The complete guide to bicycle gears — bicycle transmissions explained
All too often you will see people spinning their pedals manically or laboriously grinding their way along, barely able to move the bike. We can’t help but feel life would be a little bit easier if they were using their gears properly, so we’ve put together a guide for those that need to learn how to use the gears on a bike.
Gears are one of those lovely inventions that allow us to ride faster, get up hills more easily and get a lot more enjoyment out of our riding.
Gears convert the effort you put in at the pedals to a certain output at your wheel. There’s only so much force your muscles can produce and usually an optimum cadence (how fast you spin your pedals) at which you’ll be most efficient.
Changing your gears based on the terrain and conditions to stay broadly in that band lets you move forward more efficiently.
There are a few different systems that bikes use to change gears, though by far the most common is the external drivetrain.
Bicycle external drivetrains explained
An external drivetrain with a front and rear derailleurOli Woodman / Immediate Media
The majority of bikes on the market today have external drivetrains, which have been refined into simple, lightweight and efficient systems.
Gears are changed on the cassette (a set of sprockets on the rear wheel) by the rear derailleur. This shifts the chain up or down the cassette. As the derailleur moves to change gear it forces the chain against ramps or steps, moving it onto a bigger or smaller sprocket.
The bike may also have a front derailleur, which shifts the chain between chainrings attached to the cranks.
The gears at the front provide large jumps, which effectively change the range of your gears, so that they are more suited to high speed, flat terrain or low-speed climbing. The cassette allows you to select your gear more precisely within that range as you modulate your effort.
You will usually find between one and three chainrings (single, double or triple chainset) and up to 11 sprockets (12 exist too in the form of SRAM Eagle and Campagnolo Record) on the back wheel. That gives you a huge range of gears to choose from.
A Shimano Alfine 11-speed hub with Gates Carbon Drive beltJonny Ashelford
Hub gears are a popular option for commuters and those who want a robust and relatively maintenance-free drivetrain. With service intervals ranging between 3,000–5,000km, internal hub gears are great for the less maintenance-inclined.
There’s also no doubt that derailleurs are relatively exposed and susceptible to damage. Having everything nicely packaged away inside your rear wheel lets you breathe that little bit easier. During the winter having your gears protected from the elements doesn’t hurt either.
There’s lots of hub gears options available, but the most common are available from Shimano, SRAM, Sturmey Archer and the well-known manufacturer, Rohloff. With systems ranging from three to 14 gears there’s a wide range of options for whatever terrain you find yourself on.
However, the main drawback is weight. You’re riding around with a small gearbox inside your hub and that in turn contains a lot of metal parts that adds substantial heft.
Do bikes have a gearbox? What is a gearbox bike?
Pinion gearboxes have found a niche mainly on mountain bikesMick kirkman / Immediate Media
Part of the problem of a hub gear is that it adds weight at one end of the bike, which can lead to unbalanced handling.
Instead, a gearbox is integrated directly into the frame, with the weight positioned centrally on the bike. The cranks drive the gears directly and the output is converted in the gearbox and then transmitted to the back wheel via a chain.
Both gearboxes and hub gears can also be used with belt drives. This requires even less maintenance than a chain as there are no links to lube, meaning they are also much cleaner than an oily chain.
However, only certain frames are compatible with a belt drive. Because the belt is a continuous loop, the frame requires removable dropouts or a chainstay splitter that lets you thread the belt into the rear triangle.
A Gates Carbon Drive belt requires less maintenance than a traditional chainASDesign.uk.com
The majority of gears on bikes today are actuated by metal cables. However electronic drivetrains have arrived and are only likely to become more widespread as time goes on.
Instead of cables, the gear is shifted by an electronically controlled motor. The primary benefit is consistency. While cables can develop slop and stretch over time, an electronic drivetrain will maintain accurate shifting in all conditions.
The most common systems are from Shimano, in the form of its Di2 shifting, and SRAM, which offers wireless eTap shifting. Even Rohloff now offers electronic shifting for its 14-speed hub gear.
