Episode 124: Car vs. Rain

Air Date: June 17, 2009

Driving a convertible with the top down in the rain at a high speed will ensure that no water can enter the driver compartment.

plausible

The MythBusters first performed several small scale tests, using a model car and a wind tunnel, and found that at higher speeds, a sort of air bubble seemed to form around the driver compartment, giving credence to the myth. In their full scale test, they used an actual convertible as well as a 200 foot rain bar to provide the rain. In a control test, they stopped the convertible in the middle of the rain to put up the top, and the interior was soaked. Then they drove through the rain at 70 mph (113km/hr), and saw that the interior was significantly less wet than the control. Next, they then drove the car through the rain at 90 mph (145km/hr) and saw that the interior was not wet at all. The MythBusters attributed this to the car’s windshield, which served its function as well as creating an air bubble over the interior of the car. However, they decided to declare the myth “plausible, but not recommended” due to the inherent danger of driving at such high speeds on wet roads.

You can pop popcorn instantly by detonating a propane tank.

busted

The Build Team placed popcorn kernels on top of the propane tank and detonated it with high explosives. The explosion failed to cook or pop any of the popcorn kernels because the blast blew the kernels away before they could absorb enough heat.

You can pop popcorn instantly by igniting dairy creamer.

busted

The Build Team loaded popcorn kernels into a cannon filled with flammable dairy creamer and ignited it, but this failed to pop any of the kernels. As with the propane, the speed and energy of the fireball dispersed, but did not cook, the popcorn kernels.

You can use a plane-mounted 5 megawatt laser to cook popcorn, and when using enough popcorn, it can expand with enough strength to break open a house. (Based on a scene from the movie Real Genius.)

busted

Since a 5 megawatt laser doesn’t currently exist, the Build Team used a 10 watt laser and still successfully popped a kernel. Even though this proved that lasers could pop popcorn, there currently isn’t a laser powerful enough to cook such a large amount, so the Build Team resorted to using a large pan to cook popcorn through induction. They then placed a panel representing the wall and window of a house over the pan to see if the popcorn could break through it. However, the popcorn lacked the power to push through the window. They also tested the expansion potential of already-popped popcorn by loading popcorn into a small model house and using a piston on the floor to push up on the popcorn until the house’s roof broke. This, however, required several tons of force, much more than the popcorn can create itself via popping.

40 Comments

  1. paully1212 says:

    haven’t watched the episode myself yet, but i talked to a friend who did, and i’m surprised by the results of the car v. rain part. from my personal experience, one can drive as low as 30-40mph without getting any rain drops in a convertible. my experiences are with a chrysler sebring and a vw eos. some ideas on why my results have differed from theirs:

    1) body style and windshield angle differences between cars. perhaps the more aerodynamic porsche interrupts air flow less -> smaller vortex.

    2) vertical speed of rain, size of droplets. the internets tell me that rain falls anywhere from 2-9 m/s depending on drop size. do you know the speed the artificial rain fell at? (temporarily excluding vortex fun and busting out some napkin geometry) if the top of the windshield is say 0.75m above the top of the frame, a 2m/s raindrop would take 0.375s to fall that distance. meanwhile, a car at 40mph (aka 18m/s) travels 6.75 meters (22ft) in that time, much longer than the distance from the windshield to the back of the back seat. for a faster 9m/s raindrop, a 40mph car travels 1.5 meters (5 feet) in the 0.83 seconds it takes to fall. note that in both cases backseat passengers are probably getting their heads wet, but driver and front seat folks should stay dry, and no water should land inside the confines of the car. when you add in some vortex effects, the results should only get better.

    the times i’ve been driving top down and been surprised by rain, my head and car have stayed completely dry until i’ve had to come to a stop. fortunately, most times i’ve found a convenient overpass to stop under. but until i did find one, i’ve been better off by staying moving rather than getting drenched during the 30 stationary seconds it takes to put the top up.

  2. Jim Benson says:

    You guys must have grown up on mars! Roll up the windows and drive about 45 mph. You don’t need a $100,000 car. Try a 1970 mgb!

  3. Felix Holt says:

    Just make sure you’re not driving anywhere with traffic lights!!

  4. Luc Botes says:

    This has nothing to do with any of your myths but, could help you in the future. By using custard to make ballistics gel the gel will not be succeptible to melting in hot conditions as heat is used to make it in the first place. I discovered this by trying to make custard with a microwave. I wanted to make a non newtonian liquid and therefore did not add any sugar. I mixed 3/4 custard with 1/4 water. I used the measurements the wrong way round. I really think this could help you guys and the reason I had to send a message this way is because my e-mail isn’t working.

    Luc Botes
    South Africa
    Durban

  5. nicole says:

    hi mythbusters im only 12 years old but i think youre experiments …..keep the great job guys..i know i will be watching more because youre myths are getting more interesting …..even if my friends keep think im very different from them cause they cant understand what i always watch….

