How these rides are measured

Where the numbers come from

Everything on a ride page is worked out from the GPS trace I recorded — position, altitude and time. There is no power meter and no heart-rate strap in the data, so anything resembling power is modelled rather than measured, and it is worth knowing how.

Distance, climbing and speed

Distance is the sum of the great-circle hops between fixes. Climbing uses hysteresis rather than a running total: a barometer wanders by a metre or two while you stand still, and adding up every small rise turns that wandering into hundreds of metres that were never climbed. Height is only banked once you are decisively above the last reference point.

Barometers also fail outright, and they fail by reporting a number rather than a gap. Day three of the Burundi tour records an altitude of exactly zero for two stretches in the middle of a ride at 1,700 m. Readings that would require an impossible rate of climb are discarded, as are any that sit implausibly far from the ride's own median height.

Top speed is the fastest five-second average, not the fastest pair of fixes. A single dropped fix between two good ones implies a speed no bicycle reaches, and taking that as a record would be flattering but false.

Stops, and the marks on the route

Three things are marked on the map. The fastest point is the middle of the quickest five seconds; the steepest is the sharpest gradient sustained over two hundred metres, so one abrupt pair of readings cannot claim it.

A stop is harder to spot than it sounds, because the recording does not stop when you do — the watch keeps logging while you stand at a junction. So a stop is found as movement of less than twenty-five metres over more than two minutes. Anything shorter is a junction rather than a stop, stops within a hundred metres of each other are counted as one, and only the longest eight are drawn: a map with forty dots on it tells you nothing.

Effort

Power is estimated from the physics of riding a bicycle, using the model in Martin, Milliken, Cobb, McFadden and Coggan (1998), Validation of a Mathematical Model for Road Cycling Power, Journal of Applied Biomechanics 14(3), 276–291. It adds up what you are working against — air resistance, rolling resistance, gravity, and the cost of accelerating your own mass — and multiplies by speed. Against a real power meter the model correlates at R² = 0.97.

Air thins with altitude, so air density is computed from the height the trace recorded rather than assumed. At 1,700 m the air is 15% thinner than at sea level, and ignoring that would overstate the cost of the hardest rides here.

That power is then turned into an effort score the way a coach would: normalised power by Coggan's method, which weights hard efforts more heavily because the body does; divided by a threshold power of about 206 W, estimated as 95% of my best twenty minutes anywhere in this collection; and scaled so that one hour at threshold scores 100.

Heart rate, where I was wearing a monitor

Modelled power is a good guess, but it is still a guess. Heart rate is a measurement, and on the rides where I was wearing a watch it replaces the estimate entirely. It is scored as Banister's TRIMP: each second is weighted by where the heart rate sat between resting and maximum, on an exponential curve, because ten minutes near the top is far more than twice the cost of ten minutes near the bottom.

My resting rate is 47 bpm, a twelve-month average from the watch, and my maximum 191 bpm, recorded on a climb in May 2026 and held for half a minute — long enough that it cannot be the optical sensor misreading.

The great advantage over the modelled figure is wind. My heart already paid for the headwind; the physics has no way of knowing there was one. Comparing the two across the rides that have both found a real fault in the model, which is the argument for keeping both.

Rides from before I wore a monitor keep the modelled figure, converted onto the same scale using the median ratio between the two measures across the rides that carry both. It is approximate — the typical error is about a fifth — but a five-band rating is coarse enough to absorb that, and the alternative was leaving thirteen years of riding unrated. Those figures are marked with an asterisk in the log.

The heart-rate chart on those rides is banded by training zone, set as fractions of heart-rate reserve rather than of maximum. Reserve is the better basis when a resting rate is unusual, and 47 bpm is unusual: measured against maximum alone, an easy hour would land in the wrong zone entirely.

The rating panel

Four measures, each scored one to five against the rest of these rides rather than against some absolute nobody shares. A five means "among the hardest, longest or fastest rides I have recorded", which is the only comparison that means much without a peer group.

Spice: Annie's word. She rode Burundi with me and brought it from the army, where it describes the point at which fun and danger start to overlap. Here it blends top speed, steepest descent and how much the road turns per kilometre. All three matter: a fast straight road is not spicy, and neither is a twisty flat lane. Each part is capped so that no single one can carry the score — without the cap, a five-kilometre potter round the middle of town won on sheer quantity of turning, which describes a one-way system rather than a descent.
Grind: Metres climbed per kilometre ridden. A short steep ride and a long flat one can share a total; this separates them.
Distance: How far. The plainest of the four.
Effort: The training-stress figure described above.

What these are not

Wind is unknown and is the single largest source of error. A 20 km/h headwind can double the power needed to hold a speed, and nothing in a GPS trace reveals it — so a hard day into a westerly and an easy day with it behind can score the same. Drag area and total mass are assumptions (87 kg of rider, bike, kit and bottles), and the effort figures scale with both. Drafting is invisible.

So these numbers are consistent with each other and useful for ranking one ride against another. They are not measurements, and I would not present them as such.