Imagine you are about to start a car race. You are on the grid, waiting for the green light. What should you do in order to optimize your start?

Some people would say that a drift start would be the best. Namely, pressing the clutch and then pressing the throttle, to suddenly let go the former and let the wheels start drifting before making the car move. This seems to be a good way to start - the wheels have been already spinning at a high speed, so when you stop pressing down the clutch you will not have to wait for the wheels to start spinning fast, as they've already been doing it for the last seconds. Ergo, the moment you let go the clutch, the wheels are already spinning and at a high speed, so the car will go out faster.

Others might argue that this is not the best way, because dynamic friction is always less than maximum static friction. So, if one could start in such a way that the force produced by the wheels is $mg\mu_{s}$ (i.e. starting with the wheels not sliding but rolling), it would generate a better start than if the wheels were already spinning to start sliding after letting to the clutch, because


where $m$ is the mass, $g$ the acceleration of gravity, $\mu_s$ the coefficient of maximum static friction, and $\mu_k$ the coefficient of kinetic friction.

Which option is the best and why?


2 Answers 2


I believe the second case should be better because the maximum value of static friction is more than the value of kinetic friction; because $\mu_{s} > \mu_{k}$ and normal reaction is same in both the cases (equal to weight of car).

The best possible case can be when the wheels apply a torque such that we get the maximum static friction to act. Drifting would make the kinetic friction act and that is lesser than the force experienced by the car in the case of rolling, causing lesser acceleration to the body and thus a worse start.

Notice that in sports cars there is a mode called launch control which is there specifically to provide a better start in a race. This mode controls the acceleration of the car in such a way that the car does not drift and only rolls.


The first option is better. Friction comes only if you need it, If I don't touch a mug, there will be no force of friction. Static friction does have a higher maximum but the force of friction that will push the car forward will be equal to the force of the car acting on the ground. Kinetic force is indeed less then the top of Static force but it is constant, which means that the force acting on the car will be constant and pretty high because car wheels are designed to have a large coefficient of friction.

The second option will push the car with the force that it is pushing the ground, and in the begging it's not a high force because the wheels aren't spinning that fast.

  • 2
    $\begingroup$ This doesn't really explain why it would be better. The kinetic friction and maximum static friction are both determined by the normal force and by the motion being resisted. The car has the same normal force either way, and the static friction has a higher maximum. Therefore, it should be ideal to move the tires fast enough to achieve maximum static friction; gaining more acceleration than if you spun them too fast and caused slipping. $\endgroup$
    – JMac
    Jul 31, 2019 at 17:51

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