Edge705 + powertap = wrong speed calculation.. Help!

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Edge705 + powertap = wrong speed calculation.. Help!

Postby gogo419 » Wed Mar 13, 2013 12:38 pm

I have had a powertap connected to my garmin edge 705 for 12+ months now but recently the speed calc has become wrong.. 10-15kmh slower than what i am actually riding at. (Verified by riding partners)

I did a total reset and calibrate on the garmin, powertap and cadence/wheel sensor last night and had it all working. However after 1km of riding this morning. An alert pops up saying auto wheel size calibrate complete and the current speed showing on the garmin dropped by 10kmh to what it was doing before.. If I turn power ant+ off during the ride then the speed goes back to what it should be showing..


Anyone had the same problem of got any tips??

If I haven't explained this well enough? Let me know? C

Gogo
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by BNA » Wed Mar 13, 2013 12:57 pm

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Re: Edge705 + powertap = wrong speed calculation.. Help!

Postby twizzle » Wed Mar 13, 2013 12:57 pm

What wheel size did it calculate?
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Re: Edge705 + powertap = wrong speed calculation.. Help!

Postby Summernight » Wed Mar 13, 2013 1:05 pm

Can you set the wheel size to manual? I have done that for my Edge500 and it seems to work better than when it was automatically calculating the size.
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Re: Edge705 + powertap = wrong speed calculation.. Help!

Postby twizzle » Wed Mar 13, 2013 1:16 pm

I did a total reset and calibrate on the garmin, powertap and cadence/wheel sensor


And, does this mean you have a speed/cadence sensor in addition to the Powertap which is also putting out a speed & cadence signal?
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Re: Edge705 + powertap = wrong speed calculation.. Help!

Postby gogo419 » Wed Mar 13, 2013 2:00 pm

Summernight wrote:Can you set the wheel size to manual? I have done that for my Edge500 and it seems to work better than when it was automatically calculating the size.


Yes! I think that could be the problem. I know it is on auto.. So i will change it back to custom and change the size back to 2100mm and then it should all hopefully work..

Although originally the wheel size was set to custom before i got the powertap so not sure how it magically changed.. :)

Thanks to the other guys for replies as well! Yes i have a speed sensor as well as the powertap.. This was put on last week thinking it might help solve the problem.. Originally i thought the GPS sensor must be stuffed before i realized it was isolated to only using the power tap.

cheers gogo
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Re: Edge705 + powertap = wrong speed calculation.. Help!

Postby Summernight » Wed Mar 13, 2013 4:24 pm

The settings may have changed through an upload of the trips to Garmin Connect or by connecting the device to your computer - I've noticed that if the bike settings have been changed on the computer or the device it will ask which settings to keep - if you say yes and choose the computer's settings and you configured the device settings to manual wheel (but not the computer settings to manual wheel) then you may have inadvertently switched it back to auto?
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Re: Edge705 + powertap = wrong speed calculation.. Help!

Postby Robthommo » Thu Mar 21, 2013 5:34 am

Had exactly the same issue. Couldn't work out what was wrong. Searched forum after forum for answer with no result. Realised that I had never changed the battery in the gsc10 sensor after 4 plus years of abuse. Replaced battery, problem solved
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Re: Edge705 + powertap = wrong speed calculation.. Help!

Postby Robthommo » Thu Mar 21, 2013 5:34 am

Had exactly the same issue. Couldn't work out what was wrong. Searched forum after forum for answer with no result. Realised that I had never changed the battery in the gsc10 sensor after 4 plus years of abuse. Replaced battery, problem solved
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Re: Edge705 + powertap = wrong speed calculation.. Help!

Postby twizzle » Thu Mar 21, 2013 12:09 pm

That's some kind of record.

A GSC10 that didn't nuke itself after 12 - 18 months!
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Re: Edge705 + powertap = wrong speed calculation.. Help!

Postby nickobec » Thu Mar 21, 2013 6:05 pm

Had the same problem got a new G3 powercap under warranty, popped the wheel on and race a 16km TT, the speeds was a little slow, the time was right, but according to my Garmin I only rode 14km. Yep the wheelsize got reset to auto for that bike (wheel) and decided I was riding a really strange 24" wheel size. Set it back to manual and 2098, not issues since.

My favourite Garmin issue, rode single speed with GSC10. 1st half of journey 15km in 30 minutes, 75rpm at average of 15kph, adjustedposition of speed magnet, next 15km in 30 minutes 75rpm at 60kph , estimated 1800w average. Strava does not show my best power figures anymore.
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