Paul Janiak explains how one innovative company is using a new technique to create durable e-scooter frames
A new approach to sheet metalworking in stainless steel has been developed by Swedish e-scooter startup Stilride to bring style and sustainability to two-wheeled transport.
As lifelong scooter enthusiasts, Stilride’s founders, Jonas Nyvang and Tue Beijer were excited by the growing popularity of e-scooters. However, they realised that there was huge untapped potential to develop a new breed of e-scooter with a design that harnessed aesthetic appeal, as well as integral sustainability.
Currently, market-leading e-scooters are built on a chassis made from carbon steel tube, with the addition of external bodywork and components in multiple types of plastic and rubber. However, this leaves a lot to be desired in terms of looks, as well as sustainability. While it keeps the price down, it’s hard to make a polymer shell into a design classic, and the mixed plastics are hard to recycle. In addition, the carbon steel tube has a high environmental impact and is vulnerable to corrosion, which limits the e-scooter’s life.
Therefore, when developing this alternative e-scooter design, Stilride put the circular economy and carbon footprint at the heart of its design choices. Its CEO, Jonas Nyvang, explains: “Many people are unaware how much manufacturing contributes to the environmental impact of the products they buy. We knew that our manufacturing process had a clear environmental lead over the market-leading electric scooter from China. Therefore, we decided to quantify it.”
Instead of the usual approach of using tubes to build a frame, Stilride has developed a new design and manufacturing technique called Stilfold. It is inspired by origami, where sheets of paper are folded to form complex and curved three-dimensional shapes. However, instead of fingers and paper, the startup uses industrial robots to precisely control the bending and shaping of stainless steel sheets.
The technique was developed with support from stainless steel producer Outokumpu. It had been researching a related metal forming process in the early 2000s and shared the output of this with the startup after a chance meeting at a technology networking event.
Paul Janiak, Outokumpu’s R&D manager for design and fabrication says: “We’re always keen to promote the use of stainless steel, so we were pleased to share our experience to help Stilride take the concept forward.”
The Life-Cycle Assessment
The result is an e-scooter design that makes the most of stainless steel, according to Nyvang: “With Stilfold, we are using high-strength stainless steel to create a design statement and a structure in one. The result is a simple, lightweight and corrosion-resistant chassis with fewer components – and a smaller environmental footprint. We commissioned a life-cycle assessment (LCA) so that we can quantify the carbon footprint and compare it with a conventional e-scooter.”
The LCA was developed by the Swedish Environment Institute (IVL). It provides a comparison of the environmental footprint of the materials needed to build and transport the two scooter chassis. It only covers the chassis, so IVL could exclude components that are identical (or almost identical) to both models, such as batteries and motors. It also excludes the energy used during manufacture, as that data was not available to the study.
The initial finding of the LCA was that the materials used in a Stilride Sports Utility Scooter One have a carbon footprint of around 50kg CO2. That is a significant saving compared with 160kg CO2 per chassis for the reference scooter.
Strength For Lightweighting
One of the reasons for this impressively low carbon footprint is the choice of a high-strength alloy – Outokumpu’s Forta 301 temper-rolled stainless steel sheet. The process of temper rolling creates a work-hardening effect that gives high mechanical strength compared with other steels.
As a result, the first prototype of the Sports Utility Scooter One chassis can carry the same rider using less structural material, making it lightweight, at only 15kg of the bike’s total 80kg weight. In comparison, the reference scooter has a 45kg chassis and weighs 110kg overall.
Commenting on this, Nyvang says: “Lightweighting has multiple advantages; the most noticeable for riders being the better acceleration and ride quality. However, it also improves the range and preserves battery life. The 30kg saving on the weight of the scooter plus its rider will reduce energy consumption by a respectable 5%.
“In the longer term, it creates an opportunity for scooters for city deliveries and logistics fleets that can carry 30kg more payload than other bikes, something we’re looking to develop in the future.”
A further benefit is that the chassis also has fewer components than a conventional scooter (around 20 compared with 150). In turn, manufacturing and logistics chains become simpler, and there is less need for complex sourcing of components and subsystems from different manufacturers.
Riders also benefit, as it’s easier for them to carry out maintenance on their scooter.
