Don't understand Hills


Active Member
Could someone explain the categorization of a hill? What gradient is a category 2 hill? What does it mean when it says a hill is 6-7%?


Well-Known Member
As far as I understand it, it's all to do with what gear the car had to be in to go up the damn thing in the early days of the Tour de France - and the condition of the road surface. 4/3/2/1/Hors Categorie. So if the car could only get up in 1st gear - it's a good indication the climb is a proper test. ''Hors Categorie'' or ''Beyond classification'' is too difficult to classify - ''We couldn't get the car up it!"

A 20% incline is what we used to call a 1 in 5 - i.e. for every 5 metres travelled forward, you gain 1 metre in altitude. So a 20% slope is jolly steep! The bigger the number, the worse the pain. 25% is a 1:4 in old money - only 4 metres forward for 1 metre of height gain. Very difficult but not unknown on a British sportive.

You can still find some old 1:X signs in the UK - the lower the number the worse the pain - a 1 in 1 would be a slope of 45degrees - almost steep enough to have to crawl up.

Mostly what you'll see will be percentage inclines - harder to calculate just how steep - but it's what our continental cousins use.
it's about a group of wealthy spoilt teenagers in california going out into the big wide scary real world and not adjusting successfully to it.



Ahem. You couldn't be much more misinformative!

Whatever the origins of the car gearing story, it's certainly not the case nowadays. Categorisation of climbs is entirely at a race organiser's whim, and bears in mind such factors as length, average gradient, maximum gradient, exposure, and context within the stage; what might be a second-cat climb on an otherwise flattish stage may not be classified on a high-mountain stage.

The more usual way of calculating gradient is as the sine of the angle (vertical displacement/displacement parallel to the slope). This only differs greatly from the tangent (vertical displacement/horizontal displacement)expression at large angles. 45 degrees is thus 70% or 1 in 1.4

It's worth bearing in mind that road signs in the UK usually give a pretty rough estimation of what the maximum gradient is. The actual maximum gradient is likely to occur around the inside line of corners (which, as a cyclist, are lines you're not likely to take).

Skip Madness

New Member
Legs, if I'm following (and I'm not convinced I am) - are you saying the difference between the sine and the tangent is that the sine is the distance of the tarmac and the tangent is the distance of the ground beneath the tarmac? Ie. because the tarmac gains altitude, 100m going uphill will not travel as horizontally far as 100m flat? Or the other way round? Or both wrong?

Anyway, to Mr Vandal: percentages kind of work in reverse to the fractions that 515mm describes - 7% means that over 100m you'd gain 7m. That's why 1 in 5 = 20% - if over 5m you gain 1m, then over 100m you'd gain 20m.

As for climb categorisations; it varies from race to race, and they aren't always internally consistent. In the Tour de France you'd be looking at something like this as a base guide (these are very rough and don't take into account fluctuations in the slope, but as a broad rule of thumb they'd be reasonable I think):

Cat. 4 - A 12% average gradient over 0.5 km; down to a 3% average gradient over 2.0-5.0km. Any gradients in between would have to be of a distance somewhere in between.

Cat. 3 - 12% would probably need to be the average over 0.5-1km; and a 3% average would need to be 5-8km.

Cat. 2 - 12% over 1.5-4km; 3% over 8-20km.

Cat. 1 - 12% over 4-6km; 3% over 20-40km.

Cat. H - 12% over 6km+; 3% over 40km+.

You could tone all of these figures down immensely for the Tour of Britain. Category 1 climbs there are often the equivalent of Category 3 climbs in the Tour de France (this is down to the organisers being rubbish, there are some decent climbs in this country as most here will well know).

Like I said, undulations in the slope can distort figures, which is why those are only rough. The Coll de Pradell is a good example of a climb which going on the figures alone you'd say was first category, but take a look at the profile and you can see it would be an hors category climb.

Molecule Man

Well-Known Member
I have no idea about how climbs are categorised for racing, it has always been a mystery to me too.

I always thought the % gradient was simply (height gain)/(horizontal displacement), i.e. (vertical side)/(horizontal side) for the corresponding right-angle triangle, but now I am not so sure. I guess it depends how it is measured. If it is measured from mapping data, then it would have to be that surely? But if you take your measurements directly from travelling along the road, then that will mean that the
(vertical side)/(hypotenuse) ratio would be more appropriate, wouldn't it?

Whatever the details, I have come to learn that anything over 10% is hard work for me on the way up and scary on the way down!

Skip Madness

New Member
Hypotenuse makes more sense, 1km at 7% should mean 1km of riding. EDIT: It would either way, wouldn't it? But it just changes (marginally) the definition of 7%.


Chandler's Ford
As I recall (from the time when we changed from the 1 in x system to the % system for gradients) one of them was ratio of height to horizontal distance, t'other was ratio of height to the hypotenuse (or distance travelled).
But I can't remember which was which, but it did mean that 1 in 4 was not equal to 25%


Skip Madness said:
Legs, if I'm following (and I'm not convinced I am) - are you saying the difference between the sine and the tangent is that the sine is the distance of the tarmac and the tangent is the distance of the ground beneath the tarmac?
Yep, precisely. But there's next to no difference between sine and tangent at small angles (below 20 degrees, which is actually exceedingly steep for a road), so the point is a fairly moot one.

Skip Madness said:
Hypotenuse makes more sense, 1km at 7% should mean 1km of riding.
I agree with this. ;)

Fab Foodie

hanging-on in quiet desperation ...
It's all simple really. Hills come in different gradients, some you can ride up, some you can't. The more you train and practice hills, the more you can ride up. Practice enough and the gradient or category becomes irrelevent, they're all there to be ridden.
The way I've always remembered it is the % gradient = distance up/ distance across and if you '1/x' it you get the old fashioned 1 in X.

With races the category means nothing to me it's not until the commentator starts talking in % or 1 in X terms that it makes sense to me.

Skip Madness

New Member
I thought you were sarcastically "agreeing" with my rather tautological point. I still suspect you were, and your last response is mocking me even more. I'll let it go, though...

*kissy kissy*
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