- Bike Gears Explained: A Beginners Guide To Bike Gears
- Front Gears (Chainrings/Crankset)
- How Many Gears?
- Teeth & Bike Gear Ratios Explained
- Different Gearing Set Ups
- How Do We Use Gears?
- Additional Reading and Useful Links
- Gears – How do they work? – Different types explained and compared
- What do gears do… and how do they do it?
- How do they do it?
- Why do we need gears?
- Changing gears
- Five different ways to use gears
- Where did you get those gears?
- AngryAsian: Gear down to go faster
- I need a bigger gear to go faster! (Probably not)
Bike Gears Explained: A Beginners Guide To Bike Gears
On the surface, understanding your bike gears is pretty simple. You push the lever one way to make it easier to pedal, and the other to go faster. choosing the right gears to install on your bike however can be much trickier.
Most of us just end up riding the gears that came with our bikes, but if you don’t think about swapping out for different scenarios, you might end up making things much more difficult than they need to be.
The gear ratios you want to use for a hilly cycling holiday in Mallorca are not the same as the gears you want for a time trial, criterium, club ride or city riding. Our complete guide to bike gears takes the mystery out, and will have you joining in with all the other bores banging on about ratios in no time at all.
Front Gears (Chainrings/Crankset)
The front gears are referred to as chainrings, or as a crankset, or by the less jargon-savvy cyclists, ‘the front ones’. Actually, the whole assembly with the crank arms and the front gears together is properly known as the ‘crankset’, or sometimes ‘chainset’.
Most cranksets have either two (called a double or 2x), or three (called a triple or 3x) chainrings. Single (or 1x) chainrings are gaining popularity, particularly among mountain bikers and cyclocross riders, but are still a fairly niche application. On the crankset, the smallest chainring is closest to the frame.
The smaller the chainring, the easier the pedalling. As we move the chain away from the centre line of the bike, the pedalling gets harder but you go faster. Typically the chainrings are identified by mentioning their position (“inner”, “outer”, or, in the case of a triple “middle”), or by their size “big ring”, “little ring”.
On a triple they’re usually called “outer/big”, “middle” and the smallest one has a special name – “granny gear” or just “granny”.
The gears on the rear wheel are called ‘cogs’ and when you put a few of them together in ascending size and attach them onto your back wheel, they are referred to as a ‘cassette’.
Most bikes built in the last few years have between 8 and 11 cogs in the cassette. The largest cogs are closest to the wheel and the gears are numbered from the inside out.
The larger the cog the ‘lower’ the gear and the easier it will be to pedal, but the slower you will go.
How Many Gears?
When we talk about how many “speeds” a bike has, there can be some confusion. The marketing department s to multiply the number of cogs by the number of chainrings because big numbers are impressive.
But the fact is there’s actually a lot of overlap, so a 9×2 doesn’t really have 18 gears.
People who actually ride bikes only refer to the number of cogs in the cassette, so an 8 speed, a 9 speed etc… They may also mention whether they have a single, double, triple crankset, or they may simply say “9×2” or “2×9”.
‘Derailleur’ is pretty hard to pronounce, but – fortunately – pretty easy to understand. The chain gets moved from one cog to another or one chainring to another by means of a derailleur. The front derailleur is a fairly simple device that simply pushes the chain off of one chainring to be picked up or ‘caught’ by the next.
The rear derailleur is a little more complex as it has two jobs. the front, it guides the chain from one cog to the next, but it is also responsible for maintaining chain tension and taking up the slack when we move from bigger gears to smaller ones.
The rear derailleur has two little gears (actually called ‘pulleys’) in it, and the chain makes an ‘S’ turn through them. The upper pulley (closest to the cassette) is referred to as the ‘jockey pulley’ and the lower pulley is called the ‘idler pulley’.
The pulleys are held in position by the ‘cage’.
