The BIG BOX has become the must-have accessory for many Vespa GTS and GTV enthusiasts. By replacing the narrow original under-seat bucket, it provides a unique storage upgrade to easily fit your helmets (jet, full-face, or modular) while preserving the iconic lines of your scooter without the bulk of a Top Case.
However, a few users have occasionally reported an issue: the bottom of the storage box seems to rub or hit against the engine block during heavy compressions. Our partner Robert, from the YouTube channel Scooter 47 United, looked closely into this matter in his latest video.
His conclusion is clear: the issue does not come from the product itself, but from a wrong adjustment or wear of the rear shock absorbers! Let’s dive into the mechanics and solutions to restore optimal riding comfort.
The Feedback from Scooter 47 United: A Revealing Road Trip
Robert and his wife just returned from a trip to Tuscany, a beautiful region but well-known for its severely damaged roads. Equipped with our under-seat storage solution, they fully enjoyed the extra space daily, whether throwing in some groceries or storing their travel gear.
If you remember their first BIG BOX video test, they were already won over by the gained space. This journey on rough Italian roads only confirmed their excellent first impression. Despite potholes and bumpy roads, they experienced absolutely no rubbing issues. Why? Simply because their Vespa's rear suspensions were properly adjusted and adapted to the load.
Understanding the Mechanics: What Is Negative Travel (Sag)?
To understand why your under-seat box might come into contact with the engine, we need to look at how your rear shock absorbers work.
Suspensions have two major roles: guaranteeing a comfortable ride, but above all, ensuring safety by keeping the rear tire in permanent contact with the road, no matter the imperfections.
To achieve this, a suspension must be adjusted taking into account the negative travel (commonly known as sag or Negativfederweg in German):
- The Theory: When your Vespa is on its wheels with no one on it, it sits at its maximum height. As soon as you sit on the saddle, the scooter should compress slightly (about 10 to 15% of the total travel, which is roughly 1 cm on a Vespa).
- What is it for? This margin allows the rear wheel to drop and "follow" the road profile when passing through a dip or a pothole, preventing the scooter from losing grip or bottoming out brutally.
The Direct Link with the BIG BOX
Our device maximizes the available space under the seat to give you the largest possible storage volume. As a result, the clearance between the bottom of the box and the engine is tighter than with a stock Vespa bucket.
If you carry a certain weight, ride frequently with a passenger, or if your suspensions are set to the softest position (often the default factory setting):
- As soon as you get on the scooter, the suspension already compresses by several centimeters, eating up a large portion of your useful travel.
- At the slightest bump or speed hump, the shock absorber reaches the end of its stroke (it bottoms out).
- This is exactly when the engine moves too high up and hits the bottom of the storage box.
How to Fix the Issue?
The solution is simple, quick, and free: adjust the preload of your stock shock absorbers!
On the original rear shock absorbers of your Vespa GTS or GTV, you will find a silver notched ring at the base of the spring. Using the specific wrench provided in your scooter's tool kit, you can turn this ring to compress the spring (moving from position 1 to position 3 or 4, for example).
Important technical note: Increasing the preload does not make the spring "stiffer" itself. It simply raises the rear ride height of the scooter under load to preserve all the necessary travel required to absorb road bumps.
How to Measure Your Suspension Sag:
- Have a friend hold your Vespa straight up (off the stand).
- Measure the height between a fixed point on the rear bodywork and the ground.
- Sit on the scooter with your usual riding gear (and your passenger if you often ride two-up).
- Take the measurement again at the exact same spot: the scooter should only drop by about 1 cm. If it drops more than that, tighten the preload.
What If My Shock Absorbers Are Worn Out?
If the issue persists despite adjusting the preload to the maximum setting, your shock absorbers are likely worn out. Robert points out that after 25,000 km (around 15,000 miles), stock shock absorbers significantly lose their hydraulic efficiency.
Investing in a pair of quality aftermarket shock absorbers (such as the BGM sport series) completely transforms your Vespa's handling. As many riders state, upgrading or properly tuning your suspension feels like riding a "brand new scooter": more stable, more precise, and infinitely safer in corners.
Conclusion
The BIG BOX is designed to offer uncompromised storage convenience for your daily rides. To enjoy it fully and safely, take 5 minutes to check and adjust your rear suspensions. Your back, your handling, and your scooter will thank you!
💡 Read Also: Do you own one of the latest models or want to optimize your comfort even further? Check out the full BIG BOX test on the Vespa GTS 310 and the Kit BIG BOX + conducted by our collaborator Ozett!
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