After digging into user feedback on Pack Dynamics 4.1, Zwift discovered, “Currently the progression inside the groups in PD 4.1 is harder than it should be. It’s like a game stuck in the hardest difficulty.” So they came up with a fix and enabled it on Monday, Oct 2.
Below are the results of our standard 4-rider drafting tests using PD4.1.1 (what we’re calling the bug-fixed version of PD4.1) and road bikes. We will follow up with a test using TT frames in a drafting TTT scenario, but we believe the same conclusions will be drawn from both sets of tests. Let’s dig in!
History of Our 4-Rider Speed Tests
Our original TTT speed test post from 2020 gave team time trial riders some very welcome guidance about how to ride their races most efficiently. Then in 2021, Zwift rolled out Pack Dynamics 3, and we ran a second test to see what, if anything, had changed. (We found speeds hadn’t changed, it was just harder to hold an efficient single-file formation due the lack of sticky draft.)
In August 2022, Zwift+WTRL announced enhanced TTT features, including the ability for TT frames to draft in TTT events. So we ran our tests using TTT frames. Then several months later in April 2023, Zwift announced the rollout of Pack Dynamics 4 game-wide. So we ran our standard tests with PD4.
In August 2023, Zwift released Pack Dynamics 4.1 slowing packs and reducing churn on the front, so we ran our tests with PD4.1.
This week, Zwift rolled out Pack Dynamics 4.1.1 (officially just a bug fix for PD4.1) You know what that means… time for more tests!
Test Goals
We set out to answer three questions with these tests:
- Is road bike power savings in the draft with Pack Dynamics v4.1.1 different than the savings with Pack Dynamics v4.1?
- Does Pack Dynamics v4.1.1 alter pack speeds, and if so, how?
- Are there any other observable differences between PD4.1 and PD4.1.1?
Test Parameters and Methodology
All test riders were set to 183cm height, 75kg weight, and rode Zwift Carbon road bike frames with Zwift 32mm carbon wheels.
Tests were done in an isolated event on Watopia’s Tempus Fugit route because it’s the flattest on Zwift and has a timed section (Fuego Flats Reverse, 7.1km long) which could be used to measure the speeds of each test formation precisely.
All tests were done with four riders.
Tests and Results
Test 1: the Churn
For our first test, we put all riders at the same 300W power setting. This results in a very inefficient pack of riders, but it lets us test the slingshot effect. Here’s a quick snippet of what we saw:
The pack seemed to churn a bit more in PD4.1.1 compared to PD4.1 (see that video here), while still being much more stable (less churn) than PD4.
- All riders @ 300W
- Segment time 10:31.9
- Speed: 40.44 kph
Our test segment was completed 4.5 seconds faster in PD4.1.1 compared to PD4.1. We attribute this small time savings to having a bit of churn on the front, but it’s worth noting that the churn with PD4.1.1 is very minor compared to PD4, which turned in a time 27.4 seconds faster in this test!
Test 2: Single File @300W
The second test had the lead rider holding 300W, with the other three riders in single file behind, holding the minimum wattage possible to stay in formation. This is what you would see in an outdoor team time trial:
- Rider 1 @ 300W, Rider 2 @ 225W, Rider 3 @ 202W, Rider 4 @ 187W
- Segment time: 10:36.3
- Speed: 40.19 kph
Notes:
- The “minimum wattages” stated for riders 2-4 on this test and other tests below should be considered approximations, as it is impossible to figure out the precise wattage required to hold formation due to Zwift’s dynamic physics engine and very small undulations in terrain, even on Fuego Flats.
- Riders received power savings of 25%, 32.7%, and 37.6%. The first 3 riders had essentially the same numbers as PD4.1, but the last rider could stay on with less power, indicating that perhaps the “fall off” point of the draft has been extended in PD4.1.1.
- In a TTT situation with all riders taking equal pulls on the front at these wattages, each rider would average 228.5W. (With PD4.1 the average was 232W.)
- With PD4.1, test 2’s segment time perfectly matched test 1’s. This isn’t the case with PD4.1.1, because there’s a bit of a churn/slingshot effect happening.
- It’s worth noting that we did a solo rider test at 300W steady, because we were curious if there was any advantage to the front rider if there were riders behind. There is not. Our solo rider turned in the same time as this 4-rider group.
Test 3: Single File @400W
This test was similar to Test 2, we just bumped the front rider up to 400W, then increased the power of the riders behind accordingly.
