Bicycle (OSRM) does not find shortest route

On when asked to find directions from -35.1352, 149.1963 to -35.1094, 149.2467 using Bicycle (OSRM) chooses an 11km route while Car (OSRM) [and curiously Bicycle (GraphHopper)] chooses the more direct 5.7km route. My Garmin Zumo, using an OSM map, when set for Motorcycle use, also chooses the longer route but when set for car use chooses the shorter route.

What is it about the two wheel vehicle setting that causes the different choice?

I assume the reason is the surface=unpaved on Mulligans Flat Road

That what I was thinking. I’ve corrected that section of road now - it’s been paved for years - so we’ll see what happens, but if that is so, I don’t understand why Bicycle (GraphHopper) takes the shorter unpaved route.
My Zumo didn’t take the unpaved road because it was set to paved roads only. It would be nice if OSM/directions had a similar paved/unpaved setting.

For bicycle routes you can try brouter, it can be configured:

I’ve corrected the road on OSM now - I’d missed a bridge that was also listed as unpaved. Bicycle (OSRM) still won’t use it. So the problem isn’t due to the road surface as far as I can see. There is something about the OSRM router that I don’t understand. Hopefully the OSRM forum will enlighten me.

This problem began when I installed the OSM maps on my Zumo. I use that almost exclusively on my motorcycle, and it routes differently for that than it does in car mode. I’ve yet to install the corrected OSM maps, so we’ll see.

I can’t see now that this is a problem with OSM. It must be the router.

You may have to wait until OSRM updates its data.

I just got a reply from the OSRM forum about that routing engine:-

“The OSRM instance accessible from has “Car”, “Bike” and “Foot” routing graphs, each of which prioritises certain types of roads/paths. So in that way, it’s certainly possible to set up an instance that has a “Bike, paved only” and a “Bike, unpaved fine” or even a “Bike, prefer unpaved” graph.
However, the people who kindly operate the routing server used by have chosen to operate those three graphs only.”

So OSM could fix it if sufficiently motivated.

I just checked that route again and the map has been updated by OSM. “Bike (OSRM)” now routes through that corrected section, so I know now that “Bike (OSRM)” means paved only.