Best answer
GearSecondStan
Think of Second Gear as Luffy's version of going Super Saiyan. Speeds up his blood flow, making him stronger and faster. Also, Luffy looks super cool while using it.
All answers
PirateKingFan101
Second Gear is a technique used by Monkey D. Luffy in One Piece. It's basically Luffy pumping his blood faster, which boosts his strength and speed dramatically. It's like hitting the turbo button on a video game character! He first uses it during his fight against CP9. The visual cue is steam coming off his body, looking all kinds of epic.
HakiBeliever
Second Gear? Overhyped IMO. Yeah, Luffy gets faster and stronger, but it's all about that Haki in the later episodes.