Wheel Circumference and Garmin Edge 305

If you have the cadence sensor, it makes a difference.  If you do not you can ignore the rest of the reply.

The cadence sensor for the Edge 305 (and the Forerunner too) has pickups for both the pedal rotation and wheel rotation.  The wheel rotation gives a measure of distance and speed by counting the number of times the magnet on the wheel passes the sensor.  The speed calculated from the speed of revolution is proportional to speed of the bike by the circumference.  So that is what it is used for.   The Edge uses the wheel measurement of speed and distance whenever the GPS does not pick up (for example in cities where the GPS satellite reception is blocked by buildings).   It also can use the signal when the bike is on the trainer.

One built-in feature of the Edge is the self-calibration of the wheel sensor to measure the circumference of the wheel using the distance measured by the GPS back calculate the circumference constant.   The calibration occurs automatically when you first pair the sensor to the  Edge base unit.  You can also force a recalibration of you need to from the accessories setup page.  The instruction manual is pretty clear on how to start the recalibration.

TW 

You always have the answers to my Garmin questions, thank you!  So, from what I read above if I have paired the unit to the sensor I should not need to change anything.  Is that right?  If that is the case, is the tire size measurement found in the bike profile irrelevant?

Thanks again.

No problem.  I am fascinated by the engineering that goes into these devices.

To check your wheel calibration setup, first click the MODE button until the History, Training, Navigation, Settings page is displaced.  Use the arrow buttons to select Settings.  Press enter. The page should change to Data Fields, System, User Profile, Bike Profile, Zones, and Data Recording.  Use the arrow keys to select Bike Profile.  Press Enter.  The page should show fields for Bike, Weight, Sensor Mounted, Wheel size, and Tire size.  Be sure that Wheel size says "Auto".   Also check that the Tire Size field agrees reasonably closely with the size for you 650 mm wheels.  It should.   If it is not, then when you are about to go for your next ride scan for the cadence sensor again.  If the Auto calibrate is selected, the Edge will recalculate the wheel size.  While it is doing this, it will say something on the screen like Wheel size calibration.  If you are geeky like me, you will stop your bike after the calibration is complete and look at the wheel size field to see if the unit got it right.   Ok I may be the only person in the world who has ever done that.  You could be the second.

 TW