For those that are wondering about the massive injury increase with the four strokes, the biggest factor is weight. Sure they are "easier" to go faster on, so that is definitely a factor, but they really have a tendency to drive you into the ground, and the inertia plays a major factor in this. Where you can get a two stroke back under control usually during a fairly big swap, do the same on a four stroke and you are going down hard. Also, the four strokes are much harder to regather if you hit a kicker on a jump face etc. The weight behind them does you no favours. This was the biggest thing I noticed going from two, to four, and now back on the two strokes. You can correct and save a big mistake on the two bangers, but on the four stroke you just know you are going down hard !!