Originally Posted by
jimmuter
Keep in mind that a GPS works by using satellites. I love mine, but every once in a while, it'll blip and say my max speed was 400 MPH or something like that. In general though, it works well. It doesn't work as well if you use it amongst tall buildings and it doesn't work at all if you can't see the sky. I've found that I use it when I drive now too. I'm chronically lost. It's a cool toy.
A lot of cyclometers will do that as well.
A handheld GPS is NOT a good replacement for a cyclometer. It is not designed for vehicular use. Further, the altitude readings from a garden variety GPS wildly inaccurate. I guess someone reasoned knowing WHERE something is AND it's altitude are pretty critical to putting a missle on in it ;-)
In any case, the Garmin bike GPS units have barometric altimeters in addition to the GPS reading. You can also use a wireless speed sensor that will work regardless of cloud/leaf/building cover. You can also use wireless cadence and heart sensors with them. These are also things cyclists consider important.