Quote Originally Posted by kitcat
...for a motorbike championship where I would like to measure the speed of passing bikes. Basically I am running a pyrotechnic effect near the track and would like to synchronise the effect with the passing bikes.
I think you don't really need to measure the speed.

For each class of starters I would assume the average speed (and acceleration) between two points of the track is something known.
(There wouldn't be a scooter competing with a speedbike would it?)

So all you need is a trigger right at the start, from that you can calculate all the timing for the fireworks along the track.