If you’ve ever driven your pickup truck on the highway with a tonneau cover installed, you may have noticed it starts to billow up and flap around at higher speeds. This can be annoying, damaging to your cover, and potentially unsafe. But what causes this phenomenon? Here’s a deep dive into why tonneau covers billow at highway speeds and what you can do about it.
What Is Causing The Lift On My Tonneau Cover?
When your truck reaches highway speeds, there becomes a difference in air pressure between the air flowing under the tonneau cover and the air flowing over it. This difference in pressure leads to lift, which makes the cover billow upward.
This is the same principle of physics that allows airplane wings to generate lift for flight. As the wing moves through the air, the airflow above it must travel farther than the air below it. This difference in distance traveled results in lower pressure above the wing and higher pressure below it. The pressure differential creates an upward force called lift.
So just like an airplane wing, when air flows over your tonneau cover faster than it flows underneath, it creates an area of lower pressure on top. This causes lift, making the cover billow up.
What Speed Does A Tonneau Cover Start To Billow?
Most tonneau covers will start to billow somewhere between 50-70 mph. However, the exact speed depends on several factors:
The Style Of Tonneau Cover
- Roll-up covers – These vinyl covers are the most prone to flapping at highway speeds. Less than 50 mph may cause billowing.
- Folding covers – More rigid than roll-ups, but still susceptible to flapping above 50 mph.
- Retractable covers – With their tight integration, they can withstand higher speeds of 60+ mph before billowing.
- Hardshell covers – Most resistant to air pressure billowing due to their solid, seamless construction.
How Well The Cover Is Installed
A cover installed loosely with uneven tension across its surface will billow at lower speeds. Proper installation creates an evenly taut cover that can better resist air pressure.
The Truck’s Speed
The faster you drive, the more likely the tonneau cover will billow upward. Even hardshell covers can flap at speeds over 75-80 mph.
Gusty, windy days can cause tonneau covers to billow at lower speeds than normal. Strong crosswinds are especially problematic.
Is It Bad For My Tonneau Cover To Billow?
Moderate billowing of your tonneau cover at highway speeds is not necessarily harmful. But over time, flapping can cause issues including:
- Premature wear or cracking – The repetitive bending and stress can damage vinyl and other cover materials.
- Delamination – The outer layer of the cover can separate from inner backing.
- Loosening – Constant wind lift works against the cover’s attachments, slowly loosening them.
- Cargo shifting/falling out – Flapping covers won’t secure cargo as well.
- Noisy rumbling – Annoying noise and vibration inside the cab at higher speeds.
So while occasional billowing won’t immediately destroy your cover, the long-term effects make it best to minimize flapping whenever possible.
How Can I Prevent My Tonneau Cover From Billowing On The Highway?
Here are some tips to reduce highway billowing and flapping of your tonneau cover:
Ensure Proper Installation
Carefully follow the cover manufacturer’s instructions to install it evenly and securely. This provides optimal tension across the entire surface. Periodically check for loose screws or cloth.
Tighten The Cover
Many covers have tension adjusters at the tailgate you can incrementally tighten to remove any slack in the material. Start with the factory settings, then tighten more if needed.
Use A Support Bow
For roll-up covers, a support bow installs above the cover to add a centered contour. This shape provides more wind resistance. Just don’t leave it on when rolling up the cover!
If your speed is causing extreme billowing, reducing by 5-10 mph may help minimize flapping. But keep with the flow of traffic.
Restraining cargo like dirt bikes on top of the cover can help weigh it down. Or ratchet straps across the cover increase downward force. But weight limits still apply.
Buy A Rigid Tonneau Cover
Hardshell covers offer the most wind resistance and ability to drive at higher speeds without billowing. Low profile designs are best for cutting through the wind.
Use Side Storage
For severe billowing, storing gear in bedside storage boxes reduces wind resistance compared to central cargo. But you lose bed space.
