Fear is best conquered incrementally in small steps. As mentioned above, select a safe place to practice for 5-10 minutes, or whatever you feel comfortable with. Gradually raise your time on the bike while you also start to move from your secure practice area to a multi-use trail or similar. Each step you take and master, give yourself a pat on the back. Reflect on what you did well and on areas to improve. Fear can be used to your advantage since if you think of conquering it as a challenge to overcome. By taking small measured steps, you eventually will be able to look back and say, that really was easier than I expected.
Best wishes.
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Road 🚴🏾♂️ & Mountain 🚵🏾♂️