Road bikes are used on hard surfaces, where a slick tire will give the most traction/friction with the least rolling resistance. MTBs are intended to be used off road, where knobbly tires are needed to dig into the sand/dirt/mud in order to provide traction/friction.
It's the same reason behind jeeps and 4x4 cars having much knobblier tires than ordinary road cars.
Chat with our AI personalities