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Chung method, automated

Test your tire speed with the Chung method

Upload a FIT file from a test ride and get your tires' rolling resistance (Crr). No sliders: the virtual elevation is fitted for you, the file is checked, and wind is taken into account.

See the tire speed results

Weigh yourself with the bike and kit. Every kilogram counts: 1 kg off moves Crr by about 1%.

Your file is read in memory and never kept.

How the Chung method works

Your power meter says how much energy you put in. What does not go into air drag, rolling resistance and speed must have gone into climbing. Summed up second by second, that gives a virtual elevation profile.

With the right Crr and CdA, the virtual profile matches the real road. In tools like Aerolab you move sliders until it does. We solve it exactly, show how well it fits and how certain the result is.

Braking and gusts show up as stretches that do not fit, and are left out by themselves.

How to ride a tire test

  1. Find a loop of 1 to 3 km with little traffic, gentle hills and no need to brake.

  2. Set your tire pressure, warm the tires up for 10 minutes, and zero your power meter.

  3. Ride at least 6 laps in one position: half of them easy, half of them fast. Different speeds let us tell rolling resistance from air drag.

  4. Press the lap button at every pass of the start, so you can pick the test laps later.

  5. Do the same with the other tire on the same day, then compare.

What the FIT file needs

  • Power from a power meter.
  • Recording every second (no smart recording).
  • A wheel speed sensor. GPS speed works, but less precisely.
  • Altitude from the head unit's barometer.

Wind

Wind is the biggest source of error in the Chung method. With a Wahoo ELEMNT ACE we read the air speed from its wind sensor every second, so a breezy day still gives a result.

Without a wind sensor, test on a calm day. We check the weather for the time and place of your test and tell you if the result may be unreliable.

Want us to support a wind sensor other than Wahoo? Write to us and send one ride file from it.

Privacy

We never keep your FIT file. A saved result holds the tire, the conditions, the numbers and the nickname you choose. No route, no positions.

To check the weather we send Open-Meteo the place rounded to about 10 km and the hour of the test.