# a little math help please

Discussion in 'Getting Started' started by railroader9731, May 5, 2008.

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i want to know how to configre grade percents such as a rise of 24 inches over a 13ft span thanks all
2. ### nachomanGuest

grade, in percent, is rise/run*100. An important note: KEEP YOUR UNITS THE SAME!! In your case, you can either use inches or feet easily. Convert the 24 inches to feet by dividing by 12 inches per foot. 24/12=2. Now you have a rise of 2 feet divided by a run of 13 feet, or 0.154. Multiply by 100, and you have a 15.4% grade. In case you were wondering, that is WAY too steep.

You can also calculate using inches by multiplying 13 feet by 12 inches per foot or 156 inches. 24/156 = 0.154, or 15.4% grade. If you don't get the same answer, you did something wrong

Kevin
3. ### Mountain ManActive Member

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And the real railroads solved this by using switchbacks and loops in order to accomplish an otherwise impossible climb within a short linear distance. To put your grade into perspective, 16% is about the steepest highway grade permitted.

You must be planning some phenomenal scenery!

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thanks for the reply guys and yes there will be some awsome sceanery number of bridges and a few gorges to cross.
5. ### TriplexActive Member

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Realistically, 4% is about the maximum, and that's a definite pusher grade. And that'll get you about 6" in 13' of run. Without pushers, you're restricted to a lot less, especially if running steam as much model steam pulls poorly.

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by the book and the railroad we tend to model it calls for no more than a 3% grade and im limited to get to a 2.3% grade in a 17ft run.
7. ### Russ BellinisActive Member

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I don't know what sort of prototype you are modeling. If it is logging or mining, the prototypes were not concerned with speed, and usually used switch backs to gain elevation without excessive grades. On Class one railroads, and most short lines the two methods for reducing grades are the helix and curves. The Tehachapie loop is a prototypical example of the use of a helix. Where the railroad curves and snakes it's way up a mountain is how they gain the necessary elevation without having too steep a grade.

What sort of equipment are you going to run; or, more appropriately, what is your minimum radius? The tightness of your minimum radius will determine how many "S" curves you can fit in a 13 foot long bench.

How much width is available to you for the bench work? A 4 foot wide bench would allow you to make longer "S" curves and get more footage in the 13 foot length. You can't reach the back of a 4 foot bench, so you don't make the front of the bench straight. You would have a "bump out" on the front of the bench wherever the the "S" curve came to the front of the bench, and a "walk in" wherever the curve goes to the back of the space. The idea is that the track should never be more than an arm's reach from the outside of the bench work. Where you have a "bump out", you can build an impressive mountain range behind the trains. Just don't put any track to the back where you can't reach it. Also as the elevation gains, your reach shortens. You can reach farther when the layout is at waist height than at shoulder height. At eye level, you will need a step stool to reach the back of even the narrowest bench if there is any scenery in front.