The ratio of chainring to sprocket, made comparable in gear inches: around 80 moves you a good 6 metres per pedal revolution, 123 almost 10.
Your gearing decides whether you spin a light gear quickly or grind a heavy one — and with it whether your cadence stays in the economical range. Gear inches make different bikes comparable because wheel size is baked into the number: beginners on the track ride around 80 (a good 6 metres per stroke), sprint specialists closer to 100, elite riders up to 123 and therefore almost 10 metres. The classic mistake is a gear that is too big: cadence drops, you push with raw force, and your knees pay for it. Shift before the climb rather than in the middle of it, and ease off the pedal for a moment as the chain moves, or it will jump. What often goes unnoticed: a higher number is not automatically faster. It only means more distance per stroke — and worse acceleration from a standstill.