Measuring slope

Qualitymark

Reading Dervla Murphy as she cycles through Pakistan and Afghanistan, and she's talking in terms like a "one in fourteen" slope on a hill.

How do you judge the figures on the degree of a slope, and are they normally mapped? (I know Michelin maps have, or used to have, a useful guide to how steep a hill was, using chevrons on the road image; have a feeling they've given this up, sadly.)

godtabh

For every 14m in the horizontal the road rises 1m. The closer to 1 that the horizontal is the steeper. 1:1 very hard. 1:200 flat as a pancake

D3PO

theres no perfect way but most decent bike comps have barometric altimeters on it which use atmospheric pressure to guage altitude and in conjunction with the gps they can then measure the gradient.

a more crude way is to just use the gps and let strava, mapmyride, ridewithgps measure it based on detail they get from different altitude scources which are then sued to guage gradient.

fyi a 1:14 slope would generally be referred to as a 7% gradient meaning for every 14 meteres travelled you ascent 1 meter in altitude. Steep but not uber steep.

Cee-Jay-Cee

My Bryton 35 displays slope (I'm not sure if my Garnin 500 does too?) but it's measured as a %

godtabh

Cee-Jay-Cee wrote: »

My Bryton 35 displays slope (I'm not sure if my Garnin 500 does too?) but it's measured as a %

Garmins measure slope in the same way

godtabh

godtabh wrote: »

For every 14m in the horizontal the road rises 1m. The closer to 1 that the horizontal is the steeper. 1:1 very hard. 1:200 flat as a pancake

Corresponds to a grade of 7.17% if you break out the pythagoras theorem.

Qualitymark

And what's the normal way of expressing slope - Pythagorean or one-in?

What would, say, Knockree be, or the Knockmaroon Hill, or the gentle slope up to Rathfarnham from Harold's Cross?

seamus

The "one-in" slope grading is more imperial/U.S.

In Europe and for cycling in particular, percentages tend to be used because they're easier to calculate, especially when you're averaging over a long distance.

Strava and MapMyRide will both give % values if you create a segment or a map.

Strava lists Knockmaroon Hill at somewhere between 9 and 10%: https://www.strava.com/segments/714676

The "Climb" from Harold's cross to Rathfarnham is nothing at all. Between the ups and downs the change in elevation is probably no more than 20m. Total climbing is probably 0.2% or less.

godtabh wrote: »

For every 14m in the horizontal the road rises 1m. The closer to 1 that the horizontal is the steeper. 1:1 very hard. 1:200 flat as a pancake

"very hard". I think that's putting in somewhat mildly. You wouldn't climb a 1:1 hill on a bike, you'd barely be able to walk up it for any kind of distance.

Qualitymark

Qualitymark wrote: »

And what's the normal way of expressing slope - Pythagorean or one-in?

What would, say, Knockree be, or the Knockmaroon Hill, or the gentle slope up to Rathfarnham from Harold's Cross?

Percentage rise over the run distance.



Most cycling apps use percentage to describe hill grade.

See Knockmaroon hill on Strava for example: http://www.strava.com/segments/714676

Seaswimmer

This is a useful link for working out gradients using Google maps. Simply plot your route as normal and then on the graph you can select various sections (which are then highlighted on the map) and it will give you altitudes and the gradient as %


http://www.doogal.co.uk/RouteElevation.php

Wishbone Ash

Qualitymark wrote: »

...or the Knockmaroon Hill, or the gentle slope up to Rathfarnham from Harold's Cross?

It really depends on where the start and and points are as many short climbs may include flatter sections. The steepest part of Knockmaroon would probably be 10/12% but the whole climb would be a lot less.

Harold's Cross to Rathfarnham is barely noticeable - I'd hazard a guess at about 2%.

Wishbone Ash

The other thing to factor in is the length of a climb when gauging how difficult it is. I did one last year which only averaged 4% but went on for 30k. It nearly killed me.

DirkVoodoo

seamus wrote: »

"very hard". I think that's putting in somewhat mildly. You wouldn't climb a 1:1 hill on a bike, you'd barely be able to walk up it for any kind of distance.

Lol!

Some good analysis here using a bit of basic physics: http://www.wired.com/2013/03/whats-the-steepest-gradient-for-a-road-bike/

Summary:

"Let’s just put in some values here. Suppose the bike plus rider has a mass of 75 kg with an average speed of 2 m/s. If the grade was 30, this would require a power of 422 Watts. That’s some serious power. It’s possible, but it would wear you out quickly. I don’t have a good feel for the power of a cyclist, but I asked my brother who rides quite a bit."

Lusk_Doyle

Qualitymark wrote: »

And what's the normal way of expressing slope - Pythagorean or one-in?

What would, say, Knockree be, or the Knockmaroon Hill, or the gentle slope up to Rathfarnham from Harold's Cross?