  6. jesus says:

    hola q tal me llamo jesus tengo 21 años soy de mexico me gusta mucho su serie pero aver cuando hablan sobre los mitos de los latigos ai le doy algunos mitos sobre esto romper una silla (como la pelicula tesoro de la amazona),sujetase y balaciace( la pelicula la ley del zorro) otro mito es q es capas de trapasar la carne humana asta los huesos

  7. Bill says:

    I totally agree with paully1212. The aerodynamics of the body shell, especially the forward portion, plus the windshield shape will affect the results.

    I learned to drive on a ’56 Jaguar XK140 roadster and I owned a ’66 MGB for many years. Both were smaller 2-seaters. Neither were a problem in the rain even at lower speeds (the Jaguar was better). I also owned a ’67 Pontiac convertible, a very large car, for many years. It was terrible in the rain.

    I recently had occasion to drive a 2009 Rolls-Royce Drophead (aka “convertible”). It is quite a large car. Admittedly it was dry, sunny weather but there was absolutely no wind buffeting or turbulence, which would indicate that the wind was flowing smoothly up and over it and so it would probably not draw rain in.

  8. Mike: says:

    I have an idea for a show. How about showing that a car with larger tires can go faster than smaller tires. At 50 MPH standard tire verus a tire with twice the circumference at same engine speed should go 100 MPH. Thus we all could have a car that goes 200 MPH theoretically, or 500 MPH if the tires are big enough.

  9. leonardo says:

    hello loved Adan and Jeimy an of venezuela have 11 years and an fans of the cerie them envio.this letter so that they put to proof the mith that them envio treat of a man mounted in a valancin that falls him a rock and of 2 tonnes of 18 subways of altura the man goes out flying to 100 subways of altura and falls alive on the sand and want to know if the mith is truer o falce

  10. wayne says:

    hi gang. lovin your program. i watched one the other day when you said you cant beat a speed camera. we have a program here in england called top gear and they did this test. they used a tvr car and had to do 173mph to beat it so you are the ones busted because you can beat them you just have to drive faster. keep tryin wayne in hastings england….

  11. golden Lion says:

    Build a tank that is dressed like a fireman and has a blade on it for firefighting and can have a tank of water or b feed water from a fire truck.(A Fireman and machine)The first one is a riddle for u.

  12. Don says:

    A car with larger tires will reach a higher top speed but will not accelerate as quickly as a car with smaller diameter tires. The diameter of the tires changes the gear ratio.

  13. Don says:

    In addition, drag would prevent most cars from reaching 200 miles per hour. The horsepower required increases exponentially. You need at least 1000 horsepower for virtually any street driven car.

  14. pootpoot says:

    Don, I’m not entirely sure if this is what you were saying, but a car doesn’t need at least 1000 hp to reach 200 mph. There are several street cars with about half that power that have a top speed of 200 mph or more. The Bugatti Veyron with its 1001 hp reaches a vmax of 255 mph.

  15. Mabuisa says:

    Hola (Hello) I have seen many chapters of you and I have noticed some errors, example when Baxter launched with parachute timber as the error is that you drop the direct vacuum there was no wind drag, another example is when they put cookie dough, in the car you had no idea how long had the mass of manufacture that can change the results because the fermentation changed, should not be so literal must implement certain variables without the hype get to say that if all the Chinese jump simultaneously and with equal force for a long time can produce an earthquake, in Venezuela there is a girl who was or is an actress who fell from the top if not double parachute or the companion paramente (her boyfriend) died but she is now well not say who was unhurt but sobrevvio to fall, there is also the case of a child of about 6 or 8 years under vacuum released by the balcony apparently buddies were calling him and perhaps thought that it was faster, fell on the antenna of a car that went through his spleen and fell on the floor being alive (this was in Barqusimeto) and saw my sister, to review some of the myths that lie before, saludos desde Barquisimeto Venezuela

  16. Varun says:

    if you some dry ice in a glass bottle will it brake

  17. Dominik says:

    can you parachute with a blanket.

  18. lloyd sykes says:

    Driving in the rain at 30 – 40 mph , look not at
    the speedo try the direction as you corner, can you steer out of the situation an point your car in the
    right direction with the other yelling! thats hard
    you want to say shut up! but its instinct if youre
    driving habits are there otherswise its like a bug
    hitting the wind shield its the other car rear,
    rc cars are good on school pavement or a parking
    lot if not alot of other traffic, if you cant drive those then , drive what youre use toits
    the name or the price you pay for the vehicle.

  19. Chris P says:

    Don is right in that the larger tires will change the gear ratio. The max speed is more a function of the engine HP and the aerodynamics of the car. FYI: C5 corvette hits 183 mph with a 350 HP engine.

  20. Neat says:

    Plausable???????

    Why did you even do the Rain VS Car experiment when in the end even though the Results CONFIRMED the myth you still Said Plausable?

