Friday, March 11, 2016

PowerTap - Zero the Offset

PowerTap Announcement:

Of the three power meters that I own the G3 hub has served me well in all seasons of weather and has been stable. I've been in good habit since starting to train with a power meters in 2008 to zero the offset (some call it calibration) before starting to train or ride. The value on the G3 for me is generally about 496 and the hub has been tested to within 2% using a static weight test so I feel pretty good about the hub. I think most want to see a number around 502, but it doesn't have to be right on that number or the user doesn't need to fret that it is slightly off from 502. My understanding that it can be within a range near that value and still be trusted for use. 

You can go to the link provided above to get the straight story of what PowerTap is doing across the board with their latest power meters.. In short the value for "zero" will now be zero (0). If the offset value falls out of range it will report to the user on the display 'Failed', which means that the power meter is in need of service.

Please Note: This firmware update is for G3 / GS, C1 and P1 power meters.

I have an ANT+ G3 hub and will apply the firmware version 16.063 this evening using the following directions from PowerTap using the PowerAgent application.

Instructional Video Link
  • Spin the wheel/axle a couple times with the Powercap still on to "wake up" the Powercap
  • Take Powercap off by removing the triangular nut and pulling Powercap straight off (do NOT twist)
  • Remove the CR2032 battery from the Powercap 
  • Plug the Powercap without the battery into your computer using a micro USB cable
  • Open PowerAgent
  • Navigate to Tools > Firmware > Check for Firmware Update
  • Click OK to begin the firmware update
  • Firmware will install. With some new versions of firmware, Window OS will need to “re-find” the attached PowerCap. Let it run to completion. 
  • When PowerAgent says the update was successful, click OK and unplug Powercap 
  • Wait 10 seconds, plug battery back into the Powercap
  • Install PowerCap back on PowerTap hub 

Follow Up:

I know some users are always apprehensive about being the first to apply a firmware update and want to get some feedback from those bold enough to take the first step and make sure it doesn't foul up something that is already working well. I hope to make the update this evening and will report back. 

Previous Firmware Offset

New Firmware Offset After Install

The offset value right after the firmware update is -12 and must fall within the acceptable range. I will see if it changes after a few rides and report back. Just as a note I changed the battery while I had the hub cap off. 

From PowerTap's FB page on the range limits: A unit will automatically notify a rider if the unit is outside of the offset limit. This limit is +/- 30 Nm for ANT+ and +/- 3.0 Nm for BLE.


Anonymous said...

Have you noticed much variance in your calibration readings? I've got a G3 hub that reads beween 524-526 on calibration and zero torque. Been more than happy with it and the readings seem accurate and consistent from my very unscientific field testing. Oh and I am one of those people who doesn't like to be first to apply a new patch or update!

Did it take long to install?

The Cycling Addiction said...

I believe it took about 15 minutes total time. That includes the whole process. The firmware update was pretty fast. So far my G3 is still running great. Best wishes!

Les Akins said...

Mine is new as of a couple days ago and the zero offset value is - 15 but I did that while it was on the stand rather than when I was coasting with my feet out? I wonder if the - value means it is measuring light whereas a positive value might give you higher values... Can't find anything online indicating what offset value is associated with lower numbers versus higher numbers?

The Cycling Addiction said...

Les, you did right by zero the offset while standing off the bike and not moving and especially feet off the pedals. Your number of 15 is good and hopefully you that number will stay near that each time. There is a range that can be slightly negative to positive that indicates the hub is in good working order. I am not able to explain it better. Before each ride zero the offset (calibrate as Garmin calls it) and you are good to go unless that number is well out of range.

Les Akins said...

Hey thanks The Cycling Addiction... so today I somehow got a positive offset value and I think the PT is reading lower than what I would expect? Intuitively, it seems to me that if you want our PT to be as sensitive as possible you should calibrate the wheel while it is off the ground (e.g. on the bike stand)?? Thoughts??

The Cycling Addiction said...

Les, I wish I were more tech savvy like DC Rainmaker. I'm not sure. When I had concern for PT hubs I've done static weight test to confirm accuracy using a known weight. I've done it on a bike stand and off. Good luck and I hope your PM is in good shape.