What I wonder about: When I select fastest route for routing, my garmin oviously prefers bigger roads than small biking roads.
It should be the other way around.
I guess, this works byt the “maxspeed” for the streets, is that correct?
Could one not, for creating biking maps, set the maxspeed for a bigger road to much lower than a biking road?
Is that already done for biking maps?
I can’t comment on that particular map as I’ve not used it, but I’ve seen a couple of other comments about the same issue recently.
It might be worth trying some other specific maps for cycling, in particular: http://openmtbmap.org/.
Failing that you could look a creating your own map. Mkgmap for example allows you to specify your own style files. This allows you to set the type of road, its class (which seems to be for routing priority), speed and access. For example you could set motorways to have access=no, and then set trunk roads to have a low class (ie. low routing priority) and low speed (which will discourage routing on those roads).