Power meter crank length

Hello,

I am using a garmin vector 3s(single sided) power meter. The crank length on my road bike is 172.5 mm and 170 mm on my mountain bike. Does the crank length setting on my head unit(edge 820) affect the power reading? I keep changing the pedals on a regular basis so I sometimes forget to change the crank length on my edge.

Yes.

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To expand a bit, yes, it does matter.

Depending on the situation, you will have:

  1. Correct power data.
  2. Inflated power data (higher reported vs real).
  3. Deflated power data (lower reported vs real).

If you care about your power data, you need to make sure to change it every time you swap the pedals to a crank of different length, period.

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Youre probably already aware of this, but in case not -

On the edge 810 you can have multiple bike profiles and set a crank length for each. So you just need to pick to correct bike each ride.

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Thanks Chad! that helped. @R_H I am using the edge 820 and I can only set up activity profiles and not bike profiles. I also cannot change the crank length through activity profiles.

Power is linear with the arm of force, so you will be off by +/-1.5% at most though.

I am in a similar situation: 175 cranks on my race bike that I use for hard intervals outdoors, 172.5 cranks on my training bike that I use for Z2 rides on the rollers.

I just set the pedals on 175 and don‘t worry about the 5 watts overread on the rollers :blush: That‘s similar to the margin of error of the power meter, and well within my margin of error taking a ramp test :blush:

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