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Discussion Starter · #1 ·
My wife recently decided she needed to upgrade from a Garmin 200 to a 510. We installed everything and went riding. The speed would switch between whatever we were riding, say 19 mph, to 4 or 5 mph. Caused all sorts of problems with total mileage, average speed, etc. She got a replacement but is still having the same issue. All the tolerances are within the Garmin specs so I'm at a loss. The unit detects the speed and cadence sensor just fine and displays both accordingly but that fluctuation in speed is a mystery. Wheel size, etc. all checks out. Anybody have any ideas? She rides a 51cm Cervelo R3.
 

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Pathlete and Pedalphile
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I use satellite to track my speed with my Garmin and the cadence sensor for cadence. No wheel magnet required. I know it doesn't answer your question but it will solve the problem (hopefully).
 

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If the speed is fluctuating, the sensor is not being picked up correctly. Distance and fore aft alignment both matter. People tend to put the spoke magnet so it passes through the middle of the pickup. Slide it back so it passes more through the end of the pickup.
 

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Discussion Starter · #15 ·
OK, may have figured it out, sort of. I went back in and rechecked the wheel size and noted that the unit gave an option of entering the wheel size manually or automatically. When we switched to automatic, it seems to read correctly. I don't really understand but it seems to have corrected the problem.
 

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fu
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OK, may have figured it out, sort of. I went back in and rechecked the wheel size and noted that the unit gave an option of entering the wheel size manually or automatically. When we switched to automatic, it seems to read correctly. I don't really understand but it seems to have corrected the problem.
This was suggested in reply #6 :D
 
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