Legalize it is wrong. As long as the ratio is different then there will be no change. The whole chainring/cog/chain system is simply a torque miltiplication system and it doesn't care if you're at 50/25 or 40/20 or 30/15. Torque multiplication of the system is identical. If you change crank lenght or wheel size then you change the input or output moment arm of the system, if you change the gearing you only change the torque mulitplier.