Jack and Richard were placed third and fourth respectively in the 1903 Timaru to Christchurch road race which was over a distance of 112 miles (180 km).

Rough shingle roads and unbridged streams and rivers made for hard going but he covered the distance in 12 hours and 31 minutes.

His brother, Richard Arnst, and another person paced the rider on motorcycles, and a car followed carrying food and spares.

The record was never recognised officially as the Arnst team had failed to include an observer from the League of Wheelmen who controlled such matters.

Arnst enlisted with the New Zealand Expeditionary Force and served as a private with the Canterbury Regiment.