Is it better to fill tyres with nitrogen than air?

While pure nitrogen does have some advantages over air for racing car tyres, where pressures are subject to more potential fluctuation due to temperature changes, the use of pure nitrogen for road car tyres is less essential.

Remember that regular air is already 78 percent nitrogen, so paying extra for pure nitrogen (which may not actually be pure nitrogen) would for most people be poor value for money given the imperceptible difference it would make.