How many watts can you save with XY upgrade?

This question pops up an awful lot, but to be honest, it is not really correct.

Generally, it is meant for things regarding aerodynamic drag – here it is really incorrect to talk about a specific watt saving without specifying a set speed. The same upgrade – same change in CdA means radically different power savings at different speeds. For example, a 0.04m2 CdA reduction saves 1.5W at 30km/h, 3.5W at 40km/h and 8W at 50km/h due to the non-linear nature of aerodynamic drag.

Therefore, while “2W saved at 30km/h” might not sound like much, but it is actually quite a lot, and “2W saved at 60km/h” is a very marginal difference.

Things are simpler when we talk about drivetrain losses and rolling resistance. These have a linear correlation to power output, respectively tire load and speed. These need to be specified to give you a correct understanding of the savings.