Trail Running Race Time Calculator: GPX, Vertical Gain and VAM

From one road personal best it takes your flat pace with Riegel, Cameron or Daniels-Gilbert, for the flat distance the course is equivalent to. Then it runs the course stretch by stretch, about every 100 m of the GPX (or a synthetic profile from the ascent and descent you type): each stretch costs the flat pace times a gradient factor from the measured energy cost of running on slopes (Minetti 2002, normalised to the flat: 1.3 at 5%, 1.66 at 10%, about 3 at 25%), times a terrain factor for its class. Climbs steeper than 15% blend into your vertical speed and from 25% are all vertical, since there the vertical speed stays constant however steep the slope (Kay 2012, Giovanelli 2016). The equivalent flat distance and the pace depend on each other, so the model iterates to a fixed point, usually in three or four rounds. Altitude, weather and the run after a bike are added as on the road.

VAM is your vertical speed, metres of ascent per hour (velocità ascensionale media, a term from cycling). Take a climb you know from a race or a Strava segment: 600 m of ascent in 50 minutes is 720 m/h; a vertical kilometre in 45 minutes is 1,333 m/h. Enter the vertical speed or the climb and the model paces the steep sections at it, lowered for a longer race, since a VAM held for an hour is not held for six (Riegel's exponent on the speed). Typical values: 1,000 m/h and more for elite mountain runners, 600–800 m/h for a fit amateur, 400–500 m/h at a hiking pace with poles. Without an entry the gradient curve alone decides.

A is a road, gravel road or forest track: no cost beyond the gradient. B is a groomed trail with firm paths: about 5% on the flat, 3% on the climbs and 10% on the descents. C is technical single track with roots, rocks, steps and narrow passages: about 12%, 6% and 25%. D is alpine terrain with scree, boulders and exposed ridges: about 20%, 10% and 45%. The surcharges are the 5–20% the literature reports for trail against road, most of it on the descents, where braking work and footing limit the pace, not oxygen (Vernillo 2017). With a GPX file every section can carry its own class; without one you pick one class for the course.

Yes. After an upload on the trail it reads the roads, paths and land cover around a few points of every section from the map data (Mapbox): a surfaced road is A, a track or a path through woods and meadows B, a path through scrub or over bare ground, steps or no mapped way C, bare ground, rock or snow without any way D. On the real map the big alpine ultras come out mostly C with B in the valleys and A on the roads. The classes are suggestions: a pill overrides a section, the button reads the map again. The sample coordinates go to Mapbox the way the map tiles already do; the GPX file itself stays in your browser.

Running gets cheaper down to about −10%, where the pace is some 14% faster than on the flat (Townshend 2010). Beyond that the braking work takes over: by −25% a descent is as slow as the flat, the critical gradient of race records (Kay 2012), and steeper is slower still. The energy minimum at −20% (Minetti 2002) is no pace minimum, as grade-adjusted pace from millions of runs shows (Strava 2017, Crowell 2021). On technical ground the descent surcharge is the largest of all: 25% for single track, 45% for alpine terrain.

The International Trail Running Association's measure of a course: the distance in kilometres plus the ascent in metres divided by 100, so 42 km with 2,500 m of ascent is 67 km-effort. The calculator shows it as information next to the equivalent flat distance; the prediction itself comes from the stretches, since 100 m of ascent cost very different times at 5% and at 30%.

A road or flat race, because the model takes your flat pace and adds the course; a trail result as the reference would count the terrain twice. Take the longest recent one within a factor of two of the equivalent flat distance: for a 42 km trail with 2,500 m of ascent that distance is around 60 km, so a marathon or a half marathon is the right reference and a 5 km is not.

As on the road, and with the course: the wet-bulb globe temperature comes from the race-day forecast for the course midpoint (temperature, humidity, sun, wind and the pressure at the course's elevation), with the penalty per 5 °C by level and acclimatisation and the ±2 °C band; the cold starts at the level's optimum. Altitude costs every stretch at its own elevation, so a race from 1,000 m up to 2,700 m loses more on the top sections than on the valley floor; with a GPX file this is always on, without one from the altitude field. Both are percentages of the moving time over the course.

Yes. Choose "After your bike" and enter the bike's hours and intensity, or take them from the cycling calculator on a click: the run is planned slower by that load, not by a standard distance, so an extreme triathlon (an XTRI World Tour race, for instance) with its mountain bike leg and a trail marathon at the end fits, as does any long course. The slowdown is a percentage of the moving time over the course, as on the road; the standard triathlon distances are road races and are not offered on the trail.

Yes. A file that climbs at least 20 m per kilometre or has a sustained climb of 12% or steeper switches the page to the trail and says so; Road puts it back. The distance then comes from the file, and the ascent and descent sliders reach to 6,000 m.

A race model from one reference is an estimate. Validations of segment models of this kind report mean errors around 10% for mountain races of 10 to 50 km, and three things widen it here: the terrain class (one class off moves a technical course by 10–20%), the reference race (take the longest recent one) and the day. Beyond the marathon every prediction model continues with Riegel's exponent of 1.06; the specific fatigue, the night, the aid-station stops and the walking of a 100 km or 100-mile ultra are not modelled yet, so an ultra prediction reads as the moving time of a well-paced day and tends to be optimistic. An ultra mode is planned.

Yes. Under the predicted finish time, "Take into race plan" writes the time and the trail distance into the triathlon planner, which shows where the split came from and re-sums the finish time; the nutrition plan takes the splits from there.