In most jurisdictions, it is recommended and often legally required to wear a helmet at all times when riding a motorbike, regardless of the speed. The purpose of a motorcycle helmet is to protect your head in the event of an accident or impact, regardless of the speed involved.
Motorcycle accidents can occur at various speeds, and the severity of head injuries can be significant even at lower speeds. The impact of a fall or collision can cause head trauma, which can result in serious or even fatal injuries. Wearing a helmet helps protect against these potential risks and should be worn consistently whenever riding a motorcycle, regardless of speed.
It is worth noting that specific helmet laws can vary between countries, states, and regions, so it's essential to understand the legal requirements in your jurisdiction. However, regardless of legal obligations, prioritizing your safety by wearing a helmet every time you ride is strongly recommended.