Remove The Tonneau Entirely
If your cover billows excessively and you want to drive at high speeds, taking it off completely prevents any flapping. Just store it securely at home.
When Should I Replace My Billowing Tonneau Cover?
If your cover flaps constantly, even at moderate speeds, it may be stretched out and need replacing. Signs your cover is too far gone:
- The material has cracks, holes, or permanent creases
- It won’t stay tightened and lays loose across the bed
- The cover has partially separated from its frame/bindings
- Driving without billowing requires going much slower than other traffic
- It lets in a lot of dust/debris due to poor sealing
While cover treatments like vinyl conditioners can help, once the material loses its integrity, replacement is the permanent solution. Measure your bed size and order an upgraded replacement cover that better withstands air pressure.
Will Adding A Topper Help Reduce Tonneau Cover Billowing?
A truck topper or camper shell creates a smoother aerodynamic profile compared to an exposed tonneau cover and cargo. This can help break up the difference in air pressure and resistance that leads to billowing covers.
The sloped rear window and caps on the topper disrupt the air, allowing air to flow more evenly over the tonneau cover. However, toppers are only a partial remedy and billowing may still occur at high speeds.
The gap between the topper and cover can also create turbulence if items in the bed protrude above the cover. But for certain covers like soft roll-ups, a topper can help minimize flapping by eliminating the gap.
Should I Remove My Tonneau Cover When Towing?
If your tonneau cover already billows a lot at highway speeds when not towing, it will only get worse when towing a trailer. The added aerodynamic drag makes air pressure and turbulence behind the truck much more severe. This can cause even rigid covers to flap violently.
Removing the tonneau before towing prevents flapping and the cover being possibly ripped off or damaged. But it also leaves your cargo exposed. For high value gear, it may be better to leave the cover on and drive slower. Or detour trailering duties to a vehicle without a cover.
Just take care not to exceed the tonneau’s speed rating when towing, typically 65-75 mph. Installing tie-downs may also help stabilize the cover if keeping it on.
Will Adding A Bed Liner Help Stop My Cover From Billowing?
Bed liners help protect your truck bed from damage, but they generally don’t do much to reduce tonneau cover wind flapping. The small textured surface of spray-in liners isn’t enough to significantly disrupt airflow. Other smooth types like drop-in plastic liners don’t affect the wind resistance at all.
However, adding a bed liner can provide these billowing benefits:
- Prevents long-term wear/chafing of cover undersides against the bare metal bed
- Creates a more even surface to mount the cover for better hold-down
- Adds protection if cargo shifts under a flapping cover at speed
So while liners don’t directly stop the billowing itself, they make the installation more secure and can mitigate some of the potential damage from a flapping cover in the long run.
Will Putting A Toolbox In The Truck Bed Help Reduce Billowing?
Mounting a toolbox against the front of the bed can potentially help minimize tonneau cover flapping at speed. The box serves as a barrier that smooths and redirects airflow over the cover.
This is most effective for covers that don’t attach at the bulkhead. A secured toolbox divides the bed into two sections. Air flows over the box, then the cover’s mid-section billows, before air pressures re-stabilize at the tailgate end.
But for covers secured at the bulkhead, toolboxes have less impact. Air still flows evenly over the entire cover. The box may reduce mid-bed billowing, but flapping still occurs towards the rear.
In either case, ensure the toolbox contacts the cover evenly with no gaps for air to penetrate. And don’t overload a toolbox so weight negatively impacts cover attachment.
The Bottom Line On Billowing Tonneau Covers
A tonneau cover billowing at highway speeds is a nuisance but typically not a major issue if it happens only occasionally. Make sure your cover fits tightly across the bed and tighten or replace it if the material loses integrity.
Driving a properly secured rigid cover at moderate speeds will minimize air pressure lift and flapping. But at 75+ mph, even premium covers run into the laws of physics, so slow down and be prepared for some billowing.