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1 in 9 or 9% - how to read the steepness of a hill.

garrynolangarrynolan Posts: 625
edited April 2010 in The bottom bracket
Still work in 'old money' but never really understood those signs that said '1 in 9' (9 whatever horizontal = 1 something vertical??). Now we have the % signs. How do these work? What is the difference between 10% and 30%? Which is steeper? 10%/30% of what? Anyone?
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  • ProssPross Posts: 22,137
    1 in * means it rises 1m every * metres. Percentage wise 1 in 1 (or 45 degrees) would be 100% so 1:2 is 50%, 1:4 is 25% 1:10 is 10% etc. therefore 30% is steeper than 10%.
  • pneumaticpneumatic Posts: 1,989
    We did this a few months ago and it turned out to be horribly complicated - something about doing the calculation off a map being inaccurate because you are interpreting horizontal distance by measuring the hypoteneuse rather than the base line. (or was it the other way round?)

    Anyway, I like percentages best. Except on the Ventoux from Bedoin where I was so delirious that I decided that someone had helpfully spray painted the percentages on the road. It was only when, after a km at 10 percent, it increased to 11 for a km and then 12 for another km, that I realised what was going on! :oops:


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  • ProssPross Posts: 22,137
    :lol:
    I reckon the good old British 1 in x system is better as it is straight forward despite using percentage gradients everyday of my professional life.

    With regards to the plan distance v actual distance, this showed big time on my walk at the weekend. I'm not sure what the 20 mile plan distance equated to but it must have been at least 23 miles.
  • pneumatic wrote:
    We did this a few months ago and it turned out to be horribly complicated - something about doing the calculation off a map being inaccurate because you are interpreting horizontal distance by measuring the hypotenuse rather than the base line. (or was it the other way round?)

    Though I'm bobbins at maths, I'd say it was the other way round. When you look at a road on a map, you're looking vertically downwards. If, to keep things simple, you imagine a perfectly straight road on a map, the line you see is the horizontal one. The road you cycle up, though, is the hypotenuse, and will actually be longer than the road you see.
  • ProssPross Posts: 22,137
    Yep, your maths isn't that bad cos you're spot on! :wink:

    I've been trying to work out if Map My Ride takes that into account but as a 4% gradient average on a 60 mile ride would add on less than 0.05 miles it doesn't make much of a difference!
  • rolf_frolf_f Posts: 15,959
    Pross wrote:
    Yep, your maths isn't that bad cos you're spot on! :wink:

    I've been trying to work out if Map My Ride takes that into account but as a 4% gradient average on a 60 mile ride would add on less than 0.05 miles it doesn't make much of a difference!

    Indeed so - I live in a hilly part of the country. My mileage for the year is 1400 so far - can't check til tomorrow but I think my overall climb is less than 80000 feet; that's only 15 miles.

    The digital terrain maps used in Bikely and the like are going to be much less accurate vertically than horizontally but even if they are out by 50 percent the difference is still tiny compared to horizontal distance travelled.
    Faster than a tent.......
  • Pross wrote:
    Yep, your maths isn't that bad cos you're spot on! :wink:

    I've been trying to work out if Map My Ride takes that into account but as a 4% gradient average on a 60 mile ride would add on less than 0.05 miles it doesn't make much of a difference!

    Phew :o Anyhow, it's yet another reason for taking so long to get up hills, I suppose...
  • holmeboyholmeboy Posts: 674
    http://maps.google.co.uk/maps?hl=en&ie= ... 12453&z=14


