garmin 500 auto zero function...who knows?

[teamgomez]

Every time I calibrate, I see "Auto Zero" and wonder so I called CycleOps and they seem to believe it is a half-hearted attempt from Garmin to use PT terminology to 'auto calibrate'...so I called Garmin and they told me that "with auto zero boxed, any data at 0 watts will be discarded thus raising your average power for the ride".

Guess its easy enough to validate....but does anybody really know? Do you box 'auto zero' or not???

I use WKO FWIW to get my numbers/data for training purposes. Don't know if WKO disregards the zero value when calculating, say, your best 20 min average (assumption is that it would include it...but how can it if you have auto zero boxed???).

 

[RapDaddyo]

WKO+ computes its ride file statistics from the raw data. The settings you use in your Garmin setup such as the rolling average watts or whether to count zeros or not for watts, speed, cadence affect only the Garmin display during your ride. When you transfer the data to WKO+, you are transferring the raw data captured and WKO+ computes its ride file statistics from the raw data. The one setting you want to avoid is Smart Recording because it affects the recording of raw data. You should always use the shortest recording interval available (e.g., 1 sec) unless you have a really long ride and don't have enough memory to capture the entire ride.

 

[bgoetz]

You also want to avoid using non-zero avg power because anytime you have zero power it does not average it on the Garmin. However if downloading to WKO I think it uses the zero average. The zero function just calibrates the Garmin to the device, basically says "this is zero" and the Garmin uses that info to determine power, so you want to calibrate before every ride.

 

[Sam1971]

My understanding is this...

Having the auto zero box ticked on the Garmin head unit allows the power meter to zero itself without going through the manual "calibration" zeroing process.

So if you have a Quarq...

And the auto zero not selected..to zero the meter before you ride you must go through the menu the the manual zero "calibration" section...and allow the Quarq to zero itself...it returns the zero offset value to the Garmin so you can look at it. If you want to rezero duringa ride you have to stop and get off the bike and do the same thing again...you can also do it at the end of the ride to check how much the zero has moved around...which tells you if your data is consistant.

With the auto zero selected...you just back pedal at least 4 times and the Quarq zeroes itself...you can do it off the bike or on...any time you back pedal 4 times it rezeroes...this is what I do. The only thing is when you back pedal the Quarq doesn't return the zero offset to the screen so that you can see what the zero is doing...this isnt a big deal if you trust that the Quarq is working correctly. When I first got my Quarq the zero took a week or so to settle down and I was back peddling all over the place. I think the key to good data with the Quarq is to regularly zero it on the ride by smoothly back peddling.


If you have a Powertap...

Auto zero not selected...same as above..go through the menu.

Auto zero selected...the PT auto zeroes itself every time you free wheel...this is what I do. This setup is simple and really reliable and it just never misses IMO.


IMO the reason why the Quarq can't auto zero on zero cadence like the PT is because any pressure on the pedals even with no tension on the chain/no torque on the spider can still produce significant readings on the strain guages...when you back pedal the Quarq reads the strain signal as you back pedal and uses some sort of average.

When I got my Quarq I ran the PT as well to get a feel for how the Quarq behaved and to work out how to zero it best.

Sam