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Old 02-05-2017, 04:53 PM
Melbourne Melbourne is offline
Join Date: Nov 2009
Posts: 3,562
Originally Posted by Chefguy View Post
We were at the local train museum yesterday. They have some old locomotives that are enormous. The wheels on them are as tall as I am. Why were they so large? Was it a casting problem or because of an inferior alloy that would overheat a smaller wheel? Or some other reason that escapes me?

I was also impressed with the engineering skills it took to design those behemoths.
Additional factors for very early engines was the stess put by the wheel on the rail, and the slip when starting up.

Larger wheels have a larger contact patch, which meen they are less likely to break the rails.

If you watch the old film clips of steam engines starting up, you'll see the drive wheels slip. This is because the tourqe is not constant - it pulses. Faster engines with smaller wheels have faster pulses, which only works when the whole engine-wheel-rail system is better designed.

Conversely, larger wheels put the axle higher up, which is a bad thing.

Last edited by Melbourne; 02-05-2017 at 04:54 PM.