Road surface condition determination device

A road surface condition determination device comprising a tire side device attached to each tire of a vehicle, and a vehicle body side system provided in a vehicle body, wherein:

• the tire side device includes a vibration detection unit configured to output a detection signal varying with a magnitude of vibration of the tire, a first control unit configured to generate road surface data indicating a road surface condition appearing in a waveform of the detection signal and measurement data for use in measuring a reception strength by the vehicle body side system, estimate an existence angle indicating a position of the tire sided device relative to a predetermined position of the tire based on the waveform of the detection signal, and cause a transmission of the road surface data at a transmission timing determined based on the existence angle, and a first data communication unit configured to transmitting the road surface data or the measurement data;
• the vehicle body side system includes a second data communication unit configured to receive, by bilateral communication with the tire side device, the road surface data and the measurement data transmitted from the first data communication unit, and a second control unit configured to determine a road surface condition of a traveling road surface of the vehicle based on the road surface data, measure a reception strength of the measurement data, store a reception strength of the measurement data in one rotation of the tire, and set a transmission angle to the existence angle at which a reception strength of the measurement data is higher than a predetermined value in one rotation of the tire;
• and
• the first control unit is configured to transmit the road surface data from the first data communication unit when the existence angle becomes the transmission angle.