18 Speed Bike vs 21 Speed – What’s The Difference?

18-speed bikes and 21-speed bikes are two of the most popular gearing groupset among most cyclists. But what are the main differences between the two?

18-speed bikes are cheaper, suitable for shorter and rougher terrains. On the other hand, 21-speed bikes are faster and smoother but expensive.

I’ve ridden both 18-speed bikes, and 21-speed, and in this guide, I’ll go through the technology involved in these different gear systems, and the differences between the two. By the end, you’ll know what’s right for you based on a range of factors that will be personal to you.

Understanding Bike Gears

The number of gears is determined by the number of chainrings at the front and the number of sprockets (or cogs) at the rear wheel; the gear ratio by multiplication between the both.

For instance, the gear combinations of a bike with 6 sprockets and 2 chainrings will be 12, and it’ll be called a 12-speed bike. 

Contrary to the popular misconception that the purpose of gears is to make the bike faster, the gears offer cyclists the ability to maintain a preferred and comfortable paddling speed on different types of routes and terrains.

The more the number of gears, the more options and the broader the range will be in various situations.

The highest gear in any bike is achieved by combining the smallest sprocket and the largest chainring.

Similarly, the smallest gear is achieved by riding with the chain moving on the largest sprocket and the smallest chainring.

Higher gears are suitable for riding fast with relatively little effort and on descending routes. Smaller gears are used for climbing up on steep hills. 

What Are Triple Chainring Bikes?

As the name suggests, triple chainring bikes have three chainrings at the front.

The biggest of these chainrings (outermost chainring) is usually 50t, the middle one is 39t, and the smallest chainring is 30t (can be smaller in some bikes). This combination is preferred mainly by cyclists in hilly areas or those who travel with a lot of luggage. 

Both types of bikes this article is concerned with, i.e., 18 speed and 21 speed, are triple chainring bikes. 

21 Speed Bikes

A 21-speed bike has 7 rear gears (7 sprockets on the rear wheel) and 3 front gears (3 chainrings at the front). When you multiply both figures, you get 21.

You can achieve many gear ratios by switching the chain between chainrings and sprockets. 

21-speed bikes offer cyclists a wide variety of gear combinations, enabling them to use their energy most efficiently when climbing up a steep route and paddle relatively less for a much faster pace. 

The bikes are specifically designed for those who prefer to enjoy views from the saddle.

The gear arrangement helps riders to worry less and apply smaller force at high speed.

When shifted to the highest gear, the chain sets itself on the largest chainring and the smallest cog on the back. This setting makes the rear wheel spin more with the same amount of paddling, pushing the bike further. 

As aforementioned, the second perk of riding a 21-speed bike is the ability to exert more power than possible with most bikes.

When the chain is set on the lowest gear, it jumps to the smallest chainring on the cassette and the largest sprocket. This setup requires more paddling for one spin of the rear wheel. 

Gear overlapping is common in bikes with a high number of gears.

It happens when two or more chainring and rear sprocket combinations result in the same ratio and cadence. For example, the two combinations: 53×19 & 39×14, result in the same gear ratio.

This overlapping is unavoidable in 21-speed bikes and occurs much more than the slower bikes, such as 7, 12, or 18. 

18 Speed Bikes

18-speed bikes, as the name suggests, consist of 18 gear combinations.

This number is achieved by different chain positions using 3 front gears (3 chainrings fixed to the seat tube) and 6 rear gears (6 cogs on the rear wheel). 

For cyclists who want to upgrade from their lower-speed bikes, 18 speed bikes are great. Not only do these bikes offer more momentum-building features, but they are also more compatible than high gear number bikes for rough terrains. 

Although 18-speed bikes have just 6 sprockets, gear working logic is exactly similar to 21.

The smallest gears are the best gear ratio for uphill cycling, while the highest gear setting provides maximum momentum and fast speed. 

Cyclists riding narrow gear option bikes, like 7 speed, 12 speed, or 14-speed bikes, are used to paddling with more force to achieve a high speed and are unable to use the maximum potential of their leg muscles to ride on an inclined route.

So, when upgraded to 18-speed bikes, they can enjoy and benefit from much more comfortable and efficient rides. 

