Originally Posted by
box opener
The derailleur has to work harder, which means it need to be pulled harder by the cable and thus it has to do with the cable tension, am I getting it wrong please?
The derailer (proper spelling
) works by "derailing" the chain during shifts. When you are climbing a hill, you have more tension on the chain which means that it takes more force to "derail" the chain to the next cog. With a traditional freewheel and "regular" teeth, the derailer may not be able to push the chain off the cog to the next one, especially if you are trying to downshift, i.e. pull the chain onto a larger cog. The derailer works a bit harder but it's the chain that is really doing the work.
Modern index systems use ramps on the cogs to assist in shifting so that the whole process is smoother and less difficult. When you "click" the shifter, the derailer will start to move and as soon as the chain catches one of the ramps, it moves. A momentary relaxing of pressure on the chain helps. Old unramped cogs will clatter more and you have to put a bit more pressure on the shifter to make it move, which usually results in an overshift.
Generally, modern cogsets have negated the issues of downshifts for bikes. If you click, it will shift.