As a new bike buyer, all those numbers get overwhelming. Frame geometry, wheels standards, axle widths…before long, you feel like you’re reading an engineering textbook.
But if there’s one set of numbers worth understanding, it’s the ones we use for gearing. That’s because gearing determines a large of of how your bicycle will work and feel in use.
If you’re trying to figure out the right gears and gear ratios for your needs, but aren’t sure where to begin, then you’re in the right place.
By the end of this article, you’ll understand what all the jargon and figures mean, why they matter, and what you should choose for an enjoyable ride.
This is how many gears your commuter bike really needs
A single speed is enough for bike commuting on flat or mild terrain, but choose at least 3 speeds to deal with headwinds, heavy loads, and mild climbs. If your commute is hilly, then opt for at least 7 speeds. If your commuting bike will be used off-road, then get at least 9-11 speeds on an extra-wide-range cassette. If it will be used for sport/training road rides, then get at least 16-18 speeds with a front derailleur and standard-range cassette.
Below, we’ll take a closer look at what the common gear configurations are, how they’ve changed in recent years, and how they affect your riding experience.
First, a quick look at how we can objectively measure gearing in the first place.
Gear-inches are the simple way to compare gears
Easier gears are slower but, well, easier…and vice-versa.
But isn’t that pretty relative? What’s easy for one cyclist is tough for another, so is there any objective way to say so how do we actually figure out whether a given bike’s gearing will feel right?
The most common and intuitive is called gear-inches. That number tells you how far the rear wheel rolls with each full rotation of the pedals. Higher gear-inches means more effort but more speed, since a single pedal stroke will propel you farther. That’s the definition of a higher gear (and vice-versa).
The math is simple: it’s just the ratio of the front to rear gear size, times the circumference of the rear wheel. (That works because the gears are attached directly to the cranks and the rear wheel, so changing the relative sizes of the gears changes the torque you create from the exact same pedaling power. If that doesn’t quite make sense, don’t worry. We’ll cover it in more detail toward the end of this article.)
Front and rear gears have to accommodate the same chain, of course, so their teeth are identical. Obviously some have more or fewer teeth than others, but the teeth themselves have identical size and spacing. We can count the front teeth, count the rear teeth, and divide the two to get the gear ratio.
As for the rear wheel’s circumference, we need to measure around the tread of the tire, since that’s the part that contacts the ground. Your best bet is a calculator like this one, where you simply enter the labeled tire size and let it figure out the circumference. (Tire widths vary by a few millimeters even with the same labeled size, but this will get you plenty close.)
That linked calculator will take the tire you select, the gear tooth counts you’ve entered, and spit out a table for every possible combination.
Generally speaking, something around 30″ is good for extremely steep roads, reasonably steep off-road routes, as well as climbing with heavy loads.
On the other end of the spectrum, something like 100″ will let you zip along at a solid 30+ mph without having to pedal too quickly. Just don’t expect to make it up significant hills in that gear!
The middle of the range–let’s call it mid-50s to around 70 inches–is good for stop-and-go city riding. (For reference, my single-speed city bike is geared to 63″. But more on that below.)
Note that different people like different gear-inch measurements in the exact same setting.
Heavier, stronger, and/or more aggressive riders can apply more force (especially when standing) and might therefore like a harder but faster gear, meaning higher gear-inches. If you’re lighter, less powerful, or just not looking to work so hard, you’ll prefer lower gear-inches for an easier but slower ride.
Speaking of which, let’s see just how many gears are actually helpful in different settings.
The minimum number of bicycle gears a commuter bike needs
You can, of course, have a bike with just one gear. Single-speed bikes can actually be great for commuting, as this article discusses, since they’re inexpensive and low-maintenance. But the obvious disadvantage is having to work extremely hard on climbs, then struggling to maintain high speeds even while you spin like crazy.
An optimist would say a single speed is always the right gear, a pessimist would say it’s always the wrong gear, but all would agree it can be a lot of work!