- Rider 1 @ 400W, Rider 2 @ 310W, Rider 3 @ 275W, Rider 4 @ 240W
- Segment time: 9:33.5
- Speed: 44.53 kph
Notes:
- Riders received power savings of 22.5%, 31.3%, and 40% (2nd, 3rd, and 4th rider, respectively). Again, the first 3 riders’ numbers didn’t change much from PD4.1, but the final rider saw a significant decrease of 18W.
- In a TTT situation with all riders taking equal pulls on the front at these wattages, each rider would average 306.25W. (With PD4.1 the average was 309W.)
Test 4: Hybrid
Lastly, we tested a formation that many Zwift TTT teams have used, wherein there is one designated rider in front, and the riders behind simply churn in the front rider’s draft. This reduces the hassle of trying to maintain single-file positioning while receiving some of the benefits. But how does it impact efficiency?
- Rider 1 @ 400W, Riders 2, 3, and 4 at @ 296W steady
- Segment time: 9:33.4
- Speed: 44.53 kph
Notes:
- If there wasn’t at least 1 rider holding 296W or more in the pack of 3 behind the front rider, the pack of 3 would get dropped.
- With PD4.1, the pack of 3 needed to hold 308W. Why the lower wattage in PD4.1.1? Because the pack of 3 was benefiting from the churn/slingshot while sitting behind the front rider. This increased their speed a bit, allowing them to hold onto the front rider while holding 12W less than they did with PD4.1.
- In a TTT situation with all riders taking equal pulls on the front, each rider would average 322W. (With PD4.1 the average was 331W).
- The hybrid format was a solid option with PD4, and terribly inefficient compared to single file formation in PD4.1. With PD4.1.1 its efficiency improved a bit, but based on average power it’s still not nearly as efficient as a single file formation.
Conclusions
Let’s answer the three questions we stated at the top of the page:
Is road bike power savings in the draft with Pack Dynamics v4.1.1 different than the savings with Pack Dyamics v4.1?
Absolutely! Here’s a table showing approximate power savings with various versions of Pack Dynamics based on your position in a TTT group of 4 riders:
| Position | PD3 | PD4 | PD4.1 | PD4.1.1 |
| 2 | 17% | 28% | 24% | 24% |
| 3 | 25% | 33% | 33% | 32% |
| 4 | 30% | 37% | 34% | 39% |
As you can see, the big difference in draft power savings between PD4.1 and PD4.1.1 is for that 4th rider.
Does Pack Dynamics v4.1.1 alter pack speeds, and if so, how?
Yes. Pack Dynamics 4.1.1 will speed up packs slightly due to the increased churn/slingshot effect on the front. It’s worth noting that this slight pack speed increase is nothing compared to the major pack speed decrease that PD4.1 delivered! Overall, packs are still significantly slower today than with PD4 and earlier.
Are there any other observable differences between PD4.1.1 and PD4.1?
Yes. PD4.1 made it rather difficult to move forward in a pack, allowing riders to “waste watts” by pushing harder than necessary to hold a pack position (see video). That’s not the case with PD4.1.1. Now, increasing your power results in moving forward in the pack as it should. Additionally, it feels as though rider inertia has increased, because once you start moving forward, you tend to keep doing so!
Also, as noted above, it appears that the draft “fall off” point has been lengthened, so the draft “shadow” extends even further behind each rider. This is the only way we can explain the 4th rider’s ability to hold on with less power in our two single-file tests above.
What It Means for Road Racing
For road racers on Zwift (vs TT), we believe Zwift’s Pack Dynamics 4.1.1 will greatly reduce complaints from riders who said it was too hard to sit in. (Those riders were mostly complaining because they were wasting watts, but in the end, the truth is that it was harder for them.)
Pack speeds are still lower compared to PD4 and earlier, though. This means breakaways stand a chance of surviving, which means riders will be attempting more breakaways! The end result is races that feel more punchy/dynamic… harder.
This isn’t a Zwift physics issue, though: it’s an evolution of the Zwift racing mindset.
Your Comments
Got comments or questions about Pack Dynamics v4.1.1? Share below!
Do the Zwift people know what the effects of their changes are when they release the updates? Or do they read your tests, like us, to find out!
if they test stuff… they need to fire all the staff and get knowledgable staff. i think we have a large group working at zwift, which are not up to whats required…. in many departments.
I suppose posting ad hominem attacks without evidence may make a person feel superior, but it provides no insight and is not constructive in the end, just drags discourse down.
Zwift test the changes a lot pre-release and tune them based on feedback.
There are very large, very active threads where the Zwift developer(s) implementing the changes post test events and riders that participated in the test events provide feedback.
