Congratulations! You have a bike with derailleur gears.

People are sometimes confused by the idea that their bike has – say 10 or 18 or 24 or 30 or however many gears. I shall use a 24 gear derailleur as an example here, because I own nominally one but possible as many as two of these. The term “24 speeds” is also used for this very same thing.

It is simpler to think of a 24-speed derailleur set-up as a 3-speed chainset driving an 8-speed back wheel. It is, after all, a simple system. Likewise, a 10-speed is a 2-speed driving a 5-speed back wheel, and a 33-speed is a 3-speed chainset driving an 11-speed back wheel. No-one ever talks about 4wds having 10 gears – such vehicles are described as 5-speeds with a 2-speed transfer case.

The reason that derailleur bikes have lots of close gears is to squeeze out the maximum speed out of however hard and fast the rider wishes to pedal, whether up or down steep hills or on the flats, whether the legs feel like iron or like cardboard. Big trucks have lots of close gears so that there is always a gear which provides the right ratio to keep the engine at the speed where it delivers its power with the best economy (and a gear for starting, or perhaps wheelspinning, on the steepest hills), and racing cars have very close ratio gears so that the engine can be kept screaming at maximum power, which is almost certainly near maximum revs. So whether a biker rider chooses to pedal hard and fast or slowly and gently, the gears can be used to keep the bike moving at whatever maximum speed is possible. The gears are there to make the rider’s life easier, or at least faster.

On my 24 gear bike (s), the shifter for the 3-speed chainset is on the handlebar on the left side, operated by my left hand. The smallest chainwheel is called Low, L, or the granny gear, and pulls the chain very hard but slowly. I use this very rarely, and only for the steepest hills. The middle-sized chainwheel is called mid or M, and I use it for hills and often for starting from rest. The biggest chainwheel is called high or H. It pulls the chain the fastest, but with the least force. I use H for riding on the flat, going fast, and for some gentler hills, typically those climbable in H3 or higher.

The shifter for the gears on the back wheel is on the right side of the handlebars, and operated by my right hand. The gears on the back wheel are called 1^st to 8^th. 1 to 8. 1 is the biggest sprocket. It is turned by being pulled by the chain, and as it is the biggest, it makes the wheel rotate with the most force but the least speed. 8^th is the smallest sprocket, and makes the wheel go around the fastest, but with the least force. !st is easier to ride up hills in than 8th. With the chain on the appropriate chainwheel, the gears on the back wheel can be shifted down or up for quick starting, easy manoeuvring, hills that get more or less steep, headwinds, tailwinds, full speed on the flat, even giving your legs or lungs an easy time if you’re starting to feel a bit tired.

There’s more. Head over to My Definitive Guide, Part 2 to learn about shifting and all that stuff.