Motorcycles come in all shapes and sizes, and there will always be one that suits your riding style. Just like motorcycles, their engines too come with various cubic capacities and configurations. The higher the displacement of a motorcycle, more the number of cylinders you will need to have on it to make it run smoother. While most motorcycles are powered by a single cylinder engine, they may have up to four cylinders. In India, however, single-cylinder engines are the most popular and form over 90% of the total number of motorcycles on the streets. They are followed by twin-cylinder engines, with the triple and four-cylinder engines being a relative rarity. Since single cylinder and twin cylinder engines are the most common, let’s understand what these engines really are, and what are their respective pros and cons.
Single And Twin Cylinder Engines - Understanding The Basics
The first difference between both the engines is the number of cylinders they have. Since there is an extra cylinder on twin cylinder bikes, there is naturally an extra piston as well accompanied by all the associated components. With all that extra componentry twin cylinder engines are more complex, and generally more expensive to manufacture. Also, while it’s not a rule of thumb, single cylinder engines are mostly used in relatively lower displacement motorcycles whereas twin cylinders are used in bigger displacement engines.
Single cylinder engines are simple to produce, and they come with a ton of advantages, with ample torque, fuel-efficiency and low-end grunt being their biggest USPs. Having said that, for their cubic capacity, the size of the piston and other components is heavy. Also, as the piston goes up and down the cylinder, it creates a force, which isn’t often balanced, and if not checked, leads to vibrations. Quality motorcycle manufacturers, eliminate this vice effectively using counterweights. These counterweights, or additional weights meant to counter the engine imbalance, are generally located at the end of the connecting rod, opposite to the end that connects to the piston. Engines which have such a counterbalancing mechanism are known as counter balanced engines. Another method to negate the vibrations of a single cylinder engine is to use rubber mounts at points where the engine is bolted on to the chassis, although this method is not as effective as adding counterweights. Rubber mounts absorb a good part of the vibrations released by the engine, and reduce the sensation of vibrations for the rider, though they don’t eliminate the vibrations at their origin like counter balancers.
Twin cylinder engines, on the other hand, are better balanced. With twin cylinder engines there are various configurations available, such as parallel twin, V twin, L twin or flat twin engines. On top of the engine layouts, there are also firing orders, which can vary from 90 degrees to 360 degrees. Twin engines are better balanced than single cylinder engines, and, some configurations such as flat twins, also known as boxer engines, are the most naturally balanced, as the disbalancing forces effectively cancel themselves out. This makes twin cylinder engines more refined and vibe free as compared to their single cylinder counterparts.
To displace any given cubic capacity, a single cylinder engine makes use of bigger, heavier components. For the same cubic capacity, a twin cylinder engine will have lighter componentry as the cubic capacity to be displaced is divided in two parts, and a smaller volume needs smaller and lighter components to be displaced. Do note, that while the internal componentry will be lighter, with the need of two separate cylinders and additional parts, the overall weight of the engine will be heavier than a similar capacity single-cylinder engine. The lighter componentry, however, along with a relatively balanced and vibe free nature of twin cylinder engines, makes them more revv happy, so they can reach a higher rpm and produce more power for any given cubic capacity.
On the other hand, while single cylinder engines aren’t the most high-revving, their longer strokes and heavier componentry allows them to create a lot better torque, and that too at the lower end of the rev spectrum, making them very usable and tractable in low to mid revs.
A single cylinder engine creates more torque lower down the rev range, while a twin creates more power higher up the rev range, with somewhat compromises torque delivery at the lower end. This makes single cylinder bikes more suitable for applications such as ADVs, dirt bikes, commuter bikes and for all the applications which require more torque and better acceleration in the lower revs. Twin cylinder engines on the other hand are more suitable for sportbikes, where the lighter componentry has to make a wee bit more effort initially to lift the load and get moving, but ultimately can deliver better performance higher up the rev range.
