Model Railroading > Scale MPH?

How do you figure scale mph??Is there an easy,read easy,LOL,way to figure this?Dave

Dave. In answer to your question about scale speed here is a rough way to estimate it close enough for government work.
There are 5280 ft. in a mile so figure 61 ft. in a scale mile. Call it 60 ft. to make things easy. If you go a mile in a minute in your car, that's 60 mph. If your train goes 60 ft in a minute, that's 60 scale mph. This is in HO because you didn't tell us what scale you model in.
In a minute;
60ft. = 60 mph
30ft. = 30 mph
15ft. = 15 mph
etc.
This is not exact but is close enough.
Ralph.

Yep HO,thanks,didnt dawn on me to scale out a mile and go from there,,,,shesh,,,,sometimes,,,,,,,LOL

At the La Mesa Model Railroad Club in the San Diego Model Railroad Museum, where I run trains from time to time, there are speed tables at each control station. You time the train between one milepost and the next, and the table converts the time into mph. This is what the real railroads used to do, I understand, before the advent of accurate speedometers.

That's all fine if you're sitting in the cab of your engine, but I'm 87x HO scale, so I don't fit. An easier way if you're viewing the railroad from outside the train is to count seconds as your engine moves past a fixed point, say a signal pole, and convert that into feet per second. Say it takes 2 seconds for an SD45 to go by a fixed point. Since an SD45 is about 69 feet long (68' 10", according to my reference), that means it is travelling at 34.5 feet per second. To get miles per hour, multiply by 0.682 (which is 3600 seconds per hour divided by 5280 feet per mile), and you get 24 mph.

Now, obviously you can't do this in your head (at least I can't!), so you whip out your trusty calculator and do it ahead of time for your favorite engines. On our Tehachapi line, the speed limit on the hill is 25 mph, and our uphill (eastbound) trains rarely make over 15 mph. So I know I want an SD45 to take no less than 2 seconds to pass a point for 25 mph, and 3 seconds corresponds to 15 mph. You can do this accurately enough by counting, "One Mississippi, Two Mississippi,..." as your train goes by.

Here are a couple of examples:

SD45 (69 feet long)
1.0 seconds = 47 mph
1.5 seconds = 31 mph
2.0 seconds = 24 mph
2.5 seconds = 19 mph
3.0 seconds = 16 mph
3.5 seconds = 13 mph
4.0 seconds = 12 mph
5.0 seconds = 9.4 mph

AC-12 Cab-forward (124 feet long)
2.0 seconds = 42 mph
2.5 seconds = 34 mph
3.0 seconds = 28 mph
3.5 seconds = 24 mph
4 seconds = 21 mph
5 seconds = 17 mph
6 seconds = 14 mph
7 seconds = 12 mph
8 seconds = 11 mph
9 seconds = 9.4 mph
10 seconds = 8.5 mph

You can do this sort of exercise for your favorite engines and either print out a reference table, or else you can keep a couple of important speeds (like your prevailing speed limit) in your head, and remember them. Usually, we're only striving for approximate speeds, say, between 20 and 30 mph, so we don't need to get too exact. If I know that my Cab-forward is going past the grade crossing in around 5 seconds, then it's doing about 15 mph, that's usually good enough.

The simplest way that I have found for HO is to estimate how many inches it travels in 5 seconds ("one lollipop ...").

The inches in 5 seconds equates directly to scale MPH.

1) Measure how many feet per second you're going.

2) Multiply that by scale (87 for HO, 160 for N, etc.)

3) Multiple that answer by .0114

Answer is scale mph accurate to within 1%

You may want to measure for several seconds and divide the number of feet traveled by how many seconds you timed for a more accurate figure to start with.

The formula in my previous answer is for feet per MINUTE.

Feet per SECOND would be as follows. Sorry if I caused confusion.


1) Measure how many feet per second you're going.

2) Multiply that by scale (87 for HO, 160 for N, etc.)

3) Multiple that answer by .6818

measure off 15 feet.... count the seconds it takes for any portion of the train to travel it.... Some quick figures

15 sec. = 60SMPH
20 sec. = 50SMPH
25 sec. = 40SMPH
30 sec. = 30SMPH

simple enough?

An extension of Barry's equation would be to time how long it takes to travel the length of any piece of 3' flex track on the layout. This would let you use it almost anywhere on most layouts.

Then, it would be:

3 seconds = 60 SMPH
4 seconds = 50 SMPH
5 seconds = 40 SMPH
6 seconds = 30 SMPH

Of course, as we keep shortening the time to distance ratio, the sampling error increases...