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geofitz13 03-18-10 02:43 PM

help in calculating grade
 
Not neccessarily a 50+ topic, but I could use some help.
Trying to calculate the grade of a hill I go up.
According to Gmaps pedometer, the hill is .7809 mile, and elevation is 731 feet. Converted the miles to feet and came up with 4123 feet, and calculated a 17% grade. Could this be right? I knew it was a steep hill, but, egad....

DougG 03-18-10 03:06 PM

I think that the basic mistake you're making is that the bottom of the hill is probably not at sea level (0 ft.). You have to subtract the elevation at the bottom of the hill from the elevation at the top (call this value the "rise").

There's also a slight inaccuracy that you'll get by using the distance along the road from the bottom to the top (.7809 miles) as the value to divide the rise by. Strictly speaking, the grade is "rise over run" where the "run" is the horizontal distance from the bottom to the top. If you remember the terminology of a right-angle triangle, the rise is the length of the vertical part of the triangle, the run is the horizontal bottom leg, and the distance you actually ride along to get up to the top is the hypotenuse. For a typical grade of a few percent, however, the hypotenuse is not much longer than the "run", so it's OK to use that as an approximation.

maddmaxx 03-18-10 03:08 PM

Typically, anything between 90 and 100 is an A grade, between 80 and 89 is a B grade...........................................:D


Oh, the hill. Looks like your calculations are just about right.......Compared to the exact calculations of the previous post, the difference will be tenths of a percent.

Cone Wrench 03-18-10 03:37 PM

Here's how I determine the grade of a hill, from the gentlest to the steepest:

-breathing easy, can still accelerate
-breathing harder, would rather not talk, can accelerate with difficulty
-can feel my heart beating, feeling my legs, can only accelerate by standing
-muscle burn is setting in
-should probably stand if I'm going to make it
-drop into my small chainring on a triple
-and finally: holy cr@p, please, please, please, make the pain stop.

Robert Foster 03-18-10 08:55 PM

Quote:

Originally Posted by geofitz13 (Post 10544624)
Not neccessarily a 50+ topic, but I could use some help.
Trying to calculate the grade of a hill I go up.
According to Gmaps pedometer, the hill is .7809 mile, and elevation is 731 feet. Converted the miles to feet and came up with 4123 feet, and calculated a 17% grade. Could this be right? I knew it was a steep hill, but, egad....

Do you ride up this hill all the time and how hard is it for you to climb? I find an 8 percent climb hard enough. 10 percent makes me want to cry and anything more would take a triple at least. What is the elevation at the bottom of the hill and what is it at the top?

stapfam 03-19-10 10:10 AM

1 Attachment(s)
I look on the garmin when I get home or for the road signs. Both of them are wrong for them at this time of the year as this must be a 25%. Seems to flatten out after a couple of months of training though

Garmin shows it as 18%- although the camera doesn't- but it is only 200yards long.

geofitz13 03-19-10 04:36 PM

Quote:

Originally Posted by DougG (Post 10544759)
I think that the basic mistake you're making is that the bottom of the hill is probably not at sea level (0 ft.). You have to subtract the elevation at the bottom of the hill from the elevation at the top (call this value the "rise").

There's also a slight inaccuracy that you'll get by using the distance along the road from the bottom to the top (.7809 miles) as the value to divide the rise by. Strictly speaking, the grade is "rise over run" where the "run" is the horizontal distance from the bottom to the top. If you remember the terminology of a right-angle triangle, the rise is the length of the vertical part of the triangle, the run is the horizontal bottom leg, and the distance you actually ride along to get up to the top is the hypotenuse. For a typical grade of a few percent, however, the hypotenuse is not much longer than the "run", so it's OK to use that as an approximation.

You hit the nail on the head. I did not take into account that the elevation at the bottom of the hill was not sea level. But you folks did confirm that I am at least doing the math right. So, when I went back and got the real evevation change, it turned out to be a 5% grade. Now...I really stink at climbing, and find this one to be pretty difficult. The entire hill is a little over a mile, with a couple small breaks in climbing, but is mostly a steady climb. I can do it, but I am not particularly happy about it. I really wanted to get an idea of what the grade was on this climb, just outta curiosity.
Is a 5% grade considered somewhat difficult, or am I just a weenie?

cruzMOKS 03-19-10 04:51 PM

Being a weenie is relative. I know 5% for a mile would be very hard for me. (You are probably in the top tier% of your age bracket.) It seems a hill like this that is not too steep would be a good training hill to gain strength.

DnvrFox 03-19-10 04:51 PM

IMHO, 5% is a significant grade - but then, I am a definite weenie!

cyclinfool 03-19-10 06:01 PM

Quote:

Originally Posted by DnvrFox (Post 10549986)
IMHO, 5% is a significant grade - but then, I am a definite weenie!

Being an experienced educator I would have thought you had more sage advice on determining grades.

DnvrFox 03-19-10 06:14 PM

Quote:

Originally Posted by cyclinfool (Post 10550262)
Being an experienced educator I would have thought you had more sage advice on determining grades.

5% of my students always got grades.

oilman_15106 03-19-10 10:21 PM

The other thing that makes hill grade percentage calculations all wrong is that a hill may be .5 mile long at a calculated 6% but if say it has a 10 or 12%
section within that number it is a lot tougher climb. I always wondered why I had so much trouble with a short hill in our area until I discovered the middle part of it is 14%! even though the whole thing is less than 10% when you do the math. The road would be illegal to build today according to our township manager.

stapfam 03-20-10 01:30 AM

2 Attachment(s)
Quote:

Originally Posted by cruzMOKS (Post 10549984)
Being a weenie is relative. I know 5% for a mile would be very hard for me. (You are probably in the top tier% of your age bracket.) It seems a hill like this that is not too steep would be a good training hill to gain strength.

Plenty of 10 to 12% slopes for 1 mile round here and they are easy once I am up to fitness. Even the 16% for .7 miles is achievable with training. But the one that gets me has an average of 5% for 2 miles. Lots of it are just a rise in the road and a few short bits at 10%- but that slight rise is one I only do if I have to. Mainly because it is right on the coast and always seems to have a headwind- but I don't even like it in reverse.

Couple of pics attached and it is nothing. One from the top looking back and it starts from the white cliffs in the background and the other taken about halfway up.


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