Newbie

[shooter357]

I just purchased a 2015 CX 5 after doing a lot of research and I like the car. However it's not without it's problems like every other vehicle. Today the weather was nice enough to lower the windows. To my surprise and consternation when I lower just the back windows it sets up a very evident vibration. When I lower any of the front windows a little it goes away. I would have thought in designing the car that the engineers would have discovered this in wind tunnel tests. I guess I'll just live with it.

 

[bmninada]

I just purchased a 2015 CX 5 after doing a lot of research and I like the car. However it's not without it's problems like every other vehicle. Today the weather was nice enough to lower the windows. To my surprise and consternation when I lower just the back windows it sets up a very evident vibration. When I lower any of the front windows a little it goes away. I would have thought in designing the car that the engineers would have discovered this in wind tunnel tests. I guess I'll just live with it.

Welcome and congrats. Thou should not blame Mazda, yet! I have no such vibrations and I haven't heard of any similar complaints - yet. Yours is still under warranty - just take it 1st. to the dealer.
Also - did you not take a test drive when you bought it? Being 2015, obviously its not new so ideally one would have checked doors, windows, etc ?

 

[piotrek91]

Welcome and congrats. Thou should not blame Mazda, yet! I have no such vibrations and I haven't heard of any similar complaints - yet. Yours is still under warranty - just take it 1st. to the dealer.
Also - did you not take a test drive when you bought it? Being 2015, obviously its not new so ideally one would have checked doors, windows, etc ?

Every CX-5 has that same vibration. Sounds like a helicopter flying in the car.
My 07 rav4 also does it and it can be very very loud when a passenger unexpectedly opens a rear window.
Many SUV's get this "helicopter" effect when just the rear windows are down and as OP already learned, the fix is to simply open one of the front windows as well.

 

[banjos-n-beer]

Yeah, the pressure can get quite bad with just the rear windows down.... its that way in any newer vehicle.

Crack the fronts and you'll be good to go.

 

[Ricsta]

Yeah, the pressure can get quite bad with just the rear windows down.... its that way in any newer vehicle.

This isn't unique to newer vehicles. My 2003 Toyota Highlander did the same thing. Its matter of physics. As others have stated, crack the front windows and it goes away.

 

[banjos-n-beer]

"Newer" being subjective. To me, I guess that's any vehicle I've had since high school. Don't really recall the issue when I was younger driving mid-80s cars. But it certainly gets worse with each new car purchase.

 

[erhayes]

All the vehicles I've had will do this. Some of the cause is the improved aerodynamics in the last 15 years or so. Deal with it. Ed

 

[MikeM.]

"Newer" being subjective. To me, I guess that's any vehicle I've had since high school. Don't really recall the issue when I was younger driving mid-80s cars. But it certainly gets worse with each new car purchase.

That's the price you pay for aerodynamic efficiency resulting from smooth, laminar airflow. A big, aerodynamically dirty vehicle is going to be more tolerant of disruptions to the airflow because the more laminar airflow of modern cars contains more energy closer to the skin of the vehicle.

 

[ColtX-5]

"Newer" being subjective. To me, I guess that's any vehicle I've had since high school. Don't really recall the issue when I was younger driving mid-80s cars. But it certainly gets worse with each new car purchase.

Squarish 80s 4 door sedans did not have aerodynamics that made the air stream lay close to the body like vehicles after 2005, or so, do. I have had 2 or 3 cars do it, a 2005 Altima was so loud it was intolerable. That ultra low bass sound is turbulence in the air stream beating against the body. Opening a window lets the pressure wave into the interior.

Physics is pretty cool!

 

[banjos-n-beer]

Um, yeah, I know its physics... and it doesn't bother me cause I know what causes it and how to defeat it. I merely stated the more aerodynamic (newer) the vehicle, the worse it gets.

(dunno)

 

[doopie]

I'm always learning sumthin' new here on this board.

 

[mazdadude]

I also notice that if I have my Moonroof Open or vented, the sound will change when I move the HVAC control from FRESH AIR to RECYCLE modes. I have never thought to try changing the mode button when only having the rear windows down...

 

[MikeM.]

I also notice that if I have my Moonroof Open or vented, the sound will change when I move the HVAC control from FRESH AIR to RECYCLE modes. I have never thought to try changing the mode button when only having the rear windows down...

Good tip!

 

[Chris_Top_Her]

Have you looked at mods?

 

[Unobtanium]

I just purchased a 2015 CX 5 after doing a lot of research and I like the car. However it's not without it's problems like every other vehicle. Today the weather was nice enough to lower the windows. To my surprise and consternation when I lower just the back windows it sets up a very evident vibration. When I lower any of the front windows a little it goes away. I would have thought in designing the car that the engineers would have discovered this in wind tunnel tests. I guess I'll just live with it.

With my Grand Jeep Cherokee, I had a BAD! "buffeting" when I lowered the rear windows only. Like, crazy bad. I think it might be "unavoidable physics". For example:

"Want 0.2CoD less? Well...it's going to route air like so..."

I need to test this on my CX-5 to see if it does it more/less/the same as the Jeep, but I'd bet it's not near as bad.

 

[mazdamarty]

My 2002 Honda CRV did the same thing, bad. Haven't noticed it yet on my CX-5, hasn't been nice enough to have the windows down yet.

For my CRV, the best way to get fresh air was open the front right, and back left, and maybe the front left just a smidge if it was really warm.

 

[shooter357]

Welcome and congrats. Thou should not blame Mazda, yet! I have no such vibrations and I haven't heard of any similar complaints - yet. Yours is still under warranty - just take it 1st. to the dealer.
Also - did you not take a test drive when you bought it? Being 2015, obviously its not new so ideally one would have checked doors, windows, etc ?

Yes I did test drive it but it never occurred to me to wind both back windows down at 40 mph at temps of 47 degrees

 

[vroom]

Yeah, as others have stated, it's just a consequence of the car being more aerodynamic, which is usually a good thing!

Since the car is very aerodynamic, air wants to flow very close to the back windows smoothly and at high speeds. When you open the windows, the fast moving air wants to suck the air inside the car out (think airplane wings). That create lower pressure inside the car which in turns wants to suck outside air back in. This goes back and forth quickly causing the noise you hear. Cracking a front window open, even just a little bit, causes the internal pressure to maintain equilibrium more easily, disrupting the high-low pressure cycle. Same goes for cranking up the fan in fresh air mode. This pumps air in the car causing positive pressure which helps prevent the air being sucked back in.

This also happens with the moon roof. Open it on the highway and you'll hear a constant hiss noise. That is the sound of turbulent flow caused by the moon roof deflector. If you lower the deflector with your hand you cause the air flow to become smooth, fast and close to the opening (as MikeM said, this is called laminar flow). The noise will instantly become "booming" in nature, caused be fast alternating low and high pressures in the car.

This geek moment was brought to you by physics, we now return to you regular scheduled programming...