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learn me about Strava and GPS

Last Post 03/10/2014 11:29 PM by Darrell Edwards. 22 Replies.

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Posts:50

03/10/2014 11:47 AM
One more thing to add re: GPS accuracy. I have an issue with elevation totals with my 705. My buddy rides with an 800 and our elevation totals for the same ride are never the same, and often WAY out of whack. I've researched this, and even called Garmin, and they say the issue is the unit grabbing the correct starting elevation. If this doesn't happen, you get discrepancies. In the end, it's not a big enough deal to worry about for me, but I do wonder why. Are the new units more accurate? Do I have a lemon? If anybody has any answers I'd love to hear them.

Posts:4209

03/10/2014 11:53 AM
I never pay attention to the elevation stats.....1) it is pancake flat here. Doesn't mean anything to me. 2) When I can get elevation gains (or losses) on my swims, I figure the technology is pretty much worthless.

Just say "NO!" to WCP!!!!

Posts:12

03/10/2014 11:55 AM
The system said that it had satellite lock, so I assume it was good. I thought my Garmin 500 would have been more accurate than it was, although it didn't surprise me that it wasn't. Considering that you are traveling only about 30 feet/second the accuracy of GPS position (+/- a foot or more) error can come into play. Not so much a deal with cars since they are traveling at 90 feet/second and have better satellite reception usually. The speed would jump around a lot. 19.4 then 19.3 then 19.5.... Annoying. Maybe they solved this with some better programming to smooth out the data and/or more frequent sampling rates on the newer units. If so, the inaccuracy is still there, it's just hidden from the user. The problem solved itself when I added the speed/cadence sensor (which you'll probably want anyway so you can use the cadence feature of your Garmin. The grade % feature works really well, which is odd since altitude determination with GPS is even less accurate than lateral position location. Still, there is a noticeable delay between starting the climb and the unit displaying the grade %. I assume the programming is collecting data points and doing some statistical manipulations. It's very accurate, however, since when I climb bridges with profiles I know I see the grade percentages changing just as they should.

Posts:3180

03/10/2014 12:07 PM
CK, elevation gains swimming I take with a grain of salt, but elevation losses? Now that's one I take dead serious. As in, I'm a sinker. That could be real! Ben

Posts:4209

03/10/2014 12:24 PM
@ prof - I use a Powertap hub, which gives me cadence along with my power. No need for the GSC device. @ Ben - HAH! Good point! Luckily I do all my open water swims in a wetsuit, so sinking is not an issue.

Just say "NO!" to WCP!!!!

Posts:4499

03/10/2014 12:28 PM
That's funny, cumulative vertical kms is my main cycling training metric. Horizontal kms are easy :-) For swimming the metric should be water temperature.

Posts:229

03/10/2014 10:25 PM
Funk my 705 seems accurate, with both elevation speed and cadence. Once in a while after I download the data cadence just flat lines, but that's it. I say this because I ride with friend who has the 500 and we both get compatible data read out. I am wondering if it has to do with the GPS mapping and the location where you live.

Posts:66

03/10/2014 11:29 PM
I guess I will start looking at a Garmin 500. Elevation change here means the 10 foot rise over the golf cart overpass. You can figure that it is really flat here with an elevation of 49 ft and being 40 miles from the coast. thanks P.S. over 20 posts on a bike stuff question. The forum's not dead yet!!