# Speed of car to overcome a pothole

• kidontheblock

#### kidontheblock

Hi
I was having a discussion with a friend yesterday and we debated whether the speed of the car can make it "fly" over the pothole, ie. not come in touch with the hole at all. My moot point is that it would depend on the radius/dia of the wheel in relation to the radius/dia of the pothole. The tires need to have traction with the ground to stay linear, any loss of contact with the ground would make the tires dragged down by gravity. There would be displacement and the tires would indeed fall to come in contact with some of the inner pothole. I guess I am thinking in terms of first law pf physics "any body will remain in rest or motion unless an external force" makes it do otherwise.

Is there any research on this? Am I not using a right principle here.

Appreciate any help.

Hi
we debated whether the speed of the car can make it "fly"

good one.

9.8 m/sec*sec
how much 'thump' on the other side do you consider as 'missed it', or flew over it?
or is it ; I was fast enough, with my big tires over that little hole that I never even felt it. :)

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This car would not have noticed a 20' pothole:

Seriously, the question can not be answered unless there is no atmosphere and no suspension and even then at relativistic speeds the car would be trying to go into orbit and barely touch the ground.

On a more practical level, active suspension that could detect the pothole and raise the wheel just before reaching it, would make the pothole almost unoticeable. It could do the same trick with a kerb or brick in the road.

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There is a much greater force than gravity to be considered hear. The tires of your car are constantly holding up the weight of the car, which is transferred to them through springs. If you take the ground out from under a tire suddenly, the tire will accelerate downwards at a rate far greater than freefall, as the springs push it down.

Now, as for "missing the pothole altogether," no. No amount of speed will reduce the tires downward movement to "zero." So, you need to decide how little downward movement is a negligable amount, and that is a purely subjective decision. It can be said, however, that at a certain slow speed you will feel a certain amount of impact (the feeling of acceleration that makes the pothole "uncomfortable"), and as your speed increases that impact becomes worse, as the distance the tire descends into the pothole is decreasing, but the acceleration from the tire making contact with the pavement increases. As you contiue to accelerate the force of deflection increases due to the greater speed, but the amount of deflection decreases. At a certain critical speed, the overall acceleration force you experience inside the vehicle stops increasing and begins to decrase.

But again, the acceleration will approach never reach "zero."

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Mythbusters did a segment about whether or not the ride was smoother on 'washboard' roads at higher speeds. It's not quite the same problem, but similar. Strangely, their instrumentation showed the ride to be rougher, but their little stack of wine glasses full of water and their subjective experience said that it was smoother. I can't remember the details.