I always wore a helmet on longer or faster motorway journeys, not so much for safety as comfort. There was a speed range that caused some involuntary head movement in the airflow (and I'm not tall) but easy to go faster
Richard
2018 Roadster 3.7 1966 Land Rover S2a 88 2024 Royal Enfield Guerrilla 450 1945 Guzzi Airone