It may also be the shoes - they might mean your feet are angled inwards or outwards, which might be putting stress on your knees you're not used to.
Do you have one leg longer than the other? When pedalling do you notice your feet turning inwards or outwards?
@deleted started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
It may also be the shoes - they might mean your feet are angled inwards or outwards, which might be putting stress on your knees you're not used to.
Do you have one leg longer than the other? When pedalling do you notice your feet turning inwards or outwards?