Garmin Edge 305 Question

[SadieKate]

gw_12 (whom I like to call geek_12) over on bikejournal sent me this explanation of GPS-only elevation gain/loss problems:

Consumer grade GPS is just not very good for accumulated elevation measurement (that’s why survey grade GPS units still cost about $5000). As you probably know consumer grade GPS can be off in the horizontal plane by 5-10 meters or so at any time. In the vertical plane they can easily be off by 2 to 3 times that much. While that drift in the horizontal plane may not produce an unacceptable error in the distance measurement of a bike ride (lots of horizontal travel vs relatively small errors), 2 to 3 times that error in the vertical plane over the same amount of time and much less vertical travel makes the accumulated elevation data practically worthless. Note that the indicated elevation is typically with 50 feet of actual, but varies over the ride from -50 to +50. The system has no way to discriminate between actual climbing and descending and error drift.

I, personally, have experienced gain/loss data 3x the actual with the Forerunner. So the deals to be had on the Edge make it worth having both.

The FR has been useful to Izaak the Wonder Poodle as he is currently racking up the mileage to the coffee shop and back. And I'll use it for snowshoeing once we move to Bend. It will definitely come in handy. Besides, I'm sure that yellow has dreams that someday she'll convert me to trail-shuffling.

[7rider]

So wait.
Let me state what I think may be obvious to some, but not to me.
SadieKate...
the gist of what you are saying is:
ForeRunner: GPS elevation only. Much variation/error. Essentially worthless for elevation readings.
Edge: GPS and barometric elevation readings. Some variation/error. Generally more accurate than GPS alone. Not perfect, but okay for consumer grade.

(that is the general sense I've gotten from other folks over the year I've had my Edge, at any rate).

[SadieKate]

Regina, I've done a little editing. Make sure you differentiate between the measurement of the elevation of a certain point on your route (i.,e., at the top of Mt Diablo it is X feet high) and the calculation of the total feet you've climbed (i.e, I just rode up Mt Diablo and climbed X feet total). These are two different things.

ForeRunner: GPS elevation only. Much variation/error on gain/loss calculations (only available once you've downloaded your data to the Training Center or MotionBased). Essentially worthless for elevation gain/loss readings but fairly accurate for measuring the elevation of a certain point.

Edge: GPS and barometric elevation readings and gain/loss calculations. Some variation/error. Generally more accurate than GPS alone. Not perfect, but okay for consumer grade.

[silver]

Regina, I've done a little editing. Make sure you differentiate between the measurement of the elevation of a certain point on your route (i.,e., at the top of Mt Diablo it is X feet high) and the calculation of the total feet you've climbed (i.e, I just rode up Mt Diablo and climbed X feet total). These are two different things.

ForeRunner: GPS elevation only. Much variation/error on gain/loss calculations (only available once you've downloaded your data to the Training Center or MotionBased). Essentially worthless for elevation gain/loss readings but fairly accurate for measuring the elevation of a certain point.

Edge: GPS and barometric elevation readings and gain/loss calculations. Some variation/error. Generally more accurate than GPS alone. Not perfect, but okay for consumer grade.

I agree. like I said, I got myself the forerunner 205. I don't really care about elevation and climbing data. I don't like to be bothered with HRM and cadence. On the bike I really only want to know distance and speed, so I really only use my cateye. I've strapped the forerunner on a few times to map out a route. I got the forerunner because I wanted it for running. Good basic GPS for distance and speed and easy to wear when I run. Anyone buying one of these products needs to understand their abilities and limitations and know what they want from them.

[onimity]

Hey SadieKate,

I did write to Garmin about the elevation gain/loss issue and their suggestion was to use Motionbased but I will write to them about the way they market the product and why I'm returning it. If you look at the feature lists you would not understand that the Forerunner doesn't track elevation gain/loss accurately. I would have purchased the correct device in the first place if they had been clear about that or not included that as a 'feature' of the device.

I agree that simple things like release notes would be nice. You'd think that with so many products they might have some organization or standard processes... Actually, I've always been really impressed with their device software.

Lifesgreat,

Don't I wish it could track the wind speed!! It should count as uphill when you have to pedal going downhill just to keep going!

[tygab]

This is from their help page:

Choosing to apply the Tune-Up features here will apply the information automatically when submitting from the Inbox to the Digest. You may always override this preference by choosing to edit the activity.

* GPS Corrections - cleans up location information that can sometimes produce erroneous values
* MB Gravity - cleans up elevation information by cross-referencing the location with an elevation dataset

Please note that MB Gravity is not necessary with the Edge 305 as it has a built in Barometric Altimeter.

I think the algorithms are probably well done. I suppose the only way to know that for sure is to do a side by side with the Edge. But, for my purposes I am believing it as accurate enough.

Edit: haha we just may get to do this as I am convincing my husband to get his Edge with the good deals out there... [he has been coveting my Forerunner data].

[SadieKate]

Tygab, these are the notes from two rides I did recently. I've called Garmin about the inaccuracies and they confirmed that the ForeRunner gain/loss data is incorrect whether you run it through GTC or MB.

Mt Tam mtb ride of 24+ miles:
FR 305 in GTC = 6,456
FR 305 in MB with gravity correction = 4,613
maillotpois' Edge 305 = 3,247 (and based on similar rides and my legs, this is correct)

Lake Solano road ride of 21+ miles on a nearly flat road:
FR 305 in GTC = 1,551
FR 305 in MB with gravity correction = 1,139
Polar and Ciclo data from past rides = 400-405 (and verified by the almost flat road)
MP's Edge 305 = 547

Jobob and Trekhawk could probably give their results from this last ride also if you feel that you need more stats for comparison. I've used a Ciclo and a Polar for a few years now. All of my results are comparable to Edge results. Forerunner results are from another galaxy far, far away.

[bikerHen]

Well I did it! Ordered one this morning! Thanks for all your encouraging words! The new bike wants it and the mount is broken on the computer on my road bike. So I really do need a new toy! I mean computer! bikerHen

[kelownagirl]

I love my Edge and have had very few "anomolies" other than a few artificially high heart rates. The elevation data has been fairly accurate so far and I run my data thru the garmin software as well as Motionbased. Motionbased has never been down when I've been online yet although I have not yet upgraded to a full account yet. I may once dh starts using his garmin as well.

I DID set my garmin up with my bike data and it was fairly easy to input the weight of the bike and the wheel size from their chart. It is possible to set it up for 3 different bikes so next time I use my MTbike, I'll add that as well. I also use my garmin for running - I just carry it in my hand or pocket. It was awesome to have it on our bike tour in France this summer - so cool to be able to see the graphs and maps online.

FWIW, DH and I bought two Garmins for ourselves as a wedding present last March...

Enjoy yours!