Speech recognition should be as an eyes-free and hands-free interface. To realise this technology, we need to clarify acoustics in a helmet and determine how much high-level riding noise affects captured speech data. This paper describes the acoustics in a helmet and transfer functions of the microphone position. We constructed a data collection system and collected the speech data of motorbike riders on city roads and express highways. Speech recognition experiments were conducted and we obtained a recognition rate high of 83.1%.