On the highways it’s not the surface, it’s the width of shoulder that counts.
WA? They are often great.
South Australia? Tight.
But that’s not where you are going to be spending your time. The highways have way too much traffic of the moronic kind.
The old unsealed boneshaker highways are slowly but remorselessly being improved. The governments have realised with the increased traffic that it’s better to spend the money to reduce overall maintenance costs. They are seriously considering completely sealing the Tanami Track and it won’t be the one lane the first 130km currently is. Even the Gibb River Road is nothing like the 4WD track it was 15 years ago where if you hadn’t popped the tops off half your bottles of beer at the end it wasn’t too rough a trip.
Many of the big name unsealed roads are regularly maintained: Great Central Road, anything in the Northern Territory.
Rain causes problems with washouts etc but there are huge fines for hacking up a wet road when trucks or cars ignore the road closed signs. Add water to some of the clay based roads and they become impassably sticky, clagging right up.
Maintenance on a road may be great news for those in a 4WD as the corrugations disappear but for those on a bike this can have a different consequence. Moving the loose stuff around can just make the entire road width equally soft and needing considerably more effort to traverse on two wheels.
The good news is that many of the remote roads have little heavy traffic to smash them up and they can be great riding.