A soft roll-up tonneau cover is a popular truck bed cover that provides protection and improves gas mileage. However, over time the vinyl canvas may start to sag and loosen. This not only looks bad, but can lead to leaking and other issues. The good news is that sagging canvas can usually be fixed with some simple adjustments and maintenance. In this comprehensive guide, we will go over several effective methods for tightening canvas and preventing future sagging on your roll-up tonneau cover.
What Causes Canvas To Sag on Tonneau Covers?
Before we dive into solutions, it helps to understand what causes tonneau cover canvas to sag in the first place. Here are some of the most common culprits:
Weathering and UV Damage
Exposure to the elements can take a toll on tonneau canvas over time. The sun’s harsh UV rays will gradually break down the vinyl material, causing it to become brittle and sag. Rain, snow, and extreme temperatures can also wear down the canvas.
If the tonneau cover is not kept tightly stretched across the truck bed, gravity will cause the canvas to gradually sag and loosen. Poor initial tensioning or failure to re-tighten the cover can lead to premature sagging.
The various brackets, clamps, and tension adjusters on a roll-up tonneau cover need to be properly tightened to keep the canvas taut. If any of these fittings become loose, it can result in cover sag.
Loading heavy items on top of the tonneau cover adds outward pressure that can cause loosening and stretching of the canvas over time. Overloading the cover beyond its weight capacity will speed up sagging.
Age and Wear
Even with proper care, tonneau canvas has a limited lifespan and will eventually start to sag as it ages. Years of use, rolling/unrolling, and exposure eventually take a toll on the material.
Now that we know why tonneau covers sag, let’s look at 5 ways to fix it…
1. Adjust the Tension Block
One of the most effective ways to tighten a sagging tonneau canvas is to adjust the tension block. This small block is located at the front edge of the cover and can be tightened to keep the material taut. Here’s how to adjust it:
Locate the Tension Block
When rolled up, look for a small square block attached to the underside of the canvas near the tailgate end. This is the tensioning device.
Loosen or Tighten
There are two common types of tension blocks. A set-screw style can be tightened by turning the screw clockwise using an Allen wrench. On a spring-loaded style, push down to release tension, then shift the block and allow it to click into a tighter position.
Test and Repeat
Roll out the cover and check if the tension improved. If not, repeat the process until the canvas is adequately tightened. Be careful not to over-tighten.
Regularly adjusting the tension block as needed will help stop canvas sag over the long run. Just be sure not to make it too tight or the canvas may tear.
2. Install Mounting Brackets
In some cases, sagging tonneau canvas can be prevented by adding mounting brackets along the top rail of your truck bed. Here’s how they work:
What are Mounting Brackets?
Mounting brackets (or “bed caps”) are rigid strips of plastic or metal that attach along the top of your truck bed rails using clamps or screws.
How They Help
With the tonneau cover rolled out, the upper edge of the canvas fits into the mounting bracket channel. This helps keep the material taut across the bed without sagging.
Getting the Right Ones
Make sure to get mounting brackets specifically designed to work with your truck model and tonneau cover brand. Measure the bed rail width first.
Attach the full length of both mounting brackets tightly and evenly to maintain consistent tension. Follow the manufacturer’s instructions.
Installing good mounting brackets can provide long-lasting sag prevention by holding the canvas edges in place. Just don’t make them so tight that the cover binds when unrolling.
3. Use a Support Bar
For tonneau covers with severe sagging in the middle of the canvas, a support bar may be needed to keep things tight and prevent pooling of water.
What is a Support Bar?
This is a rigid bar that traverses the width of the truck bed under the cover. It props up the sagging canvas in the center.
Where is it Installed?
Position the support bar about halfway down the length of the bed for optimal sag support. Use the holder clamps on the bottom of the cover.
Extend the telescoping support bar until it provides enough upward tension to make the canvas taut. But don’t overdo it.
Test that the support bar is still exerting the right amount of pressure on the underside of the cover. Adjust as needed.
A sturdy support bar is an easy DIY solution for fixing tonneau covers with severe mid-canvas sag. Just take care not to overtighten it.
4. Clean and Condition the Canvas
An important part of maintaining any tonneau cover and preventing sag is regular cleaning and conditioning. Here’s how to care for the canvas:
Use the Right Tools
Clean the canvas with a soft wash mitt, sponge, or brush. Avoid harsh bristles. Use a vinyl protectant, not household cleaners.
Aim to clean the tonneau every few months. This prevents dirt buildup that can abrade the canvas and make it sag.
Roll Up When Wet
Never roll up the cover when the canvas is still wet. The moisture can cause mildew and stretching when stored.
Condition After Washing
Once fully dry, apply a vinyl conditioner to protect, restore, and maintain proper flexibility of the canvas.
Examine the fabric binder edges for wear or fraying. This can cause loosening. Reseal if needed.
Proper canvas care and conditioning will maximize the life of your cover and minimize any loosening or sagging over time.
5. Check for Loose Fittings
It’s also important to periodically inspect all of the various clamps, screws, brackets, hinges, and tension adjusters on your roll-up tonneau cover. Here’s what to look for:
Make sure the canvas buckles and straps at the tailgate are tightly secured. Loose buckles can lead to major sagging.
Check that the clamps securing the cover to the side rails of the truck bed are tight enough. If clamp teeth are worn, replace them.
Be sure the hinge springs or tension knobs that hold the rolled cover closed are adjusted properly to avoid sagging at the front.
Incorrectly aligned or bent side rails will prevent proper tensioning and lead to canvas drooping. Have these inspected if concerned.
Look for any missing or broken brackets, screws, or parts that may be affecting the cover’s fit and ability to stay taut.
Tightening loose or worn fittings is key for keeping canvas as tight as the day it was installed. Identifying and replacing broken parts also helps.
That covers 5 great tips for fixing a sagging tonneau cover canvas and keeping it nice and tight for years to come! With some simple adjustments and proper care, you can get rid of annoying canvas sag and prevent it from coming back. Your truck will look like new again in no time.