well.

The diameter is 75 cm. To calculate the peripheral you must multiply the diameter by 3.14.

**p=R*PI** (for your example the p=235.5 cm)

In every wheel turn, your bike will have comer p centimeters. For every p centimeter, the controller will have receive 8 pulses. So, for every pulse, your bike will have cover p/8 centimeters.

So, you only have to measure the mSec (this may change according to the range of speed you want to cover and the bits that you have available to measure) from one pulse to another.

**Example**Suppose that one pulse to the other had gap of 100mSec. This means that in 100mSec your bike covered 235.5/8 cm = 29.4 cm. you measure cm per mSec but you want Km per Hour. To convert cm to km you need to divide by 100.000 and to convert mSec to Hours you need to divide by 3.600.000. The final number will be:

Km/h = (36/time [mSec])*29.4 =>Km/h = (36/100)*29.4 = 10.58 Km/h

So you do not run so fast...

If the delay was 50mSec, the speed would be

(36/50)*29.4 = 21.1 Km/h and that's a little bit faster