How much dropper travel do I need on a groad bike?

For most riders on groad terrain, 60-80mm of dropper travel is sufficient. This provides enough saddle drop to shift your weight back on steep descents without requiring a very long seatpost insertion depth. Aggressive riders on very steep terrain may want 100-120mm. The limiting factor is usually frame insertion depth — check the manufacturer's maximum insertion depth before buying a dropper. Many groad frames are designed around specific dropper posts, so verify compatibility.