I have been using a CycloMaster (CycloSport) 436M for a few months. It is similar to the HAC4 but lacks the heart monitor capability. I did the Death Ride this year (www.deathride.com) and collected a full data set for the ride (geocities.comdeathride2003Open ↗). I only measured a total climb of about 14,500 feet as opposed to the advertised 16,000 feet. a large error that seemed unlikely. I have worked as an engineer in data acquisition and analysis for many years so I decided to check for errors. By comparing my data elevations and topo elevations (www.topozone.com) at 13 points along the ride, I found that the error varied with elevation. I set up a spreadsheet and did a linear regression analysis and came up with a correction (or calibration) factor. My first analysis of the data after applying the factor came up with a climb total of 15,900 feet - good enough for me.
So, I guess my point is - don't trust altimeter data until you have done a calibration check.
I have been using a CycloMaster (CycloSport) 436M for a few months. It is similar to the HAC4 but lacks the heart monitor capability. I did the Death Ride this year (www.deathride.com) and collected a full data set for the ride (geocities.comdeathride2003Open ↗). I only measured a total climb of about 14,500 feet as opposed to the advertised 16,000 feet. a large error that seemed unlikely. I have worked as an engineer in data acquisition and analysis for many years so I decided to check for errors. By comparing my data elevations and topo elevations (www.topozone.com) at 13 points along the ride, I found that the error varied with elevation. I set up a spreadsheet and did a linear regression analysis and came up with a correction (or calibration) factor. My first analysis of the data after applying the factor came up with a climb total of 15,900 feet - good enough for me.
So, I guess my point is - don't trust altimeter data until you have done a calibration check.
Or, get one that's built into a GPS and therefore self calibrating 🙂.
I've experienced the same thing with an Avocet Vertech watch. Its altimeter is extremely accurate -- it matches an aircraft altimeter in level flight (I'm a pilot) --but has more lag in climb and descent. This, combined with the fact that its accumulator looks only at 10-ft increments, may explain why the Avocet logs fewer vertical feet than you actually climbed.
A friend uses a topo database to plan road rides. Assuming his data to be accurate (why not?), my Avocet watch shows about a 40% deficit on flattish-to-rolling routes vs. 20% on seriously hilly routes.
Mike Yankee
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I've experienced the same thing with an Avocet Vertech watch. Its altimeter is extremely accurate -- it matches an aircraft altimeter in level flight (I'm a pilot) --but has more lag in climb and descent. This, combined with the fact that its accumulator looks only at 10-ft increments, may explain why the Avocet logs fewer vertical feet than you actually climbed.
Not so. It logs less altitude gain because it rejects dither from atmospheric change and undulating terrain less than 10 meters. It rejects things like railway underpasses although it take account of the bottom of the dip and records any gain beginning at 10 meters above this previous low. This means that on a flat road that undulates as much as +-5 meters, no accumulation... a feature that riders in the mountains (and that's what it's for) prefer.
This method is used in both the Vertech and AVO50 bicycle altimeter (no longer available).
Quoted message said:
A friend uses a topo database to plan road rides. Assuming his data to be accurate (why not?), my Avocet watch shows about a 40% deficit on flattish-to-rolling routes vs. 20% on seriously hilly routes.
Not so. It logs less altitude gain because it rejects dither from atmospheric change and undulating terrain less than 10 meters. It rejects things like railway underpasses although it take account of the bottom of the dip and records any gain beginning at 10 meters above this previous low. This means that on a flat road that undulates as much as +-5 meters, no accumulation... a feature that riders in the mountains (and that's what it's for) prefer.
The actual vertical climb is infinite if you get down to infinitely small detail. -- Ron Hardin [email hidden]
I've experienced the same thing with an Avocet Vertech watch. Its altimeter is extremely accurate -- it matches an aircraft altimeter in level flight (I'm a pilot) --but has more lag in climb and descent.
This doesn't mean that it gives accurate altitudes, just that it accurately measures atomspheric pressures. Barometric altimeters, including those in aircraft, can easily be off by hundreds of feet if the atomspheric conditions don't match the 'standard atmosphere model' and the unit hasn't been recalibrated periodically to compensate for atmospheric changes.
Quoted message said:
This, combined with the fact that its accumulator looks only at 10-ft increments, may explain why the Avocet logs fewer vertical feet than you actually climbed.
It will log less if you're on a road that tends to go up and down repeatedly but less than 30' each time. This usually isn't an issue on rides in hilly areas.
Quoted message said:
A friend uses a topo database to plan road rides. Assuming his data to be accurate (why not?), my Avocet watch shows about a 40% deficit on flattish-to-rolling routes vs. 20% on seriously hilly routes.
Not clear what method he uses with the topo database, but in my experience using a computerized topo map and drawing the route on it tends to give substantial overestimates of climbs. Looking closer at the topo data showed that it was including lots of little ups and downs along sections of road where I knew we were constantly ascending (or constantly descending). The topo data may have been valid if we had hiked that section before the road was built, but the road builders flatten out lots of the little irregularities in the land and reduce the total amount of climbing needed.
This doesn't mean that it gives accurate altitudes, just that it accurately measures atomspheric pressures. Barometric altimeters, including those in aircraft, can easily be off by hundreds of feet if the atomspheric conditions don't match the 'standard atmosphere model' and the unit hasn't been recalibrated periodically to compensate for atmospheric changes.
Opening the window changes the indicated altitude by a couple hundred feet, in the primitive planes I used to fly. Air motion does the same thing on a bicycle except there's no window to test it with.
Stand on the windward and opposite side of a mountain peak and see.
Anything that changes the direction of the air motion indicates a pressure difference due to air motion.
A pure GPS altitude is unaffected by wind, whatever else may be true about it. It varies over a hundred feet over a day, but not quickly. So probably for cumulative computations it's better. -- Ron Hardin [email hidden]
The actual vertical climb is infinite if you get down to infinitely small
detail.
Yep, I agree. When I first looked at my data I decided that the low value for total climb was because the unit measures steps in altitude and it had simply missed some of the small steps. However, the ride is a series of 5 big climbs and descents. No flat segments and no rolling terrain so this should not have been a problem. I had forgotten to set the altitude at the start so I expected an offset error of a couple hundred feet due to changes in barometric pressure. The offset I calculated to correct was different for the high and low points which led me to the conclusion that there was a calibration error or the atmospheric pressure model was wrong. Atmospheric pressure does not vary exactly linearly with elevation and temperature and this secondary effect may not be accounted for by the designers. My ride varied from about 5100' to 8700' and I found that the measured elevation change was about 93% of the actual.
