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What is a slope percentage?

littledove44littledove44 Posts: 871
edited March 2014 in Road general
I always thought that it was the slope angle percentage from vertical so, if the angle of the hill was 45 degrees it was a 50% slope. Don't know where I got that bit that's what I though.

I now read that it is the ratio of climb to travel, so a 45 degree slope is actually a 100% climb.

So when I climber a hill over 30% recently I thought I was going up at 27 degrees. Actually it was 16.7 degrees.

How disappointing.

http://en.wikipedia.org/wiki/Grade_(slope)

Posts

  • crescentcrescent Posts: 1,088
    edited March 2014
    Hills used to be identified on road signs as a ratio eg: 1:4 (for every four feet horizontally it will rise one foot vertically). I think it changed to percentages in the late 70s or early 80s and nowadays 1:4 would equate to 25%, 1:10 would equate to 10% etc etc. You're right about 45 degrees being 100% as this would equate to a ratio of 1:1. To work out the angle of the slope would require you to use a bit of trigonometry. A 1:4 (25%) works out at just a shade over 14 degrees.
    Ribble Gran Fondo
    Bianchi Impulso
    BMC Teammachine

    “When I see an adult on a bicycle, I do not despair for the future of the human race. “ ~H.G. Wells
    Edit - "Unless it's a BMX"
  • CiBCiB Posts: 6,098
    1 in 4, 1 in 8, that used to mean something. 12% is just a number. So much for progress.
  • ai_1ai_1 Posts: 3,060
    CiB wrote:
    1 in 4, 1 in 8, that used to mean something. 12% is just a number. So much for progress.
    I don't see the problem. Nothing has actually changed except that it's been standardised as always being X in 100, so for example 12% is not "just a number". It's 12 in 100. No different from 1 in 4 or 1 in 8 really.
    I much prefer the use of a percentage. It's a far less cumbersome way to communicate this information and no more difficult to understand. It's also more convenient for calculations.
  • mfinmfin Posts: 6,724
    CiB wrote:
    1 in 4, 1 in 8, that used to mean something. 12% is just a number. So much for progress.

    But progress in education now results in most people having a grasp of basic mathematics? :)

    With percentages on the signs, most people who don't 'get it' will at least instantly be able to see that a higher number means something steeper. Then, just like us(?), they can then conveniently use that number as a proportional trigger to the amount of fear and trepidation they should feel when approaching a hill (but without understanding at all that they have just naturally sussed out the basic principle of proportionality).
  • vertigo16vertigo16 Posts: 91
    More to the point, because STrava seems a bit of a maverick when it comes to calculating heights/gradients, I have no idea in numbers of the difference between a gradient I won't notice, one I'll enjoy and one I'll be scared of.

    How bad is 10%, is that tough?
  • neilo23neilo23 Posts: 783
    Imagine a 100m running track. The start line is at 0m above sea level and the finish line is 10m above sea level. The slope would be a 10% "hill".
  • neilo23neilo23 Posts: 783
    vertigo16 wrote:
    More to the point, because STrava seems a bit of a maverick when it comes to calculating heights/gradients, I have no idea in numbers of the difference between a gradient I won't notice, one I'll enjoy and one I'll be scared of.

    How bad is 10%, is that tough?

    Not insanely tough but a lot harder than it looks if drawn as a line on a piece of paper. The start of Alpe d'huez is about 10% and even on tv it looks as if the riders are approaching a wall.

    That gravity is a right b*+$£¥ard.
  • ai_1ai_1 Posts: 3,060
    vertigo16 wrote:
    More to the point, because STrava seems a bit of a maverick when it comes to calculating heights/gradients, I have no idea in numbers of the difference between a gradient I won't notice, one I'll enjoy and one I'll be scared of.

    How bad is 10%, is that tough?
    Not sure if you're saying you don't know how to interpret Stravas figures or actual gradients.

    If you're trying to get an idea of what actual numbers equate to it's hard to say since different people with different fitness, weight and equipment will have different feelings about just how difficult or enjoyable a climb is. Also there's a big difference between a 300m long 10% climb in the middle of an easy 20km spin or a 3km long 10% climb towards the end of a century sportive.
    Anyway, here's my best attempt at some guidance. Please bear in mind beginners, heavy riders and/or riders with limited gearing options will typically find hills harder and plenty people are sure to disagree with my evaluation!

    0-3%
    Easy going. Probably doesn't really count as "climbing". You'll be able to maintain a reasonable pace.

    3-5%
    Moderate gradient. Will slow you down noticeably but most people will have no trouble keeping going.

    5-8%
    Beginners or heavy riders will be starting to find it hard going.

    8-10%
    Most people who don't do a lot of climbing will consider this a very steep climb. Gearing options will matter. Beginners or very heavy riders may have to dismount.

