Hello, I have a chinese retro 50cc scoot. when I take off the engine accelerates at 3,000-3,200 rpm throughout, and tops out just over 30mph around 3,200rpm. I know what the 3 spring on the centrifugal unit do.. I understand how the CVT works, but have never tuned one. It seems the variator weights, and this work together tuning wise. If I was just to change this spring, how would it change?? Also if I was just to change variator weights, how would it change?? thank you for your time. I am going to buy the springs from you, for your help. – Spring has sprung in Springfield
First the torque spring, or what some call the big spring. This controls the rear driven pulley sheave. Lighter springs let the sheave spread soon, stiffer later. A heavier spring is equivalent to a larger sprocket on the rear of a motorcycle, and vice versa. If your having trouble climbing hills or you hear the engine bogging a little just after take-off, you likely need a stiffer spring. To the extent that you have the above symptoms, the stiffer you need to go. Also, the heavier you and you passenger is, the stiffer you should go.
The clutch springs determine the engine speed that the clutch engages. The stiffer springs allow the engine to spin up higher, giving you a harder launch. The drawback is that you will not engage in lower engine speeds, making it kinda racy everytime you take off.
1K is good for a torque spring on a street bike. 1.5K is good if you have steep hills/mountains to deal with. 2K is only useful on a race bike. As you go heavier, the belt is pulled down sooner when you add torque to the rear wheel (as in going up hill). The CVT is balancing the torque of the rear wheel resistance against the torque the engine is producing, so with a heavy spring you get pulled back sooner off the throttle too. This means a the heavier the torque spring, the more throttle you have to give to maintain speed even down hill (2K is like always being in 1st gear). Also keep in mind the the stronger torque spring you have the heavier variator weights you need to maintain your rpm constant. Stock to 1K makes the best riding experience for most on the road.
The over simplified explanation that is very common is that heavier weights give you more top speed, and lighter weights more take off. This is true to a point, but not really. The variator weights control what is called the “constant engine speed”. I’m sure you’ve noticed when you give your scoot full throttle it holds a certain engine speed while the vehicle accelerates. The variator controls this engine speed. If your engine is above it’s maximum torque because of too light of of weight, it will not accelerate like it could. If your engine is below it’s maximum torque because of too heavy of weight, it also will not accelerate well as it will bog. So, this being said, you can actually gain top speed AND acceleration by lightening the rollers. This is true for a number of reasons. Your engine has a certain engine speed, RPM, that is it’s most powerful and most efficient, this is called the torque peak. You cannot get maximum performance without being at this RPM. Second, remember that the variator get to it’s maximum contraction almost immediately upon acceleration, and holds there, it’s the rear pulley that slowly contracts as rear wheel speed increase, thereby increasing the ratio between engine and wheel, making for more road speed.
To conclude and simplify: lighter rollers increase the “constant engine speed”, and heavier rollers decrease it.
I prefer sliders over rollers.
To get a direct interchange between rollers and sliders, go 1 gram higher on your sliders. The reason being is sliders do not need as much force to throw them out, so you do not loose 500-600 rpms like you would with every gram of rollers. Sliders expect around 300 rpm change verses 500-600 rpm changes with rollers.
Thank you for your inquiryMo