A multitool is a highly versatile piece of repair equipment that can address most of your maintenance needs. Ideally, you should use it before a ride to tighten and adjust everything properly, but sometimes it’s necessary on a ride as well. If you encounter a loose screw, realize your saddle height is not right, or that your brakes need tightening, you will be happy to have it.
Friction gear systems are a lot simpler to adjust, because the movement of the derailer cable can be modulated as you ride, every time you change the gear- they require less cycle maintenance. Modern index shifting systems are a little more complicated because each ‘click’ must release the exact right amount of cable to allow the derailer to move the correct distance to move the chain from one gear to another. Setting up and adjusting a derailer is not difficult and requires only basic tools, but there is a methodical procedure to follow.