You’ll find it’s much more difficult to shift your front gears while the chain is pulled really tight, so you should lighten your stroke a bit when switching chainrings. The rear derailleur is much more effective at switching gears while pedalling hard. It is important to note however, that in order to switch gears the chain must be moving forward.
With both the front and the rear derailleur, when the shift cable is pulled, it will move the chain to a larger gear. When the cable is released, it will move the chain to a smaller gear.
Just remember that larger gears at the rear mean easier pedalling but more torque, and larger gears at the front mean harder pedalling but more speed.
Going from “easier” gears to “harder” gears is called “upshifting”, and the reverse is called “downshifting”.
Teeth & Bike Gear Ratios Explained
11 cogs on the rear cassette and two on the front chainring essentially gives you 22 different options (though some of these may cross over so not strictly true).
The key element that will determine how hard you work is the difference in the number of teeth (the wee pointy bits that hook through the gaps in your chain) between the front chainring at the front and your selected rear cog.
Let’s take my bike as an example:
The chainring (front) on my bike is 50/34T. That means the outer ring has 50 teeth and the inner ring has 34 teeth.
The rear cassette is 11 speed 11-32. This means there are 11 cogs ranging from 11 teeth up to 32 teeth (the exact cogs are 11/12/13/14/16/18/20/22/25/28/32).
The combination of your selected chainring and cog determine the gear ratio. The gear ratio, combined with the circumference of your wheel and tyre determines how far you will travel with each revolution of the cranks.
The Hardest Gear
Let’s say I am in the hardest gear on each which means I would be riding on the 50 tooth ring on the front, and the 11 tooth ring on the back. To get our gear ratio we divide the number of teeth on the front by the number on the back:
50 ÷ 11 = 4.55
This is expressed as 4.55 : 1 meaning that for every 1 turn I make of the pedals at the front, I will turn the back wheel 4.55 times. This is the gear I would use on the flat. It is going to take quite a lot of effort to get it moving, but when I do I will move quickly.
The Easiest Gear
This would be the opposite end, the small ring on the front and the biggest on the back. The reason for this is that they are the closest together, meaning you get a really low ratio. On the bike I ride this is 34 teeth at the front and 32 at the back – so really close.
34 ÷ 32 = 1.06
1.06 : 1 means I am only just moving the back wheel through more than one revolution for every turn of the crankset. This would be the gear I am using on the very toughest of climbs allowing mean to spin the wheels quickly to get my cadence high.
Different Gearing Set Ups
Crank Set (Front Gears)
You may sometimes hear cranksets referred to as ‘compact’ or ‘standard’. A compact crankset typically has a 50 tooth (50T) big ring and a 34 tooth (34T) little-ring. Standard cranksets are typically 53T/39T.
In most cases, you can change your chainrings to have different tooth counts, but as a general rule you don’t want to have more than a 16-tooth difference between the big ring and little ring or you may have shifting issues. As for triples, they tend to run even smaller gears and more closely spaced 26T/36T/46T and 52T/42T/32T are common triple crankset configurations.
With 10 and 11 speed drivetrains becoming the norm, we’re seeing triples fall fashion and even single ring cranksets are becoming popular because of the wide range of ratios an 11-speed cassette can span.
Cassette (Read Gears)
As mentioned earlier, today’s bikes typically come with 8 to 11 cogs in a cassette. When choosing cassettes, you can choose a cassette that has a narrow range of ratios but closely spaced between each cog, or you could choose a cassette that offers a wide range of ratios but at the cost of bigger jumps between cogs.
Choosing a bike that has more speeds reduces the tradeoff some, and gives you more versatility. If you do most of your riding in a place that is generally flat, it’s probably best to opt for a narrow-range cassette with small ratio jumps as that allows you to really fine-tune your cadence and effort level.
If you live in an area that has more varied terrain, a wider-ranged cassette may be the better choice to help you get up those hills.
