Tyre choice affects grip, rolling resistance, and comfort more than most other single component, and matching tyre type to terrain makes a bigger difference than most riders expect.
Slick or lightly-treaded tyres roll fastest and most efficiently on smooth pavement, since there's no loose surface for aggressive tread to grip. Knobby, deep-tread tyres do the opposite trade: more rolling resistance on pavement, but real grip advantage on loose dirt, gravel, or mud where a smooth tyre would slip.
Width matters alongside tread: a wider tyre run at slightly lower pressure absorbs bumps better and grips loose surfaces more confidently, while a narrower tyre at higher pressure rolls faster on smooth roads. A mountain bike's wide, knobby tyres and a road bike's narrow, smooth ones aren't just styling choices — they're matched to genuinely different surfaces.