I was hoping someone wouldn’t have to explain it 
There is no right answer to the default CdA value that is used, but by using a low one (as they do now) it works against many of the objectives described in this topic. A smaller increase to the default CdA would improve Zwift as a whole considerably, however I don’t think it will happen when the mantra is Fun is Fast. There’s a reason why so many riders default to Fuego Flats… I blame Strava year in review.
I do agree with the maths and I do agree irl.
On Zwift, I think the riders behavior will screw it, if you increase the cda, everyone will go slower, I agree. You might expect it to make breakaways easer but the races are so short that everyone rides at maximum power for all the race, without any reason to keep unburnt matches.
So by increasing the cda, you’ll make the breakaway slower (as if three or four people collaborate they will still tire fast) but you will have the pack just working a little harder, and go almost as fast as before because of the draft savings…
Irl they would look at each other in the pack and that is what would let the breakaway get away. In Zwift, it won’t happen.
So we need to have other mechanisms to make breakaways work.
For example, bonuses.
Or different cda depending of the size of the pack…
we shouldn’t recreate the reality but create a proper environment for fun races.
but speed is just a byproduct of cda and power, no? i’m not against the idea but my intuition (which i have to rely on, because my gcse in physics isnt helping me here) is telling me that a flat cda increase for everyone in zwift just means slower breakaways and slower sprints too
Jamie is right, irl the power you need to add to breakaway is lower at lower speeds.
So breakaways are easier at lower speeds. That’s why for example teams ride fast in front to prevent breakaways.
But in Zwift I think it works differently because of no breaking, because of the possibility to jump over other riders and because of the shortness of the races, so riders don’t have to save power and also don’t have to be good on staying in the good part of the pack before difficulties.
This is a very interesting idea. At first my thought was increasing cda will just slow everything down.
But now I am thinking you might be onto something. This may need to be tested in a race or two. 
You also need to consider air resistance, as Jamie explained. But as Cyrus notes, the reduction in speed might not make much of a difference given rider behavior in short Zwift races.
i think i get it now. practically speaking then i would guess that an already established breakaway would maybe have a higher chance of surviving but a harder time getting established. i do think it’s worth a look
I’m not even sure that the way zwift races go will matter.
If everyone is slower for the same current power as now then to get away requires less of an increase than now, if you go as hard as currently a good gap could happen quickly.
Yes it also requires less to chase but it will still making racing more dynamic and tactical than now. Multiple attacks and counter attacks, people will tire and breaks will happen.
Now so many races just wait for the sprint as it’s hard to get away, PD4 has helped but the pack still goes too fast IMHO.
Fair point. It seems like it might be worth testing—assuming Zwift models air resistance correctly!
Please don’t mess with the speed of solo riders. Any blanket Cda adjustment is not a solution. Problem lies within the wonky draft mechanics in a large pack. The ideal solution should control pack speed at the front, while allowing smooth drafting in the back. I think PD4 hit the mark on the former, but at the expense of smooth riding in the back of the pack. A lot of people Zwift solo, there is no point messing with their experience so breakaways can form easily.
The experience is wrong though, the CdA is far lower than 99% of riders can achieve IRL. The game will be exactly the same just speeds will be slower.
Surely no one cares that their rides on Zwift are 25% faster and further than they can do IRL.
How cares if you can ride 100km in 2.5 hours on zwift instead of the more reasonable 3:25?
Moon air 
Why is my speed solo IRL is very close to my speed solo Zwift then? Am I an outlier riding at 200-250W at 79kg and 180cm? Your hypotheticals based on an online CdA estimator does not match my reality. Given my metrics, I doubt it will match many Zwifters reality either.
I wonder if Zwift’s drafting algorithm uses the CdA of the riders in front, or if it is just based on some other approximate (e.g. #of riders + distance + speed).
If CdA is used, the draft effect in the group should be greater with an increased CdA because of greater drag for the riders in front, even if each rider gets an increased CdA themselves.
Or at least allow race organizers to choose a Cda within a reasonable range with the current value as the minimum.
You did not see the complaints when the jungle surfaces change and people got slower, many of those people refuse to ride the jungle because it is slower. They want a paved bypass to the alpe so they don’t have to ride 4 km of downhill dirt to get to the alpe. LOL
If a change in cda is going to make racing more fun I am all for it.
It should also be across all of Zwift not just racing like PD4. We need to be able to train and race in the same environment.
Totally agree.
It’s definitely worth investigating and beta testing. If the feedback is overwhelmingly negative, it can be binned.
I also think it should become the new default across all rides and all worlds (if implemented). I don’t think having it as a (race-organiser) switchable option is a good idea, TBH.
proof of this claim?
200-250w is very wide range of watts
I’m wondering if anybody at zwift has ever been in a irl small group doing 25+ mph and how much effort it takes to stay in that group. Then how much effect it takes to jump to the front on the group and pull. I’m not taking crit racing, I’m talk 100km or longer. It’s fairly easy to do on zwift, but most would fail irl. The pack dynamics need to change. The one thing that was mentioned was single rider speed is very close to irl…
Here, from you beloved online CdA calculator that apparently is the source of all truth for you. I picked rides with similar elevation profiles, so your mind doesn’t bend trying to take into account the effect of elevation on speed differences.
First is my solo IRL ride:
Second is from a Zwift race with gravel course, which is probably the best representation of road surface in the Chicago area. I was in a small group for most of this race (75%), so the slightly lower CdA is likely due to that.
Forgive me for not having identical power in these two events, as I don’t go out riding thinking that I would experiment with speed differences in Zwift and IRL rides. As you can see, additional 50 watts leads to a few kmh higher speed in nearly identical elevation.
