I cant beleive the tosh you guys have written. The overlap stroke of a four stroke is what produces grip. When engines of similar power and torqe are deployed in any sport, the four stroke will win hands down in the grip department. Hence Speedway ,grasstrack ,motocross, Ducati in world superbike etc. The only thing that four stokes have suffered with is a relatively poor power to weight ratio. Thihgs have realy changed in recent years with fuel injection,engine management system,multi valves,air type valve return,variable valve timing etc. The only downsides being expence and very complicated engineering both mechanical and electronic. Do we need the modern four stroke in our sport? The customers will vote with their wallets.