Has anyone turned the cross braces on the roof rack around to get rid of the noise the roof rack makes. I noticed the cross braces are in the shape of a tear drop and the fatter end faces towards the front of the car. Logic would tell you that the pointier end should be facing towards the front of the car for aerodynamic reasons. Maybe the braces are just installed wrong. Any thoughts?
Reversing roof rack canceling noise?
- Thread starter loccusst
- Start date
Aerodynamic reasons would tell one that you would create more turbulence (noise) with a reverse teardrop profile (airfoil). You would effectively need a profile that was "streamlined" - pointy to pointy, but even that would cause noise as the leading edge cut through the air causing sick amounts of eddy currents to cary over the top surface and "collide" with currents running off the trailing edge.
Design your own airfoil here:
http://www.grc.nasa.gov/WWW/K-12/airplane/foil2.html
Design your own airfoil here:
http://www.grc.nasa.gov/WWW/K-12/airplane/foil2.html
ELEmental59437
Member
- :
- 2002 P5, 1978 F250
are the crossbars even reversible? I dont think so...
Put it this way: Mazda has a wind tunnel for testing at their disposal. You (nor I) do not; I will note that their engineering design of the matter, however "loud" it may be, is the best option for the particular design/setup (all things considered)
If you're really picky about the design, I'd suggest removing the bars and the strips altogether (dropping the headliner, etc) and getting a setup from Thule or Yakima (towers, bars, etc)
Personally, I took mine off for the winter; it's loud in the summer too, but I usually drive with the windows down, so it's loud anyway!...
If you're really picky about the design, I'd suggest removing the bars and the strips altogether (dropping the headliner, etc) and getting a setup from Thule or Yakima (towers, bars, etc)
Personally, I took mine off for the winter; it's loud in the summer too, but I usually drive with the windows down, so it's loud anyway!...
Actually I remember that they cut down the flat edges to reduce the noise, there is a TSB or something out about it. I also thought that the racks might work better the other way, but they are mounted that way for some reason. An easy was to find out if it would quiet down is put some tape on the flat edge to round it out and see if it's quieter.
Well, actually if there's anything on the bars intent to cut down on noise it is those "teeth" on the bar; they're designed to break up the air flow so that there isn't such a large velocity (read: noise) of air running over and under the bar.
I also think that the fact that the bars are so low to the roof has some to do with it. I'd love to have Subaru or Audi/VW wagon style rails - basically the side rails running parallel with the length of the car and leave the cross bars off (basically pick up an aftermarket or OEM supplied set similar to Yakima or Thule, etc).
Looks like a winter project
I also think that the fact that the bars are so low to the roof has some to do with it. I'd love to have Subaru or Audi/VW wagon style rails - basically the side rails running parallel with the length of the car and leave the cross bars off (basically pick up an aftermarket or OEM supplied set similar to Yakima or Thule, etc).
Looks like a winter project
Loccusst,
I meant to write about this when I bought my P5 a month ago. When I was mentioning all the noise everyone talks about in the forum to my salesman, he told me that Mazda instructed the dealers to reverse the cross bars to reduce the wind noise problem. Mine look like this: Front bar has the rubber bumps up front. Notice the little "spoiler" (similar to the back of our car) is also in the front. Rear cross bar does not have the bumps, but the little spoiler faces front.
Here's my theory (and I'm a mechanical engineer who's done a little work with this kind of thing). Mazda probably designed the bars to be smooth end front and spoiler in the back. The bumps in the back would serve as vortex breakers. Vortices are the little eddies (like off of a rowboat oar) that shed off of a trailing edge of a surface. Depending on the speed of the air (or the car in our case) these vortices can form at a frequency that causes lots of noise.
(Side note: Look at some tall smoke stacks in some industrial areas and you'll see plates just sticking out of the side on the top half of the stack. These are to break up vortices to avoid failure similar to that famous bridge collapse.)
Dimitrios mentioned the proximity to the roof. Maybe the designers had a great cross bar design that they tested independent of the car. Maybe it didn't work so hot on the car and reversing them was actually an improvement, a cheap workaround. I won't open my sunroof until the spring now, but I don't think the wind noise is so bad. At 70 mph, I'm hearing the engine and wind around the windshield as much as noise in the roof area. Not saying the car is quiet. I just don't think the rack is the worst culprit.
The true test of all this would be to reverse them and listen, which I have no intention of doing. Would be interested to hear the results if someone else does.
I meant to write about this when I bought my P5 a month ago. When I was mentioning all the noise everyone talks about in the forum to my salesman, he told me that Mazda instructed the dealers to reverse the cross bars to reduce the wind noise problem. Mine look like this: Front bar has the rubber bumps up front. Notice the little "spoiler" (similar to the back of our car) is also in the front. Rear cross bar does not have the bumps, but the little spoiler faces front.
Here's my theory (and I'm a mechanical engineer who's done a little work with this kind of thing). Mazda probably designed the bars to be smooth end front and spoiler in the back. The bumps in the back would serve as vortex breakers. Vortices are the little eddies (like off of a rowboat oar) that shed off of a trailing edge of a surface. Depending on the speed of the air (or the car in our case) these vortices can form at a frequency that causes lots of noise.
(Side note: Look at some tall smoke stacks in some industrial areas and you'll see plates just sticking out of the side on the top half of the stack. These are to break up vortices to avoid failure similar to that famous bridge collapse.)
Dimitrios mentioned the proximity to the roof. Maybe the designers had a great cross bar design that they tested independent of the car. Maybe it didn't work so hot on the car and reversing them was actually an improvement, a cheap workaround. I won't open my sunroof until the spring now, but I don't think the wind noise is so bad. At 70 mph, I'm hearing the engine and wind around the windshield as much as noise in the roof area. Not saying the car is quiet. I just don't think the rack is the worst culprit.
