Teeth in mesh · spinning for real

⚙️ Gear Ratio

Two gears mesh and spin at their true speeds: count the teeth, read the ratio. Small drives big → slower but stronger, like first gear on a motorbike. Slip an idler in between and the output flips direction while the ratio stays put — the trick inside every gearbox.

Drive Z₁ 12 Driven Z₂ 30 Input RPM 40 rpm

Ratio i = Z₂/Z₁

Output RPMRPM·Z₁/Z₂

Torque ×ideal, no friction

Direction

Meshed gears share the same tooth speed at the contact point, so RPM₁·Z₁ = RPM₂·Z₂. Power is conserved: what you lose in speed you gain in torque. A bicycle does the same with chainring and sprocket; an idler gear only flips direction — its tooth count cancels out.