    = 1 in 3 or 30% or fecking steep!
  • garrynolangarrynolan Posts: 625
    Thanks for that. On a - sort of - related note, what is considered the steepest bit of road in UK/Ireland? Also, what would be the tipping point i.e. the gradient that is too steep to ride?
    Visit Ireland - all of it! Cycle in Dublin and know fear!!
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  • oldwelshmanoldwelshman Posts: 4,733
    I worked in a coal face that was 1:1.4 boy was that hard to walk up !! :lol:
    Not nice when things fell in there either :cry:
  • iain_jiain_j Posts: 1,941
    For some reason when I get to a gradient sign at the base of a hill, I have to convert it to the "other" type in my head, say if the sign's 17%, work out what it's "1 in" gradient is. It's insanely difficult, my brain just switches off completely when I'm climbing. I've even struggled converting 10% to 1-in-10.
  • JamesBJamesB Posts: 1,184
    Steepest bit of road I know is the tarmac lane below Harlech castle, Nth Wales, signed 1:2 at bottom if I recall. :D
    As for tipping depends on the gear you pedal / body position--- a lower gear will produce more rear wheel torque and a tendency to do a wheelie
  • olddgregolddgreg Posts: 53
    JamesBwmb wrote:
    Steepest bit of road I know is the tarmac lane below Harlech castle, Nth Wales, signed 1:2 at bottom if I recall. :D
    As for tipping depends on the gear you pedal / body position--- a lower gear will produce more rear wheel torque and a tendency to do a wheelie
    I think the sign at the top slightly exaggerates the gradient:
    http://www.geograph.org.uk/photo/105618
    Still, it is the steepest bit of road in the UK, although you can only go down it apparently.
    Other contenders are Hardknott Pass and Rosedale Chimney bank.
    I've never cycled or driven up/down these though, of the roads I have driven up, Lynmouth Hill and Porlock Hill in Exmoor are very, very steep, the steepest I've come across.
  • rml380zrml380z Posts: 244
    Maths has never been a problem for me, but both of these measurements of gradient totally confuse me. Anybody know why we just don't use the angle from horizontal in degrees?
  • Tom ButcherTom Butcher Posts: 7,137
    If you get a sheet of paper and draw a 1 in 10 hill it looks like a gentle slope - even a 1 in 5 doesn't look too bad - so how come when you ride a bike up them they seem much worse - the steep bit on Hardknott feels more like 45 degrees when you ride it when of course it's nothing like.

    it's a hard life if you don't weaken.
  • keef66keef66 Posts: 13,286
    That's cos it's much easier pushing a 10g pencil across your desk than it is pedalling an 8kg bike uphill. Simples!

    I can draw a 50% gradient without breaking sweat, but when it comes to the bike I'm often knackered by the time I've pumped the tyres up.
  • nasahapleynasahapley Posts: 717
    rml380z wrote:
    Maths has never been a problem for me, but both of these measurements of gradient totally confuse me. Anybody know why we just don't use the angle from horizontal in degrees?

    Because a true mathematician would use radians, not degrees!
    Pross wrote:
    With regards to the plan distance v actual distance, this showed big time on my walk at the weekend. I'm not sure what the 20 mile plan distance equated to but it must have been at least 23 miles.

    In which case good old Pythagora's theorem tells you that you must have climbed between 15800 and 30000 feet - a good walk indeed!
  • What's up with using %, it's simple.
  • ProssPross Posts: 22,137
    nasahapley wrote:
    rml380z wrote:
    Maths has never been a problem for me, but both of these measurements of gradient totally confuse me. Anybody know why we just don't use the angle from horizontal in degrees?

    Because a true mathematician would use radians, not degrees!
    Pross wrote:
    With regards to the plan distance v actual distance, this showed big time on my walk at the weekend. I'm not sure what the 20 mile plan distance equated to but it must have been at least 23 miles.

    In which case good old Pythagora's theorem tells you that you must have climbed between 15800 and 30000 feet - a good walk indeed!

    More like 60,000 by my reckoning! :lol: It was actually 6,000' of climbing which by my reckoning adds only 0.03 miles to the 20 miles. Measured distance was nearly 22 though so they obviously got their plan distance wrong.
  • nasahapleynasahapley Posts: 717
    Pross wrote:
    Pross wrote:
    With regards to the plan distance v actual distance, this showed big time on my walk at the weekend. I'm not sure what the 20 mile plan distance equated to but it must have been at least 23 miles.

    In which case good old Pythagora's theorem tells you that you must have climbed between 15800 and 30000 feet - a good walk indeed!

    More like 60,000 by my reckoning! :lol: It was actually 6,000' of climbing which by my reckoning adds only 0.03 miles to the 20 miles. Measured distance was nearly 22 though so they obviously got their plan distance wrong.[/quote]

    I assumed that you would have ended up at a similar altitude as you started though, and not over 11 miles up :wink: I do a fair bit of hill walking/running myself and always feel a bit short changed at how little extra distance the ups and downs add on. Same with cycling - even over something really hilly like the Fred Whitton route the hills only add a fraction of a % to the total distance.
  • grayo59grayo59 Posts: 722
    Can't you just divide the % number into one hundred to get the 1 in number?

    E.g. 12% you divide 100 by 12 to get 8 with 4 remainder so the 1 in number is 1 in 8.333 rec.

    or 20% you divide 100 by 20 to get 5, so 1 in 5.
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