Tern GSD

Strength is Safety: How We Tested the GSD

If you own a GSD—or have looked into getting one—you’ve probably heard about the GSD’s 200 kg Maximum Gross Vehicle Weight (MGVW). Admittedly, we have a habit of boasting about it. You may have even tested it out yourself with an extra-heavy load once or twice.

But what do we mean when we throw that number around? Why do we feel confident sharing it with riders who carry their families, themselves, and sometimes their livelihoods on the GSD?

To put it simply, it means we’ve put the GSD through rigorous testing to prove that it’s safe and reliable up to the claimed load limit.

In this article, we’ll explain how that process happens. By the time you’re done reading, we hope you’ll understand what goes into our claim that the GSD can safely carry your most precious cargo.

Planning for a Heavy Capacity from the Start

Creating a durable e-bike capable of hauling massive loads requires careful planning from the earliest stages. We start by defining the limits under which the bike will operate, including:

  • The bike’s cargo capacity,
  • The maximum weight of the rider (120 kg [264 lb]), and
  • The terrain where the bike is permitted to be used.

With these limits in mind, we use specialized software to simulate the stresses we expect the bike’s frame and fork to face. The software helps get us in the right ballpark before we start making real prototypes.

Next, we make and ride a series of prototype bikes. We typically put a few thousand miles on these, making improvements with each new prototype design.

After this lengthy iterative design process, we begin lab testing the frame and fork to ensure that they can withstand the forces associated with the claimed weight capacity. We perform multiple rounds of internal testing on-site at our factory using the relevant testing standard (more on that later).

During internal testing, we generally try to "test to destruction" to identify the weakest parts of the frame or fork. However, a few of our recent frames have just been too strong for that—and at that point, our lab turns the machines off.

Next, it’s time to move on to even more demanding testing at an external laboratory.

Reputable Third-Party Testing for Peace of Mind

We work with EFBE Pruftechnik, a German company that is an international leader in bike durability testing.

EFBE testing simulates hundreds of thousands of cycles of multi-directional stress to the bike’s frame and fork. For example, one testing station simulates pedaling forces, while another simulates braking forces.

The EFBE testing protocol truly takes the bike’s frame and fork to its limits using a relevant testing standard.

A New Cargo Bike Testing Standard Sets the Bar

A rigorous and comprehensive German standard for cargo bikes was finalized in 2020. The new standard accounts for usage differences between cargo bikes and city bikes. It aims to ensure that cargo bikes are safe and reliable under heavy load. The standard factors in a cargo bike's claimed load as well as its weight and geometry.

That means the testing for a cargo bike that claims a capacity of 120 kg vs. 140 kg vs. 200 kg is drastically different, which makes sense since the forces applied to the fork and frame increase dramatically with increased gross vehicle weight.

Pushing the Limits with the EFBE Tri-Test

The founder of EFBE was one of the principal authors behind the new German standard. Using findings from the standard drafting process, EFBE has developed its own custom testing protocol for cargo bikes called the Tri-Test

The GSD has already passed EFBE’s Tri-Test up to the claimed load limit, which means it meets the requirements of the German cargo bike standard.

To understand how tough the Tri-Test really is, let's compare the Tri-Test with the testing protocol for ordinary commuter bikes.

The EN Ciy/Trekking Bike standard, a European standard for ordinary city bikes, requires a single test condition for all bikes, with no adjustments for different usage scenarios.

But since the heavy loads that cargo bikes carry change and magnify the forces on the bike's frame and fork, the German cargo bike standard requires test forces that scale with system weight (meaning the weight of the bike, rider, and any cargo or passengers). This scaling makes EFBE's Tri-Test—which is based on the German standard—much more rigorous than testing for ordinary city bikes.

The Tri-Test includes 10 demanding stress tests using forces proportionate to the bike's claimed load. One single frame must pass all 10 tests—so any damage to the frame or fork caused by one test will carry over to the remaining tests.

Knowing just how intense the Tri-Test process is gives us peace of mind that the GSD and HSD are fit for use. For instance, the amount of stress applied in one of our GSD fork tests was over 300% greater than the amount applied to a fork in the EN City/Trekking Bike test.

Why does that matter? Imagine the amount of braking force applied by a strong disc brake when trying to slow a 200 kg vehicle—the fork must be designed properly to be safe in those conditions (and as you can see from the GSD, you end up with a pretty burly-looking fork!).

GSD frame and fork

Testing the Rack for Strength and Stiffness

Beyond a bike’s frame and fork, racks also have weight capacities. And there is a European test standard for racks to test their strength.

But we find that this standard isn’t comprehensive enough. Just because a rack is strong enough to support a certain weight doesn’t mean that it’s stiff enough to prevent uncomfortable and unnerving sway while you ride. You don’t want to feel sway when you’re threading between cars in traffic, and your child on the back rack moves slightly.

So when we give a weight limit for a rack, it means that we’ve already tested the rack at the claimed weight capacity (and then some) using the European standard plus we’ve done hundreds (or thousands) of kilometers of ride testing to ensure that the bike is comfortable and safe when the rack is fully loaded.

That's how we know it's safe to load up the GSD's back rack with tons of cargo, as long as the bike's total MGVW is observed.

Do all cargo bikes undergo this kind of testing?

Some do, but many don’t.

In the bicycle industry, companies are only required to self-certify that their bikes meet certain safety standards. But the lack of a standard for cargo bikes has made this hard for cargo bike companies. In fact, most standard test machines can’t even accommodate a long cargo bike.

The cargo bike companies that are committed to testing devise their own custom tests that require them to make custom jigs with companies like EFBE.

It’s a costly and time-intensive process, but we think ensuring the safety of riders and passengers is more than worth it.