How to Predict Your Run Race Times at Different Distances!

Written by Jim Levesque, Head Coach at Grit Endurance. Learn more about Jim’s background here!

There are several race time predictors out there that can help you take your finish time from one distance, and predict your estimated finish time at another distance. One of them is called the Riegel formula, which is a commonly used algorithm: “T2 = T1 x (D2/D1)^R” (don’t worry, you don’t need to actuall know the formula).

Skip this next paragraph if you hate math…

Basically T2 is your predicted race time at a certain distance (D2), and is based on your time (T1) at a different race distance (D1) based on the average R value (fatigue factor) of 1.06. The problem with this model, is that we are all physiologically different, and you might be more geared toward longer distance races or vice versa than average. So to get a more accurate prediction for you specicially, you can actually figure out your R value, and how it relates to the average. All you need to do is have 2 quality race finish times of different distances: “R = log (T2/T1) / log (D2/D1)” (again, you don’t need to know this formula).

Don’t want to do the math? No worries, just type the following prompt into ChatGPT: “If my half marathon time is X and my 10K time is Y, what is my Riegel value and my predicted finish time at Z distance?”

For example, I just typed in ”If my half marathon time is 1:30 and my 10K time is 39 minutes, what is my Riegel value and my predicted marathon finish time?”. Here is what I got: “Your Riegel R value is approximately 1.12, which indicates a slightly higher-than-average fatigue factor. Based on this R value, your predicted marathon finish time is 3 hours and 15 minutes. This assumes consistent pacing and similar training levels across all distances.”

This is a very quick and simple way to take advantage of the race time predictors but to go one step further and make sure the calculation is factoring in the type of runner you are. The other main thing you have to consider is your fitness level, race execution and pacing, as these models assume consistency in these areas. Any questions on this, please reach out!