Developed specifically for the Arctic/Yamaha Z120 this kit will increase both acceleration and speed without sacrificing any of their abilities to go through deep snow. When testing and developing this kit, we use our stalker ats system to ensure that our results are both accurate and honest. Stock spped is about 8MPH, this kit can boost speed up to 12-15 MPH depending on rider and snow conditions. These kits are easy to install (under 1 hour) and include a gear, hub, chain and governor rod/spring. ISR legal. Uses #40 chain. We also recommend a billet chain adjuster,(Part# 430-215) this helps eliminate unnecessary wear, reduces friction and allows kit to perform to its potential.