Powertap/Garmin calibration

[maddox]

Hi,

 

I've been using the entry level PT on my road bike with the Edge 500 for about 18 months. I haven't had any calibration problems and have only needed to calibrate after a battery change. A couple of weeks ago I got a PT for my MTB. I've now had to calibrate both PT's and am not entirely sure how this is meant to work when sharing an edge between two PT's. Can anyone enlighten me on the following:

 

- should the Edge automatically pickup which bike you are using (ie auto identify the PT)? Mine doesn't - I have to manually select the bike from the system settings every time I move the Edge.

- how often should I need to re-calibrate and should this be done when moving between road and MTB PT's?

- what exactly do the calibration numbers mean and should I be taking notice of them?

 

thanks.

[Tankman]

Yup! You have to manually change bike profiles.

[Minion]

- should the Edge automatically pickup which bike you are using (ie auto identify the PT)? Mine doesn't - I have to manually select the bike from the system settings every time I move the Edge.

- how often should I need to re-calibrate and should this be done when moving between road and MTB PT's?

- what exactly do the calibration numbers mean and should I be taking notice of them?

By calibrate, I presume you mean selecting the calibrate button and waiting for it to display the numbers? This is not actually a calibration, but it resets the zero point for the power meter. A true calibration involves hanging known weights from your pedals, checking the torque levels displayed by the Edge (I believe the latest firmware update allows you to do this) and then changing the power meter's slope value. You can only check the slope on a Powertap - you cannot change it.

 

- you need to manually switch bike profiles. If you don't, the Edge will do a full rescan until it finds a power meter - this takes a while and may not pick up the correct hub.

- the zero value is stored on the hub itself. The Edge sends it a signal to re-zero and then displays the result. It's good practice to reset the zero value at the start of every ride since it can change with temperature. You can also tell the hub to auto zero. This resets it whenever you're coasting.

- the number displayed for the calibration is the hub ID. This is the unique identifier for that hub. It's a good way to check that it's picking up your hub and not someone else's. It's not quite a serial number, since it cannot go higher than 32768, so there must be some duplication at some point.

Edited January 3, 2012 by Edman