Road Cycling - Computer with Altimeter?

Hello All,
I am considering stepping out of the dark ages and purchasing a
computer for my road bike. I want to get one that provides the
basic diagnostics such as average speed, current speed, odometer,
etc. plus cadence and altitude. Does anyone have any recommendations
for a computer which has these options and _accurately_ measures
altitude? I am concerned about the accuracy of barometric altimeters
especially those which do not account for temperature in calculating
height.
much thanks,
-astrocub

Barometric altimeters can never be totally accurate because they measure air pressure which changes with temperature. If you ride from a warm area to a cool area (a canyon for instance) your 'pressure altitude' will change. So the computers with the altitude feature are general at best. There are newer GPS units that calculate altitude based on your location, however not cheap.

i am aware of the inaccuracy of measuring alitude using a barometer
without accounting for temperature fluctuations. my question is whether
anyone knows of an accurate (say within +/- 50 feet) altimeter cyclocomputer.
-astrocub

Although not a true cyclometer the Polar heart rate monitors feature a decent altimiter sensor with (I believe) temperature compensation. I use a Polar 710i which also performs the standard bike computer functions.

The HRM reads temperature and it gives some wonky readings if I leave my warm house on a cold day after calibrating so I'm pretty sure there's a compensation happening.

If the weather doesn't change then I get +/- 2m accuracy over a 2+ hour ride. I've got 6 months of data showing nearly identical start and end altitudes over most my rides that start and end at home.

However, I've also got data where the weather was nice when I started and stormy when finished. Then there is a definite calibration problem over the course of the ride.

Vetta also makes a computer with an altimeter function.

-Ryan

Non of the cyclocomputers/HRM's with altimeter functions are going to be +/- 50' accurate unless it's constantly re-set for the local barometric pressure. I believe that one of the HRM's has an algorithm for the temp/altitude scale, but it stills depends on pressure readings for it's main altitude information. The altitude error will be cumulative as the ride progresses.

A friend of mine owns a Specialized computer with altimeter and is very please with it. Accuracy is good, but I don't know the specifications. You might check with Specialized or read the reviews on it.

I have been on tours in mountainous regions. Other riders have brought along computers with altimeter functions and these actually keep track of the elevation climbed. Nice. Of course, if you get changes in barametric pressure, you will get a false reading. So they are not totally accurate. But they are still fun and they do give reasonable results. So if you do a number of hilly rides on a semi routine basis, that option could be quite nice.

I have a Ciclosport CM-434 and it does say the altimeter is weather dependent. But it does have a temp gauge too. Not sure if "weather dependent" means it doesn't calculate the temp affects but if anything, it can gauge when there is a low pressure front moving in. Even if it doesn't become windy...

I've only used it for a day or two, however, I have used a Garmen Vista GPS with the bicycle mount on a tour before. I could check the altitude to see how accurate the CM is. The Vista doesn't have a % grade or culmultive climb/descent like the CM does though.

Jay

I have the Vetta V100A and live in the mountains. Seems to work pretty good when it is sunny (high pressure). When the weather changes (low pressure) and a system is rolling in it is all over the board. I use the summit elevations and have some other points of reference of known elevation to check the computer when riding. On some rides I reset it to the current elevation and it seems to be ok for the remainder of the ride. Best is to get a topo map (electronic map for your computer) of the area you ride and get the base elevations off of those. My topo map program will also build profiles of the areas I ride.

Snowblower

Most of the cyclocomputers with altimeters are not very accurate, here is a thread they discussed them before.
http://www.bikeforums.net/showthread.php?s=&threadid=24415&highlight=Altimeter

I use the Polar 710i and calibrate it before every ride, it only takes 10 seconds to do.
I went for a 100km ride last week and set the watch to 370metres at the end of the ride the altimeter read 380 metres. Not too bad.

It must be calibrated outside, not in an air conditioned house.

CHEERS.

Mark