[ndsipa_pomu]

Weight isn't that important for bike racing unless you're specifically doing hill climbs. Aerodynamics will make more of a difference, so there might be some advantage in having a bit of belly fat to enable a smooth airflow.

Also, heavier riders are generally faster downhill as they have a greater terminal velocity.

[magic_smoke_ee]

> have a greater terminal velocity

No, unless they're Russian, they're not free falling. They have greater potential energy. And also increased traction, increased rolling resistance, and increased losses in wheel bearings and drive components due to friction.

[ndsipa_pomu]

Terminal velocity can still apply when cyclists are going downhill. Essentially it's the speed that a cyclist will reach when the gravitational force is equal to rolling resistance (roughly proportional to speed) plus the air resistance (roughly proportional to the square of speed) assuming that they're just free-wheeling and not pedalling. If two cyclists have a similar air resistance, but different weights, then the heavier cyclist will reach a quicker speed. There's the argument that a heavier rider will be bigger and thus have more air resistance, but that effect is smaller than the weight difference. (NB. this can be trivially tested).

[loeg]

Terminal velocity still applies. Yes, it is because they have more potential energy (per CdA).

Rolling resistance increases are pretty marginal with compensating tire pressures (i.e., higher). Wheel bearing losses are de minimis.

Drivetrain component friction is not a function of rider weight.

[magic_smoke_ee]

> Drivetrain component friction is not a function of rider weight.

Wheel bearing friction, duh. If the rider stands up while pedaling, it does. :)