Pack Dynamics are perhaps the most challenging thing to “get right” when it comes to indoor cycling simulations like Zwift. Accurately replicating the speed and movement of a lone rider isn’t easy, of course. But accurately representing a pack of such riders is another challenge entirely! (It took a Cray supercomputer to analyze the fluid dynamics of a peloton, after all…)
Zwift has iterated through various pack dynamics “versions” over the years, with the most recent major release being pack dynamics 4.1 around two years ago.
However, pack dynamics on Zwift are never released as singular major updates. It’s better to think of them as something that is being regularly tested and tweaked, with specific goals in mind. And they’ve had various iterations of the latest pack dynamics (version 5) enabled in certain Zwift activities for almost a year.
Pack Dynamics 5 (PD5) was created to improve two key avatar behaviors:
- Collisions: Zwift wants fewer collisions between riders’ avatars for a more realistic-looking ride experience
- Draft Seeking: Zwift wants your avatar to find the draft more quickly, but to do so in a realistic-looking way that honors your steering choices
PD5 went live for free rides in Watopia in late 2024, and I shared a post in January 2025 with an update on its current state and lots of details about what was changing. Since then, the team at Zwift has been iterating and testing PD5, steadily broadening its use in the live game as wrinkles were ironed out.
Then last Thursday, Zwift’s James Bailey posted the following message to the Zwift Riders Facebook Group and the Zwift Forum:
Hi everyone,
Over a number of months, we have been testing, privately and publicly and making iterations to our 5th version of Pack Dynamics. This is presently live on all free ride, group ride and RoboPacer activities.Pack Dynamics V5 (PD5) has two goals. Firstly to improve collision avoidance – so you do not ride through other riders. Secondly it improves how quickly you are able to find the draft after having been overtaken – great news if you ride in TTTs!
Most recently, a number of our event organisers have been helping us test this new feature in races and we’ve also run a week of the Zwift Crit Racing events using PD5. We have received no negative feedback as a result.
We will be turning on PD5 for races (and thus all Zwift activities) tomorrow (July 24) around 1300 UTC. This will give racers a chance to use it in the Thursday Team Time Trials, as well as having a full month of ZRacing to get used to the new dynamics before our peak racing season begins with the launch of Zwift Racing League in September.
As always, if you ever have any feedback after having tried using PD5 in races, we’d be delighted to hear it.
Many thanks,
James
In summary: Pack Dynamics v5 is now live across the entire game.
If you’re curious, here are some of the changes Zwift made to earlier versions of PD5 before last week’s release:
- Made the collision more “soft” between players because it was creating unwanted left/right movements in big packs
- Removed the possibility of “bullying” another player using manual steering (i.e., a player should not be able to push another player laterally)
- Fixed an issue where players in big packs would get stuck at the center line of the road and create an unnatural line of overlapping players
Zwift says they “have not changed how drafting and air resistance is calculated, so no difference is expected when catching up to another player or pack of players.” I may still run some updated TTT tests just to make sure, though!
Discussing PD5
There’s a long Zwift forum thread, begun in January, with hundreds of replies from Zwifters providing feedback on PD5 as it evolved. (This thread is now closed, but you can read it for historical context if you’d like.)
If you’d like to share your thoughts on PD5 in Zwift’s forum, you should do so on this new thread from James.
You can also share your thoughts below. Ride on!
wpDiscuz
