A coroner has warned drivers of the dangers of being distracted in the car after finding a young motorist caused the death of a cyclist.

Jackson Costa was 19 when he crashed into the back of Geelong sporting identity Rex Sizeland and one of his two riding companions outside Torquay on the morning of December 21, 2009. Mr Sizeland, 66, died the next day in hospital from a head injury.

Coroner Kim Parkinson found Mr Costa was responsible for Mr Sizeland's death.

Ms Parkinson said in her report that she was troubled by the timing of the receipt of a text message on Mr Costa's mobile phone and the collision, which happened shortly after.

A police officer who investigated the crash told Mr Sizeland's inquest he believed Mr Costa was probably reading the text message when he hit the cyclists. Mr Costa denied this.