Climbing
Posted: Mon Jul 14, 2008 1:28 am
For any given ride, there is no single correct answer for how much climbing you did. Another way of saying that is that you should not expect two different cycling devices to agree on their climbing numbers for any given ride. Let me briefly explain:
Climbing is a sum of positive elevation gains during the ride, ignoring the small elevation gains and also ignoring elevation gains that happen over such long stretches of road that the grade is insignificant. The basic problem is that there is no standard definition of what elevation gain is too small or what road grade is too small to be included in the climbing totals. Gaining 200 ft of elevation in a mile is a climb. Only gaining 20 ft of elevation on a straight incline that is a mile long is not a climb. For most riders, the aerodynamic frictional losses are much greater than the work done against gravity for that mile. Now the question is is a 20 ft gain in only 200 ft of riding a climb? I think most people would want to include that effort in their climbing tally. The issue is that you have to draw the line somewhere, and there is no standards body out there that I know of defining what should and should not be included in the climbing sum.
Imagine for a moment that you have 2 different devices that make perfectly accurate elevation measurements. They would produce elevation profile that perfectly agree with each other; however, they would disagree on their reported climbing numbers because the software in each device will be using a different filter to remove the insignificant elevation gains from the climbing totals. The problem is actually worse on roads that are nearly flat or mildly rolling because are large portion of your ride is near those filter thresholds. One device might include lots of little elevation gains that the other device ignores. Over time, those differences add up to a big disagreement. If you are doing serious climbing up a mountain, both devices will have an easier time agreeing with each other; however, you will still have differences when the grade temporarily levels off.
Note that the exact same issue exists for geological survey data. Say that there is a perfect source elevation data for a ride that you do based on survey data accurate to a mm grid. Again, the climbing total calculated based on that perfect elevation data has to make the same judgment call about what elevation gains are too small or take too long to be included in the climbing total.
So even if you have two devices that have perfect elevation accuracy, they will disagree on their reported climbing numbers. The problem is magnified when you consider that neither altimeters nor GPS devices make perfect elevation measurements. They each have some noise in their signals that has to be filtered out. Yet another source of disagreement is that both types have some systematic errors. Altimeters suffer when atmospheric pressure changes and GPS-based systems are even less accurate on the vertical axis than altimeters.
The bottom line is is that you should not expect two different devices to agree on their climbing totals. If two do happen to be close to each other for a given ride, you should not expect them to repeat the agreement on a different ride with a different profile.
Travis
Climbing is a sum of positive elevation gains during the ride, ignoring the small elevation gains and also ignoring elevation gains that happen over such long stretches of road that the grade is insignificant. The basic problem is that there is no standard definition of what elevation gain is too small or what road grade is too small to be included in the climbing totals. Gaining 200 ft of elevation in a mile is a climb. Only gaining 20 ft of elevation on a straight incline that is a mile long is not a climb. For most riders, the aerodynamic frictional losses are much greater than the work done against gravity for that mile. Now the question is is a 20 ft gain in only 200 ft of riding a climb? I think most people would want to include that effort in their climbing tally. The issue is that you have to draw the line somewhere, and there is no standards body out there that I know of defining what should and should not be included in the climbing sum.
Imagine for a moment that you have 2 different devices that make perfectly accurate elevation measurements. They would produce elevation profile that perfectly agree with each other; however, they would disagree on their reported climbing numbers because the software in each device will be using a different filter to remove the insignificant elevation gains from the climbing totals. The problem is actually worse on roads that are nearly flat or mildly rolling because are large portion of your ride is near those filter thresholds. One device might include lots of little elevation gains that the other device ignores. Over time, those differences add up to a big disagreement. If you are doing serious climbing up a mountain, both devices will have an easier time agreeing with each other; however, you will still have differences when the grade temporarily levels off.
Note that the exact same issue exists for geological survey data. Say that there is a perfect source elevation data for a ride that you do based on survey data accurate to a mm grid. Again, the climbing total calculated based on that perfect elevation data has to make the same judgment call about what elevation gains are too small or take too long to be included in the climbing total.
So even if you have two devices that have perfect elevation accuracy, they will disagree on their reported climbing numbers. The problem is magnified when you consider that neither altimeters nor GPS devices make perfect elevation measurements. They each have some noise in their signals that has to be filtered out. Yet another source of disagreement is that both types have some systematic errors. Altimeters suffer when atmospheric pressure changes and GPS-based systems are even less accurate on the vertical axis than altimeters.
The bottom line is is that you should not expect two different devices to agree on their climbing totals. If two do happen to be close to each other for a given ride, you should not expect them to repeat the agreement on a different ride with a different profile.
Travis