Recycling To The Rescue
Another important benefit of the use of stainless steel is the circular economy. Stainless steel is the ultimate recyclable material. A study by Yale University found that 85% of stainless steel is recovered as scrap metal at the end of its life, and it can be processed and resmelted over and over again without affecting quality. However, only 44% of new stainless steel is based on recycled scrap.
According to Camilla Kaplin, Outokumpu’s senior manager – environment, recycling makes a huge difference to the carbon footprint. Using one tonne of recycled austenitic scrap material instead of virgin iron ore avoids the emission of 4.3 tonnes of CO2.
She says: “At Outokumpu, we have the lowest carbon footprint in the stainless steel industry. We base more than 90% of our production on recycled materials and our Tornio mill in Finland is home to Europe’s largest recycling centre. We also purchase low-carbon electricity and use energy efficiency programs to minimise our carbon footprint.
“We publish a set of Environmental Product Declarations (EPDs) on our website so that our customers can compare our environmental performance with other producers. They can also use our data to calculate the environmental impact of their own products and services, with IVL’s lifecycle assessment of Stilride’s chassis as an example.
“Typically the data in an EPD is valid only for a certain period of time, usually up to five years, so as we update and revise our EPDs, they will reflect our ongoing efforts to decrease our carbon footprint. Last year we renewed our CO2 reduction target, and set a new, even more ambitious long-term goal.
“We intend to decrease our carbon footprint by 30% between now and 2030, which corresponds to a reduction of 42% compared with our baseline years 2014-2016. To achieve this we are initiating a number of projects, from switching to low-carbon fuels to investing in new low-emission cargo ships to transport products between Tornio and our distribution hub at Terneuzen in the Netherlands.”
LCA Analysis Over 10 Years
While IVL found that Stilride’s scooter has a lower environmental footprint from day one, the LCA also compared the two scooters’ emissions over one year and 10 years on the road. This was calculated by taking into account energy used to charge the batteries for driving the average European annual mileage of 5,800km.
The study found that the emissions from riding form the bulk of the lifetime emissions from both scooters. When they roll off the production line, the reference scooter’s footprint is more than three times Stilride’s at 160kg versus 50kg CO2. However, the gap widens over time due to Stilride’s lightweighting advantage. After 10 years, the footprints have become 1,030kg versus 890kg CO2.
So, while the reference scooter may have narrowed the gap in terms of percentage, Stilride has extended its lead in raw numbers.
Nyvang comments: “Over 10 years, both scooters consume a similar amount of energy for riding, meaning that, at a glance, it looks like the competition narrows our environmental lead – but they can never catch up.
“Being a Swedish company, we also wanted to check the impact of our energy mix compared with the European average. Sweden is rich in clean energy such as hydropower, therefore our electric power grid has an unusually low carbon footprint.
“When we looked at the impact of this energy mix over a 10-year life, we found that in Sweden, the typical rider for the reference scooter would have a climate change impact 80% higher than that of a Stilride customer. It’s an interesting point as it highlights how renewable energy influences the overall impact of driving any type of electric vehicle.”
Avoiding The Rust
The final sustainability advantage of using stainless steel is corrosion resistance, which is provided by alloying elements that form a microscopically thin protective layer on its surface. This prevents the iron in the steel from oxidising and even reforms immediately when scratched.
Kaplin comments: “Producing stainless steel is energy-intensive as we need to smelt steel, but it can be seen as an investment in energy. Yale University’s study found that products made from stainless steel have an average lifespan of 20 years, and often much longer. One famous example is the spire of the Chrysler Building in New York, which has remained pristine ever since it was built in the 1920s.”
In contrast, the carbon steel reference scooter will corrode much sooner, while the stainless steel bike remains pristine. Over the bike’s life, its rider will switch out motors, batteries, lights and accessories while keeping the original sheet metal structure.
It’s impossible to give an accurate estimate of how long either scooter will last as that depends on many factors such as humidity and salt in the air. However, stainless steel’s corrosion resistance will ensure it lasts much longer. Therefore, the sustainability advantage calculated by IVL could be just the tip of the iceberg in terms of its whole-life carbon footprint.