Although I have a heavy box-shaped car, I was thinking about the Mercedes G63 specifically. That is a powerful engine on a non-aerodynamic car, what happens if you take it over 100mph and get hit by a gust of 60mph wind? My car gets literally pushed around lanes during heavy winds at highway speeds, has anyone ever even gotten a G63 past 150mph?
In: Physics
Most of the other answers pointed out how strong winds are able to more easily push you off course at higher speeds by changing the car’s direction. However, I’ll take a second to talk about how the wind can blow the car *sideways* without changing the car’s direction.
The main force that stops your car from moving sideways is the friction between the wheels and ground. This friction depends on the force of contact between the car and the ground, which is basically the weight of the car that pushes down onto the road. The heavier the car, the more the resulting friction, the better the grip, and the less likely it is to slip.
However, this friction also depends on whether the car is moving or not. The friction is strongest when the car is stationary (static friction), a little less when the wheels of the car are rolling perfectly (rolling friction), and at its lowest value when the wheels experience some slipping on the surface of the road (sliding friction).
When the car is standing still, the only force acting on it is its own weight, which is all supported by the tires, so we have the situation of the maximum weight (which should actually be the contact force between the wheel and the ground), as well the maximum friction coefficient due to it being static friction.
When the car starts moving on the road, while the weight remains the same, the wheels shift to experiencing rolling friction, which is less than static friction, so the car has less grip with the road, but not by much. So at low speeds, cars don’t easily lose their grip on the road.
However, roads are not perfectly flat. Curves, slopes, bumps and other imperfections on the road can all cause one or more wheels to temporarily lose contact with the road or not rotate at the right speed relative to the speed of the car. If the speed of the wheel is not ideal, it will take a short moment to speed up or slow down to the correct speed, during which the wheel is slipping against the road and so experiencing sliding friction, which can sometimes be only half as strong as rolling friction. Even worse is if the wheel loses contact, leading to a moment when the car only has three wheels to maintain grip with the ground, which can cause it to slide more easily.
On top of that, the car itself vibrates – sometimes because of imperfections on the road, but more often because of the vibration of the engine itself. As it vibrates, the contact force between the wheels and the ground also varies at the same rate of the vibration, leading to some moments where it experiences stronger than average grip, and some moments where it experiences weaker than average grip.
Finally, all cars experience something called *aerodynamic lift*. This happens because the speed of air that passes below and above the car isn’t equal, which can lead to the air around the car pressing up or down on the car. This is the same force that acts on the wings of airplanes to keep them in the air. In general, with the shape of modern cars, the overall lift force is upwards, which reduces the apparent weight of the car and causes a lower contact force with the ground, leading to less friction. This lift depends on the speed of the car. At low speeds, this lift force is almost negligible and you’d never notice the effect. However, at higher speeds, this lift can significantly decrease the apparent weight of the car, causing the wheels to have almost no grip with the road. It’s for this reason that formula one cars have those strange shapes with wing-like structures and large spoilers – these all provide *negative* lift that pushes the car back down so that it keeps its grip with the road and doesn’t just fly away.
In summary, as you speed up, your car’s wheels can lose grip with the road because:
* Wheels experience less friction when rolling than when static
* Unevenness of the road can cause your wheels to lose contact or slip on the road
* Vibrations in the car can cause the grip to vary as well
* Faster speeds can cause the car to experience lift like airplane wings
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