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Vector 3 Calibration Best Practices

kennakata
over 6 years ago
I've been really liking my Vector 3's recently and swap them between my TT and road bikes frequently. I also have two Quarq DFour power meters (one on each bike) and a PowerTap G3 on my TT bike. I bought the Vectors primarily for travel when I can't bring my bike but my collection of power meters allows me to also do some power comparisons. In general, the Vectors track really well with my other power meters, but when I move them between bikes, there is always a period where they are "off" by 5-10 watts compared to the other power meters-- sometimes they run too high and sometimes they run too low. Nevertheless, that's still up to a 20 watt difference when I've mostly been riding at less than 200 watts! This happens despite manual calibration after each swap. Also recalibrating after a few sprints seems to help (but not cure) the problem. I haven't had any extended rides since I've had them. Also, power changes around quite a bit if I put the washer in or remove it (the axle easily clears the chain without the washer).

So now the questions:

(1) Are there any tips or best practices for doing a manual calibration (e.g. pedals in a specific position)?

(2) Apart from rider safety, should I care about pedal installation torque in terms of accuracy? What about using the washer? Is there a general preference one way or the other in terms of accuracy?

(3) Most importantly, does accuracy improve time? In other words, do the pedal "settle in" over a few hours of riding and "auto zero" begins to make up for smaller calibration differences?

Thanks! All in all, the Vector 3's are a great product and I really like them!

--Ken
  • 0 over 6 years ago
    (1) Are there any tips or best practices for doing a manual calibration (e.g. pedals in a specific position)?

    Static zero calibration is independent of the crank position.

    (2) Apart from rider safety, should I care about pedal installation torque in terms of accuracy? What about using the washer? Is there a general preference one way or the other in terms of accuracy?

    From a safety perspective it is important to torque the pedals to at least the minimum recommended by your crank manufacturer (some lightweight cranks have lower torque limits). The Garmin manual still recommends 25 to 30 foot pounds (34 to 40 N-m), and this is driven by safety and durability considerations. The force measurement accuracy is good over a broad range of spindle installation torque - wider than it was with Vector 1 and 2. If you don't need the spacer washer to obtain chain clearance, or for pedal Q adjustment, then it's simpler not to use it and it avoids the possibility of the washer somehow affecting your installation.

    (3) Most importantly, does accuracy improve time? In other words, do the pedal "settle in" over a few hours of riding and "auto zero" begins to make up for smaller calibration differences?

    It should only take about ten minutes of riding (with some hard efforts) to settle in the pedals, but this also depends on how flat and square your crank surface and pedal threads are. Doing a manual zero offset at the start of at least the first few rides will ensure that you're tracking any tweaks that may occur during that time.


  • 0 over 6 years ago
    Perfect. Thanks t_smit! Good torque along with a few minutes of settling it is then.
  • 0 over 6 years ago
    The force measurement accuracy is good over a broad range of spindle installation torque - wider than it was with Vector 1 and 2.


    How critical is it to use a torque wrench? I don't have one, and now that my Vector 3 is only 10 days away (again), should I be investing in a torque wrench? The accuracy is not super critical to me, it's more about the consistency. ie, it's important that the same effort today and next year gives me the same result. It's less important (to me) that if I'm pushing 450w then I see that reading to within 1%. I'm less concerned with comparing with others, it's more about comparing my efforts today verses my efforts next week/month/year.
  • 0 over 6 years ago
    How critical is it to use a torque wrench?

    From a power measurement point of view, you are going to get consistent functionality over a broad range of spindle installation torque.
    From a safety perspective, it is important to torque the spindles so they will not come loose under pedaling and road-shock loads, and so that the spindles and cranks don't get damaged from fretting. The minimum torque for reasonable safety is higher than the minimum torque required to get good measurements.

    If you feel you can safely install pedals with a regular pedal wrench then you should not have accuracy or consistency problems with Vector 3. If you have never done any mechanical assembly on a bicycle then a torque wrench may be a sound investment, and a beam type wrench is not at all expensive. Note that you will also require a 15mm crowfoot to use a torque wrench.
  • 0 over 5 years ago
    Is the calibration on edge suppose to never found a fixed value on the Vector 3?

    What you are seeing is normal. The display is showing the torque being sensed by the pedal at that moment, so you can do a torque measurement validation if you need to.

  • 0 over 5 years ago
    I use a (pretty heavy) torque wrench set to 34 Nm when I am swapping the pedals at home. While traveling I use a much lighter pedal wrench without any specific torque setting. Using the torque wrench at home gave me at least an idea, what 34 Nm feels like and in general I am more or less good to go right from the start. When traveling I usually try to ride for 30min with a couple of sprints before doing a fresh calibration and trusting the power numbers again.

    One thing for the triathletes out there with regards to best practice: Turn off Auto Zero when you like to keep your shoes clipped to the pedals in T1. Otherwise your shoes (probably attached with rubber bands) will mess up the Auto Zero that happens a couple of minutes after the pedals are at complete rest.