I have the gear sensor in hand, don't know if I will get to an experiment real soon though. I'd like to put it on the rabbit with a guino and see if I get a speed signal anyway (haven't figured out fuel consumption on the tdi yet)
here is the pinout, it might be cleanest to point it at the inside spokes on the rear wheel (if steel wheel), the front inner hub might not have clean protrusions or too many small gaps. It will make a lot of clicks per mile though, which is normally a good thing, but I might have to tighten up the vss parameters in the guino or revisit the algorithm.