Do you modify the motorcycle transmission correctly? How to distinguish the condition of the motorcycle transmission?
Data:2018-12-24

I often see a lot of people asking questions about the transmission of scooter. From the discussion, I also found that everyone has different opinions on the adjustment of the motorcycle transmission.

Many newcomers, even veterans who ride motorcycles for quite some time, have little knowledge of the motorcycle transmission.

In the end, it causes a lot of people to make decisions by relying on what they heard, what the rumor said, and what the store owner said. Therefore, many problems and disputes generate.

Today we want to using data to share with you how to know the condition of your motorcycle transmission and has the modification of your transmission done right?



Before we start, please make sure what kind of the motorcycle you own and engine characteristics first. If you can’t figure these out, no matter what I say is useless.

Today, we are using Cygnus-X of YAMAHA as an example.
According to the data from OEM, the biggest horsepower of this engine is 7500 rpm and the biggest torque is 6000 rpm.



The Mileage of this motorcycle is not much, but the owner’s riding habits are very bad. He said, when he tried to accelerate, he felt he lost the engine speed. He was not able to accelerate.



We took his motorcycle and used app to measure acceleration data.



When the cellphone was set-up, we can begin the actual road-test.
We just want to test the acceleration from 0 km/h to 80 km/h.



By using APP, you can get a data chart as below:
Except for the time used for the acceleration, the most important thing is the curve line of the data.
The orange curve line is for the rising of engine speed. The green curve line is for the car speed.

The first zone of engine speed is when the clutch and the housing connect to each other, and the motorcycle begins to move.  The second zone of engine speed is the highest speed of the acceleration.
The third zone of engine speed is in acceleration when the secondary sliding sheave opens.
According to the data of the second zone, we know at the instant of the acceleration, the engine speed is rising to 8000 rpm then quickly falling.  That means some kind of slipping happens in the transmission.
According to the data of the third zone, we can see the engine speed is falling to 6500 rpm and then rising to 7000 rpm.
That means the timing of the secondary sliding sheave opening is not right, that’s why the engine speed falls so quickly.



Now we know what is the problem, so we can take the correct actions to solve the problem.
We buy the belt drive, the weight rollers and the big spring from OEM for change.

Now we know what is the problem, so we can take the correct actions to solve the problem.
We buy the belt drive, the weight rollers and the big spring from OEM for change.



After we change the components, the test data of the new transmission.
Because it is still in the break-in period, the whole performance of the acceleration is worse than the original.


From the first zone of the chart, you can see that the highest engine speed does not rise to 8000 rpm, and it’s about 7000 rpm.
From the second zone of the chart, you can see that the engine speed just falling slightly, but it’s not perfect enough yet.



After we let the new transmission run for more than 10 minutes, it almost tides over the break-in period. 
The whole chart and the acceleration time are clearly much better than the original.



From the first zone of the chart, you can see that the engine speed of the starting acceleration is about 6700 rpm, and that means the slipping has been improved.

From the second zone of the chart, you can clearly see that the speed losing problem has improved. This is a correct CVT speed variation chart.

But some sharp-eyed Internet users may notice one thing. After using the new transmission and with the correct CVT speed variation chart, although we need less time to accelerate from 0 km/h to 80 km/h, why do we need more time to accelerate from 0 km/h to 50 km/h?

In order to let everyone understand the results of the experiment, so we found the transmission kit of Cygnus-X which was developed by a well-known Taiwanese manufacturer to test.



The transmission kit includes pulleys, three different weights of weight rollers and the big spring.



First, we just change the pulleys and weight rollers (same as the original). Let’s see the acceleration performance.



After the running-in, to accelerate from 0 km/h to 80 km/h is 0.5 second faster than the original.



From the chart, you can see that the pulleys set the starting acceleration speed at 7500 rpm. That means it use the biggest horsepower to start the motorcycle, therefore it needs less time to accelerate to 80 km/h. But high rpm will definitely affect the fuel consumption.



Since changing the weight rollers and the big spring can let us have the correct CVT speed variation chart, now we further change the big spring, and what kind of performance can we get?



After actual test, if we change both the pulleys and the big spring, to accelerate from 0 km/h to 80 km/h will be a little faster.



From the engine speed chart, you can see after changing the big spring the red square area is shorter than before. That means that the time from clutch engagement to full acceleration becomes shorter, and the rest is identical.

In addition, some people may ask that the biggest horsepower of Cygnus-X is 7500 rpm, so why can the modified transmission with 7500 rpm to 8000 rpm have a better performance?

Because this Cygnus-X has a complete ECU, so the biggest horsepower is 8600 rpm.

And the power performance of the whole segment is like climbing up the plateau, to pair up with this kind of transmission can get the best effect.



I hope that through the above analysis, you can understand the operation status of the transmission on your motorcycle better, and let everyone know clearly whether the modified products that you install are really effective.

Of course, because the actual test was done on the road, the test data is somewhat affected by the wind, temperature, and slope of the road.

But you can compare the data before and after, the objective data will tell you the difference, no longer rely on feeling.



If you install some kind of modified product, and the test results are always worse than the original, then you can reasonably doubt that this modification only increase the horsepower of the spirit.