Tuesday, February 9, 2016

Power struggle much improved

In my last post I shared the problems I had encountered with my Garmin Vector pedals. Since then I have done a lot of testing and fiddling, and have learned a lot. The significant points are
  • The pods are a snug fit, so tighten pedals carefully
  • Be extra precise reading torque wrench
  • Equal torque is just as important as tightness
  • Always perform spin-up and calibration before ride
  • Do spin-up right after plugging in pods
In the last two weeks these procedures have yielded 100% satisfaction.

While writing this post I came across this item on the Garmin web site:
What best practices are recommended for achieving consistent, accurate and reliable results from my Vector or Vector S pedals?

My life would have been a lot easier had I known about this page sooner. Oh well. Here is a wrap-up of what I learned on my own:

I did have a burr on one pedal pod and was successful in smoothing it down, but even so both pods are a snug fit on the pedal shafts.  This means that as I tighten the pedals I should expect a lot of drag on the pods -- they will try to rotate with the shaft -- and this will continue for more than a full rotation until the shaft shoulder finally makes contact, at which point the tightening process feels normal. To my experienced mechanic's hands this feels like something is wrong, but it is not. At least that is what I believe to be the case. For now.

I wanted to buy a click-type torque wrench but the only one in stock in Honolulu only works on right-handed threads. Apparently this is not that unusual, as even some models of Snap-On wrenches are left-hand challenged. Parks tools makes one, and I really ought to get one. Anyway, I have my simple, inexpensive Craftsman beam type wrench that does read left and right, but I have to be very careful to position it so that the crow foot does not rub against the pod and I can clearly see the indicator. A nice, smooth pull to 25, spot-on, and that is it. Exactly the same both sides.

The jury is still out on this power-up procedure but here is what I have observed. Say I have a ride with an early start time, and the pedals need to be moved to the bike I want to use, so I move them the night before. Next day I am likely to get erratic power readings. Typically starting at 60-40 balance, then deteriorating to 100-0 (the high-low relation can be either way), then no power at all. Solution: reboot the system. Meaning get off the bike, unplug the pedal pod connectors, power down the head unit, count to ten (slowly), plug in the pods and power up the head unit, then get on and spin for awhile. Ta Da, much better.

So, I do not plug in the pods after a pedal move (after they have been unplugged) until I can proceed with the spin-up drill at the same time. Leave them unplugged until I arrive on location, set up the bike, plug in the pods, go for a short ride to complete the spin-up process. This has been working very well.

In the early edition of the Garmin software the spin-up procedure required pedaling backwards. Somewhere along the way Garmin tossed the back spin method, so I assume that there is a window of opportunity right after a pod plug-in event where normal pedaling is used to set the "installation angles." If this is not done properly the left-right balance will be off, and perhaps even the overall power output. My typical Tuesday morning Tantalus ride presents a challenge here, because the gathering place is on a hill. This morning I started "backwards," a downhill run with brakes on and pedals spinning easily above 70RPM until the power reading appearing on my Edge 800 head unit. I turned around and went uphill, and saw that I had about 45-55 balance. Close, but it could be better. I stopped and did a static calibration -- feet off the pedals, cranks parallel to the ground -- and after that I got 50-50. Garmin recommends doing all that calibration on a trainer; I wish I could afford a house big enough allow me to set up my indoor trainer indoors. You do what you have to do.

The numbers from this morning's ride look good. NP was 141 watts, just over my current FTP of 130, average power 117 and max of 554. I was by no means doing this all-out, only approaching that on the steep sections and shooting for zone 3-4 on the easier parts. Respiration matched these numbers perfectly, so I am confident my FTP value is good -- I was way off a few weeks ago, but that is typical of a new power meter user. All this fiddling with power numbers can throw off Training Peaks' assessment of my workout. For Tantalus I usually get a TSS of 80 but today I got 131, and that was not all-out. Let's wait and see what a few more weeks of data reveals.

This is curious: Garmin Connect shows power balance for this ride as 48% L / 52% R. Training Peaks gives Pwr. Bal. 52.6/47.4%. So which is correct?

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