Sardinia doesn't ease you in gently. The island's interior bucked me off any romantic notions of effortless Mediterranean cycling within about twenty kilometres of leaving Cagliari — the roads rear up without warning, and the climbs are relentless, punchy, and often repeated in quick succession.
A south-to-north traverse from Cagliari to Sassari runs roughly 450–500 kilometres depending on your route choices, and most riders spread that across eight to twelve days, though you'll want the longer end if you're carrying loaded panniers or stopping properly at the nuraghi sites that appear, stone-dark and ancient, at the edges of fields and hilltops throughout the Barbagia interior.
The surface is genuinely mixed. Main roads are smooth enough, but the quieter SP routes — which are absolutely where you want to be — range from good asphalt to crumbling chip-seal with grass growing down the centre line. That is not a complaint; it is, in fact, the whole point.
Traffic on the back roads is almost nothing, and you can spend entire afternoons riding through cork oak forest without seeing another vehicle. Coastal sections near the Gulf of Orosei are spectacular, though short stretches share narrow roads with summer camper vans, so timing matters.
Accommodation is workable rather than seamless — agriturismo stays in the interior are genuinely wonderful but require advance booking and sometimes a phone call in basic Italian. Bike hire exists in Cagliari and Alghero but quality varies; I'd strongly recommend bringing your own or hiring a quality gravel bike through a specialist operator. The train network offers a useful bailout if your legs give out near Oristano or Nuoro.
Ride in April–May or September–October — summer heat above 35°C combined with exposed climbs and scarce water stops makes July and August genuinely risky.