Do I need to tighten the nut on the valve against the rim?

This applies to when you are running inner tubes.

The outer nut sits on the rim surface and winds around the inner tube valve’s thread. It keeps the tube’s valve from disappearing into the rim.

Here at Two Tyres, the way we do it is to use a 12mm spanner on that outer nut and to tighten it up until it’s hand tight. We’re talking Mr Muscle not Hulk Hogan.

The reason being that you then have a little bit of float on the tube and valve and you won’t wring the valve right out of the inside of the rim, potentially tearing the tube, causing deflation.