Wider-ranged cassettes with higher cog counts typically have the ratios more closely spaced on the smaller cogs, and then have the bigger jumps in the bigger “climbing” cogs to give you a little of the best of both worlds.
The key learning from all this information is to make a conscious choice when you purchase a bike as to the gear range that you want.
If you are climbing, then the natural choice is going to be a compact crankset, or in extreme cases a triple, but think about the rear cassette. My first bike had an 11-28, but I really keeping a high cadence on the hills, so on my new bike I have opted for 11-32.
This means I still have a nice fast high gear, but the lowest gear is significantly easier to pedal. If you are a keen time trial rider then you may want to opt for a standard crankset, as it will give you a higher top gear.
This paired with something an 11-23 rear cassette would be great for flat course as it would give you very small changes between the gears meaning you could keep the cadence exactly where you wanted it.
The key is to know the kind of riding you are planning to do with the bike you purchase and choose the gearing accordingly. I have produced the chart below to help you understand the typical ratios available. Remember the higher the ratio, the harder/quicker the gear is going to be.
How Do We Use Gears?
So now you’ve had a quick intro to how your gears work together, here are three final tips to take with you on your next ride.
- Avoid ‘cross-chaining’: Cross-chaining is when you have a little/little or big/big combination. This puts stress on the drivetrain and can cause premature wear of the components. It’s OK if you occasionally find yourself cross-chained – say for a short, steep climb – but it is something you’ll generally want to avoid. The rule of thumb to follow is that when on the big ring, only use the smaller two-thirds of the cassette. When on the inner (or middle) ring, only use the inner two-thirds. When in ‘granny gear’ limit yourself to the largest two or three cogs.
- Anticipate your shifts: Keep an eye on the road ahead and shift before you have to. You’ll maintain a smoother power output, and you’ll be shifting at a time when there’s less stress on the drivetrain – so your shifts will be smoother too. As you approach a red light or stop sign you should also downshift a couple of gears, in anticipation of getting rolling again as smoothly as possible.
- Keep pedalling!: It is much more efficient to keep a constant, steady power rather than ‘burst and coast’ riding. It sure feels you’re getting better exercise when you make that big effort, but you’re putting all the load on your muscular system, which isn’t really good at sustained effort. Spinning light and fast ends up putting out the same amount of power, but shifts the load to your cardio-vascular system, which is good at endurance activity.
Additional Reading and Useful Links
RitzelRechner Gear Calculator
CyclingTips.com – Understanding Gear Ratios and Why They Matter
Gear Ratio Basics
Yellow Jersey offer bicycle insurance to protect your equipment and travel insurance to cover medical mishaps while cycling overseas.
Gears – How do they work? – Different types explained and compared
by Chris Woodford. Last updated: May 29, 2019.
Have you ever tried pedaling a bicycle up a really steep hill? It's prettymuch impossible unless you use the right gear toincrease your climbing force. Once you're back on the straight, it's adifferent story.
Flick to a different gear and you can go incrediblyfast: you can magically make your wheels turn round much faster thanyou're pedaling. Gears are helpful in machines of all kinds, not justcars and cycles.
They're a simple way to generate more speed or poweror send the power of a machine off in another direction. In science, wesay gears are simple machines.
Photo: Typical machine gears. An opened-up gearbox on show at Think Tank, the science museum in Birmingham, England. In a car or a motorcycle, the gears “mesh”so the teeth of one wheel lock into the teeth of another; that stops them slipping, which means power is transmittedmore smoothly and efficiently.
In a bicycle, the gears don't link by meshing together directly. Instead, alubricated chain connects together the gear wheels (known as sprockets) on the pedal with those on theback wheel.
That's simply because the pedal and the back wheel are some distance apart and a chain is the easiest way to link them together.
What do gears do… and how do they do it?
