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Old 03-04-10, 01:03 PM   #1
Sculptor7
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How to determine percentage of grade?

Think grade is determined by the ratio of height to length that is, a 10 foot rise in a 100 foot length would be a 10% grade. Is that correct? If so, how does one determine such other than with a rough estimate? Read often of people dealing with a certain percentage of grade but are they just estimating based on experience? Guess they must be. Any thoughts?
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Old 03-04-10, 01:13 PM   #2
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You can use a Garmin unit and download the ride data to determine the grades you covered. You can plot your ride on Map My Ride or other simular sites then click the "elevation" box to determine grades and feet climbed. Or if all else fails you can estimate the grade by how hard it felt then add 2 % since it's the internet.
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Old 03-04-10, 01:44 PM   #3
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Garmin or a computer that measures similar is the only way- but you have to remember that an average of 10% ride----The 10ft in 100--- is only an average. At times it will be a lot less and if you are lucky enough- there will be some steep bits in the hill aswell.
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Old 03-04-10, 01:48 PM   #4
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If I remember correctly the formula if you don’t have a cycling computer that gives you the grade is:
Elevation gain divided by feet and multiplied by 100.
An 800 foot climb divided by 3 miles would be 800 / 15840= .05050 x 100= 5.050505 or 5.05 percent.
That only gives you a total and in most cases there are places in that climb that will be in excess of 5 percent.
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Old 03-04-10, 07:20 PM   #5
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Garmin or a computer that measures similar is the only way.
Not the only way. You can use a bubble level, you can measure the start and end elevation of hill, you can use known elevations, many popular climbs have their stats published, etc. Ultimately you need to know how much elevation gain and how much distance travelled. How you get that information does not matter.
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Old 03-04-10, 07:27 PM   #6
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Google Earth shows altitude at any spot and includes a basic linear measurement tool. You supply the math.
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Old 03-04-10, 08:10 PM   #7
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Technically, grade is rise over run; but in practice you can use the hypotenuse (the distance on the road itself) and it's close enough for gov'ment work. You can get a bubble level that mounts on the handlebars and is marked for up to 10 or 12% grade, but I can't seem to find a link.
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Old 03-04-10, 08:19 PM   #8
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Old 03-04-10, 08:59 PM   #9
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Fudge a little bit when you mount it and you can really impress people!
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Old 03-05-10, 12:57 AM   #10
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Technically, grade is rise over run; but in practice you can use the hypotenuse (the distance on the road itself) and it's close enough for gov'ment work.
Right...it's elevation change divided by horizontal distance (and then multiply by 100 to get %), but for small angles, using the distance along the road instead of horizontal distance is close enough. The difference is the difference between sine and tangent of the angle...using horizontal is the tangent, using road distance (hypotenuse) is the sine.
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Old 03-05-10, 08:55 AM   #11
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Originally Posted by Sculptor7 View Post
Think grade is determined by the ratio of height to length that is, a 10 foot rise in a 100 foot length would be a 10% grade. Is that correct? If so, how does one determine such other than with a rough estimate? Read often of people dealing with a certain percentage of grade but are they just estimating based on experience? Guess they must be. Any thoughts?
Slope, I think, is the technical word. http://cs.selu.edu/~rbyrd/math/slope/
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Old 03-05-10, 08:56 AM   #12
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Slope, I think is the technical term. http://cs.selu.edu/~rbyrd/math/slope/
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Old 03-05-10, 12:54 PM   #13
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Be warned: If you go measure the 8% hill and can't find a single spot on it that measures over 5%, it won't matter, everyone will still be convinced it's an 8% hill.

One of the steeper places I measured is a little dip in between two hills where you can just coast through it from either direction, and it doesn't occur to anyone that it's steeper than the 5% hill down the way.
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Old 03-05-10, 01:19 PM   #14
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www.bikely.com , after plotting a route click Show -> Elevation Profile
www.gmap-pedometer.com , click elevation Large

You still have to do math on these, but they will give you distance and elevation.
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Old 03-05-10, 02:47 PM   #15
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Originally Posted by BlazingPedals View Post
Technically, grade is rise over run; but in practice you can use the hypotenuse (the distance on the road itself) and it's close enough for gov'ment work. You can get a bubble level that mounts on the handlebars and is marked for up to 10 or 12% grade, but I can't seem to find a link.
Yup. Good enough til about 10% then errors begin to be significant. At a true 100% grade calculating the wrong way gives 70%.

Few roads are over 10% for any distance. Excluding Fargo street, a road in Los Angeles where the Wheelman have an annual hillclimb event the steepest I have been on in a bike related situation was 13%.
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Old 03-05-10, 09:49 PM   #16
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Here is a steep hill

http://www.youtube.com/watch?v=NxWceFTkLRU
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