Recently there was a question on twitter regarding how we pick routes for biking.
There are many properties that should be and can be considered when biking. First of all we need to determine the speed to estimate the arrival time. The speed depends on the surface, type of highway and also elevation and potential other properties.
Additionally we put a penalty on ugly or dangerous road settings like a road without a cycle path which gets even more dangerous when you have this setting in a tunnel or when cars can go faster than 50km/h. Furthermore we prefer certain roads like the one that are part of an official cycle network or where the road is a pure bicycle-street.
These settings are highly tuned and can be even further improved. So if you find something wrong - please let us know!
You can this bike mode (and all the others via clicking on the dots) in GraphHopper Maps and the full details can be viewed in our open source routing engine as Java code.