Just tried to measure a short distance across Adelaide, using Google Maps "Directions" and noticed that, for the first time, Google gave me the option of "cycling" (in addition to the usual options of driving, walking and public transport).
The cycling directions are in Beta.
At this stage, it doesn't look like the directions favour minor roads over main roads.
I experimented by seeking directions to Elizabeth and it suggested using Hamnpstead Road to Pooraka and Main North Road to Elizabeth!
However, Google is asking for feedback so there may an opportunity to improve this tool!