My brothers whacky idea (he's an engineer)

[tgsho]

my friend has a g-tech in his kenwood cd player... it is installed on a jeep tj which is basically useless but would work great on a car.

 

[SHOZ123]

The ABS sensors put out a half square wave AC signal. Combined with a timing device it would be very accurate. FWIW the V8 SHO uses the ABS for it's speed signal, control the struts and power steering.

From what testing I've done the fronts put out twice the signal as the rears. This is probably due to size and number of teeth.