No problem! The overall diameter of a IRC 140/70-17 tire is 626 mm according to IRC's website http://irc-tire.com/mce/tires/rx-01.html.the speed sensor signal of 4 signals per revolution is correct, not sure about the crank signals though.
now, if we knew how many pulses per mile or (PPM) the speed sensor will output, we can easily fit an electronic cruise control to the bike
Thus, the bike moves forward 1966.6mm or 1.966 meters per tire revolution.
That is 508.6 tire revolutions per kilometer.
508.6 X 42/14 = 1525.8 countershaft revolutions per km X 4 = 6103 sensor signals per km. 5696 pulses per km if you use a 15 tooth sprocket.
If you live in the US, the rear tire makes 818 revolutions per mile and that works out to 9816 pulses per mile, 9162 pulses per mile with a 15 tooth sprocket.