Possible Speedo Fix
I'm sure lots of people have the cheapo Wal-Mart Bell/Schwinn wired cycle computers.
I just got one and it just doesn't seem to work very well at all. No matter how close to the sensor I get the magnet, it never reads correctly and is very slow to respond to changes. I even shut the engine off to rule out interference with no change. Also noticed the faster I go, the worse it gets. Sometimes showing zero when at full speed.
What I found was that the magnet is pretty weak, and MAYBE not closing the circuit long enough to register. The faster you go the less chance it has to do it. Seems to make sense. So, I've ordered some neodynium discs that fit into the supplied plastic housing perfectly. I'm going to try it out and see what happens. If it works and anyone else wants some, they are super cheap at kjmagnetics.com.
Order part #D63-N52 to fit the stock screw on plastic housing. If you're wondering, you just hold the plastic barrel and push on the screw and the whole thing just slides out.
Life's too short to ride slow.