migrantwing

Can someone please explain the fundamentals in elevation and gradient of climbs/hills.

There are quite a few good hills around here but I never manage to find out exactly what gradient they are (unless they are signposted).

The route below shows the maximum grade as 12.7%



Yet, a section of the exact same route (below) shows the maximum grade as 24%.



Why is this and how is the factor reached? I may be missing something simple but it baffles me

TIA

Seattle Forrest

50 feet (or meters) rise in elevation over 100 feet/meters distance = 50 % grade.

But the truth is hills are graded on a pass/fail system for cyclists.

Jiggle

Rise over run, just like the graph math you learned in grade school. You can get a pretty good estimate by using the Line tool and elevation numbers in Google Earth.

DonBjr

Signs will list a grade but the hill it's labeling will often vary in steepness so I've assumed it's the average grade. Other than that I'm not sure what you're trying to say with the included pictures. If it's that the elevation profile looks steeper for a less steep grade, it's probably just the scale on the elevation profile graph that's exaggerating the way it looks.

migrantwing

I thought my question was quite obvious. I included the pictures to show the variation in max grade. I wasn't referring to the peaks and dips in the actual graph. I couldn't make the screenshot any larger. Sorry.

OK. If I ride from point A to point C, I will travel through point B. Point B is a hill that is, for instance graded at 20%. The first picture I included is of the whole route, the second picture is of a section/segment/climb within that said route. My question is, as previously asked, why the variation in percentage of grade when the hill/climb/segment is the same object? The hill doesn't move or shrink, does it?

Example: If I have five coins in my pocket, it doesn't matter if they are all in one pocket or in numerous pockets, there are still five coins. If I travel 10 miles, it doesn't matter if it's at 12mph or 30 mph, the distance is still 10 miles.

So, with that said, how can a climb have two different max grades when taken from the same route, as the pictures show?

I don't know of any other way to ask the question.

Leinster

In this case, it's probably using a smaller base distance unit as you zoom in.

Your first map shows a segment of 20km. It probably breaks this up into units of, say, 100-200m for purposes of determining average gradients etc, for the sake of not overloading on data points. The largest elevation difference between the start and finish of any of these 200m sections is maybe 25m, giving a gradient of 12.5%.

On your shorter segment, only 2.5km in length, this segment can be broken up into smaller data points, as there are less of them. So for a 20m piece of that section, there might be a 4.8m change in elevation. Thus giving a 24% gradient for that 20m of road.

The 24% section probably only reaches 24% for a short distance. You maybe rode 20m at that gradient. The 20m immediately before might have been 10% and the 20m after only 8%. Stretch it out to 200m, and it would have averaged about 12.5% for that bit of road.

migrantwing

Gotcha! Thank you for a great response and explanation.

I haven't ridden that route yet. I was planning on doing it tomorrow. I know it's a pain of a climb that keeps going and going just before you get into complete countryside. Not looking forward to it

RR3

In life, we have

1. Lies
2. Damned Lies
3. Statistics
4. Software
5. Politicians

migrantwing

t595

so the equation is this: Elevation rise divided by horizontal distance times 100 equals percent of grade. So a short section of the ride may have a 5 foot rise in elevation over a 20 foot horizontal stretch which is a 40% grade ((5/20)*100). However if that is the ONLY elevation change over a 100 foot section of road, then the average grade is 5% ((5/100)*100). So overall most sections are measured at the begining and at the end of the hill to get total elevation gain and horizontal distance, ignoring the little localized steep stretches. The little localized steep sections though are the ones that always hurt the most. Just sayin....

migrantwing

Nice explanation. Thank you!

I've looked for the particular stretch of road on Strava to see if there's any info on it, but there's none. I may have to be the first participant to record it. It's not a nice climb. LOL! Still not 100% sure my figures are correct. I always sucked at Maths