Mahmood,

why do you want to measure pulse width? As you see, frequency is proportional to speed. Don't you think it is beter to measure frequency?

Have in mind, that what we see on speedometer, is averaged value, and real instantaneus speed of the vehicle is fluctating. 1 pulse measurement will give you just instantaneus speed whitch is not what you vant usualy.

I have found that when I was desining and testing my speed logger. I didn't expected that till I tested in a real environment!