Products / RunFast
RunFast
The heat, dew point and wind for every kilometre of a run, timed to the runner’s own pace.
- Relationship
- RunFast is an independent product created and operated by Cross Constellation.
- Canonical site
- runfast.tech
- Status
- Active public product
- Product colour
- #EE7A1F
The one-sentence definition, without comparison or superlative.
What it is
RunFast times the heat to a runner rather than to a place. Give it a route, a start time and a pace and it works out when you reach each kilometre, then forecasts that point at that hour: what it will feel like at running pace, the dew point, WBGT heat stress, rain and wind, and the weather cost — how many minutes the conditions will take off you. On race day a runner sets a goal and goes live, and anyone following sees position, pace and projected finish against that goal on a map, with no app and no account.
The operating frustration that existed before the product.
The problem we encountered
At running pace there is almost no cooling airflow, so heat, humidity and dew point decide pacing, hydration and which water tables matter. Nothing timed those conditions to each kilometre of a runner’s own route as the day warms up. Race tools cover famous courses only, pace calculators take a single temperature for a whole run, and route-weather tools are built around cycling speeds.
The founder’s account, in their own words.
Why we built it
“Operating a product surfaces the next problem. Windline forecasts wind along a cycling route because wind is what decides a rider’s day; running it in production showed that many of those riders also run, that the running population is far larger, and that a runner’s day is decided by something else entirely. The forecast engine already existed. What it needed was retuning for a different enemy and a different speed.”
How the first problem expanded into the current product.
What the product became
- Heat resolved to the runner — feels-like at running pace, dew point and WBGT heat stress for each kilometre at the hour it is reached.
- A weather cost stated in minutes, so conditions become a pacing decision rather than a number to interpret.
- Pace handled in minutes and seconds per kilometre or mile, in five-second steps from 2:30 to 15:00, so back-markers and run-walkers are timed as accurately as the front of the field.
- Live race tracking that needs nothing from the people following — a map with position, pace and projected finish against the runner’s goal, opened from a shared link.
- Club pages, where members mark themselves in and every club race gets its own live map.
Genuine dogfooding. Deployed uses only.
How we use it ourselves
- RunFast runs on the same forecast engine as Windline, retuned for running pace. One engine means the numbers are identical wherever they appear, and a correction to either product improves both. Deployed
- It shares Windline’s Strava connection and live-tracking server rather than rebuilding them, which is the practical test of whether that infrastructure was built generally enough. Deployed
Attributable support for everything claimed above.
Evidence
Where to go for the product itself.
Official destinations
Stories