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Reply To: Feet of Climb / Elevation Question

KenH, February 4, 2019 at 8:50 am

I believe that most bike computers that report climb data are relying on barometric sensors, GPS altitudes being famously undependable and GPS being entirely lacking on some computers that report climb data. Barometric sensors are potentially susceptible to wind noise depending on where their pressure port is located and how you have the unit mounted on your bicycle. Wind sensitivity potentially develops when the wind is from any direction, not just crosswind and the wind produced by your own forward motion can contribute too. However wind induced errors will tend to cancel out because they can be both positive and negative. It is a complex situation however and I would not suppose it to be impossible for wind errors to be relatively consistent in one direction. Even when they do not sum to a net gain or loss over a closed loop course, they could exaggerate the total climb and descent numbers because the climb number just accumulates all the positive excursions and the descent number the negative which excludes the possibility of cancelation.

Barometric pressure changes during the course of your ride will also affect the gain and loss reported when you ride a loop, starting and ending in the same place so that you know the net gain should report as zero. I don’t know how small aircraft operate today but back in the day when you were flying across country it was normal practice to contact the airport you were about to land at to get their barometric pressure reading. You would then dial that reading into an adjustment setting on your altimeter so that you could determine your altitude above ground level more accurately. The same altitude drift happens on bicycle rides of a few hours length unless the barometric pressure is dead steady or even on short rides if the barometric pressure is changing rapidly.

Other things like internal mathematical roundoff errors could accumulate into a net gain or loss in altitude over a loop in some cases. It is also true that the various services you might upload your ride data to could “correct” your elevation data with varying degrees of success but that’s a whole ‘nother can ‘o worms!

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