A gearbox is a component which is available in advanced mode. Gearboxes can transform torque (rotational force) into speed and the other way around. The degree of change depends on the ratio of the gearbox. A single gearbox in Stormworks can switch between two different ratios. There are currently 8 gearbox ratios to choose from: -1:1, 1:1, 6:5, 3:2, 9:5, 2:1, 5:2 and 3:1. For example, a ratio of 3:1 means that the outputted RPS or torque of the engine (depending on the direction of the gearbox) is multiplied by a factor 3.
If the gearbox is facing the engine, as indicated by the blue arrows on the gearbox, the multiplication is applied with respect to RPS. An engine limited to 20 RPS would therefore spin an attached propeller with 60 RPS (given that there are no weight constrains that withold the engine of reaching 20 RPS). The increase in propeller RPS however comes at the expense of a loss of outputted torque, which is divided by a factor 3.
If the gearbox is facing away from the engine, the multiplication is applied with respect to torque. An engine outputting 40 torque, combined with a 3:1 gearbox, would deliver a resulting 120 torque. The increase in torque comes at the cost of RPS, which is divided by 3.
When building a vehicle, it is important to consider whether a high torque or RPS should be achieved. For example, a tractor would have gearboxes facing away from the engine which result in a large amount of torque, allowing it to pull heavy objects, but at a lower maximum speed. A sports car would have gearboxes facing towards the engine, resulting in a low torque but higher RPS output and thus maximum speed. It goes faster by itself, but when carrying a lot of weight the sports car will be slower (possibly not moving at all).
A ratio of 1:-1 is used to allow vehicles to run in reverse. In the current build, Gearboxes have a 95% efficiency rating.
Often misunderstood: the blue arrows (direction of the gearbox)
The blue arrows on the gearbox block say:
When the ratio is 1:2, the pipe with the arrow pointing out of the gearbox has two times the torque and half the speed of the pipe with the arrow pointing into the gearbox. So if you want to build a car make the blue arrows point from the wheels to the engine!