Video narration
Why does a cyclist lean into a corner instead of staying upright? As the bicycle follows the curve, it needs an inward acceleration toward its centre. That is centripetal acceleration-not an extra force, but the motion produced by the road through the tyres. So the lean is not mainly what points the bicycle into the turn. It positions the whole system so gravity and the road's force balance through it. On a flat road, the faster you travel or the tighter the curve, the greater the lean angle you need. Without that balance, the system tips outward. A banked road tilts the surface. Its force already points inward, supplying some of the turn. At its intended speed, the cyclist needs less lean-but balance still matters when speed changes. So why lean? Gravity and the road force balance through the bicycle; banking supplies part of the turn.