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!
Would love it if they could fix downhill drafting, once they made the change that only the lead rider could supertuck, it’s been terrible.
Not being able to push someone out of the way is not adding to realism in racing…
Also not realistic: one rider having steering and the other not, and so can’t push back…
In the ECRO races there was a noticeable, negative change where riders would just get stuck sitting out of the pack eating wind for no reason. I experienced it with several others and there were a lot of complaints about it.
“Cray supercomputer”, not “Crazy supercomputer”
LOL, that’s a funny typo. Fixed!
I’ve never had an issue with any pack dynamic updates until this one. This update feels off. Steering, drafting, weird zig zags. I’m not sure what they were going for here but it doesn’t feel right.
I zig and zag all over the place as I have done for a months now. Today, I noticed a couple hand cyclist being kept out of the draft the entire time with maria (55km). I stayed on the center line off and on multiple times. I dont even complain anymore. I just call it a game feature. We live learn and adapt. I miss the old day, but everything changes.
Big problems with getting stuck behind people doing way less power than you. It causes splits where the back is doing more watts than the front.
Also getting shoved out of the side into the wind, especially in sprints.
It’s always hard to know because zwift shows w/kg and not watts. So a heavy rider doing less w/kg in front of you is likely doing more watts.
I was talking specifically about being in a pack with people I race regularly so I know their weights. The problem is PD5.
My bad, I wasn’t sure you knew the weights of the other riders. I actually don’t mind this aspect as a teammate since it allows me to let off the gas and let my teammate in front get a little gap during races.
Next step is to balance the benefit that the draft gives in the middle of the peloton with the greater risk of crashing. Crash Dynamics coming soon?
With a new version of Zwift Plays that triggers an electric shock when your avatar crashes.
Raced with it last night and did some pacer groups too. The draft seeking behavior does seem improved, way less time sitting in the wind waiting for the avatar to decide on who to draft. There is still a center line or gutter issue with randomly getting pushed out of the draft to the side. Draft is still a little too sticky too. Though overall, it’s better than my recent experience with pacer groups.
If non-steering players are now finding the draft sufficiently quickly, can we get rid of the option to ban steering in races? I like to be able to pick which lane I’m in and it also helps keep me more engaged.
I feel something negative has occurred with this last PD update, not sure what it is, I get a little bit behind the main pack and have a heck of a time getting back. I really am unhappy with whatever ZHQ has done.
More than that, I wish they would just quit messing with it and just leave it. I don’t mind it changes that much. It’s not knowing what’s up from one ride to another! I get used to what’s happening then it changes.
@Eric Schlange do you know if the plan is for continued iteration on this? The same problems still exist in PD5 as have existed since it came out, just to different degrees. And no one from ZHQ ever comments on anything on the forum. So will PD5 ever get better or are we stuck with it as-is until PD6?
Non-answer means this is it I suppose. Same communication strategy as ZHQ.
I don’t know ZHQ’s precise plan with PD. But I do know that they seem to regularly be tweaking and testing it (as mentioned above) so I would expect that to continue.
Zwift wants your avatar to find the draft more quickly, but to do so in a realistic-looking way that honors your steering choices. in fact, after about 10 seconds, the avatar still starts moving back to the middle of the road even if there is no rider ahead. it may look realistic, now even smoother, but it doesn’t honor steering choices.
It’s crap for those of us with steering enabled. I’ve not tried with steering disabled but in group rides and races, it absolutely sucks. I’m constantly getting pushed out of the draft and when I try to steer back in, the response is glacial. I don’t know what ZHQ has in mind here and I don’t think they do either. I’ve seen posts on the forum (chirp, chirp…) and the Zwift riders FB page saying “Everybody must love this because nobody is complaining”. Rubbish. Absolute rubbish.
And then, why oh why do they have auto steering for TT bikes? I know where I want the bike on the virtual road and I don’t need it moved to the center of the lane constantly. Completely and utterly stupid; makes no sense whatsoever.