Tyres determine acceleration of cars; not engine power
By MUNGAI KIHANYA
The Sunday Nation
Nairobi,
02 July 2023
On September 23, 2022, a team from the University of Stuttgart got into
the records books for accelerating an electric car from zero to 100km/h
in 1.461 seconds. For comparison, the best commercially available,
highperformance cars do it in about 2.8 seconds or more. Formula1 race
cars have been clocked at about 2.5s.
Interestingly, the maximum acceleration of a car depends more on the
friction between the tyres and the road than on the power of the engine.
Think about it, no matter how powerful the engine, if the road is
slippery, the wheels will just skid on the surface and the car will not
go anywhere.
So, the question then is this: how much friction is there between the
road and the tyre? Friction between two surfaces is measure by the
coefficient of friction. This is the ratio of the frictional force to
the compression force between the surfaces.
On a dry road with new and warmedup tyres, the coefficient of friction
is almost one. That is, the maximum frictional force is approximately
equal to the force of gravity acting on the car. Therefore, if the
accelerating force is greater than the car’s gravitational force, the
tyres will slip and spin as if it was on a slippery surface.
It follows, therefore, that the greatest acceleration attainable by any
car on a normal road surface is the acceleration due to gravity. This
has constant value of about 9.8m/s per second for all objects – heavy or
light.
A better way of conceptualising this figure is to convert it to
kilometres per hour. An object traveling at 9.8m/s for one hour (3,600
seconds), covers a total of 35,280m or about 35km. Therefore, the
acceleration due to gravity on the earth is about 35km/h per second. In
other words, after every one second, the speed increases by 35km/h. from
zero to 35km/h, to 70km/h to 105km/h and so on.
So, how much time would it take to reach 100km/h starting from zero
accelerating at 35km/h per second? The answer is simply 100km/h divided
by 35km/h; this comes to 2.86s. This is the shortest time for a car to
get from zero to 100km/h.
How then did the University of Stuttgart team manage 1.461s? The answer
is that that they must have used special tyres that have greater grip
than usual. That is, their coefficient of friction with the road was
more than one. Clearly then, contrary to popular belief, it is the
nature of the tyres that determine a car’s maximum acceleration, not the
power of the engine!
