Adjust the rear derailleur

Put the bike in the Work stand, or turn it upside down, so you can turn the pedals freely. Shift onto the largest sprocket, stand behind the bike and look along the derailleur: both jockey wheels should line up exactly under the sprocket, in the same plane as the cassette.

If the derailleur leans towards the spokes, the hanger holding it is bent, often after a crash or after the bike was laid down on the wrong side. No adjustment makes up for a bent hanger: have it straightened or replaced before you carry on.

The two small screws marked H and L stop the chain from leaving the cassette. Shift onto the smallest sprocket, then release the cable tension by turning the barrel adjuster. With the Phillips screwdriver (or else Multi-tool), set the H screw so that the upper jockey wheel sits right below the outer edge of the smallest sprocket.

Then move onto the largest sprocket, pushing the derailleur by hand if needed. Set the L screw so the chain climbs cleanly onto the largest sprocket, but the derailleur can never travel further towards the spokes. Screwing a limit screw in restricts travel, screwing it out opens it, a quarter turn at a time.

Go back to the smallest sprocket. Screw the barrel adjusters on the shifter and on the derailleur all the way in, then back them out one turn: that leaves room to adjust both ways. Loosen the cable clamp bolt on the derailleur with the Allen keys (or else Multi-tool).

Pull the cable with the Pliers (or else Adjustable wrench), gently, to take up the slack, then tighten the clamp bolt with the cable sitting in its groove. Shift one gear towards the larger sprockets: if the chain does not climb, there is not enough tension; if it jumps two sprockets, there is too much.

Put the chain on the second-smallest sprocket while turning the pedals. Listen: a regular ticking and a chain rubbing against the next larger sprocket mean the cable is too tight; a chain that hesitates to climb means it is too slack.

Turn the barrel adjuster a quarter turn at a time: unscrewing it, so that it comes out of the derailleur, adds tension; screwing it back in releases it. Indexing is right when the chain moves up and down one sprocket per click, silently, across the whole cassette.

The B-screw, at the back of the derailleur, sets the gap between the upper jockey wheel and the sprockets. Shift onto the largest sprocket and turn the pedals backwards: the jockey wheel should run close to the teeth without ever touching them.

Screw the B-screw in if the jockey wheel rubs or clatters against the largest sprocket, and out if it sits very far away: a gap of 5 to 6 mm suits most derailleurs. Too big a gap makes shifts to the larger sprockets sluggish.

Run through every gear one at a time, in both directions, turning the pedals at a normal pace, then do it again on each chainring. Every click should move the chain by one sprocket, without noise or hesitation.

Then take a short test ride and pedal hard up a slope: a new cable stretches a little in the first few days. If shifting becomes imprecise again, a quarter turn of the barrel adjuster usually fixes it. If nothing helps, the cable or the housing may need replacing.