    10-15%
    Very tough going. Most beginners will struggle especially if they don't have favourable gearing.

    15-25%
    Extremely steep. Most people will find it a challenge just to keep moving at 15% and many will have to get off and walk somewhere in this range. Favourable gearing options will be essential to keep moving at the upper end of this range.

    25%+Never tried it and don't particularly want to! I reckon most people will be walking unless they've got gearing below 1:1.
  • slowbikeslowbike Posts: 8,498
    ai_1 wrote:
    Anyway, here's my best attempt at some guidance. Please bear in mind beginners, heavy riders and/or riders with limited gearing options will typically find hills harder and plenty people are sure to disagree with my evaluation!

    0-3%
    Easy going. Probably doesn't really count as "climbing". You'll be able to maintain a reasonable pace.

    3-5%
    Moderate gradient. Will slow you down noticeably but most people will have no trouble keeping going.

    5-8%
    Beginners or heavy riders will be starting to find it hard going.

    8-10%
    Most people who don't do a lot of climbing will consider this a very steep climb. Gearing options will matter. Beginners or very heavy riders may have to dismount.

    10-15%
    Very tough going. Most beginners will struggle especially if they don't have favourable gearing.

    15-25%
    Extremely steep. Most people will find it a challenge just to keep moving at 15% and many will have to get off and walk somewhere in this range. Favourable gearing options will be essential to keep moving at the upper end of this range.

    25%+Never tried it and don't particularly want to! I reckon most people will be walking unless they've got gearing below 1:1.

    It also depends massively on length - I've ridden a 25% hill ... it was very short though - much tougher is the 13% climb that is 3-4 times the length ...
    Then you get the variations in the gradient - that can hit hard too - start off on a piffling 5%, throw in an 8% for a short while before relaxing back to 5% - hmm the second 5% isn't so easy ... then ramp it up to >10% for a stint before dropping back down to say 3% ... it's amazing how tough it is ...

    But yes - your rough reckoner seems about right to me! ;)
  • ai_1ai_1 Posts: 3,060
    slowbike wrote:
    It also depends massively on length - I've ridden a 25% hill ... it was very short though - much tougher is the 13% climb that is 3-4 times the length ...
    Then you get the variations in the gradient - that can hit hard too - start off on a piffling 5%, throw in an 8% for a short while before relaxing back to 5% - hmm the second 5% isn't so easy ... then ramp it up to >10% for a stint before dropping back down to say 3% ... it's amazing how tough it is ...

    But yes - your rough reckoner seems about right to me! ;)
    Agreed and thanks! :) First draft I had some more comments about length in there but decided it was getting too complicated!

    I often find longer climbs easier, sort of. What I mean is I'm often in a rush to get up short climbs and push too hard. On longer climbs I settle in for the long haul, pace myself properly and don't find it too tough unless they're really steep. I've sometimes suffered on short climbs of under 10% but I've also climbed Mt Teide from sea level on two occasions and only suffered nearing the top. That's a 35km continuous climb with an average of 6.5% and several stretches of 9-11%. I knew I was in for 3hrs+ of continuous climbing so felt no temptation to charge up the steepest bits.

    Steepest I've done is 25% too and that section was a steeper ramp in the middle of a climb maybe 1.5km long and 15% average. It really hurt! Not sure I would have made it on my usual bike setup but I'd been out riding on a gravel track with old wheels that happened to have an old 11-32 cassette mounted. I was back on tarmac and spotted this extremely steep road (not on my route) and felt the need to climb it so took a detour to try it. The 32 sprocket got some use!
  • crescentcrescent Posts: 1,088
    CiB wrote:
    1 in 4, 1 in 8, that used to mean something. 12% is just a number. So much for progress.

    Not wishing to be a pedant.... but I'm going to be one anyway, 12 is a number, 12% is a ratio :wink:

    As a very rough visual (football) reference:
    If your bike was on the penalty spot in front of the goalposts and you cycled towards the goal line up a 10% slope then by the time you reached the goal line you would be approx halfway between the ground and the crossbar.
    There, that's much clearer.
    Ribble Gran Fondo
    Bianchi Impulso
    BMC Teammachine

    “When I see an adult on a bicycle, I do not despair for the future of the human race. “ ~H.G. Wells
    Edit - "Unless it's a BMX"
  • mfinmfin Posts: 6,724
    crescent wrote:
    CiB wrote:
    1 in 4, 1 in 8, that used to mean something. 12% is just a number. So much for progress.

    Not wishing to be a pedant.... but I'm going to be one anyway, 12 is a number, 12% is a ratio :wink:

    As a very rough visual (football) reference:
    If your bike was on the penalty spot in front of the goalposts and you cycled towards the goal line up a 10% slope then by the time you reached the goal line you would be approx halfway between the ground and the crossbar.
    There, that's much clearer.

