WIND NOISE --- Understanding & Addressing Common Causes

Chief Products Roof Racks are engineered from the ground-up to be extremely aerodynamic and highly-resistant to Wind Noise. We provide this article to help you better understand what causes Wind Noise, the steps our engineers have taken to address the issue, as well as several steps you can take yourself.

WHAT CAUSES WIND NOISE?
Wind Noise (aka Aeolian Sound) is the sound produced by wind when it passes over or through objects. If the surface of the object has a consistent shape, the disturbance of the wind becomes audible. The amount of noise depends on the speed of the airflow (how fast you are driving, plus the speed of the oncoming wind) and the drag coefficient of the object. The higher the drag coefficient, the more noise is created.

HOW ENGINEERS MINIMISE WIND NOISE
There are (3) main techniques engineers use to minimise Wind Noise.

  1. Create a product that is highly aerodynamic (has a low drag coefficient).
  2. Divert air flow around objects (or parts) that have a high drag coefficient (use a wind fairing, etc.).
  3. Disturb the air flow. This breaks up the frequency of the Aeolian Sound (mentioned above) and helps reduce Wind Noise significantly.

WHAT ARE THE ENGINEERING CHALLENGES?
There are (4) main reasons why Wind Noise is a common problem in the roof rack industry.

  1. The larger the product (and the more features you include) the more challenging it is to maintain good aerodynamics.
  2. Small variations (i.e. exposed bolt head) can have large effects, especially at high-speeds (due to point #3).
  3. Air resistance rises exponentially with speed, which means Wind Noise increases exponentially with speed (a roof rack that is silent at 90kmh can be very loud at 140kmh).
  4. A large number of variables outside of our engineering team's control can affect the amount of Wind Noise a customer will hear. In short; anything that affects how air flows over your vehicle, has the potential to affect the amount of Wind Noise you hear.
    1. Vehicle Aerodynamics - Every vehicle has different aerodynamics, even different models of the same vehicle (i.e. 2015 Jeep Grand Cherokee Trailhawk is different from 2015 Jeep Grand Cherokee Summit).
    2. Aftermarket Accessories - Any accessories mounted to your vehicle can change the aerodynamics of your vehicle (i.e. Bull Bar, Spot Lights, etc.).
    3. Weather - Wind speed, wind direction, humidity and temperature can all influence how air flows over your roof rack.
    4. Configuration - How you configure your roof rack and the items you mount to it will have a dramatic affect on the Wind Noise generated.

HOW OUR ENGINEERING TEAM TACKLES THE CHALLENGES
There's no way to completely eliminate Wind Noise, but Chief Products engineers have implemented several features and testing methods to ensure our Roof Racks deliver the very best Wind Noise performance possible.

  1. Extremely Aerodynamic- One of the most effective ways to minimise Wind Noise is to make your roof rack as aerodynamic as possible.
    1. Smooth Top Surface - The entire roof rack maintains a completely smooth top surface. All fasteners are recessed or hidden. T-Nuts (for mounting accessories) are recessed into the Planks. Even our Tie-Down Plates and Anchor Points are designed to mount between the Planks and sit flush with the top surface.
    2. Rounded Edges - Our Platform Frames deliver a smooth outside border with rounded edges on all (4) sides, providing a very low drag coefficient.
  2. Hidden Fasteners - All fasteners are located inside the mounting rails or recessed into the Planks.
  3. Low Profile Design - Our Roof Racks only sit 86mm above the roofline. Upcoming versions of our Roof Rack will provide options to sit even closer to the vehicle.
  4. Extremely Thin Design - Our Roof Racks are less than 1 inch thick (25mm or 28.34mm with a Platform Frame).
  5. Stealth Air Dam - We significantly reduce wind noise by restricting the amount of air that flows through the confined space under the rack. Best of all, we're able to accomplish this goal utilising a product that mounts out-of-sight (ensuring it doesn't inhibit use of the rack or obscure views out of the sunroof).
  6. Aero - In some situations, the best approach is to divert high-velocity air flows around objects that cause wind noise. To address these situations, our engineering team has developed an aero product WK2 ROOF RACK (Aero) that can be mounted to your roof rack to maximise aerodynamic performance.
  7. Extensive Testing - Chief Products tests our products for 6-12 months in real-world conditions (daily driving and off-road adventures) before the final version is released to our customers. During that time, we also perform extensive aerodynamic testing with audio monitoring equipment in various conditions (with cargo, without cargo, off-road, on-road, high speed, etc.). Finally, we send prototypes for testing to our global network of Brand Ambassadors and Test Fit Group Members. This ensures prototypes are tested in different locations and scenarios all over the world.

TIPS TO ADDRESS WIND NOISE
Our team provides the following tips to address the (3) main causes of Wind Noise with your Roof Rack. These tips are based on extensive research and testing, as well as detailed reports from Test Fit Group Members, Brand Ambassadors and select Customers from carefully chosen environments all over the world.

 #1 -- WHISTLING SOUND 
In certain circumstances, a high-pitched whistling sound can develop. Whistling sounds are normally caused when air passes over an opening.

SOLUTION --- This issue can be solved effectively in the following ways.

