A roll-up tonneau cover is a popular truck bed cover that rolls up for easy access to the truck bed. It is made of vinyl canvas stretched over a metal frame. Over time, the canvas can start to sag in places, creating an unsightly appearance and allowing water to pool on the cover. Fixing a sagging canvas tonneau cover is possible with some simple adjustments and maintenance.
What Causes the Vinyl Canvas To Sag on a Roll-Up Tonneau Cover?
There are a few key reasons why you may experience canvas sagging on your roll-up tonneau:
Weathering and Use Over Time
Like any fabric exposed to the elements, your tonneau cover vinyl will gradually wear out over years of use. UV rays from the sun, dirt, debris, and simply rolling and unrolling it hundreds of times will cause it to lose elasticity and start to sag.
If the canvas was not stretched tight enough or evenly across the rails during initial installation, this can lead to premature sagging and loose spots. Any installation errors like rails not being straight or brackets not properly shimmed can also cause issues.
Any damage or bending of the metal rails, bows, and support bars that make up the framework underneath the canvas will often result in canvas sag. Damaged or loose framework components reduce the firm foundation needed to keep the canvas taut.
Normal Wear After Long-Term Use
Even with proper installation and care, manufacturers only expect tonneau canvas to last around 5 years before needing replacement. So sagging due to simple age after half a decade of use is common.
How Can I Tighten My Tonneau Canvas to Remove Sag?
If your vinyl canvas tonneau is only slightly sagging in a few spots, you may be able to tighten it back up and eliminate the sag. Here are some methods to try:
Adjust the Tension Knobs
Many roll-up tonneau covers have tension knobs integrated into the side rail covers. Look along the rails for any knobs or screws you can tighten to provide more tension. Simply turn them to draw the canvas tighter.
Tighten the Tension Block
Releasing the latch and rolling up the cover can expose the tension block or spring mechanism. The tension block applies downward force to keep the canvas taut. Use a wrench or screwdriver to tighten the tension bolt and reduce sag.
Ensure Even Rail Alignment
Check that both rails are straight and aligned evenly front to back. Misaligned rails twist the canvas unevenly, causing sagging. Loosen the rail mounts and nudge the rails into proper alignment before retightening.
Adjust Bow Brackets
Examine the bow brackets that hold the crossbows underneath the canvas. You may be able to shim or adjust them to better support the bows and tighten up sagging spots on the canvas.
Have a Helper Lift While You Tighten
It can help to have someone lift up on the canvas while you work underneath to tighten tension components. This takes the weight off while you make adjustments.
Roll Up Small Objects Under Canvas
For quick temporary tightening, park with the tailgate down and roll up small objects under the sagging vinyl to press it upward slightly. Items like towels or t-shirts rolled tightly will work well.
What If My Canvas is Too Damaged or Stretched Out To Tighten?
If your tonneau cover canvas is very old and stretched out, or is damaged in certain areas, attempts to tighten it may be futile or only provide a temporary fix before sagging again. Here are your options if the canvas itself is unsalvageable:
Replace Just the Vinyl Cover
You may be able to order just a replacement vinyl cover from the manufacturer, which can be installed over your existing aluminum frame. This is preferable if the frame itself is still in good shape. Installation can be DIY or professional.
Install a New Cover
For older covers with damage beyond just canvas, or unusual sizes, you may need to purchase an entire new replacement tonneau cover. Look for an upgraded version or a different brand for the best fit and long term durability. Professional installation is recommended.
Try a Tonneau Cover Support Kit
Some companies sell support pole kits that attach to the underside of the tonneau cover framework. They are adjustable and help support and tighten sagging covers. This can extend the life of a worn cover.
Remove the Cover
If funds are limited and you can live without a tonneau for awhile, you can simply remove it until you are able to purchase a replacement. Just be sure to store it properly indoors if planning to reinstall the old cover later.
How Can I Help Prevent My Roll-Up Tonneau Canvas From Sagging?
While some sagging over years of use is inevitable, you can take steps to preserve your canvas tonneau cover and prevent premature sagging:
Keep it Clean
Wash the vinyl canvas often with truck soap and water to prevent dirt and debris from degrading the fabric. Park in the shade to limit sun exposure.
Avoid Leaving Unrolled When Not in Use
Don’t make a habit of driving with the cover open and canvas exposed for long periods of time. The flapping and vibrations can damage the material.
Inspect and Tighten Components
Periodically check all clamps, tension bolts, and rail mounts. Tighten any that have loosened over time before sagging occurs. Keep bow brackets properly shimmed.
Try not to let the canvas slam down or bang around during every opening. Carefully roll it up and down to prevent damage.
Condition the Vinyl
Using vinyl conditioners and protectants can extend the life of the canvas. Helps protect against UV rays and prevents drying and cracking.
Install Properly From the Start
Making sure the cover is stretched perfectly evenly across the bed rails during first installation will minimize early sagging issues.
What If I Need To Fully Dismantle My Tonneau to Fix Sagging?
If adjusting tension components and replacing canvas has not fixed a sagging tonneau cover, the last resort is to completely remove it and take a look at the underlying frame components. Here is how to dismantle a roll up tonneau:
How Do I Remove the Aluminum Side Rails?
- Release all clamps securing the rails to the truck bed.
- At the front, detach any header seals covering rail edges.
- Remove any lock rods or crossbar retainer rods if present.
- Support each rail as your remove mounting screws along the length.
- Carefully lift each rail and remove from the vehicle.
How Do I Take Off the Crossbows and Brackets?
- With side rails removed, unscrew the bow brackets from the bed.
- Label each bow and bracket so you can reinstall in the same locations.
- Beneath the canvas, find any bow couplers or connectors and disconnect.
- Carefully bend back the canvas from each bow, then lift out and remove.
Can I Make Repairs and Improvements Now?
With everything taken apart, you can now make fixes such as:
- Straightening bent aluminum components
- Shimming/adjusting brackets
- Replacing broken or cracked parts
- Trimming bows to better fit brackets
- Ensuring even spread across bed
Reassembling properly should allow the canvas to be stretched tightly without sagging. Be sure to refer to the manufacturer’s instructions for your specific tonneau during disassembly and reassembly. Taking the cover entirely apart is time consuming but allows for a full repair.
Sagging canvas on a roll-up tonneau cover may seem like an annoying issue, but in most cases it can be fixed with some simple adjustments to tensioning components or rail alignment. For older covers with excessive wear, replacing just the vinyl canvas or the entire cover is likely needed. With proper care and maintenance, you can maximize the lifespan of your tonneau cover and prevent premature sagging.
Check all clamps and hardware regularly, condition the canvas with protectants, and avoid letting the material flap unnecessarily. And if sagging does occur, use the tips in this article to troubleshoot the problem and restore that clean, tight look to your truck bed cover.