Measuring % grade

[Reddog1]

What kind of gage are you using to measure the % grade, where did you buy it and for how much?





Wayne

 

[zachv]

You could use a cheap angle finder from Home Depot or something. Basically, 45 degrees from horizontal is 100%, 22. 5 degrees is 50%, etc.

 

[illflem]

Best way is with your odometer and an altimeter or better yet with a GPS.

Here's an article http://www.howstuffworks.com/question380.htm

 

[Thomas]

"Basically, 45 degrees from horizontal is 100%, 22. 5 degrees is 50%, etc"



I'll go along with the 45° from horizontal is a 100% grade but not with the rest of it.



If you wish to work with angles relative to horizontal then you need to express the tangent of the angle as a percent. The tangent of 45°=1 and 1=100%. The tangent of 22. 5° is a bit over . 41. A road that makes a 22. 5° angle with the horizontal is a bit more than a 41 percent grade.



Rather than involving angles, you can think of grade percents the same way that you spoke of the slope of a line in your algebra class. The slope of a line is 'rise over run', or vertical change divided by horizontal change. Express the slope as a percent and you have your percent grade.

 

[WadePatton]

Another way to look at it is how much elevation is gained per distance travelled. IOW if you travel 1 mile and gain 5280 feet of elevation, you've not only climbed a 100% grade, but also melted your EGT probe. 5280/5280 is 1 expressed as percentage becomes 100. So if you travel the same distance and gain "only" 1420 feet of elevation you've climbed a 25% grade. 1420/5280 is 1/4. For every 4 feet forward you went 1 foot upward.



These are extreme examples.



At least that's the way I see it. You can also utilize topographic maps for an average grade on a given hill. GPS is pretty shoddy when it comes to elevation changes, but excellent at Lon/Lat and things derived directly therefrom.



There is also a little hicky that called an inclinometer or something that the foresters use laying out trails and roads and such back in the woods.

 

[Thomas]

"if you travel 1 mile and gain 5280 feet of elevation,"



In this example you're traveling straight up. While not a realistic road, the percent of grade in your example would be undefined, not 100.



If you will read the link that Bill cited, you should see that the distance traveled divided by elevation change is not the correct method for calculating grade percents. His link goes on to say that the method is reasonably accurate at the small angles that actual roads make with the horizontal. For instance, a road that has a 7% grade forms an angle a bit over 4 degrees with the horizontal, a fairly small angle.

 

[illflem]

Skip the math

Most inclinometers still measure in degrees so you're stuck with the trig.

Here's one for $25 that will at least measure the percent grade the length of your truck is on. It still wouldn't be the true grade of the road though as grade is usually measured over a longer distance than a truck length. I know for trail building percent grade is measured over the course of a mile while maximum grade is measured over four feet, the length of a stride. You would have to install it on the fore to aft axis of your truck, zeroing it on a level road surface. Side of the center console with velcro would be good.

http://www.velimpex.com/about_incli...er&PHPSESSID=5ecd4ddee761155949d1e883c0b8f6af



(picture is of two of them side by side)

#ad

 

[MGordon]

Originally posted by Thomas

"if you travel 1 mile and gain 5280 feet of elevation,"



In this example you're traveling straight up. While not a realistic road, the percent of grade in your example would be undefined, not 100.

Not true. The only way you would go straight up is to gain 5280 feet while traveling zero distance forward.



Sketch it out on a piece of paper. You end up with a 45 degree "grade"

 

[WadePatton]

Originally posted by Thomas

"if you travel 1 mile and gain 5280 feet of elevation,"

In this example you're traveling straight up. While not a realistic road, the percent of grade in your example would be undefined, not 100.

Talk about mis-quoted! Straight up!



On a more realistic road: I travel 5280 feet and gain 528 feet of elevation. That IS a 10% elevation change. If "percent grade" is different, I wonder why. I like the simple math, it's close enough for me.



And it doesn't matter I'm going to pass every PSD on the way up.

 

[Thomas]

Sorry if I was confused by what you meant by "if you travel 1 mile and gain 5280 feet of elevation,". When I travel I measure distances with an odometer. The odometer doesn't show the horizontal component of my travels—just the distance traveled. Had you used the word "forward" that MGordon has added I probably wouldn't have posted.

 

[WadePatton]

cool, the altimeter in my truck is off too.

 

[illflem]

Another cheap option http://www.geocities.com/toyotashawn/85clinometer.html

 

[jponder]

Originally posted by Thomas

Sorry if I was confused by what you meant by "if you travel 1 mile and gain 5280 feet of elevation,". When I travel I measure distances with an odometer. The odometer doesn't show the horizontal component of my travels—just the distance traveled. Had you used the word "forward" that MGordon has added I probably wouldn't have posted.

Yes in reality to travel 1 mile horizontal while gaining 1 mile in elevation he woul have driven 1. 41 miles

 

[Thomas]

If you read my initial post in this thread, I'm quite familiar with 'percent of grade', various ways of calculating, and the relationships of slopes and angles. My years of teaching algebra, reading and writing thousands of word problems, have gotten me in the habit of reading things exactly as written.

 

[jponder]

Originally posted by Thomas

If you read my initial post in this thread, I'm quite familiar with 'percent of grade', various ways of calculating, and the relationships of slopes and angles. My years of teaching algebra, reading and writing thousands of word problems, have gotten me in the habit of reading things exactly as written.

I was agreeing with you

 

[Thomas]

I know Bill Fleming's link is a good overview of percent-of-grade calculation.

 

[Ladders]

Could goto a junk yard and get a gage off a RAV4. Mount it to your dash. Of course, having a Toy in the D/C might cause problems .





SOTSU!!

\\BF//

 

[Prairie Dog]

I saw this last night on a show about the autobahn. The German's started the whole grade thing and a 7% grade means you gain 7 feet in elevation for every 100 feet you travel.

 

[Reddog1]

I appreciate everyones responses. Silly me, I thought I could buy a 25 to 30 dollar gage to put on my dash.



I considered asking about an altimeter and/or an air speed indicator to compare vehicle speed to air speed (head wind?).





Thanks again





Wayne

 

[jponder]

Originally posted by Prairie Dog

I saw this last night on a show about the autobahn. The German's started the whole grade thing and a 7% grade means you gain 7 feet in elevation for every 100 feet you travel.

Okay well that is kinda different than what has been said here. If what you are saying is true, then if you travel a 100 feet and you gain a hundred feet of elevation then that is straght up. I mean that would be a rasonable way to do it but it would change some of the numbers we have been geeting, going back to what Thomas said, you said travel 100 fet and gain 100 feet. Think about if you used that method and you traveled 100 feet and went up 50 feet and you said okay that is a 50% grade. That would mean you traveled 86. 6 feet horizontally and you gained 50 Feet and your driving distance was 100 feet. The only advantage to the system being defined like this is straight up would be defined as 100% grade



If you use the other system of feet raised by feet traveled as a horizontal component, or slope of line algebraically 100% grade would be a 45% angle and straight up would be undefined. As the angle gets smaller the two would converge any way look at a 7 % grade the first way Your total travel would be 100 feet your horizontal travel would be 99. 75 feet and you would gain 7 feet up. Does anyone know absolutely if they are using feet raised divided by horizontal or total travel. I gues for our calcs it really doesnt matter as the difference on the 7% grade if you change the calcs is 7. 02% . It would matter if you needed to define grades for reasons other than driving though