Leaving tarmac for a gravel road changes what a tyre has to do. Continental explains that a higher-volume tyre can conform to surface imperfections and give a more comfortable ride. A gravel tyre typically has greater volume and runs at a lower pressure than a road tyre. That does not produce a single pressure figure for every rider: rider weight, tyre type and the permitted range printed on the sidewall all matter.
Tread has a different role on each surface. On firm, smooth pavement, contact with the road matters more than deep knobs; a pronounced pattern can reduce the amount of rubber touching the tarmac at one time. On loose gravel, a smooth tyre may instead skate over the top layer. Tread elements help the tyre engage with that material and find traction. A tyre that feels quick on the road is therefore not automatically the best choice for a route with long unpaved sections.
Before changing tyres, consider where the bicycle will actually spend most of its time. Predominantly paved routes favour a suitable road tyre, while frequent loose sections make gravel-specific traction more valuable. Once a tyre is fitted, set pressure according to that tyre’s markings rather than a universal number. Check the rubber before and after riding, too: embedded grit and wear are easier to address when spotted early. A small choice in volume, tread and pressure can make the difference between a confident mixed-surface ride and a harsh or slippery one.