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Decreasing power reported by Rally XC200

I'm using the Garmin Rally XC200 for four weeks now. I calibrate the pedals before every ride. I do it as the last step before starting to ride, when I'm already outside.

On Monday I rode the same route as the first time using the pedals a month ago. I could compare the power on the same segments, in very similar conditions. At the same speed and over the same time the pedals measured 65-80 watts less than four weeks ago.

Here's some data from one of Strava's segments on the route:

Segment

I'm starting to have doubts about the reliability of the measurement. Any advice?

  • 65-80 watts of difference sounds like much more than promised by Garmin 1% of accuracy... ;-)

    The best would be to verify somehow measurements. Is there any way to check and verify torque reported on these pedals? Like hanging weights on them etc. as possible on other pedals? Without doing such (or similar) test is hard to say if current or previous measurements are OK...

  • We should see the detailed charts from Strava, the lower power avg could be the results of dropouts (lots of 0 watts and these makes the avg so low) or due to wrong angle value (rotated spindle due to not tightened the pedal/s/ well)

  • Hi Luko79,

    Here are graphs for the longest climb on the route. They are not totally synchronized as these were two separate activities. I apologize for that.
    First the ride in late April:

    And the most recent one:

    When looking at the power graphs, I do not see clear dropouts, just a general lower readout over the whole ride.
    In the second activity I rode very similar time on this climb:

  • How is your leg balances in these 2 rides (in GConnect)?

    But: 1. Check the pedals and tighten them at 40NM. 2. Remove the batteries and put them back. 3. Check the crank length setting in head unit 4. Make a few hard sprint efforts 5. Reset the install angles in head unit (but i think the battery remove is already doing it ) 6. Spin steady and smoothly for 1-2mins at 80-90rpm. 6. Do a manual zero offset

    If these are ready, test it again.

  • I ve used pedals 3 times, but today I have seen the same behaviour with decreased power as your was getting over 50W lower power then I should…calibrating few times changed nothing!

  • What solved the issue completely: making sure that pedals are installed at 34 Nm.
    Once I did this: consistent power for many months now, spot-on when checked against Wahoo Kickr.

  • Did you get any resolution to this problem?  I think I’m switching back to a single, spider based PM. The pedals were nice when they worked. 

  • Did you get any resolution to this problem?  I think I’m switching back to a single, spider based PM. The pedals were nice when they worked. 

  • Yes, I sold pedałs. Get rid of them is the only solution. Plus they were anchors weighting 440g, literally I hated to ride dem because of the weight. Maybe it was placebo but I could feel they almost halv a kilo to spin…

    Pedals where working for 2-3 rides after hard reset with taking out batteries, and after that starting again to decrease power.

    I have a lot of power meters, assioma duo, kickr, 4ii krankarm, quarq, over 5 years of riding with power, I know when something is off when it comes to power meter.