Modern road bike tyres commonly range from 23 to 30 mm wide. Racing bike tyres are light and fast-rolling, and folding versions are even lighter and more supple. Tubeless racing bike tyres - i.e. those without an inner tube -
and especially tubular tyres roll even faster and are yet more supple. For a long time, 23 mm-wide tyres ridden by pro cyclists were also the go-to for most ambitious hobbyists. Nowadays, however, 25 and 28 mm-wide tyres are now regarded as offering the best compromise between speed, efficiency and comfort on the road. If you often ride on rougher surfaces, you should also consider tyres up to (and over) 30 mm wide.