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Edge 25 and Speed Sensor setup issues

Former Member
Former Member over 9 years ago
what is the proper way to get the magnetless speed sensor to work correctly?
I installed the sensor, my Edge 25 detects it right way, but it doesnt seem to do anything. All the time while riding in the forest my speed will drop to 0.0, and my mileage is way off at the end. If I lift the front of my bike and spin the tire it doesnt display any speed numbers.

My buddy has a 520 with the same sensor and his works perfect. If he spins his front tire the speed shows up and at the end of a ride he might show "12.2 miles" where as my unit will show "6.6miles".

Any tips or suggestions? I'm new to all this not sure what is wrong. Do I need to ride in the streets for a bit so the unit can calibrate properly? I dont see an option on the Edge 25 to manually put in tire size like the 520 has.
  • 0 over 7 years ago
    If there a speed sensor paired with the Edge and it has a calibration value then the speed sensor will take priority over the GPS data for speed.

    Not easy to verify as you need to use the FITSDK unpack the the files.

    The current size is stored in the settings.fit file. I think the activity file will store the value at the start and end of the activity, though it has been a long time since I looked at an activity file for the Edge 25.
  • Former Member
    0 Former Member over 7 years ago
    My Edge 25 is reading spot on with a speed and cadence sensor. With elevation change and switchbacks the Edge 25 GPS may not be the best tool to measure speed and distance but the speed sensor brought it in.

    Find a flat mile to calibrate sensor with GPS.

    i bought a magnet speed sensor to keep it simple.

  • 0 over 7 years ago
    GPS may not be the best tool to measure speed and distance


    This is a good point. I suggest for people calibrating speed sensors outdoors for the first time, turn GLONASS on. GLONASS reception is the reason I upgraded my 705 to a 1000 a few years back and it prevented all the dropped tracks I was getting in the woods northside of Mt Hood. With most chipsets this increases the number of satellites in the constellation and can improve positional accuracy. (I use an $11 China-branded USB dongle off of eBay to do WiFi heat mapping and it's rated down to 1.5m and works perfectly).

    Disclaimers: this is an educational guess (and doesn't account for firmware bugs).