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Degrees vs %

post #1 of 22
Thread Starter 
I just looked at the Snowbasin web page and it says that their new super pipe has a 19 degree or 34% slope. I don't understand!
If straight up and down is 90 degrees or 100% slope, and flat is 0, shouldn't 19 degrees be about 21% ?
If you understand the relationship between degrees and slope, please advise.
Thanks,
Garyskr
post #2 of 22
Straight up and down is an infinite slope. Slope is rise over run. A 100% slope is a 45 degree angel. The % slope is the tangent of the angle.
post #3 of 22
Quote:
Originally Posted by garyskr
... If you understand the relationship between degrees and slope, please advise.
It's generally called trigonometry.

As Ghost already noted:

Tan(19 degrees) = 34.43%. That's rise over (horizontal) run, which I think is the usual way people quote percentage slopes.
post #4 of 22
Thread Starter 
Thanks, makes sense.
post #5 of 22
100%=45 degrees
75%=33.75 degrees
50%=22.5 degrees
10%=4.5 degrees
on and on
post #6 of 22
When you go past 100% or 45 degrees do you start measuring from the other side and have the % get smaller, or do you go over 100%? I have always wondered that. Since it isnt a commonly used term outside of skiing i have never really learned it.
Later
GREG
post #7 of 22
Actually:

100% = 45 degrees
75% = 36.9 degrees (incidentally, this is a 3-4-5 triangle)
50% = 26.6 degrees
10% = 5.7 degrees

The function is arctan(percentage) = angle.

This all assumes that the percentage is calculated as rise / horizontal run, which I believe is what people normally mean when they talk about a percentage slope. If it were rise / distance along the slope, it would (of course) be different. Vertical would be 100% (instead of infinite), and 45% would be 1 / sqrt(2) = 71% = sin(45 degrees).

For slopes over 45 degrees, what seems to make the most sense is that the percentage slope is described as some figure greater than 100%.
post #8 of 22
Quote:
Originally Posted by HeluvaSkier
When you go past 100% or 45 degrees do you start measuring from the other side and have the % get smaller, or do you go over 100%? I have always wondered that. Since it isnt a commonly used term outside of skiing i have never really learned it.
Later
GREG
You can go over, e.g. have a 200% grade. That is one length of distance for every two lengths of fall.
post #9 of 22
In engineering and surveying % grade is the number of feet a slope rises or falls in 100 feet. Or meters in 100 meters. (It is the tangent of the angle, however, expressing it as so many feet in 100 makes it easier to understand.) Thus a hill that rises 10 feet every 100 feet is a 10% grade (5.7 degrees as stated by sjjohnson above.)

A 10% grade road is very steep. However, skiier would consider it an easy slope. It all depends on what you are standing on or sitting in.

Also, there is no relationship of % grade to color of ski slope. Green, Blue, and Black are all relative to the resort/mountain you are at. (As an engineer, I'd prefer it if there were ranges of grades related to slope color. It would make it easier to compare mountains. However, I doubt any mountain would want to "loose" their black diamonds.)
post #10 of 22
It would be great if every hill would publish length of run and vertical drop, like Mont-ste-anne does. That would allow you to compare their slopes to that of other hills. Of course, if two slopes are the same length and vertical, narrowness or other obstacles may dictate that one is ranked higher than the other.
post #11 of 22
Quote:
Originally Posted by BigE
It would be great if every hill would publish length of run and vertical drop, like Mont-ste-anne does. That would allow you to compare their slopes to that of other hills. Of course, if two slopes are the same length and vertical, narrowness or other obstacles may dictate that one is ranked higher than the other.
This is actually something that I was thinking awhile back would be really cool for Epic Skiers to do...

We could put up a running thread that would list frequently-skied runs at all sorts of resorts. Along with the run we could list the slope DEGREES (percents aren't much use to me because no one understands any of them except 100%).

Are there enough of us out here who own inclinometers who would be willing to take a few measurements on some well-know runs and post them on an ongoing basis? It would have to be the honor system with ACTUAL readings taken with an ACTUAL inclinometer because very, very few people are able to eyeball a slope with any degree (no pun intended) of accuracy.

I would be happy to start by posting some of Jackson's more popular runs once the lifts open.

Whaddaya say, some of you other resort denizens? This is something that would be very interesting to compile and I've never seen a very good list with this kind of information.

