Bike gears: shifting explained for beginners

Understanding the fundamentals of how gears work, and what effect varying the size of the front chainrings and rear cassette sprockets will have on your pedalling will help you choose the most suitable gearing for your ability.

It’s hard to know whether you need a classic, compact, or a mid-compact chainset, and then you might want a 10 speed, 11 speed or even now a 12-speed groupset to go with it. In the following article we’ll help you become more gear savvy efficient cyclists — we promise.

Bike gears: the basics

What determines the number of bike gears you have?

It’s a simple multiplication of the number of sprockets at the rear with the number of chainrings at the front. A triple chainring set-up with a 10-speed rear cassette is therefore a 30-speed bicycle — in other words, it’s possible to use all of the 10 sprockets in combination with each of the three chainrings. Likewise a double chainring paired with an 11-speed cassette is a 22-speed set-up, and so on.

Why do you need gears on a road bike?

Why have gears at all? Well, in a nutshell, gears are there to enable us to maintain a comfortable pedalling speed (or cadence) regardless of the gradient or terrain — something that no one single gear is capable of.

A high gear, sometimes referred to by cyclists as a ‘big gear’, is optimal when descending or riding at high speeds. The highest, or biggest gear on a bicycle is achieved by combining the largest front chainring size with the smallest rear cog or sprocket — expressed as ‘53×11’, for example.

Vice versa, combining the smallest front chainring size with the largest rear sprocket size results in the lowest available gear, which will help you keep the pedals spinning when the road points steeply up.

Let’s be clear about one thing — having lots of gears is not about making the bike faster. A bike with 30 or more gears is not an indication of a machine designed to break the land speed record any more than a bike with only a single gear, assuming similar ratios.

It’s about efficiency and having a much broader range, or choice, of gears for a given situation. Just like a car, bicycles benefit from a low gear to accelerate from a standstill, or to climb a steep hill, and at the other end of the scale a high gear helps you to achieve high speeds without over-revving.

Continuing with the car example, using too low a gear at high speed would result in high fuel consumption. The same is true of your body pedalling a bike. So, quite simply, more gears means more scope to find your preferred pedalling speed.

To put this into perspective, in the days of five or six-speed cassettes, a range of 12-25 teeth could only be achieved by having sizeable gaps between sprocket sizes. Modern 10- or even 11-speed cassettes with the same spread, 12-25, would have only single tooth increments for the majority of the shifting.

Why do some people opt for a single speed bike?

You don’t have to ride bike with gears – some people choose to ride singlespeed bikes. These still have a gear – which is determined by the size of the front chainring and rear cog.

Singlespeed bikes are popular among commuters living in flat areas, because they require little maintenance. They’re also used by some racers who want to drop weight and cut down on any extra complication coming from the shifting process – in this case, choosing the correct gear ratio is crucial. Finally, track bikes only ever have one gear – though again riders will change their set up to suit certain events.

The result is smoother, more precise shifting, as the mechanical difficulties the chain has to overcome to climb onto the bigger sprocket or drop down onto a smaller one are much reduced with smaller increments, but most importantly, the possibility is there to greatly improve pedalling efficiency. Cyclists are much more able to fine-tune their pedalling speed to suit the gradient or terrain, often resulting in a lower energy cost.

Win some, lose some

The reality, on a multi-geared set-up, particularly when there are as many as 33 on offer, is that ‘overlapping’ gears are unavoidable. In other words, some gear combinations will result in the same ratio as others using a different sprocket and chainring. For example, 53×19 is the same gear as 39×14.

Also, certain ‘crossover’ gears, at the extremes of the range, may not be recommended for use, due to the additional strain that is placed upon the chain. Old-fashioned advice, which is still relevant, is to avoid ‘crossing the chain’. See the diagram below for an illustration of this.

So you’re not always getting 33 gears at your disposal, but it’s not some kind of marketing trick by manufacturers, to slyly cheat you out of gears, it’s simply the nature of the beast.

As we’ve already said, the total number is not the selling point, instead it’s the ability to have such a continual progression of closely spaced gears.

There’s no need to struggle these days because there are heaps of gearing options available so riders of all abilities can get the most from their pedalling. The trick is to know what’s what, so you’ll be able to decide what will best suit your riding. Here’s the lowdown to put you on the right track.