Hi,
Now I think I got it.(I am waiting for yours reply this is rite or wrong).
Circumference of the wheel= 2πr (where ‘r’ is in cm)
= 2×3.14×30
= 188.4 cm or 1.884 metresSpeed. Let’s assume that in 1 second the wheel
completes one revolution. In other words, in one second, the bike has covered 1.88 metres. Therefore the speed in km/hour:N×1.88×3600/1000
= N×6.784 or N×6.8
where ‘N’ is the number of revolutions per second.
‘6.8’ is a constant and only ‘N’ varies; for example, if ‘N’
is 5, the speed equals 5×6.8= 34 km/hour.
I get this calculation from this link. this is correct ?.