Bob
post #12 of 22
For personal use, I recently took a course where we learned to make inclinometers. While these are not nearly as accurate as real ones they give you a good idea of the slope degrees. Here is a URL which tells you how to make your own. (Remember, this is not as good as the real thing, but it will give you a pretty good idea of the slope of a hill. This should probably not be used to report the slope of a trail as Bob Peters has suggested, but it will give you an idea.) http://www.exploratorium.edu/math_ex...keInclino.html
Directions on how to use it are here: http://www.exploratorium.edu/math_ex...seInclino.html
post #13 of 22
With a topo map you can determine the incline of a run, or even part of a run, pretty accurately. There are topo maps published for the entire country, I believe.
post #14 of 22
I like the idea. The biggest problem I see is where on the slope to take the measurement. Should there be an overall average for a slope (top to bottom rise/run) and then a measurement of the steepest section? Could be interesting to figure out what measurement method gives the best indication of slope steepness. I'm thinking of Bode's run at Bretton Woods. Overall it has a nice even pitch, but that headwall is a son of a gun.
post #15 of 22
teach,
An easier way to do it would be to attach the protractor to your ski pole, then put the pole perpendiularly into the slope. If you then take your plumbline and hold it so it hangs over the centre of the protractor, you have the angle!
post #16 of 22
T-Square said-

A 10% grade road is very steep. However, skiier would consider it an easy slope. It all depends on what you are standing on or sitting in.
I can relate to that.

Federal D.O.T. requires a max. of 6% grade on all Highways. There are exceptions. A steep grade for Class 8 Highway trucks(semis) would be 17%(loggers). Unassisted up to 21-23%. I have been lowered off 31% grade in the Rockies by 2 D-10 dozers. One was used as an anchor on top. That was the longest 700 yards of my life.
post #17 of 22
post #18 of 22
Quote:
Originally Posted by Bob Peters
This is actually something that I was thinking awhile back would be really cool for Epic Skiers to do...

We could put up a running thread that would list frequently-skied runs at all sorts of resorts. Along with the run we could list the slope DEGREES (percents aren't much use to me because no one understands any of them except 100%).

Are there enough of us out here who own inclinometers who would be willing to take a few measurements on some well-know runs and post them on an ongoing basis? It would have to be the honor system with ACTUAL readings taken with an ACTUAL inclinometer because very, very few people are able to eyeball a slope with any degree (no pun intended) of accuracy.

I would be happy to start by posting some of Jackson's more popular runs once the lifts open.

Whaddaya say, some of you other resort denizens? This is something that would be very interesting to compile and I've never seen a very good list with this kind of information.

Bob
Bob,
I agree. Maybe we could get a new topic started in the "Specialty Forum" that lists resort statistics. I think this would be the only honest way to compare the steepness of one mountain's runs to another.

I bought a pitch and angle locator at Home Depot's tool center for $6 (cheaper than most inclometers). It very accurately dial measures both degrees and pitch (inch rise per 12" run) and is easy to read. It is small enough to fit in a pocket and easily lays flat on a ski pole to measure any run.

I know you have measured many of the runs in Utah. I took it along last year and measured several famous and not so famous runs. If I remember correctly since I did not write the numbers down, I found the top of Alta's Stone Crusher and High Rustler to be about 44 degrees. The steepest I measured there was the 50 degree walls of a gully below Yellow Trail. It was short, about 3 linked short radius turns which could be a criteria to justify sustained pitch. It was powder so I did not have to wory about sliding when I layed over to measure. 52 Degree Trees at Wolf Creek was another matter. It was a little scary digging in my edges and laying on my side to measure the skidded off run. The trail map is not lying.

I posted similar findings here, http://www.skinorthcarolina.com/mess...=boulder+dash&
last season to prove to folks that there are some steeps in North Carolina. Don't laugh, the top of Sugar Mountain's Boulder Dash is a very respectable 38 degrees.
post #19 of 22
post #20 of 22
Quote:
Originally Posted by slider
Thanks for the link, Slider. That's a very interesting site.

It actually provded proof positive of what I've been saying for years;

Snowbird is steeper than Jackson Hole, and Jackson Hole is only *ONE* degree steeper on average than Vail.

Since AltaSkier doesn't seem to be around here very much these days, maybe he'll allow me to speak for him. I think the sample is somewhat "flawed".

Still, it's a pretty interesting compilation of statistics. I'm going to use it to convince all those people who think Jackson is too difficult a mountain that JH is only negligibly different from Vail.

Bob

That ought to fly.
post #21 of 22
Quote:
Originally Posted by Bob Peters
Still, it's a pretty interesting compilation of statistics. I'm going to use it to convince all those people who think Jackson is too difficult a mountain that JH is only negligibly different from Vail.
lol...comparing Snowbird and JH is reasonable regarding steepness, with Jackson probably edging out the Bird, although one could argue that it's splitting hairs. however, the much heralded "Back Bowls" of Vail would be rated "blue" at JH, and you could probably prove it statistically.

BTW...thanks for the info on the headwall and crags!

powsniffr
post #22 of 22
Quote:
Originally Posted by slider
Interesting. Acordning to this, Vail only has 21 trails. 1 expert, 14 intermediate and 6 beginner.

One ski area missing from that list is Silverton Mountain. This is from their website:
Steepest Run: 55 degrees



Easiest Run: 35 - 30 degrees (steepest run at your average ski area)

Can I get an "Amen" brothers and sisters?!
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