The author knows of no pleasant way to bike directly north or northwest out of Paris.  You have to ride on major arteries, choked with traffic, and/or venture onto the back streets of poor, not always welcoming suburbs.

            The best way to reach the northwestern or northern countryside is by train to town more than 40 kilometers from Paris. Meulan, Mantes-la-Jolie, Chars, Gisours, L'Île-Adam, Boran-sur-Oise or Chantilly are possibilities.

            If you are determined to bike directly northwest or north from Paris, you should leave very early in the morning, when there is almost no traffic. Or, take a  circuitous route from the northeast (#1) or west (#6). This will add 25 kilometers to your route, but you will feel calmer and more secure..