Re: Speed debate again - 3 ft. versus 2 ft.

Those South African two-footers were gorgeous!

However, an important point made in an earlier discussion of the speed question is that locomotive speed is more a matter of driver diameter and steaming capacity than gauge.

The old H. K. Porter locomotive catalogs included many pages of technical information written for a lay audience, and these remain an amazing resource even now. Porter had the good sense to recognize that many of their customers were contractors, plantation owners, businessmen, etc. who had no previous railroad experience but wanted to know something about the engines they were buying and how to operate them. So, if you were in the market for say an 8-ton 0-4-0T, you would want to know how much it could haul, but also the minimum weight of rail it would require, and then how many tons of spikes and joint bars would be needed per mile of track at that rail weight. It's all there, and much more -- fuel and water consumption, lubrication, valve settings, boiler maintenance, how to lay out curves, etc.

So on the speed question, my copy of the 12th edition of Porter Locomotives: Light and Heavy (not dated, but I think from about 1915?) has a handy table on page 132 with the following title: "Revolutions per Minute of Driving-Wheels of Different Diameters at Different Rates of Speed." It shows that 36-inch diameter drivers (a common size on both 2' and 3' gauge engines) would need to turn at 372 RPM to attain a speed of 40 mph, and at 558 RPM for 60 mph. That's awfully fast for reciprocating steam!

I think it's significant that 60 mph is the highest speed shown on the table.

-Philip Marshall