Altitude meters.... do they work well ?

Some computers can measure altitude and also keep track of the total altitude gain during the trip. I was wondering if these altitude meters are accurate enough to be useful.

I'm curious about experiences that people have with these computers. For example: are there people who have made a trip with a known amount altitude gain and have they compared it with the result of the computer?

Or two people who the same trip, both using an altitude meter. Do these computers show the same altitude gain at the end of the trip? Anybody tried this?

I'm also curious what happens when you make a long trip in a completely flat area. Will the computer still show altitude gain caused by accumulated measurement errors or is the reading close to zero?

Thanks!
Aernout

It may have changed but last time I had an altimeter watch it used barometric pressure to do the calculations. Since that usually changed day to day it was pretty much useless.

I have a specialized pro with altimeter and total climbed and it seems to work fine. it does have to be zeroed every use but that is easy enough if you are starting at the same place and can find the altitude on a topo or from a local airport. I've done the same ride several times and my total climbed altitude has been the same.

thats what I thought. you don't live in portland oregon where the pressure chages a fair amount some days (G) but I guess sicne I have to zero my miles that would not be much more work.

All altimeters will need to be zeroed each ride to account for weather changes

the Polar HRM altimeters seem fairly accurate and its not like +- 10-20m would really affect your training plans

I have an older Avocet altimeter 50, it works on barometric pressure, so it is not very accurate if the pressure changes during your ride. On a day that is clear and I set it at the start of the ride to a known altitude, it is very accurate. Have compared it to others who have altimeters on rides and is in the ballpark. I also have checked it against topographical maps and found it to be close. If you ride in an area with a lot of hills it nice to have it as a reference given its limitations. Avocet does not make this model any more but there are others on the market. As to your last question I can't answer that because we don't have many completely flat areas in No. California.

Over a ride distance, yes, altitude meters are excellent. I am amazed how accurately it can pick up even slight hills on a ride. However, there are some things pressure-based meters can't do well:

1. be an absolute altitude sensor. Because of air pressure variations from day to day, you'd need to recalibrate the altimeter several times a day at a spot of known altitude. They are far better as a relative altitude sensor (i.e. detecting change in altitude.)

2. react quickly (and accurately) enough to calculate things like instantaneous hill gradient. Sure it can be done (and some do this), but I wouldn't trust the figures it would give. You really need a good minute or so of readings to come up with an accurate gradient figure.

I use a Polar HRM that includes a data recorder, and leave the altimeter on all the time; I've made a comparison graph of 5 commutes to work that have taken place during Winter and Spring, so you can see how the altitude readings vary. (ref attached zip file)

The Polar analysis software includes a function to progressively self-correct for altitude drift; this wasn't used for these rides, as it requires the start and end points of the exercise to be the same point. So basically what is on that graph is exactly what the sensor recorded, without any error correction. Some, however, were transposed in the analysis software to look like they start from zero. This if anything has increased the margin of error, as it means I never bothered to re-calibrate the altimeter before riding..

You can see that the temperature variations do cause a little bit of trouble with working out the altitude extremes, but it does pick up the changes in altitude very well. You'll notice that there's a band of two plots (the bottom two) that are close together -- they were the nice, sunny days. The other three were either cold/overcast, outright raining, or a bit of everything, and I guess that's why they vary so much more.

The worst case altitude drift is about 15-20 metres; not bad when you consider these graphs are from completely different (and sometimes varying) weather conditions, and some were taken with an un-calibrated altimeter.

Attached Files

alt.zip (28.3 KB, 24 views)

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Peter
Cannondale Synapse Carbon Scalpel Cyclocross Ultra

I use the Suunto Altimax altimeter. It is fairly accurate, yet will shift some if the barometric pressure changes. The face is large to allow for easy reading...and you can use it for anything other than cycling. At $168 US, I thought it was the best thing on the market at the time. Fernando

Interesting graph!