Changing out the rollers is one of the best bang-for-the-buck upgrades there is for 150cc GY6.
Roller weights provide the up shifting forces for the CVT transmission by flinging outwards within the variator in varying stages of engine RPM. Roller weight tuning is a matter of preference and riding terrain. A lighter weight will fling outward slower than a heavier weight, slowing the up shift process. The stock 14.5g weights are rather heavy and up shift very fast in the RPM cycle, resulting in hindered acceleration and low-end grunt.
What to expect from different roller weights:
9 gram rollers - Unbeatable low-end grunt. However, this light weight will reduce top speed by 2-3 mph, and also hurts acceleration.
Best for hill climbing, mud, sand, water and other loose terrain.
10 gram rollers - Great for overall performance. Spins most stock tires from a standstill with other supporting CVT mods. Good sustainable low-end power and optimal acceleration on hard-packed terrain. Does not reduce top-speed.
Best for pavement racing.
12 gram rollers - Reduced wheel spin at takeoff relative to 10 gram rollers, and smooths out acceleration. Terrible low-end torque when compared to 9 and 10 gram weights. Otherwise they function the same as 10 gram weights.
Best for loose terrain racing.