    I mean its not very scientific in my opinion. Yes I understand the Legal implications. ie people might try it and then blame you for their accidents but whouldn’t a simple disclaimer cover you on that issue?

    the bottom line is that it is quite pointless to spend all that time and effort doing an experiment and in the end just ignoring the fact that NOT A SINGLE DROP entered the car. the results are pretty conclusive to me

  21. Rod Davison says:

    Hi Mythbusters,
    I just watched the car vs rain episode. I have a BMW Z4 and I can confirm that I stay perfectly dry at any speed above 40km/h (about 25mph). I did notice that for your test, you left the windows down. I’m pretty sure your “stay-dry” speed would have been quite a bit lower. I suggest you need to test more than one convertible before you suggest that it requires unsafe speeds.

  22. James Garner says:

    I drive a mazda miata in Montgomery Alabama.
    In light rains, I do not bother with the roof becuase, I WILL not get wet (until I stop)
    I only have to be doing 25 or 30 MPH to see this impact in light rain. In heavy rain, it is another story. I must be doing 40 or faster to notice this affect. Others have pointed to the shape of the car, whcih makes sense, as the aerodymamics will set up aroud a car (even at low speeds) and carry the water over the driver.

    Your results confirmed for me someting that I had suspected after watching the show. The potential legal implications of your determiations impct your determinations. You should separate results from iplications. State for example. Confirmed byut a BAD IDEA. (not recommended)

    The affect discussed is real. The show demonstrated it, but your chosen test mechanism showed the affect only at high speed, leaving you in the quandry, do we say yes, and leave people thinking it’s a good idea to speed in the rain (speeding is a bad idea, wet or dry, and worse wet!) or simply decare it plausible. Better testing would have shown the affect at slower speeds, avoiding the quandry.

    Please take time to determine the full nature of the myth and devise a proper test for it. I would recommend some scientifically trained staff members review tests for plausability of determining the nature of the myth in question.

    I do enjoy the show and the kids love it immensly.
    Keep it up!

    Plese take a little more time to understand the inssue and devise a test that acurately answers the question.

  23. Jack says:

    hey mythbuster guys i watch u show every time i get a chance i made a paper cross bow i kill a rabbit with it it works so gd i love it

  24. kevin says:

    They were not using the wipers what about that

  25. William Lower says:

    Just letting you know that the Mythbusters actually used a 110 kilowatt laser, not a 10 watt laser, as this was the highest wattage that was available to them.

  26. Luc Botes says:

    Can you guys test if a 2 milliwatt laser can burn/set off matches. (i saw it on youtube and want to buy one)

  27. connie says:

    well, I was driving my 96 camaro with the top down on a highway going 65 MPH when a severe downpour began and lasted around 6 minutes. The faster I drove the less wet I got, In fact there were just a few droplets of rain in the car when it finally stopped.

    • Andreas says:

      You copped out too early and at too low speeds onthis one. Here’s an extension to this ‘myth’:
      you will have noticed that driving when it is snowing you won’t need your wipers above a certain speed as the snow gets blown above the windscreen, doesn’t take much speed. You can get the same effect with rain.
      Germany of course with no speed limit, on several occasions I tested this in a fairly standard car – a VW Golf mk2 (built 83 to 92). Around 190-195 km/h (above about 120 mph) I could turn the wipers off as the rain was no longer hitting the windscreen.
      Now in the US you may not even dare test this but we’re talking legal road speed here, book your trip to Europe…

  28. Luc Botes says:

    I am disgusted with everyone’s English. Learn to communicate!

  29. Caz says:

    Honda crx convertible stays dry in rain above 30mph.it’s fantastic!!! Had one for 7 years and it never let rain in above 30mph. X

  30. Jordan says:

    The car used in the test looked like a 2009 porsche 911 carrera turbo. Considering how that model is able to close its soft top via remote at 50 mph, I don’t really see the problem.

  31. Nitesh verma says:

    what is the effect on the aerodynamics of a non-convertible car when it rains heavily. plz reply to this query ASAP.

  32. Blakec22596 says:

    It’s obvious that C4 and propane won’t pop popcorn because the heat isn’t sustained

  33. Van Cottom says:

    I know leaving the tail gate UP on a pickup builds an aerodynamic bubble and improves mileage.

  34. BuzyG says:

    I’ve driven my car accross dartmoor in light rain with the roof down at around 40mph. The interior stays perfectly dry. Also drove over to Spa in Belgium last year and it rained very heavily. Kept driving to the next rest stop before putting the roof up, definatley drier than stopping in the open to put the roof up.

  35. BJ says:

    Random question, does anyone know the name of any of those old-timey cartoons that were playing during the popcorn experiments?

    Also, I would like to see effects of larger wheels also

  36. charles says:

    They did not bust any mith they’re test did not tell you anything but that if you drive faster through a sprinkler you will not get as wet as if you were to stand next to it for their experiment to have been correct they would had to of timed how long it takes for the you to put the roof up in the rain then drove through the rain at 90 miles an hour in the same amount of time as it took for them to put the roof up in the rain then they could a calculated how much rain accumulated in the car

  37. Chris says:

    I would like to see the same Car Vs Rain myth tested but with a targa or T-top car like a corvette or camaro. I know for a fact that in a light rain at 60mph with windows up the corvette will stay dry, just did it.

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