Both single and twin engines can be tuned for their characteristics, but in general, both varieties are quite linear and user friendly in terms of power delivery. Single cylinder engines are stronger in low through mid revs, with the twins having an edge in mid to high revs.
With the basics out of the way, let’s now talk about the respective advantages and disadvantages of single and twin cylinder engines.
Single cylinder engines - advantages
Single cylinder engines are less expensive to build. With lesser components required, and the overall weight of the engine being low, the cost advantage that single cylinder engines offer over twins is quite significant, and often tilts the buyer’s decision in their favour.
Better torque and low-end performance
Thanks to their larger bores and strokes, single cylinder engines produce higher torque at lower revs, making them more suitable for load lugging and for applications where high torque is required lower down the rev range.
While there may be exceptions, where lighter materials and more modern and expensive technology is used, but as a rule, for any given cubic capacity, single cylinder engines are more fuel-efficient as compared to twins.
Lower cost of maintenance
With their simple construction and lesser number of moving parts, single cylinder engines are easy to maintain and repair. The cost of replacement of parts for single cylinder engines is also significantly lower than their twin engine counterparts.
While not exactly an advantage for everyone, some users appreciate the heavy beat from the engine and exhaust that single cylinder engines produce.
Single cylinder engine - disadvantages
Not the smoothest
As mentioned before, single cylinder engines are prone to vibrations, and while bike makers have devised various means to make them smoother, inherently, they are not the smoothest running engine design.
Lower top end performance
While single cylinder engines produce better torque in low to mid revs, their maximum power output is not as much as twin cylinder engines. They are also not as strong as twin cylinder engines higher up the rev range.
They cannot be used in applications beyond a certain cubic capacity as the componentry gets too heavy and unwieldy for practical use. Too big an engine with a single cylinder layout would be very vibey and would require an exceptionally strong construction to withstand its inner forces.
Twin cylinder engines - advantages
As discussed above, twin cylinder engines are better balanced, and thus more refined than single cylinder engines. The internal forces within a twin cylinder engine are better counterbalanced by the movement of the two pistons, and thus they can rev higher while being less vibey.
With lighter componentry, and smaller cubic capacity per cylinder to displace, twins are more eager and intent than their single cylinder brethren. The specific output of twin cylinder engines is generally higher than single cylinder engines. These engines also spin faster, creating a sportier experience for the rider.
While some users may dig the ‘bassier’ beat of a single cylinder engine, it isn’t desirable for everyone. Twin cylinder engines produce a more harmonious sound, which is often craved for by biking enthusiasts.
Twin cylinder engines - disadvantages
Due to their relatively complicated design, bigger size, and larger number of components, the production cost of twin cylinder engines is higher. The difference in the cost of a single and twin engine is quite significant which is a severe disadvantage for twins.
Bigger and heavier overall
While the internal components of a twin engine compared individually with those of a single are smaller, the former has roughly twice the number of components of the latter. The overall engine area and the larger number of parts make a twin cylinder engine heavier than a single, thus negatively affecting the overall weight of the bike as well.
Higher cost of maintenance
Not just are twin cylinder engines costly to own, their complex construction makes their spares more expensive to procure as well. Repairing a twin cylinder engine is also more cumbersome than the single cylinder.
Twin cylinder engines aren’t as efficient as their single cylinder variants and are generally heavier on the pocket from a fuel consumption perspective.
Twin cylinder engines produce less torque at the lower rev range and might feel sluggish when riding at city speeds. They produce more power higher up the rev range, but they also require more gearshifts and require to be ridden in lower gears at slow to mid speeds.
Both single and twin cylinder engines have their own perks and quirks which shape the characteristics of the motorcycles they power. It is very important for one to understand the use case and requirements from a motorcycle to choose the right engine configuration. For city use, or even a mix of city and highway, a well-made single cylinder may be the best choice, especially for a limited budget. If you are willing to dish out the extra money, a twin cylinder engine powered motorcycle might be better suited for performance-oriented applications.