PowerTap P1 Dual Sided / Garmin /Lezyne

[GParkes]

Need some input on some pairing quirks. I recently switched from crank based power to P'Tap dual sided pedals. Additionally, I'm migrating away from Garmin head units and thought I'd try a Lezyne Super GPS head unit. I've been able to pair the pedals to both head units (running parallel for a few rides to compare).

My problem - The Garmin is reading consistent power numbers from the pedals that I was obtaining from my Power2Max. The Lezyne is reading nearly exactly half of the wattage. Gone back and checked set up process on Lezyne - all seems good.

Now, I have gotten a message on the Garmin at start-up that it's not reading right pedal. I understand that the right transmits to left, and left to head unit. If the right isn't transmitting, that should only cause the readings to not be accurate from a L/R balance - but the wattage should be valid for left pedal.

The pedals have the green sensor that flashes when they become active, however, I noticed no green light on right pedal (going to swap battery to see if this is a problem). Even if the right pedal isn't transmitting, I find it hard to believe that the Lezyne would be reading just half the power.

Ultimate goal - functional pedal(s) and accurate data from Lezyne (my Garmin has a habit of dropping power and it is 5 years old). Any tips would be appreciated.

[morrisericd]

I have no experience with the Lezyne head unit but plenty with the Garmin (520). The message at startup saying "right power sensor missing" is a software bug. I called Powertap about it and they said (using memory here - watch out for accuracy) that it's an issue on Garmin's end that they need to fix. It is definitely reading the right pedal - just a bug saying it is not.

Powertap has a known issue with the early production run of battery end caps. Depending upon when your pedals were manufactured you may have a bad set. You can call Powertap and they will happily send you a new set. The bad caps wouldn't let the pedals go to sleep so they would drain the battery very fast.

I have also run the pedals on a Wahoo Element with no issues. Very happy with the pedals and the customer service. Every time I call someone answers and really seems to know and care about their products.

[glepore]

Of course it would read half the power if it only saw one pedal, there are strain gauges in each. It may have nothing to do with your problem, but if you put a dummy pedal on the left you'd see 50% readings, assuming that the system didn't stop transmitting for want of a left signal.

Suspect that the issue is firmware, though, and I'd contact Leyzne and then Powertap. The fact that the Garmin readings are good leads me to believe its a bug in the Leyzne.

[mjalder2]

Some head units only have one Bluetooth channel. If you're connected via Bluetooth, it might only pick up one side, resulting in half the power. Try checking out DC Rainmaker's review of your head unit for known power meter incompatibility. He uses P1 pedals in his testing protocol, so he would come across such an issue.


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[RonW87]

Originally Posted by mjalder2

Some head units only have one Bluetooth channel. If you're connected via Bluetooth, it might only pick up one side,

As noted above, there is only one side to pick up for the head unit. Right pedal transmits to left. Not to the head unit.

[sitzmark]

For Bluetooth P1 L&R are recognized independently - for example with Zwift iOS,OS/X, or tvOS. One or the other pedal will pair but not both. Adjusted power readings appear reasonably accurate. Very early in P1 lifecycle even Saris didn’t get it right with their CycleOps Virtual Training Program. Only recognized left pedal (BLE) and then only 50% power in the app when training. After reporting a software update resolved the problem.

No experienice with Lezyne, but best I recall Garmin ANT+ headunits don’t recognize L/R independently when pairing. Or as I recall ...haven’t re-paired in a while so don’t remember for sure.

[GParkes]

Originally Posted by glepore

Of course it would read half the power if it only saw one pedal, there are strain gauges in each. It may have nothing to do with your problem, but if you put a dummy pedal on the left you'd see 50% readings, assuming that the system didn't stop transmitting for want of a left signal.

Suspect that the issue is firmware, though, and I'd contact Leyzne and then Powertap. The fact that the Garmin readings are good leads me to believe its a bug in the Leyzne.

Not true on the of "course half power" reading. Data only gets transmitted from left in this system. Since it is transmitting data to Garmin head unit, I'm getting a single sided power reading (just like any single sided crank based). My left leg doesn't only produce half the watts, and right the other half, ergo a 50% reading in your assumption. That being said, curious to see what Lezyne now reads with active right pedal (batteries replaced, and Garmin now seeing both pedals). Thank you for the input though, I do appreciate it.

[glepore]

Don't mean to argue, but crank based is different from single sided pedal or crankarm. Its because of straingauge placement.

Crankarm systems have the gauges in the spider, so they're measuring material flex there, and the spider "flexes" regardless of what pedal you push on. It measures both sides, but can't differentiate unless it uses math or an accelerometer on each crankarm. Quarq's dual sided measurement, fwiw, is voodoo because of this.

Stages is an example of a crankarm (or pedal) system. The gauges are measuring the material strain at a place where only one side "flexes" the material. There is an algorithm is the firmware that estimates the total power (its not as simple as 2x but not far off). When you pedal on your left pedal on your system, you're not straining the right axle shaft significantly. The algorithm is why Stages comes under such internet criticism, although in practice I'm fine with it, and I've had SRM's, pt's, Quarq's etc.

I'm beginning to think the answer is above-Garmin's don't speak Bluetooth, do Leyzne? If so, it may be that the answer. What sitzmark says. It only transmits ANT from the right to left, sure. ANT is high power and drains battery. BTLE is as its name says, low energy. The signal from right to left is Bluetooth. Headunit sees pedals independently as above.

[GParkes]

Originally Posted by glepore

Don't mean to argue, but crank based is different from single sided pedal or crankarm. Its because of straingauge placement.

Crankarm systems have the gauges in the spider, so they're measuring material flex there, and the spider "flexes" regardless of what pedal you push on. It measures both sides, but can't differentiate unless it uses math or an accelerometer on each crankarm. Quarq's dual sided measurement, fwiw, is voodoo because of this.

Stages is an example of a crankarm (or pedal) system. The gauges are measuring the material strain at a place where only one side "flexes" the material. There is an algorithm is the firmware that estimates the total power (its not as simple as 2x but not far off). When you pedal on your left pedal on your system, you're not straining the right axle shaft significantly. The algorithm is why Stages comes under such internet criticism, although in practice I'm fine with it, and I've had SRM's, pt's, Quarq's etc.

I'm beginning to think the answer is above-Garmin's don't speak Bluetooth, do Leyzne? If so, it may be that the answer. What sitzmark says. It only transmits ANT from the right to left, sure. ANT is high power and drains battery. BTLE is as its name says, low energy. The signal from right to left is Bluetooth. Headunit sees pedals independently as above.

Thanks for the additional info. Yes, Lezyne is both Bluetooth/Ant+. Still working on it. Sent message to Lezyne for some more input (pun intended). Frustrating, shouldn't be this big of a deal.