Gears are used for transmitting power from one part of a machineto another. In a bicycle, for example, it's gears (with the help of achain) that take power from the pedals to the back wheel. Similarly,in a car, gears transmit power from thecrankshaft (the rotating axlethat takes power from the engine) to the driveshaft running under the car that ultimately powers the wheels.
Photo: In an egg whisk, gears help to make light work of mixing in twodifferent ways—by increasing speed and changing direction.When you crank the handle, you turn the large outer gear wheel at moderate speed.
This large wheel meshes with a pair of small gear wheels fitted to the top of thetwo axles attached to the blades. Each rotation of the large wheel (blue) makes the smaller wheels turn round several times (red),giving a dramatic increase in speed at the blades.
The gears also help by changing the direction of rotation: you crank the handle about a horizontalaxis, but the two whisk blades turn about a vertical axis.
You can have any number of gears connected together and they canbe in different shapes and sizes. Each time you passpower from one gear wheel to another, you can do one of three things:
- Increase speed: If you connect twogears together andthe first one has more teeth than the second one (generally thatmeans it's a bigger-sized wheel), the second one has to turn roundmuch faster to keep up. So this arrangement means the second wheelturns faster than the first one but with less force. Looking at ourdiagram on the right (top), turning the red wheel (with 24 teeth)would make the blue wheel (with 12 teeth) go twice as fast but with halfas much force.
- Increase force: If the second wheel ina pair of gears has more teeth than the first one (that is, if it's a largerwheel), it turns slower than the first one but with more force. (Turn theblue wheel and the red wheel goes slower but has more force.)
- Change direction: When two gears meshtogether, the second one always turns in the opposite direction. So if the firstone turns clockwise, the second one must turn counterclockwise. You canalso use specially shaped gears to make the power of a machine turnthrough an angle. In a car, for example, the differential (a gearbox inthe middle of the rear axle of a rear-wheel drive car) uses acone-shaped bevel gear to turn the driveshaft's powerthrough 90 degrees and turn the back wheels.
How do they do it?
Gears sound magic, but they're simply science in action! Look at the diagram here and you'll see exactly how they work.
The pair of gear wheels (top) works in exactly the same way as an ordinary pair of wheels the same size that are touching (middle); the only difference is that the gears have teeth cut around the edge to stop them slipping.
But a wheel is really just a lever, so a pair of wheels that touch is a pair of levers that touch (bottom).
Thinking of gears as levers shows exactly how they work. Suppose you turn the axle at point (1). The bar connecting points (1) and (2) moves faster and with less force at point (2) because it's working as a lever.
If you can't see this, suppose the red bar were a spanner and you pushed at point (2) to undo a nut at point (1) in the center. Then point (1) would turn with less speed and more force.
If you turn at point (1) instead, the opposite is true: you get more speed and less force at point (2). That's the red bar, which is just touching the blue bar. As the two bars touch, they must be going at the same speed.
Now the blue bar is also a lever, but it's working the other way: a spanner. So if we apply a force at point (2), it's magnified by the leverage of the blue bar and we get more force (and less speed) at point (3).
Putting everything together, what do we get? We apply a certain force and speed at point (1). The red bar might give us four times the speed and a quarter of the force at point (2).
But the blue bar will work the other way and maybe halve the speed and double the force. So when we get to point (3), we have twice the speed and half the force that we had at point (1).
That's what we'd expect from a pair of gear wheels where one (red) is twice the size and has twice as many teeth as the other (blue).
Why do we need gears?
Let's think about cars. A car has a whole box full of gears—thegearbox—sitting between the crankshaft andthe driveshaft. But what do they actually do?
A car engine makes power in a fairlyviolent way by harnessing the energy locked ingasoline. It works efficiently only when the pistons in the cylindersare pumping up and down at high speeds—about 10-20 times a second.
Evenwhen the car is simply idling by the roadside, the pistons still needto push up and downroughly 1000 times a minute or the engine will cut out. In otherwords, the engine has a minimum speed at which it works best of about1000 rpm.
