The ZS155 engine, although more expensive, has proven to be as reliable as its smaller YX140 counterpart. It also boasts the upgraded SDG2 frame and the Detroit plastics, as well as the updated PRO foot pegs and polished hubs. Giving a massive 17hp at the rear wheel, the ZS155 engine is a force to be reckoned with. Reliability and power make this all round awesome bike. Ready to race your mates, straight out of the crate, this bike is a sure winner!