# Bore and Stroke have no effect on Horsepower (Part 1)

So I thought if I increased either of these attributes, I would actually increase the horsepower of the engine right?

**The answer is no, bore and stroke has no effect on horsepower.** Let me explain how I figured this out.

Let’s assume that there are 2 versions of the KTM Duke 125 engine – one which is over-square (bore : stroke >1) and one which is under-square (bore : stroke < 1).

The bore stroke measurements would look something like this:

The objective of this post is to prove that **these 2 different bore/stroke combinations have no effect on the horsepower made by the engine. **

Before I do this however, I need to explain 2 concepts:

- The relationship between horsepower and torque
- How you calculate torque inside a bike engine

## Horsepower – Torque relationship

Horsepower is the power made by the engine. For a given gear ratio, it determines how fast a bike can go. The more horsepower a bike has, the better it can punch through the air and reach a higher top speed.Torque is the amount of turning force exerted at the rear wheel of the bike. It is how much acceleration or ‘shove’ a rider feels when he twists the throttle at any given speed.

Horsepower and torque are related by the following equation

Horsepower = Torque x Engine rpm

*(You have to apply different conversion constants depending on whether you use lbft or Nm)*

So if if engine rpm were constant, and we can prove that torque is independent of bore and stroke, then that must mean that horsepower will also be independent.

Next week, I will continue to explain the second concept – How torque is calculated inside a bike engine.

What do you think? If you have any comments or feedback, leave a note below!