could this be a blocked wind sensor?

[ronpei]

very strange ride. This morning i rode to work 25 km all was well with my Newton. Then this afternoon I started home basically the same distance but there was a very (and I stress very) light rain, large rain drops once in a while. At the very start the ride looked OK, then it went crazy, the speed was about double my Garmin and as you can see the distance is quite a bit further, ie 40.2km vs 23.9, and boy I wish I could ride that fast...the only things I can think of is the battery in my speed cadence unit (garmin) (though the cadence was good on both units and matched) might be weak, the wheel magnet is fine and so I am baffled at this time?

Any ideas?

[KenS]

Unlikely to be the wind port. More likely a problem in the speed sensor. Sometimes they give a double reading due to the magnet positions. Doesn't affect your Garmin because it reads distance and speed from GPS.
Basically, whenever I see a big difference in speed or distance between Garmin and Newton I check the speed sensor.

[ronpei]

well with the Garmin it is hard to say, since it does take the reading from the wheel magnet but also takes the cadence from the unit so it does baffle me, but I suspect if there is a problem with the wheel magnet the Garmin would default to GPs speed. Sill troubling, I checked the battery and it was 2.9 V so probably a bit iffy so we will see if a battery that reads over 3V is a fix but it is odd that it was wet out the same time this started to happen. Correlation however is not causation so we will see. Any other ideas or similar experiences?

[Velocomp]

Most definitely it is the speed sensor. Check speed magnet/sensor location. If that doesn't do it, then change your sensor battery.

[ronpei]

yes John, confirmed... bad speed sensor. I tried a very simple diagnostic, spin the wheel and no speed reading, so anyhow ended up needing to replace the sensor, and presto fixed, all good now!