What is a singlespeed/fixed/fixie bike?
A singlespeed bike can provide low-maintenance reliabilityJack Luke / Immediate Media
Of course, you always have the option of just one gear and that’s how bikes started out.
Singlespeed bikes use a freewheel that allows the rear wheel to rotate without the pedals moving. Fixies are even more rudimentary, with the rear wheel ‘fixed’ to the cranks, meaning you always have to pedal.
The main benefit is simplicity, with low maintenance requirements and low cost. Although there’s no doubt that singlespeeds have also become a bit of a fashion statement in many cases.
There’s no use having all these gears if you can’t change them. There are a number of different designs of shifter on the market, which may be operated in slightly different ways, but are all fairly intuitive once you get to know them.
Shifters for the front and for the rear will be separate, located on the left and right side of your bars respectively.
How to use flat bar shifters
Flat bars are common on hybrid/commuting bikes as well as mountain bikes. There are a few different shifter designs available.
Trigger shifters on a Specialized Sirrus commuter bikeOli Woodman / Immediate Media
Nowadays, the trigger shifter is the most widely spread design. It has two levers under the bars, which can be actuated with your thumbs, one to shift up and one to shift down.
Depending on the design, you may be able to change multiple gears at once or not. Shimano also has some designs that integrate shifter and brake lever into one unit.
How to use a grip shifter
A grip shift shifter for a Pinion gearboxJack Luke / Immediate Media
With a trigger shifter you can usually only change one gear at a time, but with a grip shift it’s possible to move through multiple gears very quickly.
The shifter integrates with the grip on your bars, and you change gears up or down by twisting the shifter — similar to the throttle on a motorbike.
How to use a thumb shifter
An old-school thumb shifterDaniel Oines / Flickr Creative Commons
A little more old-school, this kind of shifter still pops up from time to time. A lever on top of your bars can be moved clockwise or anti-clockwise to move through your gears.
Modern gears are indexed, meaning that a click on the gear shifter corresponds directly to a gear change. In the past shifters did not have this defined click and instead, the shifter was held in place by friction and moved continuously until the gear changed. In some rare cases you may still encounter such thumb shifters.
How to use road bike shifters
You’ll find drop bars on more dedicated road bikes aimed at speed rather than all-out comfort. Again, there are a few different designs available.
How to use STI-style shifters
STI shifters integrate shifting and braking into one unitJack Luke / Immediate Media
This is by far the most common design on modern drop-bar bikes. The shifters and brakes are integrated into one unit on the bars. There are slightly different variations on the design. They are sometimes referred to as brifters.
Shimano Total Integration (STI) shifters use a split lever design to change gears. A small lever just behind the brake lever shifts the chain onto a smaller cog, while the whole brake lever can be pushed to the side to shift to a larger cog.
SRAM DoubleTap shifters use a single paddle to shift both up and down. A short click will shift into a smaller cog, pushing the lever further will shift into a larger cog.
Campagnolo shifters are slightly different again — a lever behind the brake shifts into a larger cog, while a little trigger on the inside shifts into a smaller ring.
Most road groupsets also have a feature called ‘trim’ for the front derailleur. As you move through the gears on the cassette at the back, the chain angle changes slightly. In some cases this can result in the chain rubbing on the cage of the front derailleur.
Trim lets you actuate a change in position of the front derailleur. A half-press of the shifter moves it slightly so that the chain runs cleanly.
How to use bar end shifters and down tube shifters
Bar-end shifters slot into the end of the bars and provide a lever which actuates your gears. These are very similar to thumb shifters and are available in both indexed and friction shifter forms.
These have popped up a little more recently providing a simple way of combining a hub gear with drop-bar brake levers.
Down tube shifters work in much the same way, but as the name suggests, these are located on the down tube of the bike.
How do my gears work?
Your gears convert your input at the cranks into an output at the back wheel. Your cadence (how quickly you are pedalling) is converted into different speeds at your back wheel depending on whether you are in a high or low gear.