But that creates an immediate problem because if the enginewere connected directly to the wheels, they'd have a minimum speed of1000 rpm as well—which corresponds to roughly 120km/h or 75mph.
Put itanother way, if you switched on the ignition in a car this, yourwheels would instantly turn at 75mph! Suppose you put your foot downuntilthe rev counter reached 7000 rpm. Now the wheels should be turninground about seven times faster and you'd be going at 840 km/h or about525 mph!
It sounds wildly exciting, but there's a snag. It takes a massive amount offorce to get a car moving from a standstill and an engine that tries to go attop speed, right from the word go, won't generate enough force to do it.That's why cars need gearboxes.
To begin with, a car needs a huge amount of force and very little speedto get it moving, so the driver uses a low gear.In effect, the gearbox is reducing the speed of the engine greatly butincreasing its force in the same proportion to get the car moving.Once the car's going, the driver switches to a higher gear.
More of theengine's power switches to making speed—and the car goes faster.
Photo: Bicycle gears: Bikes have two sets of different-sized gears on the wheelyou pedal and the back wheel.
Instead of touching directly and rotating in opposite directions, each pair of gear wheels is connected by a flexible metal chain (kept taught by a springy lever and gear-shifting mechanism called a derailleur), so they turn in the same direction; technically, gears linked this way are called sprockets. When you change gear, you shift the chain from one pair of sprockets to another. For cycling at speed, you'll use a larger sprocket on the pedal wheel than on the back wheel.
In theory, changing gears is about using the engine's power in different ways to match changing driving conditions.
The driver uses the gearshift to make the engine generate more force or more speed depending on whether hill-climbing power, acceleration from a standstill, or pure speed is needed.
In practice, changing gears means meshing different sized gear wheels together, but you can't do that while the gearbox is transmitting power from the engine at high speed.
That's why you need to press a car's clutch pedal before changing gears, which disengages the engine's input from the gearbox. You can then use the gearshift to change to a different pattern of gears, before letting the clutch transmit power back from the engine to the gearbox (and the wheels) once again.
On a bicycle, it's much more obvious what's going on when you change gears because you can see it happening.
As you flick the gear shift, you can watch (and feel) the chain hop from one sprocket to another, engaging different-sized gear wheels.
On many bikes, the gear change is controlled by a clever mechanism called a derailleur, which smoothly diverts the chain from sprocket to sprocket even though you're pedaling along at speed.
Five different ways to use gears
I've made these five simple gear machines with an old construction set to illustrate a few ofthe ways in which we can use gears to do different jobs:
In this simple gearbox, I've got (from right to left) a large gear wheel with 40 teeth, a medium wheel with 20 teeth,and a small wheel with 10 teeth. When I turn the large wheel round once, the medium wheel has to turntwice to keep up.
Similarly, when the medium wheel turns once, the small wheel has to turn twiceto keep up. So, when I turn the large gear wheel on the right, the small wheel on the leftturns four times faster but with one quarter as much turning force.
This gearbox is designed for increasing speed.
If I power the same gearbox in the opposite direction, by turning the small wheel, I'll makethe large wheel spin a quarter as fast but with four times as much force. That's useful if I needto make a heavy truck go up a hill, for example.
Here I'm using an electric motor (the gray box on the right) and a long screw- gear to drivea large gear wheel. This arrangement is called a worm gear. It reduces the speed of the motor to make the large wheel turn with more force, but it's also useful for changing the direction of rotation in gear-driven machinery.
You've probably seen one of these in cliff- and hill-climbing rack railroads, but they're also used in car steering systems, weighing scales, and many other kinds of machines as well.
In a rack and pinion gear, a slowly spinning gear wheel (the pinion) meshes with a flat ridged bar (the rack). If the rack is fixed in place, the gear wheel is forced to move along it (as in a railroad). If the gear is fixed, the pinion shifts instead.