Whether that’s acceptable is a matter of personal preference, but most riders do prefer multiple gears.
As for how many, that depends on factors like terrain, your size and strength, how you balance simplicity versus efficiency, and of course your budget.
Generally speaking, modern bikes with derailleur gears (the kind you’re almost certainly used to) have anywhere from 7 to 30 speeds. Bikes with internally-geared hubs typically have 3, 7, or 8 speeds; a few have 11, or very rarely 14.
Both derailleurs and internally-geared hubs (IGHs) are common on city bikes, so we’ll discuss both.
Note that the same number of gears may fall over different ranges. For instance, a 3-speed with 55″-60″-65″ wouldn’t be nearly as useful as one with 40″-60″80″.
Why 3 speeds are enough for most bike commuters
If your commute is truly as flat as a pancake, then a single-speed bike is a sensible choice.
But that’s seldom the case.
Most bike bike commutes are on predominantly flat city streets but with occasional climbs and descents. In that setting, three speeds are enough.
- One for general riding and cruising, in the 55″-65″ range
- One for climbing, fighting headwinds, and/or starting from a stop with a heavy load (in the 35″-45″ range)
- One for descents or wide-open routes with a tailwind (in the 75″-85″ range)
Those numbers are gear-inches, as explained above. They’re only approximate ranges, since rider size, strength, and preferences vary quite a bit.
Three speeds is also common for internally-geared hubs, which require much less frequent maintenance than derailleurs and are impervious to weather. They’re a great choice for commuters, and 3-speed hubs are the most cost-effective option.
(Three-speed derailleurs haven’t existed for many decades; modern ones begin at 7 speeds. They’re affordable, but they also require a little more maintenance than IGHs.)
When bike commuters need more speeds
Some commuters and urban cyclist have more challenging terrain.
For instance, riders in hilly places like San Francisco will want a wider range of gears to be comfortable on severe climbs. (It’s also nice to have higher gears for major descent, but at least coasting downhill is an option!)
As long as the lowest gear puts measures around 30″ or lower (use this calculator), you’ll likely be fine on even the steepest hills in town.
(Mountain bikes often have even lower gears, since off-road hills can be steeper than paved ones. Touring and cargo bikes also tend to have lower gears because of the heavy burdens they’re intended for.)
So, why not just save money on a 3-speed bike with very low gearing?
Well, the catch is that a sufficiently wide range for huge climbs would need extremely wide steps between just 3 gears. Instead, manufacturers fill in that range with additional gears–usually 7-8 of them in total. That allows for comfortable intervals between gears, but wider overall range.
Seven- and 8-speeds IGHs are readily available. They often add about $100-$150 to the price of an otherwise similar bike, since their internal planetary gears are a lot more complex than adding derailleur gears. Still, they’re a good value for most regular urban riders who want to minimize maintenance.
A cheaper alternative is a 7- or 8-speed derailleur, which are the lowest gear counts available on today’s models. In fact, these are about the same price as 3-speed IGH drivetrains.
The 7-/8-speed IGHs and derailleur drivetrains usually have similar overall ranges and similar steps between gears, but these things vary by model. If you anticipate steep hills, then always check the gear-inches calculator to make sure the bike you’re considering has something close to a 30″ gear.
In any case, this gives something like the following:
- A couple gears for extremely steep climbs
- A couple for mild climbs or starting from a stop
- A couple for general cruising
- A couple for descent or strong tailwinds
That covers nearly all the situations a bike commuter will need to pedal through. Again, you can always coast downhill, so lowest gears are the most practical important in hilly areas.
There are a few cases where you’ll want even more than 7-8 speeds. This isn’t exhaustive, but below are the two most common.
If your commuting bike will see off-road use, then look for at least 9-11 speeds with a wide-range cassette (e.g., 11-46 teeth rather than the usual 11-34 or so). The main issue is getting extremely low gears for steep off-road climbs. A front derailleur would extend the range to very high gears as well, but that’s not as helpful for dirt + city riding, so a front derailleur is seldom necessary if the cassette includes extra-low gears.
