If you’re cycling part-way, many stations on the Gatwick route have bike parking
https://jeffreyizjt394.raidersfanteamshop.com/central-london-to-gatwick-airport-late-night-and-early-morning-travel-2
If you’re cycling part-way, many stations on the Gatwick route have bike parking. Leave your bike securely and continue by train to avoid busy airport road traffic.