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Old 08-28-08, 05:01 AM   #1
5kdad
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Determining % Grade of a Hill

I read about people climbing 8%, 10%, etc. grades of hills. What type of device do you use to measure a grade? Or is that info posted on a road sign?
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Old 08-28-08, 05:31 AM   #2
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My bike computer has an altimeter, and states the road grade (Though it always seems to be lower than what either road signs, or calculating off a topo map).

As alluded to, you can also get a good idea of average grade on a hill by looking at a topo map. Just use:

(Top Elevation(feet) - Bottom Elevation(feet)) / length of climb (feet)

So if the top elevation was 800', the bottom was 200', and the climb was 1 mile, you'd use:

(800-200)/5280 = 0.114, or about an 11 1/2% grade

Edit- you dont have to use feet, just consistent units. e.g.- everything could be calculated in meters.

Last edited by BlueDevil; 08-28-08 at 05:35 AM.
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Old 08-28-08, 05:40 AM   #3
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As mentioned above the formula is:

Elevation Gain / Length of Hill = % Grade.
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Old 08-28-08, 06:29 AM   #4
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There are multiple ways of doing it... Some cycling computers have an elevation feature. A GPS will tell you the grade as well. You can use a topo-map and figure it out by hand (rise * 100 / run). There are various websites that have elevation data (mapmyride.com, amoung others). Or you can do what I'm pretty sure most BikeForums members do -- make something up so that your story sounds better.

Edit: note, if you want to be accurate, the best way of doing so is to look at the US Geological Survery topographic maps.

Sometimes there will be road signs (especially on major highways) warning truckers about the % grade that's coming up. That sign usually refers to the steepest part of the upcoming downhill -- i.e., if you see "8% for next 5 miles" it means somewhere in the next 5 miles is an 8% grade, not that the next 5 miles is an unending 8% grade.
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Old 08-28-08, 09:24 AM   #5
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To be really precise, the percentage figure is

100 * (elevation change) / (horizontal distance) = % slope

For small angles of slope, there's not much difference between using horizontal distance and using distance traveled, though. It's the difference between the tangent of the angle and the sine of the angle.
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Old 08-29-08, 07:33 PM   #6
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This item could tell % grade - whatever part of the hill anyway when you check the "inclinometer:"



http://westernbikeworks.com/productdetail.asp?p=STSMI

Last edited by NottPhast_Phred; 08-29-08 at 07:36 PM. Reason: Photo no upload
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Old 08-30-08, 08:54 AM   #7
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^^^ I've use the Sky Mounti for a couple of years.
Works well for actual grade at any given point, but it doesn't give you the average grade of the whole hill.
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Old 08-30-08, 02:29 PM   #8
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I wanted to check the ramp going down to a bridge on the bike path, and used a 2' level plus tape measure. Come to think of it, that way, you are measuring horizontal distance, not distance traveled.
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Old 09-02-08, 10:04 AM   #9
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I don't know how accurate Google Earth is, but it does measure elevation and distance.
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Old 09-02-08, 10:22 AM   #10
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Google Earth does estimate elevations in between known points. It'll show a pond draped down the side of a hill, for instance.

I've ridden hills that were measured with the local government's mapping software. It's pretty easy to estimate grades within a few percent after riding various example known grades.
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