DFPM calibration -- Power Tap

[doofus]

I do the Pcal before each ride

How can I check if the PT itself is drifting -- since the "Stomp test" isn't possible with the iAero?

Been getting great watts in training...just want to make sure it's me, not the gadget going wacko

[Velocomp]

I believe the PT has a setting that makes it possible for it to zero-out itself whenever cadence is zero.

You can select that setting with your PT computer head.

[doofus]

I don't have a PT Head, just the iAero

[doofus]

feature request, then -- how about a setting for DFPM users to see raw torque values, so we don't need a second gizmo for calibration?

[Velocomp]

Noted.

[Morocco Mole]

I don't have a PT Head, just the iAero

I'm not 100% sure how this works, but I think with the Powertap 2.4 Ant+ hubs, the Zero Torque setting is retained within the hub. You still need a Powertap head unit (or a borrowed one) to turn on the feature though. The reason I say this is because I often ride with both iBike Aero and PT head units on my TT bike and also Mountain Bike and the numbers on both are in sync realtime. What this also implies is that "Zero Torque" setting can be sent to the Hub from an Ant+ compatible head unit, such as the iBike.

I also found this snippet on the internet so it must be true "The automatic zeroing works completely differently between the ANT+ wireless and previous PowerTaps (the previous ones did the zero inside the CPU; with ANT+ it is now inside the hub)."

I also read that the PT Head Unit still uses Saris's proprietary transmission protocol to talk to the Hub, not ANT+, so maybe you will always need a PT Head Unit to enable this setting?

Some questions to be answered, but certainly the ideal situation would be to enable Zero Torque from the iBike.

[doofus]

so the pcal procedure is not effective in zeroing the torque?

[Morocco Mole]

so the pcal procedure is not effective in zeroing the torque?

I have never seen the value in the PCAL screen to be anything other than 0. I assume because my hub is already doing the Auto Zero whenever I stop moving? Isn't the PCAL in the iBike a "point in time" calibration and needs to be checked often, much like the calibration function on the powertap head unit? When the hub zeroing is enabled there should be no need for PCAL or PT H/U calibration, the trick seems to be how you enable it if you do not have a PT Head Unit.

[doofus]

aha

I got a wheel on a discount and didn't get the PT head unit because I had the iBike

so, my numbers are pretty much rubbish until I buy a PT head unit

more money out the window then

[heith]

yeah it's confusing.
With the older PT hub if auto zero was turned off, watts would show up when you were not pedaling. With the auto zero on it wouldn't cause the yellowCPU would correct it. With the new hubs the correction is made at the hub before sending the information. Does this mean as long as your aero is reading zero, you are zeroed? Because technically you would think while coast pedaling(pedaling without pressure while moving) the aero would show positive watts if the torque wasn't zeroed. Anyways I always figured that if I pcal at the beginning and the watts always show zero when coasting then it's probably zeroed.

I wish I knew what was really going on and if I did I would probably use the PT hubbed wheel more often and would like too. But because of the added weight, lack of this information, wait time to start a ride doing all this, and aero's proven accuracy; i just leave the PT at home.
What I do notice is a big discrepancy on the trainer though and like to use the PT wheel on that because the aero is just using a torque curve on MPH while you are really putting down a lot more power during the accelerations but it's only showing watts of current speed. So I do use it on the trainer and during testing

[NCH1]

I don't own a Powertap, but what I have read on the Wattage forum, is that you should not rely on auto zeroing, rather a manual calibration should be done prior to each ride to ensure accuracy.

Nik

[doofus]

the manual calibration is no fix either

my PT wheel is going back to Saris for service -- the torque values are way off, giving power ratings that are around 10% off

uh...my iBike was more accurate...

all these gizmo things have their issues