"Piece of p1ss"

"Big ringable"

"Small ring only"

"Steep"

"Really steep"

"Fcuk off steep"

And various others...

07Lapierre

52x11 = Downhill
52x14 = Flat
52x25 = slight slope
39x14 = steep
39x21 = very steep
39x25 = WALL

Lusk_Doyle

07Lapierre wrote: »

52x11 = Downhill
52x14 = Flat
52x25 = slight slope
39x14 = steep
39x21 = very steep
39x25 = WALL

Failed maths then I take it?

Alek

At the end of any list there is always Kilmashogue.

godtabh

Qualitymark wrote: »

And what's the normal way of expressing slope - Pythagorean or one-in?

As an engineer I've been using both for the last 15 years so relate to both. In cycling % is more commonly used.

D9Male

****NERD ALERT****

Here is something I wondered when looking at the steep Spanish hills in La Vuelta. This question doesn't make so much of a difference for small gradients, but kicks in a bit more for hills of (say) 20% or more.

If a hill is 2km at 25%. does that mean that the hypotenuse is 2km long, or the horizontal distance (run in the chart on the first page) is 2km?

I suspect that in a lot of cases, people say "I have travelled for 2km, my altitude has increased by 500m in that time, so it is a 25% hill".

In actual fact, the hill's gradient would be 25.8% in this example.

****END OF NERD ALERT****

Qualitymark

Lusk_Doyle wrote: »

"Piece of p1ss"

"Big ringable"

"Small ring only"

"Steep"

"Really steep"

"Fcuk off steep"

And various others...

Now these are useful. Apart from the fact that I only have front gears and a rather heavy bike at the moment, and a creaky body, so mostly gradient measures are

wheee

sailll

hmmfff

pufffpufff

get off and walk

manwithaplan

D9Male wrote: »

****NERD ALERT****

Here is something I wondered when looking at the steep Spanish hills in La Vuelta. This question doesn't make so much of a difference for small gradients, but kicks in a bit more for hills of (say) 20% or more.

If a hill is 2km at 25%. does that mean that the hypotenuse is 2km long, or the horizontal distance (run in the chart on the first page) is 2km?

I suspect that in a lot of cases, people say "I have travelled for 2km, my altitude has increased by 500m in that time, so it is a 25% hill".

In actual fact, the hill's gradient would be 25.8% in this example.

****END OF NERD ALERT****

Something I have idly pondered the odd time myself. I reckon strava etc are dividing horizontal progress over the surface of the earth (run) by the change in elevation to produce the gradient value. Anything GPS-based would probably be doing the same. Something that's calculating distance off the number of revolutions of your back wheel might be different.

not yet

Qualitymark wrote: »

Now these are useful. Apart from the fact that I only have front gears and a rather heavy bike at the moment, and a creaky body, so mostly gradient measures are

wheee

sailll

hmmfff

pufffpufff

get off and walk

Jaysus this is handy, I don't know what they were all on about:

I'm not bad at this:

Deep breaths:

Mother of fcuk I can't breath:

I want my mammy:

Hello...!! is this the ambulance service.

D9Male

D9Male wrote: »

****NERD ALERT****

Here is something I wondered when looking at the steep Spanish hills in La Vuelta. This question doesn't make so much of a difference for small gradients, but kicks in a bit more for hills of (say) 20% or more.

If a hill is 2km at 25%. does that mean that the hypotenuse is 2km long, or the horizontal distance (run in the chart on the first page) is 2km?

I suspect that in a lot of cases, people say "I have travelled for 2km, my altitude has increased by 500m in that time, so it is a 25% hill".

In actual fact, the hill's gradient would be 25.8% in this example.

****END OF NERD ALERT****

I was looking at this calculation a bit recently too.

Yes you are correct. It only becomes obvious on really steep hills and even then it's a small error. On most normal gradients its an acceptable level of inaccuracy to calculate the % as rise / hypotenuse X 100

D9Male

I would say that it is done incorrectly for the profiles of professional races. They would show start of the climb at (say) 178.1k. And finish at 180.1k. And elevation for those points suggest gradient is calculated using hypothenuse as the denominator rather than the horizontal "run".

Lusk_Doyle

manwithaplan wrote: »

I reckon strava etc are dividing horizontal progress over the surface of the earth (run) by the change in elevation to produce the gradient value.

The bastards. Someome needs to alert the media.

carltonleon

Qualitymark wrote: »

get off and walk

Never ..... Stop for a minute and go again. Once you have walked up one hill it becomes easier to give in to the next one .... Oh Yeah and HTFU !!!

Qualitymark

carltonleon wrote: »

Never ..... Stop for a minute and go again. Once you have walked up one hill it becomes easier to give in to the next one .... Oh Yeah and HTFU !!!

Ah, the H is long gone from my possibilities!