Grade/percentage on hills ... which is it really?

[3_days]

Sorry of this seems like a dumb question - I wasn't sure how to search the forum for an answer ...

When we talk about the grade of a hill - I understand that 90 degrees is straight up and down 0 degrees is completely flat -

Yet, I hear commentators and cyclists talk about an "8 percent" grade - is that just another way of saying an "8 degree" grade -

I mean, a gradient is 0 - 90 and a percentage is 0 - 100 ... is there a difference or is it just an understood misnomer ...

 

[Squint]

I usually don't follow the recurrent grade threads but I was recently playing with Topo looking at some local climbs.

I believe grade is rise over run (opposite over adjacent) so a 33% grade is 33 per 100 or a 33 foot rise every 100 feet. To get the angle, do arctan(.33) which is 18.26 degrees.

 

[3_days]

Thanks for the response - for some reason, I was always under the impression that it was all done with right angle triangle calculations ...

Just to be clear, a percentage IS different than the angle of the incline! For example, if a certain distance rises 9 feet per 100, a cyclist won't rise at a 9 degree angle! It's more like 5 degrees.

Thanks again!

 

[robkit]

100% gradient = 100 feet up for 100 feet ridden = 45 degrees.

i guess then a sheer cliff (90 degrees) can only be expressed as an infinite gradient.

to complicate further we have a practise in england of quoting the fractional gradient on road signs - "1 in 8", "1 in 10" etc.


and take a look at this - hardkott pass, possibly the steepest road in england, 33%!

http://www.sentient-entity.pwp.blueyonder.co.uk/travelshots/uk/honister.jpg

 

[DannoXYZ]

The grading standards comes from civil-engineering practices. It's much easier for a bunch of guys in the field to determine the rise of a road using right-triangle (rise over run) measurements than using degrees and angles.

 

[3_days]

Yeah, it makes sense to do it rise over run ... and here I've been on my computer calculating angles from right triangle equations to try and estimate the difficulty of the hills I ride ... I'm always into doing things the hard way!

The pic- of Hardkott Pass is awesome! You oughta take a run at it in a 53/11 !!!

 

[ric_stern/RST]

100% gradient = 100 feet up for 100 feet ridden = 45 degrees.

i guess then a sheer cliff (90 degrees) can only be expressed as an infinite gradient.

to complicate further we have a practise in england of quoting the fractional gradient on road signs - "1 in 8", "1 in 10" etc.


and take a look at this - hardkott pass, possibly the steepest road in england, 33%!

http://www.sentient-entity.pwp.blueyonder.co.uk/travelshots/uk/honister.jpg

While Hardknotts and Wrynose (just next to Hardknotts) is undoubtedly horrendously steep at 33% (i love the warning signs at the bottom of the hill!) there's an even steeper climb a few km's away at Coniston -- The Old Man of Coniston, which goes up to a disused mine shaft, which is supposedly between 30 and 40%.

Ric

 

[scotty72]

100% gradient = 100 feet up for 100 feet ridden = 45 degrees.

i guess then a sheer cliff (90 degrees) can only be expressed as an infinite gradient.

a sheer cliff is most precisely referred to as "Oh Shi..."


I am far more used to the fractional gradings

eg. 2 metre gain over 50 metres is a 1/25 grade, which you might call 4% which others would call, "stop whining, it is virtually flat"

Scotty