Long Stroke Vs Short Stroke Engines

  • Author :
  • TATA AIG Team
  • Published on :
  • 12/09/2023

Freshly minted bike enthusiasts who read about the technical aspects mentioned in bike specifications often come across terms that can confuse them. However, because each element of a bike plays a distinct role in determining its functionality, it is important to learn of these discrete elements. Understanding what is stroke in a bike and the difference between short stroke vs long stroke is among the first few things to learn. However, before exploring the details of piston stroke and stroke length, it is important to understand the importance of two-wheeler insurance.

Third-party insurance for 2-wheelers is a mandatory requirement to legally ride on Indian roads. However, a third-party cover only compensates for third-party liabilities and not for own damages. Therefore, bike owners are often advised to invest in a bike insurance policy that secures the vehicle and the owner, and also covers third-party damages. With the rising number of road accidents in the country, comprehensive insurance for 2-wheelers is an indispensable requirement.

Having understood the importance of a comprehensive bike insurance policy, let us now understand what is stroke in a bike’s engine.

Understanding the Stroke in Bike

The stroke of your bike, or more appropriately, the stroke length, refers to how far the piston would be travelling in the cylinder. In other words, the distance travelled by the piston during each cycle (from zero degrees to 180 degrees) is called the piston stroke. This is determined by the cranks in the crankshaft. To understand this concept in detail, it is important to know about the engine bore and stroke.

The engine's cylinder is a circular hole carved from a block of metal. This makes for its volume and the displacement or the cubic capacity (cc) of the bike’s engine. In this context, the bore is the diameter of the circular opening at the end, whereas the stroke refers to the depth of this hole.

The Bore-Stroke Ratio

The role of engine bore and stroke make little sense unless they are understood in unison. For this, it is important to understand the concept of the bore-stroke ratio.

Understandably, there are several ways to carve out a cylinder inside a metal block. Depending on the required cubic capacity, the circular opening can be adjusted to be big or small with less or more depth. The ratio between the bore and the stroke is what determines the engine category. Essentially, these configurations are of three kinds:

Short-Stroke Engines: An engine with a cylinder configuration wherein the stroke is shorter than the bore is called a short-stroke engine

Long-Stroke Engines: When the bore is shorter than the stroke, it is termed a long-stroke engine

Square Engines: Finally, if the cylinder is made with exactly the same measurement of the bore and the stroke, it is called a square cylinder

A short-stroke engine is often called an over-square engine, whereas a long-stroke engine is called an under-stroke engine.

Now that we have understood what each of these terms means, let's compare the functionality of the short stroke vs long stroke engines.

Characteristics of a Short-Stroke (Over-Square) Engine

The bore-stroke ratio of the short-stroke engine is greater than 1 as these cylinders have a greater bore diameter than the length of their stroke. This means that the valves inside the head of the cylinder are larger. This kind of engine has a higher RPM (rotation per minute) while retaining the torque. Moreover, the piston in this engine has a large surface area, so the heat loss is much higher. This happens because the heat is dissipated not only from the top but also from the sides. These characteristics incline towards providing higher engine speeds and are typically used for lightweight sports bikes.

As the stroke is relatively shorter in this type of engine, the revving is also comparatively faster. These engines are, therefore, more suitable for riders looking for a quick power build. This happens because the stroke does not have to travel too far, so it can produce higher revs in a shorter amount of time. The peak power of a short-stroke engine is usually higher up the rev range. However, a caveat of this kind of engine is that the low-speed tractability is compromised.

Characteristics of a Long-Stroke (Under-Square) Engine

In this kind of engine, the bore-stroke ratio is less than 1 because these engines have a small bore compared to their stroke. For the engine's speed, a longer stroke would increase the engine's friction, which in turn increases stress on the crankshaft. This happens because of the higher acceleration of the peak piston.

Compared to a short-stroke engine, the long-stroke engine reaches its peak torque at a relatively lower RPM. As these kinds of engines are a lot more efficient, they are used in commercially selling vehicles. Another primary reason for its adoption is that the long-stroke engine is characterised by greater fuel efficiency. Even the heat dissipation in this kind of engine is a lot more effortless because of its greater volume-to-surface area ratio.

However, because the piston in this engine has to cover a lot more distance, the long-stroke engine does not produce as much power. Regardless, these kinds of engines create the perfect amount of torque in the lower range. Therefore, the long-stroke engine is best-suited for cruisers, tourers, and long-distance bikes.

Wrapping Up

The stroke of the engine can help determine what kind of bike a rider would prefer. If you are looking for high-speed bikes, go for a short-stroke engine. Conversely, if you are seeking a bike that would accompany you for long journeys and is also fuel efficient, you can choose a long-stroke engine. However, regardless of the bike you choose, make sure to adequately secure it with a comprehensive bike insurance policy.

Without the right two-wheeler insurance, the vehicle owner has to bear the cost of any damages, repairs, and replacements from their own pocket. With insurance for the 2-wheeler, however, both your bike and your finances are appropriately protected from unfortunate road mishaps. Whenever you buy two-wheeler insurance, make sure you analyse your insurance needs and compare two-wheeler insurance policies to find suitable coverage. With Tata AIG’s comprehensive bike insurance policy, the insurance seeker can choose from eight unique add-ons to customise their policy and enhance insurance protection.

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