    Is this a slope that the goalposts are also on? Or a slope that ends at the goal line that the ball then plops over? Either way it's a pretty odd football pitch, maybe it's some form of 'crazy football'?

    For a pedant, I can't help but think your analogy has some ambiguities, a fair few more of which I would imagine might be discussed any moment n....
  • crescentcrescent Posts: 1,088
    mfin wrote:
    crescent wrote:
    CiB wrote:
    1 in 4, 1 in 8, that used to mean something. 12% is just a number. So much for progress.

    Not wishing to be a pedant.... but I'm going to be one anyway, 12 is a number, 12% is a ratio :wink:

    As a very rough visual (football) reference:
    If your bike was on the penalty spot in front of the goalposts and you cycled towards the goal line up a 10% slope then by the time you reached the goal line you would be approx halfway between the ground and the crossbar.
    There, that's much clearer.

    Is this a slope that the goalposts are also on? Or a slope that ends at the goal line that the ball then plops over? Either way it's a pretty odd football pitch, maybe it's some form of 'crazy football'?

    For a pedant, I can't help but think your analogy has some ambiguities, a fair few more of which I would imagine might be discussed any moment n....

    No, the goalposts are not on the slope :? nor is it a real football pitch. It was meant as a quick representation of the heights and distances involved, nothing more. I'm sure it will be ripped to bits by bigger pedants than me but it's basic maths and a bit of imagination, that's all.
    Ribble Gran Fondo
    Bianchi Impulso
    BMC Teammachine

    “When I see an adult on a bicycle, I do not despair for the future of the human race. “ ~H.G. Wells
    Edit - "Unless it's a BMX"
  • ugo.santaluciaugo.santalucia Posts: 25,902
    It seems Wikipedia has the definite answer, not really a topic for discussion, is it?
  • mfinmfin Posts: 6,724
    crescent wrote:
    It was meant as a quick representation of the heights and distances involved, nothing more. I'm sure it will be ripped to bits by bigger pedants than me but it's basic maths and a bit of imagination, that's all.

    :) Please show your workings out.
  • mfin wrote:

    :) Please show your workings out.

    Very funny and didn't half take me back a few years!
    Or should that be: didn't 50% take me back >2 but <4 years? :D
  • crescentcrescent Posts: 1,088
    mfin wrote:
    crescent wrote:
    It was meant as a quick representation of the heights and distances involved, nothing more. I'm sure it will be ripped to bits by bigger pedants than me but it's basic maths and a bit of imagination, that's all.

    :) Please show your workings out.

    I looked the answers up at the back of the book :D
    Ribble Gran Fondo
    Bianchi Impulso
    BMC Teammachine

    “When I see an adult on a bicycle, I do not despair for the future of the human race. “ ~H.G. Wells
    Edit - "Unless it's a BMX"
  • It seems Wikipedia has the definite answer, not really a topic for discussion, is it?
    Quite.

    Everything in Wikipedia is completely accurate and we should never question it's validity. :shock:
  • MattC59MattC59 Posts: 5,433
    gradient.jpg
    Science adjusts it’s beliefs based on what’s observed.
    Faith is the denial of observation so that Belief can be preserved
  • MoonbikerMoonbiker Posts: 1,706
    From that pic 20% doesn't look very steep at all.
  • ai_1ai_1 Posts: 3,060
    Moonbiker wrote:
    From that pic 20% doesn't look very steep at all.
    Looks can be deceiving!

    It's all relative but relative to the ability of cyclists to produce motive power - 20% is steep
  • StedmanStedman Posts: 377
    Even the official gradient on the street signs are very subjective. If you take Winnetts Pass, although this ramps up to 28% in one place over 25% in other places, the official gradient is averaged out at 20%, however if you apply the same rule to Hardknott Pass, I am sure that it does not average out at 33%.

    All I know is that when a hill gets very, very steep, when I am sitting down, the front wheel comes off the road and when I stand up the back wheel loses traction. I also cannot unclip my feet quickly enough and if I put my foot down, I cannot get started again!
  • InitialisedInitialised Posts: 3,047
    If you're doing The Ryals in the wrong direction (downhill) there's an old school 1:6 slope sign: Streetview Strava has it as an average of 15% peaking at 21.6% http://www.strava.com/segments/1656067 so I guess 1:6 (16.6%) is closer to the average gradient than 1:5 (20%) but if the sign were replaced with a modern equivalent 17% would be appropriate. So the current system is better than the old system as the number on the sign can more closely match the actual gradient.
    I used to just ride my bike to work but now I find myself going out looking for bigger and bigger hills.
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