Edge 530 speed from wheel sensor (slowly) decreasing unexpectedly.

WouterDobbelaere
23 hours ago

I'm using Edge 530 on my track (bike) rides, and noticed on my last ride that near the end of the ride, the speed indication (which is supposed to be picked up by the ANT+ wheel-sensor) started to show lower speeds that what it should have showed. While our riding speed kept around 40km/h, the indicated speed slowly dropped down to 35 and further to around 30km/h. Initially, I thought it was just me getting tired, but the readings from my cadence sensor stayed normal and stable (we use fixed gear on track...), proving that my speed certainly didn't go down that much. What could be the reason? I did check that the sensor was still well connected the to wheel axis, so I doubt that it is slipping on the axis (but hard to prove). I might try to fix it a little more snug next time. Stillneed to check the battery status of the wheel sensor, that might be another reason. Any other things that could result into this bahavior?

  • +1 18 hours ago

    If you have the sensor set to automatic calibration, that could be a cause.  It's much more accurate to roll out the wheel next to a tape measurer and manually set the circumference.  I am very particular about it and even push down on the handlebars some to emulate my weight on the bike and roll it out for three revolutions, then divide by three and convert to millimeters.  I get extremely accurate distance/speed this way.

    Auto calibration in a indoor track may not be getting accurate GPS information to calibrate properly.  And, even outside, manual calibration is always going to be more accurate and reliable.

  • 0 14 hours ago in reply to Cranky K.

    Thanks for the reply and the suggestion Cranky K! Though the sensor has been set to Manual in the past with the correct circumference, and has been working great since a long time on my track rides. Just that it has dropped accuracy dramatically during my last ride. But surely, I will recheck that he has not "forgotten" the manual circumference setting. Good suggestion. 

    I just did check, and indeed, the setting was on AutoCalibration, and was showing 1509, which is considerably smaller than the 2096mm I have been using with good results before on this track-bike. So this was also leading to the considerable lower speeds (30 vs the expected 40) I was reading at the end of my latest track session (and the reason for this post). So that makes some sense now. Now it probably also makes sense that my speed indication had started to slowly drop over a period of about 20min, as it was trying to correlate (AutoCalibrate) the sensor speed with the gps speed (which is not giving relevent readings on the track anyway... too short and too many turns... and the main reason to use the wheel sensor). Anyway, I still guess that at some point during the ride, or during a break, the sensor has switched from Manual (which it surely was ever before) to Auto Calibration. There is a chance I made this chance by coincidence myself, and certainly unintentional, as I had been working on the my Edge530 settings lately (removing some old sensors from its list). Or the setting has jumped by itsef for some unknown reason, which would better explain that it was giving correct number for the first 2h of my track session. Only the last 30min seemed to be way off. At least, it should work again now for my next track session coming up later this week! Thanks for the suggestion!