Which climb was steepest,
and where was my VAM best?

Every outdoor ride records its elevation, second by second. None of them comes back split into climbs. To ask which climb of the season you rode fastest, you first have to decide where each climb starts and ends, and a summary of the whole ride cannot do that for you.

This article is about VAM, the number usually used to compare climbs, what it can and cannot compare, and how to get every climb out of a ride's elevation trace so the comparison is possible at all.

What VAM measures

VAM is vertical ascent in metres per hour: the height a climb gains, divided by the time it took, scaled to an hour. Gain 300 metres in 15 minutes and your VAM is 1,200 m/h. It needs no power meter, only elevation and time, which is why it is the number people reach for on rides without one.

It is a measure of how fast you went up, not of how hard you worked, and three things move it besides your legs:

• Gradient. At the same power, a steeper climb gives a higher VAM. On a steep road nearly all of your effort goes into lifting you; on a shallow one a larger share goes into pushing through the air, and less is left for height.
• Weight. VAM follows power relative to the weight being lifted, rider and bike together. A heavier bike or a full bottle lowers it at the same power.
• Wind and company. A headwind or riding alone on a shallow climb costs VAM; a tailwind or a wheel to follow gives it back.

So VAM compares well between climbs of similar gradient, and between attempts at the same climb. Between a 4% drag and a 10% wall it mostly tells you which was steeper.

Finding the climbs in a ride

Splitting a ride into climbs sounds simple, and the obvious rules each fail on real roads. "Uphill until it goes down" ends a climb at the first switchback that gives back a few metres. "Up overall" turns a rolling road into one long climb. IntervalSync finds climbs from the elevation trace this way:

• Elevation is smoothed over 15 samples first, so a single bad altitude reading cannot end a climb.
• A climb ends when, after its last high point, more than 400 metres of road go by before that height is regained, or more than 10 metres of height are lost. Both limits are needed: distance alone keeps a climb going down a long descent, and height alone breaks a real climb at a hairpin.
• What is left counts as a climb if it gained at least 30 metres at an average gradient of at least 3%. The gradient is checked after any dips inside it are bridged, so two steep pitches joined by a flat kilometre are not reported as one steep climb.
• The steepest gradient is the steepest 30-metre stretch, not a single sample. One metre of altitude error across four metres of road reads as 25%, which is not a gradient anyone rode.

For each climb it reports the distance, the height gained, the average and steepest gradient, the time, the VAM, and, where they were recorded, average power, heart rate and cadence. It also reports drift: the second half's average against the first half's, as a percentage, so you can see whether power held to the top or faded. The 25 largest climbs in a ride come back in the order you rode them, and anything left out is counted. Every limit above can be changed when you ask: a higher minimum gain to leave out the rollers on a mountain ride, a longer gap to join the pitches of a climb split by a false flat.

Find every climb over 100 m in my rides since June. Rank them by VAM, and tell me whether my power held to the top or faded on the longest three.

What it cannot tell you

• An indoor ride has no climbs. Without recorded elevation and distance there is nothing to find, whatever gradient a trainer app simulated.
• It does not know the climb's name. Climbs are found from the shape of the trace, not matched against a map of known climbs, so it describes the climb precisely and does not tell you what it is called. Comparing attempts at the same climb means telling it which ones they are, by date or by where in the ride they fell.
• A faulty power meter affects power, not VAM. If the power stream has a stuck or dropped stretch on a climb, that climb's power and drift are marked as untrustworthy. Its height, gradient and VAM come from the elevation trace and stay as they were.

Across a season

Each ride's climbs are read with a request to Intervals.icu, so ranking every climb since June takes a request for each ride. On IntervalSync's Free plan, after the trial, that is one ride's climbs a day. The trial and Pro allow up to 300 requests a day and the Coach plans more, as pricing sets out.

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