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How can I calibrate my drag using a past race and the Time Analysis Tool?

With the Time Analysis Tool it is very easy to fine tune your CdA (Drag Coefficient) using a past race or a training ride. Keep in mind that you will want to use a past race or ride in which you were on the same setup as will be used in your upcoming race and you will need to know what your average power and total bike split time was for the past race/ride.

The basic idea is to take a known course, time and average power then calculate the CdA (drag) needed to balance this equation. Here are the steps to calibrating/verifying your CdA:

  1. First you should review your Athlete Profile and your Bike Profile to ensure that they are set to match what was used on your recent race or training ride.
  2. Select or upload a course that you have already completed such as a recent race or a training ride.
  3. Set up a Race Plan using your recent race or training ride course, set the historical weather conditions for the race (for best results use the Advanced Weather (Premium Feature), then select the Normalized Power model and create your race plan.
  4. On the Race Detail page select the Time Analysis (Premium Feature) tab and adjust the power slider so that it matches your actual average power from the race/ride, then adjust the drag slider until the Adjusted Time matches your actual finish time from the race/ride.
  5. Note the Adjusted 0° Yaw CdAs shown below the Time Analysis chart.
  6. Update your Bike Profile under CdA Racing and Climbing by putting the noted CdA values from the Time Analysis Tool in the CdA field for your 0 Degree Yaw Angles. The system will automatically adjust the other yaw angles based on this initial change.
  7. To verify the adjustment to CdA, rerun the model by updating the Race Plan and check that your actual time is close to the model's predicted time. There may be a small time difference based on average power versus normalized power. You can use the Time Analysis Tool's power slider to set your average power to that of your actual average power from race day. If your CdA is correct, your Adjusted Time on the Time Analysis Tool should match up pretty close to your actual race day time without having to adjust any other sliders on the tool.

Your drag should now be calibrated and you can setup and run much more accurate power plans for future races.

Calibrating Drag With The Time Analysis Tool

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