Are Garmin Edge 305s innaccurate?

Unknown

I often find that when I'm doing a circular route with my Garmin Edge 305 I usually end up at a completely different altitude to where I started - like 50ft or more difference standing on the same spot an hour or two later. This begs the question of how accurate they actually are! I thought satellite GPS could pin you down to a few feet.

Any techies got any thoughts?

Capt. Jon

Some GPS is accurate to 10mm lat and long and 30mm alt. It depends which unit you have and which satellites it uses, also where you are.

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Deswmb

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Father Faff</i>

I often find that when I'm doing a circular route with my Garmin Edge 305 I usually end up at a completely different altitude to where I started - like 50ft or more difference standing on the same spot an hour or two later. This begs the question of how accurate they actually are! I thought satellite GPS could pin you down to a few feet.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

It's not using gps for this, it has a built in barometric altimeter. I have noticed the discrepencies too and have put them down to changing weather conditions.

If you need a more consistent reading then the altitude can be obtained via the gps plot and elevations maps instead. I'm not sure which method something like MotionBased uses though (could be a combination of the two). The built in altimeter is good enough for me and of course it's the only option if you want readings whilst you're out on the trail.

HTH

Des

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Seagull

In the UK a barometric altemeter will be in accurate by 10m or so, due to our climate the air pressure can change quite rapidly.

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Mad Splasherwmb

I don't have a bike Garmin, but do have a standard navigational one with a built in barometer/altimeter. It has the option to calibrate the altimeter to the current atmos pressure if you want accurate readings. All you need is a spot height for your starting point, plug that in and all the rest of the readings for a few hours will be spot on. I would imagine the bike versions have the same facility.

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wriggy

I heard the edge is supposed to be a little more accurate if it's left on for a while before you want to use it. I normally only use it as a guide anyway.

ddraver

Civillian GPS's have an error put into them too, so that you (or osama, whoever) can't blow the satellites up

but its way below the resoloution you ll get off a map,

but GPS altitude is always an issue, simply due to sattellite coveaage, for really accurate mapping you need a differential GPS but these are thousands of pounds and not exactly bike friendly (they re big in other words, used for MAKING maps) barometric altitudes need calibrating for accuracy obviously..

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Unknown

Well I rode from home to Bradford this morning and from Bradford to home this evening and found that my house was 222ft lower this evening. Is Ilkley sinking fast?

Unknown

I've found the altitude can vary slightly - but not much. I use my Edge 305 for running, road cycling and on the mtb. Distance seems to be spot on, I've only ever "lost" the signal in very poor weather conditions and the HR function seems very accurate too - at least on the bikes, running is another story ( I know it's not designed for running! ). Overall and excellent piece of kit - or rather - should I say - an excellent toy!! [:I]

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daxionwmb

I have the Garmin 60CSx, I'll do a loop at the weekend and check for the error in altitude other people hae noticed. There is a option to Calibrate, I know a place with a known datum where I can calibrate it then do the loop again and see if there is any difference.

We have to expect some error, but 222ft now that's just plain silly

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papasmurf.

if its a barometric altimeter don't you need to set the hieght above sealevel you are when first calibrating it to the pressure

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Unknown

Well I am not sure how to calibrate it but if you start at the same spot you finish at and you get a 222ft difference that suggests that the Garmin relies only on atmospheric pressure for its altitude readings and there is no input from satellites. One then wonders if the other readings are as inaccurate such as speed etc?