Do GPS units lose accuracy overtime?

[tlittlefield]

I have a Garmin Edge 500 that is about 5 years old. Compared to last year my avg speed is down about one mile or so.

Yes I am getting older (67) but to lose that much over a year )-;

Is it just me hitting a wall or does an older unit lose accuracy some what?

[saab2000]

It’s based on spherical trigonometry, so it shouldn’t change if the earth’s shape hasn’t changed.

A GPS is largely a calculator.

[Jaybee]

I wouldn't expect a linear degradation of GPS accuracy with time, but precision can vary on a day to day basis for a variety of reasons - satellites, horizons, interference, software translation of the signal just to name a few. This could just as easily manifest as higher speeds as lower, so I don't think that's what's going on here. If you use your GPS to plot your route, does it appear correct?

[zennmotion]

It’s based on spherical trigonometry, so it shouldn’t change if the earth’s shape hasn’t changed.

A GPS is largely a calculator.

The earth is not a sphere but is in fact ellipsoidal. And fossil palm trees are a thing in Antarctica. So the OP does have cause for concern :help:. And you should be sure how much your next runway has shifted from it's original position while you were in flight. And I have been waiting years- YEARS- to tell a geology joke in here.

[MattTuck]

Don't listen to the above two. Your GPS is giving erroneous information, you're probably going faster this year!

But actually, you probably just rode a couple more hills and had some more headwind, or took a few extra easy days. You're entitled.

[tlittlefield]

I wouldn't expect a linear degradation of GPS accuracy with time, but precision can vary on a day to day basis for a variety of reasons - satellites, horizons, interference, software translation of the signal just to name a few. This could just as easily manifest as higher speeds as lower, so I don't think that's what's going on here. If you use your GPS to plot your route, does it appear correct?

The Ede 500 does not have mapping functions.

So I guess that age is catching up to me )-;

But if you consider all 67 year old males I would assume that less than 1% could even complete 45-50 mile rides multiple times a week.

So I am grateful in that respect.

[saab2000]

The earth is not a sphere but is in fact ellipsoidal. And fossil palm trees are a thing in Antarctica. So the OP does have cause for concern :help:. And you should be sure how much your next runway has shifted from it's original position while you were in flight. And I have been waiting years- YEARS- to tell a geology joke in here.

Oh, I know it’s not a perfect sphere. It’s an oblate spheroid. (Of course, it’s actually shaped like a pizza.... :D) But I’m also sure the difference is accounted for in the math. As to the location of runways changing, if the tectonic plates shift during my flight I might have a bigger problem to manage.

[Mark McM]

I started riding before bicycle computers were common. We learned to gauge our speeds and distances by feel, and with practice we became quite accurate at it.

Later, we installed those new fangled computers on our bikes. The speeds displayed by the computers were invariably lower than the speeds we knew we were travelling before we installed the computers. But the computers were highly precise digital instruments, so we knew they must be displaying accurate speeds. We knew there could only be conclusion about the discrepancy between the speeds reported by the computer, and the speeds we knew were traveling before got the computers: The computers were slowing us down.

That's my story, and I'm sticking to it.

[MattTuck]

But the computers were highly precise digital instruments, so we knew they must be displaying accurate speeds. We knew there could only be conclusion about the discrepancy between the speeds reported by the computer, and the speeds we knew were traveling before got the computers: The computers were slowing us down.



As I was reading, was wondering where you were going with this. Made me laugh.

[NHAero]

Perhaps, especially when you consider that only 10% of them own bikes :-)
Signed
A slower than you 65 year old male



But if you consider all 67 year old males I would assume that less than 1% could even complete 45-50 mile rides multiple times a week.

[SoCalSteve]

And now for a practical answer...do you use a speed sensor paired to the 500? If so, have you checked it’s batter lately. The speed sensor fills in the gaps when the gps isn’t reading. Makes your speed average more accurate.

[BobO]

Oh, I know it’s not a perfect sphere. It’s an oblate spheroid. (Of course, it’s actually shaped like a pizza.... :D) But I’m also sure the difference is accounted for in the math. As to the location of runways changing, if the tectonic plates shift during my flight I might have a bigger problem to manage.

Ironically, for the purposes of a bike computer the pizza is probably just as valid as the sphere.:p When higher levels of precision are required, sub-centimeter survey grade equipment for instance, there are local coordinate systems that are used along with painstakingly constructed surface geoid models. Those are used as reference to do what is called localizing the data being corrected from the GPS satellite signals.

With a bike computer, a few meters here or there is of no consequence. It's just a few satellites being used to give you a rough position, probably +/- 3 meters. Vertical data is notoriously difficult with even the highest quality GPS, I imagine this is why Garmin doesn't use the it for elevation change.

ETA: as to the original question, yes, you can lose accuracy if the satellite receiver equipment is in some mode of failure. If that's the case your Garmin isn't long for the world.

[CSTRider]

Along the same lines ... i recently got a digital scale (with body fat impedance analysis etc. and bluetooth interface to a smartphone app) and notice i now weigh more than on my "old school" analog spring scale.

Is the earth's gravitational pull stronger on my new battery operated scale?

:confused:

[OtayBW]

Along the same lines ... i recently got a digital scale (with body fat impedance analysis etc. and bluetooth interface to a smartphone app) and notice i now weigh more than on my "old school" analog spring scale.

Is the earth's gravitational pull stronger on my new battery operated scale?

:confused:What's your latitude? :rolleyes:

[tlittlefield]

And now for a practical answer...do you use a speed sensor paired to the 500? If so, have you checked it’s batter lately. The speed sensor fills in the gaps when the gps isn’t reading. Makes your speed average more accurate.

No speed sensor, didn't know that obe existed.

But as I stated in my original post, I have had the Edge for 5 years and always averaged in the low/mid 18's now it is the low/mid 17's.

Probably just age catching up to me )-;

[Black Dog]

No speed sensor, didn't know that obe existed.

But as I stated in my original post, I have had the Edge for 5 years and always averaged in the low/mid 18's now it is the low/mid 17's.

Probably just age catching up to me )-;

You are having a slump. It will pass. Hurry up and wait. :)