrored exactly what my speedometer was showing. This was true at low speeds and those over 70 mph. Has anyone else noticed this, or has my speedometer somehow corrected itself? FYI, no work has been done on the car recently.

 

My Speedo is off by 3 to 5 MPH depending upon speed according to Waze.
Have you replaced your tires lately?

 

I've read before that 3 mph over actually is by design. Something about manufacturers facing heavy fines for a speedo ever showing slower than actual speed so they set it higher to cover their ***.

 

Waze always shows about 3 mph higher than the speedometer for me

 

My car's speedo reads 4 over at highway speeds on the radar signs, ie speedo shows 75 radar sign shows 71. Compared to Waze it seems to fluctuate, sometimes Waze shows the "correct" speed when on flat straight sections. I've noticed in hills or on turns that Waze tends to show higher speeds than "correct". Since it's using the GPS in the phone this seems to make sense. The GPS speed is updated once per second, and is probably averaged over several seconds.

 

Rear tire wear will "speed you up" over time.

 

I echo most of the remarks here. My speedometer is always about 4-5 mph over the GPS.

 

Pretty consistently 3 mph higher speedo reading.

 

I believe it’s due to speedometer laws in Germany and how Porsche compensated for that. My 996 also indicates 3-5mph faster than what GPS shows.

 

I know about the 3 mph differential and why it's there. I'm asking why it STOPPED. No changes, no significant tire wear. In the past my speedometer always showed 3 mph over the actual. Now it's showing exactly the same as Waze.

 

Maybe Waze technical support got sick of responding to emails saying the app wasn't accurate.

 

Yes, the default indicated speed is almost always (if functioning correctly) overestimated by 2% or something like that per engineers. In terms of your Waze et al GPS indicated speed, the error rate is probably due to the sampling rate of your GPS in the phone (i.e. slow).

If you have an external GPS puck like a GoPoint GPS that has a much higher sampling rate, your indicated GPS speed will be more accurate. The slower comparative rate of your phone GPS is also the reason why your distance estimates and turn by burn directions in the navigation aren't precise.

 

Good question. Maybe try downloading a different GPS app and see what it reports.

It’s either your phone or the car. Only way know is to test a friend’s phone or a friend’s car (and compare).

 

In the past, the Waze app used to show the actual speed vs the 3 mph cushion of my speedometer. Sampling rate is not the issue because no data point is going to be higher than the actual speed. I guess it just has to remain a mystery.

 

Mine is 3 MPH off also. There was a thread started in '04 about the same issue. https://rennlist.com/forums/996-foru...96-speedo.html