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Track Grade Confusion
Don is into HO and asks:
“I used to understand grades, but not now. What is the best or most grade you can use going up hill and how many inch’s per foot for each one?”
Don here is a handy grade calculator for you http://www.modelbuildings.org/free-track-grade-calculator.html
Don, sorry your other question wasn’t published as it required more clarity and details.
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On the earliest real railroads some grades reached to about 4% but were found to be too steep and created serious hazzards for rolling stock. Most rairoads eventually achieved 1% to 2% even over the most difficult mountain passes. Most real railroads strove to achieve ~1% maximum to the greatest extent possible.
1/8″ rise per 12″ is ~1%, 1/4″ rise per 12″ is ~2%, etc. This grade measurement works well for planning model railroads.
The percent grade (per cent; per hundred) is the units of rise per 100 units of run. A grade that rises 7 feet over 100 feet of track is a 7% grade. It seems a lot steeper when you’re on a grade than when you look at it from the side. Interstate highways commonly give warnings when grades exceed 4%. There are few roads with grades over 10%.
The early railroads generally limited grades to about 1%, not so much because the locomotives would have trouble pulling up the grade, but more because problems could develop going down. With the nose of the loco pointed down, the water in the boiler could flow off the top of the firebox, the firebox would overheat, and when the water returned as the track leveled out, there would be a steam explosion. The longer the boiler, the greater the risk. When one considers how short those water level gauges were, there was not a great margin for error. Some loco’s were designed to be able to handle a steeper grade, but 2% was still generally the limit. (There was less risk of a steam explosion at the front of the upper heat exchanger tubes after a steep climb because much of the heat would already have transferred to the water, but the risk was not totally absent.) Diesel-electrics are not bothered by this, but the physics of pulling a train still mean that it’s better to stay well under 2%.
On a model railroad one often does not have the space to permit staying under 2%, but you’ll notice a significant change in speed on anything over 4%. Given that we cannot transfer everything from the prototype to scale (curves, for example), it’s primarily a matter of personal taste as to how steep a grade a modeler wants to use.