Your gear development — how far your bike moves with each pedal stroke — is typically described in gear inches i.e. how many inches your bike will roll forward with each full rotation of your cranks.
Gear inches can give you a good idea of how hard or easy the gears are, with ranges around 20 inches being easy, 70 inches being medium and above 100 inches getting quite hard.
Gear range is often specified as a percentage that describes the overall range offered by the system. That means that a 300 percent range would offer a 3:1 ratio. Pedalling in the highest gear would move you three times as far forward per pedal stroke as in the lowest gear.
For external drivetrains, the gear range can be calculated by taking the ratio of the largest and smallest chainring teeth at the chainset multiplied by the ratio of the largest and smallest sprocket on the cassette.
The cassette specs will typically be identified by the smallest and largest sprocket. Thus a 11-28t cassette would denote a cassette with a smallest 11 tooth and largest 28 tooth sprocket.
Cranks come in a number of forms for road bikes, including standard, compact, super compact and triple.
A triple has three chainrings. While this was once the most widely used type of crankset, now it is found mainly on touring bikes or for hilly terrain where you require a very wide range of gears.
Much more usual nowadays are two chainrings. These will come either on a standard or compact crankset, generally with 53-39t or 50-34t respectively. The standard is more suited to high speeds with the larger chainrings
On occasion, you may also find a super compact chainset, which uses even lower ratios than the compact chainset making the bike more suited to climbing. Mountain bike chainsets tend to use even smaller chainrings to deal with steep and off-road terrain.
To figure out the number of gears you have, simply multiply the number of chainrings at the front by the number of cogs on your cassette at the back.
However the number of gears can be a bit of a misnomer because similar gears may be duplicated depending on which chainring/sprocket combination you are using.
For gear hubs and gearboxes, manufacturers will typically specify the range. For example a14-speed Rohloff hub has a 526 percent range, while a Pinion P1.12 gearbox has a massive 600 percent range.
What gear should I be in?
Gears are all about being efficient. Imagine trying to pedal up a steep hill in a high gear. You would have to push incredibly hard on the pedals and grind your way up the hill. Instead, in a lower gear your force input at the pedals is lower, but as a result you can spin faster.
Your energy input in each case is roughly the same. The work done is equal to the force times the distance — so if you halve the force input required, you’ll be pedalling twice as fast.
However, there’s a limit to how much force your legs can generate (and your knees can take), so there comes a point where it’s preferable to shift gears to reduce the required force input and increase your cadence.
The part about knee injury really is a key one. It’s much nicer on your body to have to push relatively lightly (but more quickly) rather than having to grind your way along.
The key thing with shifting gears is anticipation. Look ahead and try to predict how your speed will change and how you are likely to need to change gears.
As you come to a tight corner, anticipate that you will need to slow down and shift into a lower gear so you can accelerate out of the corner more easily.
If you’re riding up a hill or into the wind your perceived effort will increase so it makes sense to shift to a lower gear to account for that.
Equally if you need to stop at some traffic lights, shift into an easier gear so that you can set off more easily when the lights turn green.
One big no-no is that you shouldn’t shift when you’re at a standstill with an external drivetrain. Always ensure that you are pedalling to perform smooth shifts and shift gradually across the range of gears to find the right one.
Another thing to avoid is cross-chaining. If you have multiple chainrings, then it’s best to avoid being in a small-small or large-large sprocket-chainring combination.
The extreme angles this puts the chain at can result in increased wear and high loads on the drivetrain.
Conversely, hub gears or gear boxes can usually be shifted when at a standstill. In fact they’re often quite sensitive to shifting under load, so it helps to ‘unload’ your cranks slightly when shifting.
Keeping things clean
The key to keeping your gears running nicely is to ensure you keep them clean and well maintained. In fact, keeping things clean in general helps you keep on top of maintenance and lets you identify any potential issues before they become more serious.
As discussed previously, hub gears tend to be lower maintenance, though you may still have to adjust cable tension as it still stretches gradually over time. General maintenance like this works wonders in the long run, as a well adjusted and maintained bike is kinder on your components overall.