sumption of objects with completely different speeds and areas. Specifically,
let’s assume that the area ratio is
(Four cyclists can sit shoulder to shoulder in the width of one car.) Let’s
assume the bike is not very well streamlined:
And let’s assume the speed of the bike is 21 km/h (13 miles per hour), so
Then
So a cyclist at 21 km/h consumes about 3% of the energy per kilometre of
a lone car-driver on the motorway – about 2.4 kWh per 100 km.
If you would like a vehicle whose fuel efficiency is 30 times better than
a car’s, it’s simple: ride a bike.
Some things we’ve completely ignored so far are the energy consumed in
the tyres and bearings of the car, the energy that goes into the noise of
wheels against asphalt, the energy that goes into grinding rubber off the
tyres, and the energy that vehicles put into shaking the ground. Collec-
tively, these forms of energy consumption are called rolling resistance. The
standard model of rolling resistance asserts that the force of rolling resis-
tance is simply proportional to the weight of the vehicle, independent of
wheel | Crr |
---|---|
train (steel on steel) | 0.002 |
bicycle tyre | 0.005 |
truck rubber tyres | 0.007 |
car rubber tyres | 0.010 |