Any helmet is better than none ! Now ask yourself how fast you plan to ride. If you build a gas or electric bike and ride it no faster than someone would ride a peddle powered bike at speed, you could get by with a good bicycle helmet. On the other hand, if you plan to ride your motorized bike at motorcycle speeds then get a real motorcycle helmet. Realize also that most bicycle frames and wheels/tires are not built for high speeds, especially when you add the weight, torque, and vibration associated with these gas engines. Expect and plan to wreck, protect your noggin !!