On the schoolyard of the Leidsche Rijn College, dozens of fat bikes are in the bike shed. Thijmen (14) often sits on a friend’s fat bike. He is not happy about the helmet requirement. “I think it’s a bit nonsense,” he says resolutely. “Otherwise they should also do that with an electric bike, not just with fat bikes. I even think that older people should wear a helmet sooner, because they are more vulnerable.”