Every rider wants to go faster and if you can find some more power or top speed in your existing bike; that too without spending much money, who wouldn’t want it? The solution to more power or more top speed is chain/sprocket kit. You can get exact percentage gain that you can calculate before modification.
So let’s see how this magic upgrade works.
If you are looking for the relation between sprocket and acceleration/speed and don’t want to dive into the details here it is for you:
- A bigger rear sprocket/ smaller front sprocket will give you an increase in acceleration but decrease your top speed.
- A smaller rear sprocket/bigger front sprocket will reduce you acceleration but increase the top speed.
It is as simple as that. No guesswork. Now let’s look at the Sprockets in detail:
There are lots of options available in the market right from aftermarket ECU (for motorcycles having fuel injection), bigger carburettors to air filters and what not. All *claim* to provide a lot more power without any penalty in fuel economy or any other penalty. Today we want to take a look at one such mod that will deliver what you want. No guesswork about how much you would gain. It is simple mathematics.
Sprockets: What is this?
Let us first understand some basics about what sprockets are. A sprocket is a toothed wheel whose teeth engage with the links of a chain. Any motorcycle with a chain drive system has two sprockets and a chain connecting both the sprockets. The smaller one at the front is called the “Driver” while the bigger one at the rear wheel is called the “Driven” sprocket.
The transmission output shaft is the one that connects to the front sprocket (driver) and makes it rotate. The front sprocket transfers the power to rear wheel via chain and rear sprocket. So basically these two sprockets define the way power of engine is transferred to rear wheel.
What gain am I talking about?
The two sprockets provide an amazing opportunity to improve either acceleration or increase top speed. By the laws of physics, increasing either one of these two variables will lead to a decrease in the other (more on this later).
What is Sprocketing?
Altering the gear ratio of a motorcycle by modifying the sprocket is known as Sprocketing. Now how would you know how much you can gain by doing any change? It is just a formula.
Theory of Sprocketing:
Just to make it simple, let’s consider a bike which has 1 tooth in the front sprocket and 2 teeth in the rear sprocket. Since the two sprockets are connected by a chain, so for each rotation of the rear sprocket the front sprocket makes 2 rotation. (Another way to put this would be for 1 rotation of front sprocket, the rear makes half a rotation)
Let’s say I want to increase the acceleration. I can either increase the size of rear sprocket or reduce the size of front sprocket. Let’s say we decided to increase the no of teeth in rear by 2 (from 2 teeth to 4 teeth).
After the change, for each rotation of the rear sprocket, the front makes 4 rotations (as compared to 2 rotations of stock setup). The other way round it would mean that 1 rotation in front sprocket will cause the rear sprocket to make 1/4=0.25 rotations. Now how can it possibly lead to an increase in acceleration?
Because of increase in number of teeth of rear sprocket, the overall diameter of the rear sprocket has increased. As the chain fits on edge of the sprockets, the length from the center of rear sprocket (center of rear wheel axle) to the edge of rear sprocket would increase (how much the increase is depends on increase in number of teeth). Because of increase in length, the leverage that it would get would increase proportionately. You must have seen truck drivers using long levers to remove bolts from wheels of their trucks. Why? To increase the torque they can apply. The same principle applies here.
Second impact of this mod – As the rear sprocket is mounted on the wheel, this means that the rear wheel is also making (0.5-0.25 =) 0.25 lesser rotations after the change. It also means that the top speed in each gear will reduce.
Tips while sprocketing:
It is usually recommended to tweak the rear sprocket rather than front sprocket. There are two reasons for this:
- Reducing the number of teeth in front sprocket will cause the chain to turn around the sprocket at a tighter radius which in turn will increase friction and cause more wear & tear.
- As the rear sprocket is bigger (has more teeth), changes in rear sprocket allows for a much finer adjustment as compared to front.
Points to Remember:
- To increase low end power, you should increase size of rear sprocket or decrease size of front sprocket.
- To increase top speed, you should reduce size of rear sprocket or increase size of front sprocket.
- Before you decide to increase top speed of the bike, know whether your bike’s engine is capable of generating sufficient torque to make use of the taller gearing.
- The pitch of the sprocket should always be the same when sprocketing.
What are sprockets made of:
Sprockets are typically made from steel or aluminum. Steel sprockets are generally less expensive, and better for longevity. The best steel sprockets use hardened and heat-treated steel. Sprockets made of aluminum are significantly lighter, but have a shorter life span, and are more expensive than steel.
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