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GPS data correct, wheel speed wrong

Hello,

Yesterday I rode using a 310XT and speed/cadence sensor. When I downloaded my data, I noticed that my ride appeared short (distance) for how long (time) I had been out. I believe the 310 may have been using the wheel sensor over the GPS for some reason. Is there any way to change this, both post ride and in the device so it doesn't happen again?

Looking at the mapped data, the route tracked true to what I had ridden, but the recorded distance was short. I also noticed that several distance splits had very long times (8:00 min/mi, 12 min/mi) whereas most were in the 3-4 min range. The speed graph does show the speed dropping low, however, comparing (graphically on the map) the distances of the slow 1 mi splits to the normal 1 mi splits, the slow ones are clearly longer; the first recorded 0.9 mi is actually 2.2 mi, another 2 mi is actually 4.3 mi. HR and cadence data was also recorded and appears true to what it should be.

Thanks,
Karl

0 tigermountrider over 9 years ago

I don't know about the 310XT but the Edge series uses the sensor for speed if there is an input from it. Removing the wheel magnet would result in GPS being used. But most likely, if you have the GCS 10, the problem is poor magnet alignment. Check that the magnet is centered on the mark on the speed arm and that the gap is 2 to 5 mm.

0 KARLKLEMM over 9 years ago

Yeah I'm guessing that's the likely culprit. Though I would think it would default to GPS speed (since apparently its recording it) instead of the wheel sensor. Also not sure why it was intermittent. I'll probably just pull the magnet since I'm riding on the roads, not forest.

Any idea how I can post-process to remove the wheel speed sensor data and just use the GPS?

0 tigermountrider over 9 years ago

Sensors that I used before having the GSC10 seemed to work or not but the GSC10 can be intermittent. It varies anywhere from occasionally missing a trigger to only occasionally triggering if the magnet alignment is off a little.

The Fit File Repair tool will replace the speed data using GPS data. If you post your FIT file someone will repair it for you.

0 schinder over 9 years ago

Yeah I'm guessing that's the likely culprit. Though I would think it would default to GPS speed (since apparently its recording it) instead of the wheel sensor. Also not sure why it was intermittent. I'll probably just pull the magnet since I'm riding on the roads, not forest.

The reason they do it that way is because the sensor is more accurate when it's working right. Each wheel revolution measures about 2 meters, which is below the typical error in GPS locations. There'd be no point in even having a wheel sensor if it was the other way around.