Max Speed wrong

[texmurphy]

My ride the other day showed a Max Speed of 48.8 mph on both the Newton+ (with PowerStroke and Garmin) and later in Isaac. However my Edge 500 only recorded a Max Speed of 40.6 mph. Isaac says that 48.8 occurred around mile 14.6, yet the graph shows no speed spike.
I did not notice any variance in the average speed on the Newton until mile 40. Then while moving at about 5 mph near a traffic light, I saw the speed display on the Newton jump to near 50. No sign of this in Isaac however. I always check that the wheel speed magnet is never near the sensor when I am stopped.
Ride file is attached.

[KenS]

If you set smoothing to 0:00:00 (at the top of the screen to the left of the "Show" button) you can see two spikes

[texmurphy]

Ahhh, excellent catch, thanks!
I checked rides prior and found no spikes. The three rides since all have spikes (although not constant and the Garmin does not record them).
Then checked my SportTracks logs and found it had been over 300 hours since last replacement of the spd/cad battery. Sure enough, battery voltage has fallen to 2.9V. I popped a fresh (3.3V) battery in - should take care of the spikes.

[texmurphy]

Still getting spikes - more often then before!!! I have done a reset of the Newton+ and checked the magnet alignment. Snow this morning, so maybe a test later.
This has all been done with Fast recording enabled (PowerStroke).
I think the most likely problem is with the spd/cad sensor. I may install a new GSC-10.

[Velocomp]

Still getting spikes - more often then before!!! I have done a reset of the Newton+ and checked the magnet alignment. Snow this morning, so maybe a test later.
This has all been done with Fast recording enabled (PowerStroke).
I think the most likely problem is with the spd/cad sensor. I may install a new GSC-10.

Our experience with the GSC-10 has been spotty, especially older ones. I agree a new sensor may do the trick.

[Russ]

Texmurphy,

I agree with Velocomp but in the interest of trying to save spending money, I would first try moving the sensor further or close and possibly the magnet further from the hub if it is not fairly far away, for instance. You may find a sweet spot that works better, or not. If you can tolerate a few spikes while you experiment with it

Russ

[texmurphy]

The wheel magnet was very close the sensor and I think I was getting double triggers on magnet pass as a result. The stronger new cr2032 voltage may have even increased the extra triggers.
I moved the sensor arm and the magnet so distance is 2 - 3 mm apart. I rode today and the speed display was nice an constant. Inspection of Isaac charts showed no spikes and speed matches with the Edge 500.

[Velocomp]

The wheel magnet was very close the sensor and I think I was getting double triggers on magnet pass as a result. The stronger new cr2032 voltage may have even increased the extra triggers.
I moved the sensor arm and the magnet so distance is 2 - 3 mm apart. I rode today and the speed display was nice an constant. Inspection of Isaac charts showed no spikes and speed matches with the Edge 500.

How old is your Garmin sensor?

[texmurphy]

This gsc-10 was installed June 2012 with 791 hours of activity usage, and currently is on its third battery.
The prior gsc-10 was in service from October 2006 through June 2012, going through 4 batteries (~1500 hours) before failing with a broken speed sensor reed switch.