are altitude computers any good?

inaperfectworld

i had the misfortune too buy a trek computer with altitude, cadence and cost £100.never mind that the computer is unreliable the altitude readings seem pretty dodgy too, it's slow to respond and you are past the slope before it gives a reading anything like the reality
i need a computer for my airnimal touring bike and see ciclosport do one , but after the trek i wonder if it is really worth it. it's a nice function to have if touring in new country

sub55

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deal

http://www.bikemag.com/gear/021705_inclino/

CrookedCucumber

inaperfectworld wrote:

i had the misfortune too buy a trek computer with altitude, cadence and cost £100.never mind that the computer is unreliable the altitude readings seem pretty dodgy too, it's slow to respond and you are past the slope before it gives a reading anything like the reality
i need a computer for my airnimal touring bike and see ciclosport do one , but after the trek i wonder if it is really worth it. it's a nice function to have if touring in new country

I presume that the altitude reading on this device is barometric (rather than GPS). If it is, then unless you calibrate it at the start of every ride, and regularly throughout a long ride, it's only every going to be an approximation anyway. I presume that it's slow to read because it's trying to average out local fluctuations in air pressure.

My opinion is that without a proper calibration protocol, altitude measurement on a bicycle is little more than a gimick.

Mar ge

I ride mainly MTB and whilst I have yet to stump up the cash for my own, my club mates use Garmin 705s and the results seem good & consistent. I gather it cross references versus topographical mapping....

Mark Alexander

so, the conclusion I think could be..
You get what you pay for.

CrookedCucumber

Mar ge wrote:

I ride mainly MTB and whilst I have yet to stump up the cash for my own, my club mates use Garmin 705s and the results seem good & consistent. I gather it cross references versus topographical mapping....

A normal consumer GPS unit will usually altitude with an accuracy of about +/- 30m or so. The nature of satellite positioning means that the altitude accuracy will inevitably be a lot worse than lat/long accuracy, but some GPS units do better than others. To add to the problem, a GPS will express the altitude relative to a mathematical model of the Earth's sea level. It isn't all that unusual for that model to be wrong by more than 40m, since the Earth is not a shape that is easy to define mathematically. I've certainly stood on the beach and seen my eTrex tell me I'm 10m below see level

A good quality, calibrated barometric altitude meter will out-perform GPS n accuracy, precision, and speed of response. And they don't have to be particularly expensive.

The problem is calibration.

I used to fly light aircraft, and the calibration of the altimeter was a constant headache. The problem on a bicycle is both better and worse: it's better because you can't cover the same distance as in an aircraft, but worse in that you don't have access to a calibration source when you're on the road. In an aircraft you'd radio local airfields for pressure setting data as you flew the route. On a bike, if the barometric pressure changes on route (and it will), your altimeter is basically useless. I don't find it unusual to walk a circular route and find that my `altitude' at the end is 50m different from that at the start. This is, of course, impossible. It's less of a problem on a bike than on legs because my bike rides are generally shorter than my walks, so the meteorological conditions don't change so much.

In short, you shouldn't really expect a bike-mounted altimeter to give you anything other than a rough idea of your altitude. The one possible exception is in systems that really can calibrate the altimeter from topographic data.

The 705 can certainly process topo maps, but whether it can calibrate the altimeter from them, I don't know. My understanding is that it can't do this automatically. Of course, if you really care about altitude you can calibrate the altimeter manually by going to a place with a known altitude (either from the topo map or any other method) and then entering the altitude at that point.

lloyd_bower

I've got a VDO bike computer with an altimeter function, so long as you update it with a known altitude, I find it remarkably accurate. Height ascended is a nice to know feature. It's also got a temperature feature, though that tends to over read.

Only complaint is that it's miles and feet, of km and metres. I'm used to miles, but height in metress and metres ascended mean more to me so I've switched to Kms. I had it nicked on the last of a tour in Belize and Guatemala, but I've since replaced after managing a short while with the old bike computer.