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  1. #1
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    Garmin 705 going wonky

    Alright, so I've been using an Edge 705 (purchased from the great folks at Geoman) for almost three months now. Loving every minute of it, but something odd has begun to develop.

    It seemed to work flawlessly for at least the first 45 days or so. Then, I would notice occasional erratic behavior with the live speed output and the max speed when plugged into my computer (I'd like to think I'm fast, but I'm pretty sure I haven't hit 74 mph on singletrack, at least not yet). No big deal, I figured it was attributed to the leaves coming out on the trees and thereby giving me momentary interruptions in coverage.

    Well, the problem is getting exponentially worse. Today was terrible. I did a loop I ride two or three times each week at lunch time. The loop is 8.9 miles long and my typical average speed is anywhere from 9 - 10 mph depending on trail conditions & how I feel. Today though, the GPS told me I had only completed something like 5.6 miles and that my average speed was in the upper 6 mph range. I'm certain it's incorrect as I rode the exact same route I usually do and completed it within 2 minutes of my better times for that route.

    Interestingly, the cadence, heart rate, time, calories burned, and even elevation numbers all seem reasonable and correct. It's just the speed and distance functions that are off. I've seen sporadic speed results on a number of different rides recently, but this is the first time I've noticed the distance being totally incorrect. Something else that's odd - the map (using Ascent or the Garmin software) of my route looks correct, but the numbers don't add up.

    So, any ideas? I can readily email the TCX files to anyone if they would help to unravel the mystery.

    Thanks,

    Trey

  2. #2
    It's carbon dontcha know.
    Reputation: 6thElement's Avatar
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    Are you on the latest firmware, if not upgrade to 2.7 then do a hard reset.

  3. #3
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    My guess is that the problem deals with your speed/cadence sensor. Perhaps the magnet on the spokes isn't close enough to the sensor causing missed wheel revolutions. Or maybe the battery has become weak (though it seems too soon for that.)

    You might want to try removing the spoke magnet entirely. This will cause the unit to use the GPS signals to determine speed and distance rather than the wheel sensor. The map display is based on GPS signals but I believe that the speed & distance uses the wheel sensor if it is there. That would explain your discrepancy between the map and numbers not adding up.

    On my unit, I use a "custom" wheel size in the bike profile so the wheel runout can be manually entered rather than having the 705 automatically calculate it. It might be that the automatic calibration of your wheel sensor has been miscalculated and is way off.

    As I mentioned on another thread in this forum, a lot of people including myself have had serious file corruption problems with version 2.70 of their firmware.

  4. #4
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    Quote Originally Posted by alamere
    My guess is that the problem deals with your speed/cadence sensor. Perhaps the magnet on the spokes isn't close enough to the sensor causing missed wheel revolutions. Or maybe the battery has become weak (though it seems too soon for that.)

    You might want to try removing the spoke magnet entirely. This will cause the unit to use the GPS signals to determine speed and distance rather than the wheel sensor. The map display is based on GPS signals but I believe that the speed & distance uses the wheel sensor if it is there.
    I've wondered about this issue. So, if I simply remove the spoke magnet, but leave the sensor on the chain stay and leave the crank magnet in place, the unit will somehow "figure out" what I've done and rely on GPS for speed but still pick up the cadence, right? I may give this a shot. The other thing I need to do is take a spin on my other bike - I don't have a speed / cadence sensor mounted on that one and have a bike profile setup accordingly. I suppose that would answer a number of questions.

    Thanks for the replies. Any other ideas?

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