Due to having lesser hardware than high-speed bikes (21, 27, and 31), 18-speed bikes are comparatively lighter and easier to handle for less experienced riders.

Moreover, most new cyclists get easily confused choosing a suitable cadence for themselves, especially when exposed to too many options. So, fewer gear options also mean less managing fuss. 

18-speed bikes are undoubtedly more comfortable and faster for anyone who has been riding on fixed gear or low-speed bicycles, but for longer routes, they aren’t as suitable as some higher-end and more jacked-up options.

Bikers tend to get tired more because the number of cogs in 18-speed bikes is limited to 6. 

As far as gear overlapping is concerned, it does happen in 18-speed bikes, just like the rest of all high-speed bikes, but it is much rarer than most. 

18 Speed Bike and 21 Speed: Which Is Better?

Now that I have explained the making and functioning of 18-speed bikes and 21-speed bikes, it is time for a head-to-head comparison to decide which one is better and worth your money.  

Gears Setup

The most obvious difference between both bikes is the different number of gears and different gear setups.

Both differ by one rear gear. 21-speed bikes have 7 sprockets with 3 chainrings at the front, while 18-speed bikes have 6 rear sprockets with the same number of chainrings.

Momentum Building & More Peddling Power

As 18-speed bikes have one less cog, 21-speed bikes beat them in either of these two situations: 

• If the largest cog of the 18-speed bike is smaller than the 21-speed bike’s largest cog, it won’t be much help when climbing an inclined terrain.
• If the smallest cog of the 18-speed bike is larger than the other one, the ride won’t be as comfortable, and the highest achievable speed will be less.

Price Difference

Price is a huge factor to think about before investing in your future ride.

21-speed bikes are considered newer tech, faster, and more comfortable. These bikes offer a few features that aren’t present in any low-gear cycles.

So these perks add to the price of the bikes, making them more expensive. 

Weight

Weight is one of the most important factors to consider when buying bikes. Lightweight bikes are easier to handle and ride, thus are preferred by most cyclists. 

Although there is not much difference between the weight of 21-speed bikes and 18-speed bikes, the latter has a little less hardware (one less sprocket at the rear wheel) which, technically, makes it lighter. 

If weight matters to you a lot, an 18-speed bike is a better option to go for. 

Gear Confusion

Experienced and regular cyclists have no problem switching between gears according to varying situations.

But understanding and using gears isn’t very easy for bikers who are new to this sport. If a lot of gear options are given to someone with minimal cycling experience, chances are they will quickly get confused. 

21-speed bikes aren’t recommended for beginners to avoid gear confusion.

But if you still want to have that variety and comfort, you can upgrade to 21-speed bikes after you have gotten some experience with lower gear bikes. 

Long Rides Compatibility 

Long ride compatibility is another factor that might make riders prefer 21-speed bikes for ease and comfort.

When you switch to the largest (or highest) gear, your chain changes its position and jumps on the outermost chainring and smallest rear sprocket.

This chain setup causes the rear wheel to spin more with the same amount of peddling; such efficiency builds momentum for high speed on long routes. 

Graveyard Shift

The term “Graveyard Shift” is used for the gear shifts that cause the most stress on the chain.

In most bikes, these graveyard shifts are the smallest and the largest gear positions where the chain is adjusted on the smallest chainring and the largest rear cog, or vice versa. Riding your bike on these gears stresses the chain a lot; leading to wearing it. 

21-speed bikes have one rear sprocket more (either smaller or larger) than 18-speed bikes, and it results in a graveyard shift that is much more stressful for the chain.

Conclusion

Choosing which of the two bikes is better overall is subjective. In general, there is not a huge difference between the two types of bike.

This decision will vary from user to user, depending on individual factors and preferences. But it is essential that you evaluate all your needs and expectations, so you don’t end up spending your money on a bike just to find out that it doesn’t match your requirements well. 

For cyclists who love to ride on long routes and take on multiple steep terrains, 21-speed bikes seem to be a more suitable option.

But if you want just to upgrade your ride from a low gear bike to something better and faster, you can go for the much less expensive option of 18-speed bikes.