  1. Check that all of your ROOF RACK (Plank End-Caps) have been properly installed. If you have any open ended Planks, they can cause a whistling sound.
  2. Ensure you don't have any bolts sticking out. Air rushing around an exposed Bolt at high speeds can cause a whistling sound.
  3. Ensure none of the items you've installed on your roof rack, have an exposed opening where high-speed air can flow across that opening.

 #2 -- HUMMING SOUND (50-80kmh) 
When the Planks vibrate, they can produce a fairly deep but sometimes loud ‘humming sound’ that usually shows up around 50kmh and can increase in volume as speeds increase. This 'humming sound' occurs when the Planks vibrate at a certain resonate frequency. It is most often caused by wind rushing across the top surface of the Planks, or from road vibrations (corrugated roads, knobby mud tyres on pavement, etc.). When one Plank vibrates at this resonate frequency it can cause the other Planks to do the same.

SOLUTION --- This issue can be solved effectively in the following ways.

  1. Mount items on your roof rack. Each item on your roof rack will act as a dampener that eliminates vibrations.
  2. Ensure you've properly installed all of the Rubber Isolators (or M8 Flat Rubber Washers if you purchased your Roof Rack before January 2021). To work effectively;
    1. They need to be installed on every Plank.
    2. They need to be positioned between the underside of your Plank, and the top mounting face of your End-Cap or Platform Frame Rail.
  3. Some customers reported difficulty installing the older M8 Flat Rubber Washers. For that reason, we redesigned them. The new Rubber Isolators provide the following improvements.
    1. They cover a larger area (ensuring there isn't any metal-to-metal contact due to a misaligned washer).
    2. They 'hold' onto mounting bolts better (so they don't fall off during installation).
    3. They're manufactured from a new silicone rubber that can better withstand numerous cycles of compression/rebound (for customers that regularly move their Planks).
  4. If vibration persists you may need to 'reseat' your installation. This will allow the entire structure to settle and eliminate any tension or misalignment. This can be done easily with the following steps.
    1. Loosen (without removing) all fasteners retaining your Planks and Mounting Rails.
    2. Tighten the fasteners securing your Mounting Rails.
    3. Tighten the fasteners securing Planks.

 #3 -- WHOOSHING SOUND (80+kmh) 
A loud 'whooshing' sound can develop when a large volume of air rushes around your cargo or through the confined space underneath the rack. This air turbulence sound tends to grow louder as wind speeds increase. This can be caused by high-speed driving, high winds or a combination of both (driving at 120kmh into 30kmh oncoming winds is effectively the same as 150kmh winds).

SOLUTION --- This issue can be solved effectively in the following ways.

  1. Mount cargo on your roof rack. The cargo changes the flow of air and (in most cases) eliminates the noise associated with high-velocity winds rushing under the rack. We discovered this during our testing and it has been confirmed through numerous customer reports. It seems counter-intuitive, but in some cases mounting something to your roof rack can result in a quieter roof rack experience.
  2. Check that your ROOF RACK (Stealth Air Dam) has been installed properly. This product has been tested extensively and when installed correctly it will deliver a dramatic improvement. However, improper installation can dramatically reduce its effectiveness.
  3. Some Plank combinations/positions produce more wind noise than other combinations/positions. If wind noise persists; try repositioning your Planks or changing your Plank configuration. Moving Planks rearward usually provides the best outcome.
  4. Mount or attach something to the front Plank of your Roof Rack that has an irregular shape (i.e. rubber strips, foam pads, etc.). The irregular shape will disturb the air flowing over your Roof Rack and break up the frequency of the Aeolian Sound.
  5. If you're unsure what is causing your wind noise issue and you have a sunroof, you can perform a small test by venting (not opening) your sunroof. By venting the sunroof, you will disrupt the air flow underneath your Roof Rack. If the 'whooshing' sound is immediately reduced when you vent the sunroof, it indicates your wind noise is most likely caused by high-velocity air flowing through the confined space under your Roof Rack.
  6. Install our WK2 ROOF RACK (Aero). This product was designed to improve aerodynamic performance and reduce the associated wind noise.

IMPORTANT NOTES
Wind Noise can be extremely difficult to control. Small variations can have large effects, for that reason it's important to be detail oriented when performing your installation or when executing the tips above.

It's possible for (2) people with the same vehicle and the same roof rack to have different Wind Noise experiences. These differing experiences can have numerous causes; different items mounted to the front of the vehicle, different driving habits, as well as differences in regional wind patterns. In fact, even changes in humidity can have an effect on Wind Noise.

The factors that affect Wind Noise can change on every drive. Therefore, no two trips will ever be the same; a city drive with 30kmh crosswind, will be different from a highway drive with 20kmh headwind. This means you may not hear any Wind Noise on Tuesday when you drive to work, but then hear excessive Wind Noise on Saturday when you head out on the trails (due to changed weather conditions or different accessories mounted to your vehicle).

When we first started researching the topic of Wind Noise, our engineering team reached out to other engineers in the roof rack industry. Each engineer reported the same thing. No matter what they do, there are a certain number of customers who experience Wind Noise issues. Many of these engineers reported a willingness to accept a certain percentage of issues, saying it is impossible to solve the issue for everyone. Our approach, is to provide customers with a selection of various solutions/tips/products that can be used in various ways (or even in combination) to hopefully solve the issue satisfactorily for every customer.