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
Because at 100mph, you’re now getting hit by a 120-160mph gust when you factor in wind direction and what the loading on the car is already due to relative wind direction. It also rapidly changes the amount of down force being created by the car body.
The faster you go, the more the vehicle aerodynamics are pushing the car down on the road. Even a regular berline has pretty good aerodynamic to reduce air drag and add some downforce to improve adhesion to the road. But if you rely on the air around you to improve the drivability of the car, it means the car will get more sensitive to changes in the air around it.
When the car is stationary, gravity and the weight of the car is doing 100% of the work to keep the car on the ground, so a gust of wind has to overcome all of this to move the car. When driving, now the air you are driving through is doing a part of this work, and the faster you go, the more the air is responsible for a greater percentage. So any changes in how the air moves around the car will be felt more the faster you go.
When not moving the tire rubber would deflect slightly, said .1mm when a gust of wind pushes against the car, but then due to them being rubber and not moving it would reach some elasticity equilibrium and eventually move back when the gust stops – however if they are rolling, the “new” contact patch won’t be pre-stretched in the direction of the wind, so as the tire rolls down the road, each .1mm of deflection is accumulated with any previous deflection
It’s kinda like how turning the wheel of the car doesn’t cause it to move when it’s sitting still.
When the car is sitting still, the wind is the only force acting on it laterally, which isn’t enough to move it. But when the car is in motion, there are a bunch of forces balancing together to determine the car’s movement. Adding in a sideways wind and that balance shifts such that the car moves to the side.
It’s also worth noting that at 60+, it doesn’t take a lot of lateral motion to *feel* like a lot. The wind is probably only pushing you a few degrees off course, but at 60mph, which is 88 feet per second, being a few degrees off course will move you across the line to partially be in the next lane in a couple seconds (you can also see this when changing lanes using the steering wheel; you can move the steering wheel a couple degrees and change lanes pretty quickly)
It’s because you are moving. The car gets pushed just as much at zero mph as it does at 100mph. However since you aren’t moving at zero mph it can’t deflect your path. Also your car generates lift at speed which removes weight from the wheels, which in turn allows the wind to more easily blow it around. The overall shape of a G63 is not conducive to high speed driving.
[removed]
well little boy, maybe this will help
imagine when youre standing still and both feet are planted shoulder width apart, your friend pushes slightly but you are able to resist without having to take a step sideways to stay standing.
now imagine youre running and for simplicity sake, we imagine only one foot on the ground at a time, now the same friend is running alongside you. if he pushes you with the same force as before, your foot which is in the air is coming down (initially going straight forward) now shifts a teeny bit in the direction your friend shoved you. and if your friend keeps the shove constant, your next step and so on will keep going into the direction being pushed.
now imagine the tyre having thousands of smaaaaaaall lil tiny feet, and only one touches the ground at one time. viola the wind gets you swerving when moving but doesnt move you when stationary.
One factor is dynamic vs static friction. Remember, friction happens due to microscopic little imperfections, bumps and spikes at the molecular level. Everything has these little bumps and jagged edges, even if it feels smooth – we are talking molecules here. When you’re still, the tiny little bumps in the tyre are all settled into the tiny little bumps in the road. Getting them to move means getting them out of the tiny little spots which they’ve settled into – which is hard. When you’re already moving, though, the bumps aren’t settled – so it’s easier. As a result, friction does more to keep you still than it does to prevent your movement changing.
Standing still you have negative movement. The friction.
Add slight positive moment and you’re still negative.
While driving you’ve got positive movement. Add more positive movement and you get a new sum of movement.
The wind will exert the same force on an object whether or not it’s moving. The reason it causes you to veer is *because* you’re moving.
If the car is still, the wind cannot overcome the friction of the tires on the pavement. It will still cause the chassis to move though.
When you’re driving, the force of the wind on the car will cause the steering system to deflect, that’s why you veer. If you’re not moving, what happens to the steering can’t affect the car.
Latest Answers