That's what happens in car steering: you turn the steering wheel (connected to a pinion) and it makes a rack shift from side to side to swivel the car's front wheels to the left or the right.
In simple weighing scales, when you load a weight on the pan at the top, it pushes a rack straight downward, causing a pinion to rotate. The pinion is attached to a pointer that rotates as well, showing the weight on the dial.
If you need to convert reciprocating (back-and-forth) motion into rotation, you normally do it with a crankshaft and connecting rod; that's how pistons drive the wheels on steam engines. But you can do the same thing with gears.
In this arrangement, a small gear called a planet (which, it's important to note, is fixed to a rod so that it cannot rotate) is moved around a second (usually bigger) gear called a Sun. As the rod moves the planet back and forth, the Sun spins around.
Sun and planet gears were popularized by James Watt, who was unable to use a crankshaft in his pioneering steam engine because it was originally protected by a patent.(There's a great little animation of a sun and planet gear on Wikimedia Commons.
Notice the black lines inked on the two gears showing clearly that the Sun rotates, while the planet does not.)
Artwork: Gears can give you more speed, but only by giving less force; they can give more force, but only by giving less speed. This is why a pair of gears can't create energy. With two perfect gears, you'd get exactly as much energy out as you put in; with real gears, friction, noise, air resistance and so on mean you get less energy out than you put in.
You might think gears are brilliantly helpful, but there's a catch. Ifa gear gives you more force, it must give you less speed at the same time.If it gives you more speed, it has to give you less force.
That'swhy, when you're going up hill in a low gear, you have to pedal muchfaster to go the same distance.
When you're going along the straight,gears give you more speed but they reduce the force you're producingwith the pedals in the same proportion.
Whenever you gain something from a gearyou must lose something else at the sametime to make up for it.
If thatweren't thecase, you could use gears to create energyand make what scientistscall a perpetual motion machine—and that's absolutely forbidden by alaw of physics called the conservation of energy.
Formallystated, itsays that you can't create or destroy energy, only convert it fromone form into another. To put it more informally, as my old physicsteacher used to say: “You don't get 'owt for nowt” or “There's no gain without pain”!
Where did you get those gears?
I regularly receive emails from teachers and students asking where I got the red plastic gears I've photographed in this article. They're from a wonderful construction set I had way back in the 1970s,made by a German company called Fischer Technik,which I still have today.
It was a kind of plastic version of Meccano without all the fiddly littlescrews and things, and there was equal emphasis on both static structures and dynamic machines.From their website, it seems Fischer Technik still make educational, STEM-related toys today, but I'm not sure whether you can get the full range of gears I had in my set.
If you happen to know the answer, please do let me know!
AngryAsian: Gear down to go faster
Don’t subject yourself to needless suffering on big climbs. Stock gearing isn’t always selected with this type of riding in mind – or realistic fitness levels of everyday riders James Huang/Future Publishing Cassettes are available in a wide range of sizes.
Don’t just resign yourself to using whatever came with your bike. Evaluate your climbing abilities and adjust your setup accordingly James Huang/Future Publishing wise, chainrings are available in multiple sizes, too.
Switching to a compact crankset (one with a smaller 110mm bolt circle diameter instead of the standard 130mm standard) will afford greater gear ratio selection flexibility if you need it and usually doesn’t require a mountain of additional parts James Huang/Future Publishing An online calculator such as BikeCalc.
com can help you analyze your gearing needs BikeCalc.com
Road riders are conditioned early on that they should pedal at around 90-110rpm for optimum efficiency – spin to win, or something that.
Yet as much as people follow that guideline religiously on flatter ground, many riders are all too accepting of laboriously grinding up steep climbs at far slower cadences simply because they’ve run gears. Stop needlessly suffering on the climbs. The fix is easy.
Think about the last time you tackled a long, tough pitch. Were you fluidly dancing on the pedals or grunting away in an endless set of one-legged squats you’d been banished to CrossFit hell? You may have convinced yourself that muscling up inclines is the best way to go but it’s already been proven otherwise.
