Since removing the old mechanical speedo from my 92 Sporty, I've been trying to think of a solution to replace it.  Looked far and wide and nothing seemed to suit.  I wanted something that was out of the way, but would still give me a trip meter so I could measure fuel consumption and also something to stop me getting deffected as having no speedo is pretty obvious.

Solution - the Sigma BC509 bicycle computer. 

I did my research and found a bicycle speedo that could do a decent top speed and also one that can be confugred for wheel size.  This one does both.  It works by having a pickup mounted to your forks and then having a magnet attached to your wheel.  Hardest part to install was attaching the magnet to the wheel, I looked at different options but eventually I decided the best way to go was to glue it to the rim. 

Features:

-Electronic speedo, 199kph max speed

- Odometer

- Trip meter

- Clock

Works great, and they're cheap, this one was only $25

Here's some pics:

Here's the magnet attached to the wheel.  I just used superglue, in road test, I took the bike up to around 100kph and it hasn't fallen off:

Here's the pickup attached to the forks, I stuck it in between the gap in the front fender strut:

Here's the seedo attached neatly above the head stem bolt:

I've been running them for years on various bikes.
Very accurate and have some useful functions. Mines and older BC800 and good for 299km/h !
I use a tiny strong magnet glued to the disc, and the pickup mounted of the caliper.

Is the bc509 backlit ?

For the magnet attached to the wheel I always used a rare earth magnet - one of the little round ones that look like a watch battery. I always thought one day it would come off, but it never did.

Oh, and I've seen people hook up the Sigmas (the ones with a backing light source anyway) to the power/battery so they can be permanently back lit - might be worth looking up.

I would have thought the magnet/pickup unit would have been better on a spoke close to your hub,
How does it affect the wheel balance out on the rim?

 

 

This bloke knocks out a few digital motorcycle speedo/tacho etc too;

 

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