Modern Vespa

this is why I don't trust phone GPS for MAX speed measurements (although fine for average etc)

here's a recording from yesterday on the free way.


GPS was set to plain gps mode - not either of the 'fused' modes and bike was 2019 Supertech 300 with Pixel 7 Pro running Android 14 and Vespa Snoop

or this

btw if you did want accurate speed then one of these would be better

Dragy GPS Performance Box
https://dragymotorsports.com.au/products/pre-order-dragy-gps-performance-meter-drg70

its a box that has it's own gps in it and then sends those results (via bluetooth) to a phone app

to put it another way: devices like this exist because phone gps is not so good

A GPS made for purpose is going to be better, if for no other reason that you can set the acquisition rate. I believe most phones are set at 1 reading per second. If you assume you've got a random 15 ft error potential (not uncommon) adding 15 ft and one end and subtracting it from the other end of the distance traveled in a second can make a big difference. Most good GPS SW has filters that figure this out and adjust for it but what's installed on your phone may not. In general, average is what you likely want, even if you're trying to get your max speed in a test you'll likely hold it for 5 seconds or more.

GPS instantaneous speed is calculated by doppler shift, not change in position.

Well, on a real GPS, anyway.

Let's not start that up again.

With all your GPS woes. Just wondering has it been raining there?

Many years ago I was walking with a friend in a wooded valley. My handheld GPS unit indicated that we were over a mile away from where we thought. An email reply from the manufacturer asked me the same question as above.

Apparently GPS signals can bounce off of wet leaves giving a false result.

Either this or buy a new phone and don't keep it in your pocket.

I was told once that GPS compensates speed poorly for hills and turns but I have a digital impediment

While on a multi-day tour of the Blue Ridge Parkway several years ago, my Garmin Zumo 660 had some difficulty with accurate speed readings as well, so this is not just a phone issue.

I can state with absolute certainty that I never came close to 140 mph on my Vespa!

Interesting.

Also, i wouldn't be surprised if there devices have the same chips and firmware as phones

The lines between are getting blurry. That said, even a solid dedicated GPS will get occasional spurious speed spikes.

a little thing on battery saving

some of the in depth research write ups that I found said the typical / normal duty cycle for gps in phones is 200ms active to 800ms sleeping. one of these articles was written in conjunction with google android devs.

Wasn't expecting Android to be doing this ...

TLDR: Using 3D mapping aided corrections to mitigate errors caused by reflected GPS signals in cities.

https://android-developers.googleblog.com/2020/12/improving-urban-gps-accuracy-for-your.html



(no idea about ios and not trying to bait or fight)

Cool!