BikeChangeLog: tracking equipment changes over time

What a BikeChangeLog entry is

A BikeChangeLog row records a single change made to a specific BikeSetup, with optional CdA-before and CdA-after so you can measure the aero impact of the change. Useful for:

• Recording when components were swapped (so the right setup is known at any given date).
• Measuring the actual aero gain (or loss) from a change.
• Building an audit trail of position and equipment evolution.

Fields on a change log entry

• Bike: the BikeSetup this change applies to.
• Date: the date the change was made.
• Change summary: short description, e.g. "Switched to disc wheel", "New saddle, height up 3 mm".
• Details: longer description with context, why the change was made, conditions tested in.
• CdA before (m squared, optional): CdA measured before the change.
• CdA after (m squared, optional): CdA measured after the change.
• Created by: which user logged the change.

The CdA delta

If both cda_before and cda_after are filled in, the model exposes a cda_delta property that returns the difference (negative = faster). The aero impact of the change is then visible at a glance.

When to log a change

Log a BikeChangeLog entry for:

• Wheel swaps (training to race wheels, deep to shallow).
• Position changes after a fit session.
• Cockpit changes (new bars, new extensions, new pads).
• Helmet changes that affect CdA (open road to TT).
• Skinsuit / kit changes that you tested in.
• Tire changes that affected Crr or width.

You do NOT need to log:

• Routine tire pressure changes (just update the tire pressure fields on the BikeSetup).
• Bike washing or maintenance.
• Component swaps that have no aero or fit consequence (chain replacement, cleaning).

How to log

Currently logged via Django admin (/admin/core/bikechangelog/add/). Pick the bike, fill in the date, summary, details, optional CdA values, save.

Reading the timeline

The bike change logs for a single bike are ordered most-recent first. Coupled with CdA tests over time, the log explains why CdA shifted between two tests.

See also: CdA Field Test, Position notes and aero values.