“At a given power output, reducing the torque load by increasing the cadence can result in a higher power output,” said Allen Lim, physiologist and co-owner of Skratch Labs. “The constraint that we have physiologically is that if we push too hard we cut off blood flow to the legs.”
“There is an optimum torque for a given individual, much there’s an optimal torque range in a car,” he continued.
“Generally speaking, there is good research that shows that as power output goes up, the most efficient cadence for that power also goes up.
Someone doing 600 watts is going to be able to sustain that power better at 130+rpm, for example, while a lower power output of 200 watts may have an optimum of 70 to 80 rpm.”
Obviously, one way to increase your cadence is to improve your fitness so you can put out more power but there are realistic limits there. Plus, many recreational cyclists are simply out to enjoy a nice pedal in the countryside without undue suffering. Thankfully, there are easy modifications you can make to your gearing to ease the pain.
Cassettes are available in a wide range of sizes. don’t just resign yourself to using whatever came with your bike. evaluate your climbing abilities and adjust your setup accordingly: James Huang/Future Publishing
Cassettes are available in a wide range of sizes. Be realistic about your climbing abilities and then adjust your gearing accordingly
Say, for example, that your current bike’s easiest gear is a 39x25T and the best you can muster on your favorite local climb is about 8mph. At that speed, you’re turning over a relatively arduous 66rpm (thanks, BikeCalc.com!).
However, swapping to a cassette with a 28T cog (most standard road rear derailleurs can handle that) will boost your cadence to a slightly more comfortable 74rpm while switching to a compact crank with a 34T inner ring will yield 75rpm. Do both and you’re really cooking with gas at 85rpm – right in the sweet spot.
Related: What is a compact crank?
An online calculator such as bikecalc.com can help you analyze your gearing needs: BikeCalc.com
Consider using an online calculator to analyze your gearing needs
Keep in mind, too, that an increase in cadence might mean a decrease in perceived effort. In other words, you’re now either climbing at the same speed as before with less effort or going faster without any real increased exertion.
Even better, those equipment modifications don’t have to be terribly involved or expensive. Most modern rear derailleurs can handle up to a 27T or 28T cog, so changing a cassette would only require an adjustment and perhaps a new chain. Similarly, going with a compact crank would entail just a front derailleur adjustment in most cases and maybe taking out one or two chain links.
In some situations, you might need a whole new front derailleur, but even then, we’re not talking massive chests of gold here. A dramatic decrease in gear ratios via a triple crankset, on the other hand, is an entirely different story but modern two-by options has made those exceedingly rare – at least on the road.
Speaking of which, keep in mind that the concept of adjusting your gearing isn’t restricted to road riding. Though the specific choices may vary, the same rules apply to mountain bikes and cyclocross.
One shouldn’t be swayed by fashion when making these decisions, either.
Whereas once running a straight block and giant chainrings was an overt sign of machismo, modern-day racers are well versed in the scientific realities of what it takes to climb more efficiently.
Even world-class competitors at the Tour de France and Giro d’Italia are resorting to much smaller gears than just a few years ago.
Lim certainly has no doubt in his own mind of the advantages of going smaller.
“Almost always, running a lower gear on a climb will result in a faster speed,” he said. “At high threshold power outputs, if you’re not holding at least 80-90rpm you’re not going as fast as you could be.”
I need a bigger gear to go faster! (Probably not)
Going faster isn't quite that simple…
I recently spent a fair amount of time on the phone with someone convinced the only way he's going to go faster on his bike is with a bigger sprocket. He's currently got a 50 tooth up front, 11 tooth in the back.
(Before going any further, the basics of gearing are that the larger the front chainring, the higher the gear. For the rear, the smaller it is, the higher.
) To put that in perspective, he's already got a higher gear than the legendary Eddy Merckx had, probably the best bike racer who ever lived. And he was very, very fast!
