incorrect wattage on tacx genius

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timbiker
Posts: 6
Joined: Thu Sep 14, 2017 10:03 pm

incorrect wattage on tacx genius

Post by timbiker » Thu Sep 14, 2017 10:18 pm

Hello,
I have a tacx genius which is up to date.

During my holidays I made a bike ride which I recorded with runtastic.
Back home I exported from runtastic a gpx file and imported it in TTS4.
I attempted to ride the same path but the effort was way too difficult. On somewhat steep slopes it was almost impossible to even turn the pedals.

I had calibrated my trainer. I attach the runtastic file.

Would you have any clue what happened ?

thebigoneinfront
Posts: 2832
Joined: Sun Oct 04, 2009 6:18 pm
Location: Ludwigshafen/Rhine, Germany

Re: incorrect wattage on tacx genius

Post by thebigoneinfront » Fri Sep 15, 2017 8:41 am

I assume you used Runtastic on a standard smartphone, which means without barometric altimeter. That way altitude is detemined by GPS. There's a rather high error in single GPS altitude points that transfers into unrealistic grades calculated between those altitude points and set by the trainer. It depends to some extent on the terrain, but as rule of thumb GPS altitude data are useless for GPS Rides unless smoothed to death. One tool to smooth them is http://www.lunicus.org/tacx/GPXsmoother.htm You will be happier using barometric altitude data, these need far less smoothing to be useful on the Tacx.

timbiker
Posts: 6
Joined: Thu Sep 14, 2017 10:03 pm

Re: incorrect wattage on tacx genius

Post by timbiker » Fri Sep 15, 2017 9:47 am

Thanks, it makes sense, I'll definitely try.
I just wonder, given I have the google map license, could there not be a way that TTS takes the altitude from google map and only use the gps file to have the timings of the real ride ?

thebigoneinfront
Posts: 2832
Joined: Sun Oct 04, 2009 6:18 pm
Location: Ludwigshafen/Rhine, Germany

Re: incorrect wattage on tacx genius

Post by thebigoneinfront » Fri Sep 15, 2017 1:24 pm

I don't think so. The only program I know that can combine data from different sources into one single activity file that way is the desktop version of Sporttracks. Most training data programs, however, offer an "elevation correction" tool that replaces recorded altitude data by data from some digital elevation model (Strava does so automatically if you upload data from non-barometric devices), so you could import your ride data and re-export from there after applying elevation correction. Not all programs offer re-export of rides in their free version, though. The point is whether the digital elevation model produces useful altitude data. This is also highly dependent on the terrain and can be anywhere between horrible and so-so.

Strava develops something that improves their (generally horrible) elevation model by using elevation data from barometric devices uploaded by its users, so you could be lucky if the specific roads you want to GPS ride on the Tacx are already done, but Strava exports only in the Premium version.

Another option is just taking the GPS track and give it a try with the elevation data added by TTS from GE. You will have training data to compare to for the second and any further rides.

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