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Measuring grade

Old 08-17-17, 07:23 PM
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FlamsteadHill
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Measuring grade

I understand the general principle, I am wondering if there is a standard for the Run used by various mapping programs.

For instance there is one hill nearby that I have measured a grade of around 15-16% that shows up with a maximum Grade of 8.1% on Ride With GPS. Then there is another one that they rated at 12.4% which is considerably less steep than the they are calling 8.1%. The really steep hills around here tend to be fairly short, over maybe 100-300', so I suspect that they are measuring a "moving average" over maybe 500'?

Just curious...
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Old 08-17-17, 07:36 PM
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The run is a function of the hill itself. For an average grade they take the difference in altitude bottom to top, and use the map distance for the run.

When calculating the steepest grade, they look for the steepest section of meaningful length, ie. 10 to 25 feet, and calculate that. In reality, many hills have short lumps, where the grade will exceed the listing of steepest grade.
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Old 08-18-17, 04:24 AM
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I understand Average Grade.

And I understand Steepest Grade, but it seems to me that they must be using a much larger sample size (i.e. Run) than I would have guessed. Certainly much, much more than 10-25', based on my observations above.
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Old 08-18-17, 12:23 PM
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The programs estimate grade by interpolating contour maps which are often at 5 ft intervals or by changes in pressure if you have a bariometric altimeter. You are probably using a total station, some sort of level, or accelerometer to calculate grade which is a direct measurement.
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Old 08-18-17, 01:01 PM
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Strava explains their elevation data here.

Like most apps it began with publicly accessible elevation databases. Over time they integrated data sampling based on Strava user devices.

Overall it's pretty accurate. Here in North Central Texas we have few long continuous climbs. So it can be disconcerting to be exhausted at the end of a mile or a few miles uphill and see the segment listed as a mere 1% when you know darned well it was steeper. But in reality it's lots of short stretches of 3% here, 6% there, even an occasional 9%-11%, only 100 yards or so long at a time, interspersed among flats and some roller coaster downhills.

I've measured few myself and it turns out Strava, other apps and maps are pretty accurate. My bikes have horizontal top tubes, so I use my iPhone and level gauges and calculations to estimate grades. I'll just ride partway up a grade, stop and check the measurements... and it nearly always matches Strava and other data.

However, on actual rides the data can vary considerably when my iPhone loses GPS sync. This doesn't happen often, maybe once or twice a month it'll lose and regain sync. Seems to be an atmospheric thing, I'm not sure. We had regional t-storms this morning so that may have been a factor. Other devices may be more accurate.
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Old 08-18-17, 01:10 PM
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I just do my own on Google Earth. Use the line tool to measure a distance and record the elevation at both ends.

Or you could put your smartphone on the ground and measure the degrees with an app. Then convert to %.
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Old 08-19-17, 09:20 AM
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How much does it matter - really?

A week or so ago I asked about a specific section of road that Mrs. Grouch and I ride 3 or 4 times per week. I got some answers - 6% over the total 2 mile length of the hill with a 9% steepest grade. That's close enough that I can compare other hills as long as a gradient is provided. That's good enough for me.

By comparison, somewhere in your neighborhood right now there are some adolescent boys who are propping a board onto something to make a ramp. That's probably going to work out to be about a 50% grade. Do you think that should count?
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Old 08-19-17, 09:53 AM
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Yes I was measuring angle with my iPhone and a straight edge and "converted" degrees to grade. There are definitely some stretches of 100'+ that are way steeper than what RWGPS shows - either pre-ride or post-ride.

Just one of those little things that annoys me but doesn't really matter.
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Old 08-19-17, 09:56 AM
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Originally Posted by Retro Grouch View Post
How much does it matter - really?
Only to the extent that if the absolute maximum grade I can climb for 30 seconds is 15%, and I map a route that says "maximum grade is 12.3%" and I get to one section and have to walk...

First world problems...
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Old 08-19-17, 10:04 AM
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Originally Posted by FlamsteadHill View Post
Only to the extent that if the absolute maximum grade I can climb for 30 seconds is 15%, and I map a route that says "maximum grade is 12.3%" and I get to one section and have to walk...

First world problems...
"First world problems." That's what I think too. It's not such a bad thing.

I can remember walking up some trails during my mountain biking days and thinking that my bike was ruining an otherwise nice hike.
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Old 08-19-17, 10:08 AM
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A hill's degree, grade or % are all different ways to calculate how steep it is. Degree is a straight forward measurement based on a protractor scale, as in 360 degrees in a circle. % is based on what percent of 90 degrees a slope is. Grade is usually misinterpreted because of the 2 different ways to calculate an elevation change.
So a 15% grade is 15% of 90 degrees or about 13 degrees
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Old 08-19-17, 10:08 AM
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Originally Posted by Retro Grouch View Post
I can remember walking up some trails during my mountain biking days and thinking that my bike was ruining an otherwise nice hike.
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Old 08-19-17, 11:09 AM
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Originally Posted by Retro Grouch View Post
How much does it matter - really?

A week or so ago I asked about a specific section of road that Mrs. Grouch and I ride 3 or 4 times per week. I got some answers - 6% over the total 2 mile length of the hill with a 9% steepest grade. That's close enough that I can compare other hills as long as a gradient is provided. That's good enough for me.

By comparison, somewhere in your neighborhood right now there are some adolescent boys who are propping a board onto something to make a ramp. That's probably going to work out to be about a 50% grade. Do you think that should count?
80% of the posts on this forum don't matter. Let 'em have their fun.
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Old 08-19-17, 01:35 PM
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Originally Posted by Retro Grouch View Post
How much does it matter - really?
It mattered when I was struggling to get back into shape a couple of years ago. Back then 400 yards of a 1%-2% grade would induce an asthma attack and I'd have to pull over and catch my breath. Wish I was kidding or exaggerating but nope.

So when I consulted various maps that only guesstimated the total slope at 0% for a stretch of a few miles, it was discombobulating to discover that 10 mile ride actually consisted of roller coasters with 50 yards of 11%, a plateau, another 400 yards of 3%, a 50 yard -2% downhill, etc.

Now I just regard those roller coasters as conditioning challenges for getting faster and stronger. But two years ago it felt like a life and death struggle and not fun at all. Especially on busy streets.

Even when a busy street in traffic is wide enough to be safe, and even if it includes a bike lane, it may not be suitable for cycling with folks who aren't in good shape. I've seen that often with folks who rent city bikes that weigh about 40 lbs, and end up walking uphill when they misjudged how steep some hills are from a cycling perspective. It ain't fun to be trapped in those poorly designed bike lanes with traffic to the left and a door zone to the right from curbside parking, while huffing and puffing uphill at 3 mph on a 40 lb city bike.

And that coincided with my dislike and distrust of Google maps, which can get you killed around here by relying on it for bike routes. That's when friends tipped me to cycling apps with routes that actual local cyclists rode, with accurate descriptions of segments to help me guesstimate whether I was fit enough to tackle 'em.
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Old 08-20-17, 04:43 AM
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Originally Posted by FlamsteadHill View Post
I understand the general principle, I am wondering if there is a standard for the Run used by various mapping programs.

For instance there is one hill nearby that I have measured a grade of around 15-16% that shows up with a maximum Grade of 8.1% on Ride With GPS. Then there is another one that they rated at 12.4% which is considerably less steep than the they are calling 8.1%. The really steep hills around here tend to be fairly short, over maybe 100-300', so I suspect that they are measuring a "moving average" over maybe 500'?

Just curious...

Check out this thread ... https://www.bikeforums.net/fifty-plus...005-grade.html
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