Physics Help Page

As of this writing, Tour de Giro supports several different physics modes for scheduled races. These are described below

Default In this mode, we do our best to fully simulate the physics of road cycling. If in doubt, select this option. A rider's aerodynamic drag will vary slightly with their weight (they'll have more drag as they get heavier, as happens in real life).
Default without drafting This mode uses the same physics as the default mode, but removes drafting. If you want to simulate a triathlon or a time-trial, this is the way to do it.
Weight-handicapped This mode adjusts every rider's power and weight to make every rider an 80kg person putting out the same W/kg that they are. For example: If you're 40kg and doing 160W, then your power and mass will be doubled to 80kg and 320W. This is useful if you want to create a handicapped race
FTP-handicapped This mode adjusts every rider's power and weight to make every rider an 80kg person with a 300W FTP doing the same percentage of FTP that they currently are. If you're 40kg and have a 3W/kg FTP, then by doing 3.5W/kg, your rider online will ride as if they're an 80kg person doing 350W

Technical

If you're into the physics of bike racing, here's a less wishy-washy explanation. In this table, RiderMass is the mass you entered when setting up, and InputPower is the latest power sample from your powermeter.

ModeCdaCrrMassPowerWindDrafting
Default0.0025 * RiderMass + 0.10.0033RiderMassInputPowerNone0-38% reduction in aero drag from 0-10m
Default w/o drafting0.0025 * RiderMass + 0.10.0033RiderMassInputPowerNoneNo Drafting
Weight-handicapped0.30.003380kgInputPower*(80/RiderMass)None0-38% reduction in aero drag from 0-10m
FTP-handicapped0.30.003380kg300*((InputPower/RiderMass) / FTP_WKg)None0-38% reduction in aero drag from 0-10m