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Show RIGHT ESTIMATE OF STEEP GRADE Not One Driver in Hundred Has Proper Calculation of Incline In-cline of Road. (By ERWIN GREER, President of Greer College of Automotive Engineering, Chicago.) Chi-cago.) "How steep is the grade on that road? Well, I should say that it is all of 30 or 35 per cent. But I didn't have any trouble in making it with my car. No sir. She pulled it like a house afire. Made it on high all the way. Passed two cars laboring along in second." Has Not Projer Estimate. How often, with variations, do we hear these words from drivers proud of the achievements of their cars frequently fre-quently to the disparagement of higher-priced cars from which, presumably, a better performance should be expected. ex-pected. After listening to statements of this kind from hundreds of tourists tour-ists anxious to tell of their trips and the remarkable "exploits of their cars, one is at least convinced that not one man in a hundred has the proper estimate esti-mate of the percentage of a grade encountered. en-countered. No reliance is to be placed on such estimates expressed by any other than one who knows from actual ac-tual measurements with a gradometer. Approaching an ascent the grade naturally appears steeper than it actually ac-tually is. This, coupled with the performance per-formance of the individual car which may or may not make the grade in high gear gives rise to an incorrect estimate of the percentage of the grade. Many motorists do not understand the process by which the designation of a grade percentage is arrived at, believing that a 20 per cent grade, for Instance, is one which rises at an angle of 20 degrees from the horizontal. hori-zontal. This is erroneous. How to Find Percentage. The designation of 20 per cent to a grade means that in the grade there Is a perpendicular rise of 20 feet In 100 horizontal feet. In other words, to generalize the numerical percentage of a grade indicates that number of feet perpendicular rise in 100 horizontal hori-zontal feet. In relation to degrees it will be found that a grade percentage properly arrived at in this way forms an angle equal to about one-half of the angle formed when the numerical expression is taken to mean degrees. Definitely, a 30 per cent grade is about one-half as steep as the grade formed by a 30-degree angle from the horizontal. The steepest grade on which a car can obtain traction is 45 per cent, and this Js a very stiff grade, Indeed. Tou can be reasonably certain that if you have estimated a grade as 30 or 35 per cent and your car pulls It In high gear that your estimate of the road's steepness Is probably double or even more than it actually Is. |