It’s a rare perfect day in Chicago, where the weather typically boils down to Snow Removal and a few weeks of Road Construction Season. Warm but not too hot, the humidity and mosquito situation are remarkably peachy as well. Driving along in your ride, you feel like you’d be ticketed for not taking advantage of this rare climate event, and you hit the DOWN button on your driver’s window.
BOOMBOOMBOOMBOOM. Ouch! It’s like a jet taking off. If your kid rolls down a back window alone it’s even worse- seems like your eardrums will rupture. Opening the sunroof adds more unpleasantness. In the twelve years I owned my previous car, I think I can count on the fingers of both hands the number of times that I had the giant glass roof open; if just wasn’t pleasant to drive. Is this just my car, or are others experiencing this?
Apparently, I’m not alone, and there’s a reason for this phenomenon. I did some quick searches for ‘Buffeting’ and ‘Buffett’, and after dismissing the many links dealing with a Boomer musician that performs to thousands of aging Tommy Bahama clad fans, I found some answers.
According to a number of sources, including The Family Handyman of all things:
The throbbing, helicopter-like sound is the outside air passing over and interacting with the contained air inside the vehicle.
When the two air masses collide, they compress and decompress repeatedly. This produces the throbbing effect. It can be as loud as a commercial aircraft.
Many variables contribute to the effect: car shape and size, how far you lower windows down and your speed. The effect can happen when any single window is down, including the sunroof.
The helicopter sound is more pronounced when a rear window is down. This is because the side mirrors are designed to direct air flow away from the front windows. Lowering a rear window amplifies the effect.
So you aren’t imagining that the rear windows lowered alone always seems far worse. But why? More importantly, why can you roll down the side windows in a ’67 Impala and not experience this phenomenon so badly?
Good Aero Is Bad?
Well, good aero is certainly bad for windows down driving. Today almost all cars are very aerodynamically efficient, the air clinging tightly to the outside of the car.
As The Family Handyman says:
When a window opens, the air flow is disrupted, magnifying the buffeting effect. Older vehicles were designed less efficiently, and air leaked from their insides. The leaking air relieves the pressure caused by wind buffeting, reducing the effect.
Obviously, the one solution is to open another window, but that still doesn’t eliminate the problem, just reduces it. Is there a solution? Historically, there have been a few, and some from very unlikely sources.
[Editor’s Note: I actually wrote about this ten years ago (holy crap) and I asked an actual physicist, not some internet handyman. Here’s how Dr. Stephen Granade explained it to me:
That “whum whum WHUM WHUM” noise happens because the wind passing over the small window opening is like a bored drunk blowing over the neck of an empty beer bottle.
Air passing over an opening forms tiny tornadoes as it moves past the front edge of that opening. When those tornadoes, or vortices, reach the opening’s back edge, they make a wave of pressure that pushes air into and out of the car. Since sound is nothing more than waves of pressure, this makes noise. If you’re driving slowly the effect’s not too bad, but if you drive fast enough, you reach a resonant point. Imagine I stand by your open car window and use my science powers to push on the air inside the car, compressing it a bit. The car air then springs back out, then back in, then back out, then back in. With each cycle of moving out and in, the amount of air movement gets smaller until it completely dies away. But if I push on the car air again just as it finishes springing back out and is headed back in, and I do that over and over again, the amount of air movement gets a whole lot bigger and doesn’t die away. That’s what happens when you drive fast enough. The vortices keep pressing on the air in your car just at the right time to make big pressure waves that we can feel and hear.
The technical term for this effect is the Helmholtz resonance, though car people call it “side window buffeting”. Back in the 1850s, a scientist named Hermann von Helmholtz showed that the sound’s pitch depends on the size of your container of air and of the opening. The bigger the container of air, the lower the pitch. The smaller the opening, the higher the pitch. If you blow over a bottle, you get a medium-pitch whistle. Since a car’s a big container of air, you get a low throbbing noise.
So, there you go, from an actual, working physicist! – JT]
Cracks In History
If you’ve opened a sliding rear window in a pickup you know how that really helps airflow. Instead of the truck cab being a pressurized box or a big air scoop the wind has a place to escape. Even some cars had an answer for this, particularly Mercury cars from the sixties with power lowering rear backlights:
Mercury supposedly dropped the feature after air conditioning became popular, but if you’ve ever owned a black-on-black car you’d kill to be able to get the hot air flushed out of your ride this quickly and help the poor climate control do its job.
Another great solution came from what might be the oddest place imaginable: the designers and coachbuilders at the Italian firm Zagato., often makers of some of some of the most bizarre automotive creations ever (even by Italian standards). Maybe they discovered this by accident and made it a feature, but the hatchbacks of a number of their cars could be electrically raised by a switch on the dashboard. Here’s the feature on an Alfa Romeo Junior Zagato:
Or on this Lancia Fulvia Zagato. By the way, you could still open and close the hatch when is was raised since the latch itself moved:
If you scroll forward to the 15:00 point in the video below you can see it open. Like the later Stratos these Lancias make noise that hits the receptors in your brain in such a way that you want to triple the speed limit and not care about the consequences.
This Lancia Flavia Zagato might have been the first one to have the feature back in 1962.
Shit, look at that thing: if aliens really landed in Roswell and instead of being probed and killed they were put into slavery designing cars, you might imagine their creations looking something like this. Why do I want one so much?
Needless to say, I have heard that owners of these cars will get people at stoplights yelling at them YER HATCH IS OPEN BUD! Which is understandable.
The Matra Djet had a far less sophisticated way to deal with the airflow issue, almost out of necessity if you believe the remarks at around 4:30 by this somewhat familiar reviewer:
I’ve found that T-tops and targa roof cars are particularly bad in the buffeting department, except for cars like the Honda CR-X Del Sol or the Miata RF where you can roll down the rear backlight. Only one Nissan Z car I found to be reasonable with the roof panels off, and that was the disco-era 280ZX 2+2; it had remote control rear quarter windows to let out the pressure.
Our family had a later 1990 Z32 which had no such openings and was essentially undriveable at speed with the roof panels removed.
Banishing The Boom
The aftermarket has actually latched onto this idea, literally. There are numerous sources that offer a clip that Corvette owners can put onto their hatch to allow the thing to close and secure but leave a few inches of air gap to relieve the pressure of the big targa air scoop (at least on C4s).
I found a bunch of suppliers making these things so they MUST work, right? Why can’t mainstream OEM manufacturers latch onto this idea?
Once again, I’m using the Tesla Model 3 as the guinea pig of this device. Right on the switch panel for the windows would be a button to pop the glass on the hatch just enough to get air flow to run through. Of course, being a Tesla they’d probably make you go through a bunch of menus to open this thing, but let’s just apply logic anyway.
One detail- you might need to add a small mesh screen that raises with the window. My fear is the the airflow will be so good that your gas receipts and wedding invitations or whatever is on your seats might end up the street behind you without it.
Look, we all want fresh air now and then, but we want our eardrums not to bleed in the process. Do we need to buy a car with the aerodynamics of a brick to get that? I don’t think so, especially if there’s a trick we could employ to give us the best of both worlds.