You may find these on the zwift forums and participate in testing future releases if you are interested
I don’t know if this is related to PD, but has anyone noticed that using Zwift Play, you can get booted out of the pack (eg. far to the right). This happened to me in a race yesterday, and I had to constantly steer hard left to regain the slipstream. maddening.
Yup, except it kicks me to the left, out of the pack.
Yes and running sauce it shows you go to zero draft in the far right pocket. The draft cone is very small it appears or did appear in 4.1.
I keep getting shunted hard left in sprint finishes. Very annoying! Not using Zwift Play though, but I do have steering on (Kickr Bike).
It’s an issue for all steerers, Brian… Zwift keeps saying it’s fixed, then it happens again. Happens less now than it used to… next update supposedly has more fixes for it.
Hi Eric,
Could it be it also happens in races where steering is disabled like ZRL?
In the ZRL this week I still had the zwift play connected cause I like it for activating the power-ups.
In the sprint however, I also got steered hard left and out of the draft. While I was pushing over 1000 watts out of the draft, I saw a whole group passing me on the right who were all nicely tucked away in each others draft. And, of course, since steering was disabled, I couldn’t do anything. Very frustrating!
I experienced, more or less, the same problem…
Here is a shot of our TTT on 9/28 with PD 4.1. I’m hoping we will be able to hold our pace line this tight in tomorrows race.
The 2 riders next to each other is the previous lead rider sliding to the back of the line
please sort out the website for phone browsing! The bouncing around while scrolling as ads pop in and out is more churn than D3.1
Fully agree!
This confirms what I felt during the ZRL and personally I don’t like it. Basically, the draft is bigger than in PD 4.1, which itself was already bigger than earlier versions. On the other hand the slingshot effect is back, increasing pack speeds compared to PD 4.1 The first point makes it way harder to create a break or make a selection. > Consequence: On the Yorkshire circuit in the ZRL we had guys on the climb pushing the front with 10-11 watts/kg. Yet, the pack only stretched out in a long line, didn’t break and in the end guys… Read more »
There are also hill climb races and TTs if you want to have the strongest rider win. ZRL races in Yorkshire I saw, in B, both had a breakaway rider win. Behind it very small and split up groups. Think neither your, nor mine, with a sample size are representative of the population… PD 4.1 really sucked the fun out of Zwift races for me and went from 3/4 times a week to just one. Only heard changes were made now after the ZRL race but at least during that one I was not wondering why I was zwifting. Which… Read more »
Great write up and crystal clear. Thanks Eric 💪😤
So many versions of PD! It’s getting to be that we need an article that lists all the versions, the changes, when it was used, if it was deployed widely or just in events to keep it all straight!
Thanks for you work on this! Personally, I’ll be sad to see 4.1 go! I had my best racing in years (long breakaways were possible!), but I suspect my success was becausee most folks didn’t understand that they were wasting watts. It seems we’ve gone from the fast blob to the slow sticky snake. Maybe the snake is a bit too sticky? Theoretically, though, it should be easier to slingshot past the group for breakaways, which is great in my opinion.
When PD4.1 came out I realized in 5 minutes of race to understand that the system was not working, and it was my first race after the summer break. I had seen several influencer videos praising the new PD4.
I think the draft issues were much more complicated then we will ever know…on my ZRL Team two of us had major changes in the draft while the other four felt no difference with PD 4.1. I know the draft I got was 20%….didn’t matter where I was I got 20% and the power I needed to push to move through the draft was crazy. While riding with “Maria” I had to do 2.5 to match the 2.2 of the bot and I am 76kg…when I kicked to get ahead of the group I was able to stay off the… Read more »
ive noticed something similar – especially when going for sprints. you seem to have to really punch out of the pack (and it feels so hard trying to burst out of the pack) then once you do, seem to fly away much easier. its broken. so if you can get that sweet spot, when a chaser seems to fly through the pack and gets out of that sticky wall at front, they should just keep going.
Thanks as always Eric. What would we all do without you? Some random thoughts. 4.1 didn’t change my road races much, which was good. But TTTs were adversely affected. 4.1 made it harder to hold onto the line in the back, and harder to catch back on when you dangled a bit. Then I slingshot all the way to the front when I apply so me watts to get back in line. Teammates have been doing the same thing. Everyone gets irritated because it’s chaotic. Also, and weirdly, when I steer behind a teammate I notice that my power feels… Read more »
PD4 is great…..I like riding in the front 1/3 of a pack of 50+ and being told to close the gap.