Originally Posted by
dclaryjr
If you REALLY wanna get it down to gnat's ass accuracy, measure the rollout of the wheel the sensor is going on while you're on the bike. Easier to do with two people.
This is necessary for basic accuracy, nothing to do with a gnat's ass.
My VDO instructions say to get the magnet on the spoke to pass the sensor something like 1-3 cm. I've got disc brakes, so I'm fairly limited as to where on the fork blade the sensor can be. On mine, the magnet is close enough to almost touch when it passes by. Could be further away and still work fine, but I enjoy tight tolerances in all things.
Mine is pretty accurate, especially when compared with its' own data. I.e. I don't really care if I'm going exactly 14 mph, I just want to know what my speed is relative to yesterday, to my average, to the last hill, etc. Am I getting faster all the time, and how far did I ride? Really all I care about...