If your commuting bike will see sporty, athletic road riding, then look for 16+ speeds. More specifically, I recommend a 2- or even 3-speed front derailleur with 8-11 speeds on a standard, non-wide-range cassette. That gives you many narrow steps to help maintain a steady pedaling cadence.
A 3-speed front derailleur will also ensure low enough gears on bikes built before the 2010s, when wide-range cassettes became commonplace.
Background: the mechanics of bicycle gears
Shifting gears is intuitive, but just why shifting works might be a little mysterious. In this section, we’ll take a not-so-technical look at the physics of bicycle gears.
We’ve already covered the essentials of comparing and choosing gears, so feel free to skip this section if mechanics isn’t your thing!
Anyhow, think of your pedaling motion as one circle and the rear wheel as (obviously) another circle.
Let’s say your legs produce a steady X amount of power. If those circles are directly and proportionately connected, then X power means one pedal rotation and one wheel rotation.
Now, what if the road gets steeper? Suddenly, you’ve got to fight a lot more gravity to keep going. Your legs still produce just X power, but now some of it goes to fighting gravity, so only part of X remains to turn the wheel forward. The gear feels hard. Unless you compensate with more than X power, you’ll come to a stop.
But what if you could change how much power it takes to move the rear wheel? In other words, what if you could change the ratio of pedaling circle size to rear wheel size?
Well, it turns out you can. Not the actual size of the crankarms or the rear wheel, but the sizes of the “virtual” circles they’re connected to.
That may sound strange, so bear with me a moment.
Bikes need a chain (or belt) to transmit power, and that chain needs gear teeth on both ends to grab on to.
The front gears are bolted to your cranks and the rear gears are bolted to the rear wheel, so the front-to-rear gear ratio determines how your pedaling force gets transmitted to the rear wheel. If those gears are the same size, then one full pedal rotation means one full wheel rotation.
So far, so good?
While you only get one set of cranks and one rear wheel, you can have tons of gear ratios. That means you can change the effective size of those two circles on demand. And as the effective front circle gets smaller relative to the effective rear circle, you’re applying the same force to less rotational distance. In other words, you’re increasing torque.
That’s no coincidence. It’s precisely the point of changing gears.
Whether you shift to a smaller front gear, a larger rear gear, or both, the effect is the same: the front-to-rear ratio gets smaller so torque increases. And as torque increases, you are by definition applying the same pedaling power to less rotation, which makes it feel easier to move.
Your legs still produce just X power, but now it takes less than X power to move the rear wheel. That means X is enough to fight gravity and keep rolling instead of grinding to a halt.
The disadvantage is that the wheel won’t rotate as much with each pedal stroke, but each pedal stroke takes less effort. And when you’re going uphill or fighting headwinds, that’s a good trade-off!
The same principle works in the other direction, of course. If you make the front-to-rear ratio bigger by shifting to a larger front and/or smaller rear gear, then torque decreases and it becomes harder to move the rear wheel with the same X power.
But at the same time, you move farther for each pedal stroke, so you can maintain a higher speed.
Remember our gear-inches discussion from above? Well, that distance per pedal stroke is exactly what gear-inches measure. It all comes down to changing gear ratios in order to change torque and gear-inches.
The number of gears reflects how precisely you can set those ratios to your liking.
At this point, I hope you have a clearer idea of how the number of gears relates to your terrain and preferences. There’s no right answer, but these rules of thumb have never led me wrong.
A single speed is fine for urban riding on flat terrain, but choose 3 speeds if you’ll face a few rolling hills. Choose 7-8 speeds for significant and frequent hills, or heavy loads. Finally, look for 9+ speeds and a wide-range cassette for off-road riding, and 16+ speeds for more athletic road riding.