What’s happening with Pack Dynamics 5 on Zwift?

Quite a few comments about pack dynamics in here! I can share a bit of information about it.

The latest batch of tuning (which some call pack dynamics 5) has a few goals:

• make faster riders coming up on slower riders steer around them, vs plowing right through them. In a pack, we still will plow through, but single riders vs single riders should be much nicer now.
• Increase “draft seeking” behavior. The avatars will more actively steer to get behind somebody, within reason. I’ve not seen any instances of this seeking drafting behind a runner myself, but we’ll look into that. This does also mean you might get a few pacelines of riders as some will seek over to draft the rider who’s popped out (or steered out) to the left or right of the main pack.
• Increase collision between riders. We’re not trying to eliminate interpenetrations between avatars, but we do want to improve the situation by increasing the collision bounds a little.
• Similarly, we wanted to make it so you can’t steer through people as easily. This does mean you need to speed up or slow down if you want to get on the other side of somebody. You shouldn’t be able to just steer through avatars as easily as before.
• Ignore draft seeking behind avatars that have a large speed delta from you. Again if people are seeing your avatar seek runners, it could be you didn’t have the new code on in that case, it could be the runner and the cyclist were going similar speeds, or it could be simply a bug.
• For people who have steering inputs, make auto-steering gradually blend back on over time. For users who are actively steering they retain full control, but for those who stop using steering we’ll try to keep them in a draft after some amount of time has passed (say, half a minute)

As for how we’ve been testing it:

• All employees have been riding with it for 4-5 months
• We started turning this on for the public on October 15, sometimes only for a few hours, to see how it worked at larger scale with non-synthetic riders…real humans! We made 3 or 4 changes during late October.
• It finally got turned on and stayed on about 50 days ago for Watopia, excluding all events
• We turned it on in Makuri 40 days ago, again excluding all events
• We turned it on for group rides, and accidentally turned it on for TTT events Dec 12.
• Just after new years we turned it off for scheduled non-race group rides and TTT, because as it turns out TTT’s were considered group rides in the code we use for our switch. This will be fixed later in Jan, at which time we’ll re-enable it for scheduled non-race group rides.

So this is where we’re at today. We didn’t announce these changes as we’ve found with pack dynamics we often get lots of false positives when we announce we’ve changed anything, and we were actively changing and improving (and often disabling) the code throughout the fall. The plan was to announce and get more specific feedback once it comes time to start trying it in public races, which is where we’re getting to soon.

Next changes coming later in January:

• Fix the toggle so we can re-enable for group rides but leave it disabled in TTT.
• We’ve reduced the amount other people plowing through packs can push you around. Right now if somebody rams you from behind both avatars end up moving. We think the aggressor should be doing the moving left/right so the people minding their own business don’t have to move as much.

Beyond:

• Widen the draft seeking angle so that a steering user can’t just hug the center line and have a non-steering user not go seek their draft. This was demonstrated in the great video a Zwifter posted above that. Right now auto-steering is looking at maybe 70% of the road width.
• Turn on for all worlds, in scheduled non-race events
• Start limited testing in specific racing and time trial type events with those events labelled as PD5 enabled races.
• Change supertuck criteria as it feels annoying right now as soon as somebody gets in front of you

The tuning of our pack dynamics is a much more continuous thing than I think people realize…and I’m sure will continue for years to come. Sometimes we specifically test with a smaller group of Zwifters, sometimes we just want to start with robopacer groups and general riders in the world, and sometimes we’ll reach out to a race organizer to see if they’re up for testing something with us. Apologies for having it enabled in the TTT’s before we’d announced it – that was definitely not intentional.