Measuring Scale Speed

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Measuring scale speed - it's quick and easy.
As model railroaders, we often want to know how fast or how slow our trains are going.  We may want an exact speed for checking engine performance or we may want a quick check on speed to make sure we are operating our trains at speeds similar to the full size ones.  Either way, measuring their speed is fun and easy.

First lets look at measuring speed accurately.  Usually we want to know the speed in scale miles per hour.  But what we have at hand are the necessary tools to accurately measure speed in real feet per second.  So the question becomes how to use them and how to convert the results into scale miles per hour.

To measure speed in real feet per second, lay two reference markers beside the track.  The markers can be anything, but quarters are easily seen and are usually close at hand.  Put the markers far enough apart to make timing easy, say 3 to 5 real feet in Z scale, 5 to 10 real feet in HO, 15 or more real feet in large scale.  To simplify calculations, make the distance between markers an exact number of real feet.

Next, time how long it takes your train to travel from one marker to the other.  A stop watch is ideal, but any watch showing seconds will do.  Make sure your train is up to speed when it reaches the first marker and time how long it takes for a point on the train (say the front of the engine) to travel from marker to marker.

Finally, calculate the speed of the train.  First calculate the speed in real feet per second by dividing the distance between your markers by the number of seconds it took to travel between them.  Then multiply the answer by the rfps-to-smph factor for your scale from the table below.  The answer is in scale miles per hour.  The accuracy of this method depends mostly on the accuracy of your time measurement.

 scale 1:220 (Z) 1:160 (N) 1:120 (TT) 1:87.1 (HO) 1:64 (S) 1:48 (O) 1:32 1:29 1:24 1:22.4 1:20.3 rfps-to smph 150 109 81.8 59.4 43.6 32.7 21.8 19.8 16.4 15.5 13.8

For a quick check on speed in any scale (including full size), count how many seconds it takes a 40 foot box car to travel past a fixed point beside the track.  Then divide this number into 30 to get scale miles per hour.  For 50 foot box cars, divide the number of seconds into 36.  This quick check works best at low speeds and is a great way to keep shunting speeds prototypically slow in a yard.

In large scale, using a factor based on scale and on a common box car which can be used in all these scales may be more convenient.  The table below is based on the ubiquitous Bachmann box car.  Pick the factor for your scale and divide it by the number of seconds it takes  your Bachmann box car to roll past a fixed point to get its speed in scale miles per hour.  The table also shows this box car's length in the various large scales.

 scale 1:32 1:29 1:24 1:22.4 1:20.3 rfps-to-smph for B'man box car 30 28 23 21 19 scale length of B'man box car 40' 36' 30' 28' 26'

As a historical note, these methods are very similar to the ways engineers and station agents measured train speeds in the days before speedometers and hot box detectors.  Engineers would time the distance between mile posts, station agents would time the passage of box cars, and the railroads were run on tight schedules based on this.