2009 X5 Wind Noise Issue?

[master1917]

Originally Posted by bfeng

Here's my story about wind noise. I used to work for an OEM, and one of the areas I spent time on is the design of door seals to reduce wind noise. The acoustic transmission loss of a door seal is depending on several factors, but one of the more important ones is the compression of the seal. One thing that OEM's sometimes screw up is designing the door seal for adequate compression without taking into account the full effect of wind. Wind flowing around the A-pillars creates an area of low pressure on the front door side glass. The pressure differential is typically quite small. Crosswinds make it worse. But, given the size of the low pressure area, you can wind up with multiple pounds of force pulling the top 1/2 of the door away from the body. 5-10lbs of force is not unreasonable at higher highway speeds or with any sort of crosswind. If the design of the seals doesn't take this into account, you'll get increased wind noise at speed. Easy to test. Drive down the highway at 75mph or 80mph and then use your hand to pull the top/rear of the window frame inward (just squeeze with your thumb on the body above the door). If you hear a reduction in wind noise then you know your seals could be more compressed. I can easily hear a reduced amount of wind noise when I do this in my X5D.

In my X5D, a cross wind of 20mph will suck the door-top out far enough to cause bursts of fairly loud wind noise (at 75mph on the highway). I assume this is that outer-most seal pulling away from the body. Adjusting the trailing edge of the door inward by 2mm
or so should help a lot. Likewise, adjusting the front hinges so the top frame compresses slightly more against the body will also help.

The only downside might be a very slight increase in door closing effort. Also, if your X5 is pretty old, this will help a little to compensate for old squished seals.

John

Thank you for your advice. I know what you mean. On some of my very old $1,000 cars as I was going over 100km/h, the top corner of the drivers door would separate and make a visible gap from the body at high speeds as if someone is pulling it outwards so makes sense to me. Especially visible with frameless doors.
I am not concerned with the effort closing the door as my X5M has a soft closing doors, but wonder if the adjustment will overexpose the other parts of the door or body to water/air in all other conditions?

[ard]

Great info.


thx