How much air would it take to float a car in water?

Question

I just watched Transporter 3... There is a scene where he sank his car in a lake. He vents the air from his tires into a bag which balloons his car back to the surface. My question is, how much air would this actually take, and how much air is actually in a set of tires?

I've been guessing about 3000 lbs for the car, and we can assume his tires are filled to about 45 psi or roughly 3 bar just to give him the benefit of the doubt. I need to know the internal volume of a typical tire, and also the displacement of a car once water has filled the cab and the air spaces in the trunk and engine. The measurements of a baled car would do nicely.

Although air compresses at depth, let's also assume he inflates everything near enough to the surface to get the full volume of air at 1 bar (14 psi).

Thanks for the insight!

Charles · Accepted Answer

You must displace more water than the car weighs to keep it afloat.

what that means is that a car with no means of displacing more than its mass in water will sink like a stone.

So this depend upon the weight of the car. This Hollywood scenario is most likely a bunch of crap. In THEORY this might work if he had huge tires inflated to 100PSI and was able to expand all that air to near atmospheric pressure. Some mighty large bags/pontoons would be needed. Most cars don't have enough air in the tires to float the car even if this air was expanded. Most auto tires are inflated to about 2 to 2.5 atmospheres, and most of the time the tires are tens of times smaller than needed to float a car (anywhere from 1500 lbs to 8000 lbs)

 I drive a Scion tC and the tires have a very low volume. Just guesstimating I don't think that there is enough air in my tires to float my 1600 lb car.

As for your detailed question, this sounds suspiciously like a homework question...

gintable · Answer

This is likely not to happen.  If the air is compressed to 4 bars of absolute pressure, it will likely not expand in a flexible bag to any required volume much larger than the tire if submerged under water.

You need to remember, every 10 meters submerged equals roughly one bar.  So, if submerged 30 meters with a background surface pressure of 1 bar, deflating the tires to a flexible bag will still result in an absolute pressure of 4 bars, and thus an identical volume in the bag as it was when in the tires.

Suppose a car is extremely close to the surface (much less than 1 meter of depth suppose) that the pressure in the background water is only about 1 bar.  If one expands 4 bar absolute tire pressure in to a flexible bag at this depth, the most gain in volume one will ever get is 3 extra tire volumes for each tire.

persingerjr · Answer

Air Transporter 3

banhart · Answer

No. yet a very inflated tire on a rim ought to no longer glide the two. It relies upon on the sizes of each and every thing and how lots water is displaced. I heard an fool on a climate checklist speaking approximately how the air on your motor vehicle tires will reason your motor vehicle to compliment the flow away in a flooded roadway. he's incorrect. the vehicle, any motor vehicle, is a lot too heavy to be floated with the aid of its tires. What occurs is the dashing water pushes on the climate of the tires and the vehicle and with the slippery highway all upload as much as a motor vehicle off the line below water. undesirable place to be.

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How much air would it take to float a car in water?

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