The true test of all this would be to reverse them and listen, which I have no intention of doing. Would be interested to hear the results if someone else does.
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Flipper said:
Similar to what I had posted on the second post - I majored in ME for two years, but finished with a Industrial Engineering degree, but I still maintain my knowledge-base...
Aerodynamic reasons would tell one that you would create more turbulence (noise) with a reverse teardrop profile (airfoil). You would effectively need a profile that was "streamlined" - pointy to pointy, but even that would cause noise as the leading edge cutting through the air causing sick amounts of eddy currents to cary over the top surface and "collide" with currents running off the trailing edge.
Flipper said:
Actually, the "fins" are there to create vortices - 1/2 of one dozen, 6 of another
same thing....; shearing forces of the wind against the face of the stack are what cause structural damage over time. The fins break up the wind and create eddy currents that will dissipate the dynamic stresses put on it by the wind. Stacks have the fins because their shape inherently causes unwanted forces; eddy currents around a sphere/round object on the "trailing edge". Laminar flow ends up increasing in velocity around "rounder" objects.Stacks are usually placed in series so currents flowing off of one stack would (assuming the conditions are right) would flow into the others, causing undue stresses. Contrast this to F1 or other race cars when they trail in the currents of cars in front of them. The cars are designed such that their trailing flow will create a "vacuum" for a given distance (often why if you've ever been to an F1 or Indy race up close, you don't "feel" the car until a second or so after it passes; similar to the dopplar effect, but via air currents)
Here's a good thesis on the topic: http://scholar.lib.vt.edu/theses/available/etd-5024212489622671/unrestricted/thesis.pdf
Flipper said:
It may be an issue. I feel that design itself is flawed - everything from removing the bars (if wanted) to the very construction (I , as well as others, get "creaking" when taking turns when the rack is loaded with a bike, etc). Mazda needs to redesign a bar system as "aftermarket" that is similar to the Audi/VW or Subaru setups (honestly, I feel highly about those systems). Has anyone noticed how the Mazda3 hatchback roof-rack is setup? Any improvements?
Go Dimitrios!
I was trying to walk the fine line of conveying the information without blowing people away with technical jargon. You jumped way over the line and I enjoyed reading your positions. I opened the thesis, but will have to check out those 121 pages on vortex shedding a little later!
One comment on the stack strakes (vortex breakers). I agree they also create vortices. But the reason they work is because they are staggered and cause the vortices to be shed in more of a random fassion.
Wind passing over a perfect cylindrical shape or other symmetrical shape sheds vortices at regular intervals under constant wind velocity. If the frequency of the vortices matches the natural frequency of the structure, it'll shake like mad.
I agree with you that wind forces are also a source of stress due to the pressure (and suction on the back side). The design and analysis of the structure must be checked for both the constant stress caused by the wind pressure and also the vortex frequency vs. the natural frequency.
I'm sure somebody will tell us to get a life and go find an engineering forum now.
I must say understanding at least basic physics helps you understand a lot of stuff in life.
The knowledge still doesn't fix our cross bars though (right back on topic)
I was trying to walk the fine line of conveying the information without blowing people away with technical jargon. You jumped way over the line and I enjoyed reading your positions. I opened the thesis, but will have to check out those 121 pages on vortex shedding a little later!
One comment on the stack strakes (vortex breakers). I agree they also create vortices. But the reason they work is because they are staggered and cause the vortices to be shed in more of a random fassion.
Wind passing over a perfect cylindrical shape or other symmetrical shape sheds vortices at regular intervals under constant wind velocity. If the frequency of the vortices matches the natural frequency of the structure, it'll shake like mad.
I agree with you that wind forces are also a source of stress due to the pressure (and suction on the back side). The design and analysis of the structure must be checked for both the constant stress caused by the wind pressure and also the vortex frequency vs. the natural frequency.
I'm sure somebody will tell us to get a life and go find an engineering forum now.
I must say understanding at least basic physics helps you understand a lot of stuff in life.The knowledge still doesn't fix our cross bars though (right back on topic)
I actually was able to follow what you guys are talking about. I took some enginering in school and some drafting too. I was just curious about starting to eliminate some of the noises the car gets while going down the road. The windshield has always been a problem in the proteges, tons of noise. The rest is in the fact that the car has very little road noise deadener in it. I plan on taking care of that this spring by putting alot of it all over the car including under the headliner.
feldenkrais
Member
- :
- 2003.5 Mica Black P5
Way over the top! If you're not going to use the roof rack (putting bike or ski rack on it) then take it off! Hey- no more noise! If you are going to use it, believe me, no matter which way you face the cross braces the bike or ski rack attachments make way more noise!
The biggest problem with the cross brace design is that Yakima's wind deflector won't fit the Mazda cross brace so there's no way to reduce the noise.
I take mine off for winter to make snow removal easier and have noticed that with the moon roof open and no rack, what a difference. Unfortunately, I need the bike rack 3 of 4 seasons a year.
fks
The biggest problem with the cross brace design is that Yakima's wind deflector won't fit the Mazda cross brace so there's no way to reduce the noise.
I take mine off for winter to make snow removal easier and have noticed that with the moon roof open and no rack, what a difference. Unfortunately, I need the bike rack 3 of 4 seasons a year.
fks
- :
- 2002 BJFW, 2007 BK3P, 1979 SA22C, 2005 BK3P
and my rack doesn't make any noise.....
((runs from flinging food and stones of crowd))
seriously, with the moonroof and the wind deflector attached, i don't get any wind noise.
((runs from flinging food and stones of crowd))
seriously, with the moonroof and the wind deflector attached, i don't get any wind noise.
