Sat Nav Route preferences

[George IV]

I have my sat nav set for quickest route Need a way of setting it so it does not send me on single track roads where the speed limit is 60 but owing to farm traffic and bends i am lucky to average 20. Have tried setting it to shortest route but again it tries to send me on the same route.
On recent trip i followed sat nav and it took 90 mins on return i stayed on main roads 15 miles longer but 30 mins quicker.

[VeeFourTee]

Have the same problem.   Never worked out how to get a decent route - sometimes revert to my Garmin or just used Google Maps!