Measuring Feet of Climbing for a Ride
 

It has come to my attention that the feet of climbing people claim for rides is pretty variable depending on how they measure. Route slip and similar sites seem to give higher numbers than I would have listed for a ride and some gps with barometric altimeters give higher numbers yet.

I had typically only counted the fairly long (for here) climbs and not even tried to account for the little jagged stuff in the graph or the rolling terrain. When organized rides list a particular number how is it usually arrived at?

I suspect the way I have been doing it has resulted in numbers as much as %50 lower than would be arrived at by other methods. As a result I want to better understand how others measure and maybe "recalibrate" my own method of doing this.

I also wonder if this is a regional thing and in Colorado they might count even more conservatively than I have been doing.

Comments?

Highly debateable topic, depending on what methods that are used. I use Topo software and a VDO Cyclocomputer with altimeter which I try to recalibrate for known elevations when I can. I've yet to carry a GPS for cycling, but I imagine the barometric altimeter versus the satellite altimeter would show variation.

I look at climbing #s as relative. I use the same methods for each of my rides, so I get a general feel of the rides, and when comparing rides I know how each felt and how they relate to each other. The Boston Brevet series tends to list climbing stats, and most of my numbers have been within reasonable ranges of those published on cue sheets - so I'm comfortable with knowing, relative to me, how much I've climbed.

...and don't discount those rollers. They add up, esp on 200k and longer events!

I've heard it explained -- and it seems to make sense -- that GPS measurements will run low in rolling terrain because they're only taking measurements every so often, which results in the ride effectively being "flattened out" -- the peaks and valleys get rounded off, if you will. On the other hand, the numbers that TOPO USA gives seem to be silly high. But my understanding of that software is that it's counting every miniscule change, however small. Those can really add up. Around here, TOPO USA and my GPS (Garmin 60CSx) differ wildly on the climbing on any particular route. Error rate is about 30% -- TOPO USA being 30% higher than the GPS, that is.

Interestingly, both TOPO USA and the GPS agree on any given, sustained pitch. For example, Jack Run -- one of the nastiest, longest climbs in the state -- measures the same, bottom-to-top (a little more than 400 feet), on both. When I rode out in Mt. Rainier National Park this past summer, both also agreed on the bottom-to-top elevation change of the one big climb (as in 3.6K feet big) that I did out there. The differences seem to be in rolling terrain.

Rollers do add up in a big way, and they also really affect people very differently -- I think differently than the longer, sustained stuff. How x-amount of climbing feels in rolling terrain will depend a lot on the strength of the rider. Fast or strong folks can rock and roll in the rolling (punny!) terrain, carrying speed on the down-hill and pushing an aggressive gear over the top of the next rise, maintaining a lot of momentum. Rinse and repeat. Less fast riders might not be able to push the big ring as aggressively down the slope and might end up gearing all the way down to granny to clear the upcoming rise that the faster/stronger rider cleared without ever leaving the big ring. In this neck of the woods, riders who can effectively sustain repeated bursts of high energy are the most effective "climbers." Out West, where the "climb" is a 4-6% grade for 20 or more miles, the strong climbers are folks who can put out the highest constant wattage over a long period of time. These are very different skills, and someone who is good at one might not be so good at the other. So, anyway, by whatever decive measured, x-feet of climbing isn't the same in different places in the country. The 7,000 feet of climbing on our 200K means you're riding rolling terrain for 200K. But 7,000 of climbing in some parts of the country means you've got to climb two passes and then ride along a dead-flat river valley for 120K.

+1 the GPS software interpolates the information which leads to measurement error.

+1 re GPS errors.

GPS also errors when measuring length of a route, for the same reason.

To make things worse, GPS receivers measure the X-Y plane more accurately than they measure the Z (elevation) plane.
That means you can get by with measuring length, but not elevation.


The problem with barometric, is that it's prone to changes in weather.
Think of a straight 30km 5% climb that starts in sunshine warm weather, and ends above the clouds.


The most accurate is TOPO, but then, it might be too accurate, as mentioned here.


My 2 cents.

Tal.

I think map software counts the elevation drop and rise under bridges which is why it goes high.

The discussion of climbing measurement on MotionBased (http://wiki.motionbased.com/mb/GPS_Unit_Elevation) says that the best current measuring device is a GPS with built-in altimiter. They say:

MotionBased recommends the following methods in order of most accurate to least.

1. GPS + Barometric altimeter with auto-calibration (Garmin units only)
2. MotionBased Gravity correcting an accurate GPS device
3. GPS-only altitude as provided by many popular Garmin fitness devices.
4. barometric altimeter only device (accuracy is too dependent upon weather and user input).

Of course, since Garmin owns MotionBased, there is potentially some bias in their view.

I have an eTrex Vista CX, which has a barometric altimiter set to auto-correct. It consistently finds higher total climbing than the people who have a non-GPS bike computer with built-in altimiter (like the Specialized, CatEye, or whatever). The problem with those units is that barometric pressure will typically vary quite a bit during the day, and as we cross weather boundaries, throwing off the measurement.

When I upload data from my GPS to MotionBased, the total climbing usually goes up by about ten percent. This is probably for the reason mentioned in one of the messages above, that the GPS isn't counting small changes as "climbing" but rather as "measurement error". MotionBased must implicitly have a lower tolerance set in.

If you used the MotionBased "Gravity" corrections then it is using topo map data to correct GPS measurements. That gives the largest amount of adjustment to the raw GPS-with-altimiter data, also consistent with people's observations about the TopoUSA software. There's some discussion about bridges in MotionBased's writeup of the Gravity corrections, also consistent with the observations in the message above.

I think what's important in looking at climbing measurements is knowing how people made the measurement. I think it's typically the case that measurements have been made with non-GPS bike computers with built-in altimiter. The GPS's with built-in altimiter haven't been around for long enough, nor adopted widely enough, to be the dominant source of measurement. Most of the world's 1200K's have sketchy public information about the amount of climbing. I think BMB said something like "more than 28,000 feet of climbing" and other people had measurements amounting to 35,000 feet or 38,000 feet. After uploading my data, it says 50,000 feet of climbing on MotionBased. Ultimately, what matters is to have some sense of how published climbing compares with what your legs can handle.

Who knows? Sometimes it's a bike mounted altimeter reading, sometimes some brand of mapping software.

Off hand, my experience is that hilly areas are tougher to ride than mountainous areas. West Virginia, Kentucky as well as Missouri all have some tough areas to ride. I imagine there are really tough back roads in California and Colorado, but all I've ever ridden are the "easy" long steady grades.

That's the problem with all cyclocomputers.
It's called "Sample Rate."

On some of them you can set it, e.g. in some models of Polar computers you can set them to sample every 5, 10, or 15 seconds.
Of course, you're limited by the memory size.
You can't have it sample every 5 seconds for 90 hours.

Another example for the misses: You can achieve max speed between samples, so it won't be sampled, and you won't see it when you look at the ride graph.

Tal.

Living in Fla I don't have to worry about measuring changes in elevation.:D

Depending on the quality of your math skills and how much you enjoy calculations, you can do a visual survey from point to point over a measured distance using a transit and create a topographic image accounting for the variables of terrain using LaGuerre Polynomials!:D