Ever since I took up cycling again in 2004 I've been puzzled about something that may been obvious to everyone but me. When referring to the steepness of a hill we describe it as a percentage. Federal highways are graded at 6% or 7% maximum, I can't remember which. But the question always nagged at me. Percent of what? Surely it's not the angle of incline which would be expressed in degrees. Nope.
In studying my ground school materials for my pilot's license I found the answer that's literally been in front of me the whole time. It's simply a statement of the slope expressed as a percentage of 100. You know, rise over run. Duh.
It was discussed in the ground school material in reference to the gradient of runways. So a 7% grade on a hill means for every 100 feet of horizontal distance of the road it increases in height 7 feet. A 15% grade increases 15 feet per 100 horizontal, etc. Yep, obvious and I couldn't see it.
I may very well have been the only one who couldn't figure this out. Now I can sleep with this off my conscience.
Have fun in the Blue Ridge and ride safe.
Blue Skies!
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4 comments:
The good news is for small grades....both degrees and grade are about the same....its the law of small angles...now isnt that fun to know...
I don't think Roark's comment is quite right.
% grade is actually a factor of rise over run. So a 6 ft rise ove 100 feet of run is a 6% grade. Another way to look at is this: a 45 degree angle hill is 100% grade, since at 45 degrees 100 feet of rise would also be 100 feet of run.
I think it's actually pretty amazing to think that 12 feet of rise over 100 feet of run is enough to pretty much kick anyone's butt, especially if it is over about 1000 feet of run.
Most big hills are graded over average grade. So when a hill (like in the TDF) if graded at an average of 8% or so, it's pretty tough. It could be anywhere from 10-15% at the steep stuff, and may even have a down hill during the "hill", but still average up around 8 - 10%.
Mount Washington in New Hampshire (or is it Vermont, I think it is NH) AVERAGES up around 12% for almost 8 miles, making it largly considered the toughest hill less than 10 miles in the country. It kicks up as high as 18-20%, and has very few "easy" spots. Plus winds of 30-60 MPH on a "good" day, and 60 - 100+ on a bad day.
Mike
Actually My comment is quite corrent. sin(theta) = rise/run. And if theta is small sin(theta) = theta. Theta being the angle of the climb. The smaller the angle the better the approximations. It's called trigonometry. The kicker is angle must be measured in something called radians. The approximation has way broken down by 45 degrees. To convert from degree to radians multiply by pi/180. It's all about da math.
In case of doubt you know what they say: A visual is a worth a 1000 math theorems :)
Here, judge for yourself how close of an approximation they really are. At a 12% grade, I personally don't think they're very close ... or even at 6% really.
click here to see the visual
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