What effect do different gear values have?

[tick tock]

How does the gear value of a locomotive actually affect its performance?  I haven't been able to tell just by playing and I can't seem to find any info except that it's a "power ratio".

Thanks

[kierongreen]

The power of an engine is the displayed power multiplied by the gear value.

[Spike]

Although it is not enforced by the code, vehicles with high gear values should have low(er) topspeeds (Stems somewhere from torque and max. revolutions reasoning).