← Spark & Whetstone · Thinking in Rates
A longer race is run a little slower per kilometre. In 1981 the engineer Peter Riegel fitted one formula to the world records of his day: double the distance and the time grows a little more than double. Here it is, with its error shown, not hidden.
| Race | Riegel (1.06) | With a bigger fade (1.10) |
|---|
The formula is T2 = T1 × (D2 ÷ D1)1.06. The 1.06 came from world-record times, run by people trained for every distance. Most of us are better trained for some distances than others, so the further a prediction reaches from the race you ran, the less it is worth. The biggest gap is usually the marathon: many runners finish slower than a short race predicts, because training for the distance matters as much as speed. The second column shows what a steeper fade, an exponent of 1.10, gives. Neither column is a promise.
Predict from a recent race that is as close as you can to the one you are planning. The only comparison on this page is with your own time.
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