Ok for racing!
Suits 50cc Honda 2-stroke and 4-stroke auto scooters, as well as many two stroke 80cc and 90cc. Spring rate is higher than standard and suits mild to medium tuned scooters (modified with more engine power).
This can be used to stop bogging of the clutch on big bore engines, also helps keep RPM higher during acceleration by slowing the rate that the variator moves the belt. Additionally the pulleys grab the belt more strongly and allows less slip, improving acceleration.
This stiffer centre spring can also improve acceleration out of corners and other situations where the throttle is released then reapplied.
Also fits most Chinese 49cc / 50cc 4 stroke scooters (QMA139 / QMB139 engines), may include Ciclone, Meiduo, Fada, Sunny, JM Star, Meteor, 50QT, YYQT50, Huawin, Motostar, Baotian, Boatian, Solana, Arrow, Fierce, Forza, "Factory Built", Wolfboy, Qingqi, Kinroad, Lifan etc also other generic brands registered as "Moped" etc)