On the hoods
In the drops
Zwift automatically changes your rider’s position on the bars between the hoods and drops based on two factors: drafting and speed. (Your rider’s posture and hand position will also change for out of the saddle efforts and the supertuck but those have been covered in previous posts.)
Drafting
Zwift uses the visual cue of sitting up as a drafting indicator. Others around you may also be drafting, but Zwift only has your rider sit up (ride on the hoods), so you know you’re drafting. (Yes: what you see on Zwift is slightly different than what everyone else sees.)
In the screenshot below from Shane Miller you can see Shane’s rider is on the hoods, while everyone else is in the drops. (This also makes it easier to spot your own rider in a pack.)
Speed
Removing drafting from the equation, your rider will sit up and ride on the hoods at slow solo speeds, then move to the drops at faster speeds, much like outdoor riding.
When riding solo, you will begin on the hoods. As you speed up, when you hit 32-33kph your rider will move to the drops. If you are in the drops and begin to slow down, your rider will move to the hoods as you drop to 29-30kph.
Does Handlebar Position Affect Rider Speed?
Does changing from hoods to drops change your speed in game, like it does outdoors? Not as far as we can tell, although ZwiftHQ could change this. It is only used as a visual cue at this time.
Conclusion
Your rider will only be in the drops when you are moving at least 32-33kph and not drafting. In all other situations (as long as you aren’t out of the saddle or in the supertuck) your rider will be on the hoods.
does this apply for being in the aero position on the TT bike too?
Thanks for clarifying this. I guess I’d favor that it’s not a static value, but something more individual to each rider’s capabilities. Think that a rider of lower performance in reality might already go in the drops before reaching 32km/h. Think that this weak rider might already want to benefit of drafting effects at lower speeds. Unless drafting in Zwift doesn’t exist below this speed threshold, this weak rider would not have a reliable visual clue whether or not he’s drafting.