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Old 02-05-2017, 12:41 PM
engineer_comp_geek engineer_comp_geek is offline
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The wheels on a steam locomotive were directly driven with no gearing. If you make the wheels too small, and as the train goes faster, you exceed how fast the engine can do its thing without coming apart, and you lose high end speed. Make the wheels too large, and the torque required to get the train moving from a stop becomes excessive if you are hauling a large, heavy load.

So the wheels that you see are a good balance between low-end torque and high-end speed.

Engines designed to haul heavy freight tended to have smaller wheels, where engines designed to haul passengers (higher speed, less weight) tended to have larger wheels.

Last edited by engineer_comp_geek; 02-05-2017 at 12:42 PM.