For a long time it seemed standard 19mm rims were the only option for road wheels. That’s changed a lot in the last few years. Now we’re seeing very good rims 23mm and wider.
To some extent wide rims are a product of racing technology. A wider rim increases the roundness of the tire profile compared to the lightbulb shape on a narrower rim. When tire width closely matches rim width there’s an aerodynamic advantage — aerodynamics are key for pro racers.
In many cases race-oriented technologies don’t translate to the recreational market but wide rims offer benefits everyone can appreciate. You are less likely to experience pinch flats with wider rims; larger air volume allows for lower pressures, which can increase comfort; cornering is improved since tires experience less flop in response to lateral forces; and wide rims are typically stronger with better durability. There are downsides to consider too. You may require brake adjustment when switching between wide and narrow rims; and brake modulation may suffer.