A “normal” bike comes with a high gear that's probably a 50 tooth chainring up front, combined with a 12 tooth sprocket in back. With a 700 by 25c tire (normal for a road bike), you would be going 26.2 mph at a leisurely cadence (number of times your crank is going around each minute) of 80rpm.
A mere mortal cannot sustain that high a speed, regardless of gearing.
A highly-trained professional cyclist can maintain 30 mph on a bicycle designed specifically for time trials (for about an hour, racing against the clock, without other people around), but for the rest of us, 22-24 mph is the best we can hope for over a distance of greater than a mile or so. Seriously.
24 mph (with that 50/12 combination) is only 73 rotations of the pedals per minute, well within the range attainable by virtually anybody, regardless of physical strength (73 rotations of the crank per minute that is; 24 mph is another thing entirely). Even at 60 rotations per minute, you're still doing 20 miles per hour, and of the many thousands of my customers, a relatively small number can probably maintain that speed for any distance.
Will you go faster if you replace the stock chainring on your bike, the 50t one shown here, with a larger chainring, the 56t behind it? 99% of the time the answer is no, you will ly go slower.
That example is for a 50 tooth front, 12 tooth rear sprocket. The gentleman in question already had an 11 tooth rear, so at 60 rpm he's going 21.5 mph. To get to 30 mph, he's only pedaling at 83 rpm.
But the laws of physics won't allow him to get to 30 mph, unless he has a strong tailwind or is descending.
And if descending, he's going to go even faster if he tucks in a bit and gets a bit aerodynamic; pedaling will actually slow him down, due to turbulence.
But why not have that ultra-high-gear anyways? What's the harm? The human body is simply not made to produce optimal power at very low pedaling rotation speeds (rpm).
You need more horsepower than you have to push a really high gear at low RPMs. A tandem, where you have the horsepower of two people pedaling, can often make use of higher gears.
A normal person, even an abnormally-strong person, cannot.
Let's talk first-person here. Me. I'm known to be a high-gear sort of guy. People make fun of me because I use higher gears than most others that I ride with. How high? My flat-land cadence is typically around 80 RPMs (it should be closer to 90).
If I'm feeling good, I can do 21 mph using a 50 tooth chainring up front, with a 15 tooth rear.
If I shift to a higher gear, I will not go faster! I will simply pedal more slowly and my speed will gradually drop as my legs become sluggish from trying to push too hard on the pedals.
What about descending Skyline from Kings Mtn to Sky L'onda, where you can get to 40 miles per hour? My highest gear, a 50-tooth front/11-tooth rear, would have me pedaling at 112 RPMs to get to that speed. And yes, I can pedal that fast, if I want to.
But I will go faster if I don't pedal! Pedaling creates choppy air that slows you down.
The only exception to this is if you're drafting (following closely behind) a large truck, but even then you'll probably get sucked along behind it without having to pedal.
So how high a high gear do you need? For most, a 50 tooth front, 13 tooth rear would manage everything needed. There might be a very rare time something taller would be useful, but not too often.
At 90 RPMs, you'd be going 27.2 mph. Nearly every road bike (and most hybrids) have a higher gear than that though, typically with a 12-tooth in the back. That would give nearly 30 mph at 90 RPMs.
You might never have occasion to use a higher gear.
And if you've already got an 11-tooth in back (as many bikes come with stock), don't expect a receptive audience at your local bike shop as you're trying to explain your need for a bigger gear so you can go faster.
Don't take my word for it. Read what Kevin Metcalfe, a top racer (if 10,000 people read this post, there might, maybe, be a single person faster than him), has to say about gearing.
And a discussion in a triathlon group on the same subject.
Thanks for listening- Mike Jacoubowsky, former racer, present-day bicycle retailer, long-time cyclist and more patient than I should be entertaining people who think they need higher gears.