Our original TTT speed test post from 2020 gave team time trial riders some very welcome guidance about how to most efficiently ride their races. Then in 2021, Zwift rolled out Pack Dynamics 3, and we ran a second test to see what, if anything, had changed regarding TTT dynamics. (We found speeds hadn’t changed, it was just harder to hold an efficient single-file formation due to a 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.
Recently, Zwift announced the rollout of Pack Dynamics 4.0 game-wide. How would this impact TTT races? We tested TTT formations with TT frames and PD4, publishing the results in this post.
But we weren’t quite done! Desiring to test PD4 with road bikes and to confirm the TT frame test results, we ran similar tests using road frames. These results are summarized below.
We set out to answer two questions with these tests:
- Is road bike power savings in the draft with Pack Dynamics v4 different than the savings with Pack Dyamics v3?
- Do our findings with PD4 tests using road bikes back up our findings with TT frames and PD4?
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 of the 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 resulted in a disorganized group of riders, where some would rotate to the front then drop back after being in the wind for a few seconds. There was churn, but not as much as we saw with previous versions of pack dynamics.
- All riders @ 300W
- Segment time 10:04.5
- Speed: 42.08 kph
Notably, the segment time with Pack Dynamics v3 was 10:13.4! So even though there’s less churning happening in PD4, somehow this pack moved faster. (This is the same unexpected result we saw with our PD4 TT frame 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 @ 212W, Rider 3 @ 196W, Rider 4 @ 191W
- Segment time: 10:36.7
- Speed: 39.9 kph
- 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 29.3%, 34.6%, and 36.3% – significantly higher power savings than we saw in our PD3 tests. As expected, the further back you are, the bigger the draft effect.
- In a TTT situation with all riders taking equal pulls on the front at these wattages, each rider would average 224.8W. (With PD3, the average wattage for the same group speed was 246W.)
- Test 2’s segment time was over 32 seconds slower than Test 1’s, despite riders holding no higher than 300W in both tests. This may seem odd at first, but it’s a result of the “churn”. Riders are speeding up while in the draft, then shooting ahead into the wind, only to be slowed and have another rider shoot past them. This little speed boost accounts for a significant time difference, as we see here.
- It’s worth noting here 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 @350W
This test is similar to Test 2, except we bumped up the front rider’s wattage to 350W to make sure the group would be faster than the churning pack in Test 1.
- Rider 1 @ 350W, Rider 2 @ 252W, Rider 3 @ 236W, Rider 4 @ 217W
- Segment time: 10:02.2
- Speed: 42.2 kph
- Riders received power savings of 28%, 32.6%, and 38% (2nd, 3rd, and 4th rider respectively). Almost identical to the power savings seen in the 300W single file test.
- In a TTT situation with all riders taking equal pulls on the front at these wattages, each rider would average 263.8W (compared to 290W with PD3).
- This is the crux of why TTT formation is so important: even with Zwift’s “speed churning” from test 1, the four riders in this test beat test 1’s time by riding efficiently in single file formation at a much lower average wattage.
Test 4: Single File @400W
This test was very similar to Tests 2 and 3, we just bumped the front rider up to 400W.
- Rider 1 @ 400W, Rider 2 @ 290W, Rider 3 @ 261W, Rider 4 @ 255W
- Segment time: 9:32.1
- Speed: 44.4 kph
- Riders received power savings of 27.5%, 34.8%, and 36.2% (2nd, 3rd, and 4th rider respectively). Very similar to the power savings seen in the 300W and 350W single file tests.
- In a TTT situation with all riders taking equal pulls on the front at these wattages, each rider would average 301.5W (compared to 326W with PD3).
Test 5: Hybrid
Lastly, we tested a strategy that many TTT teams use, 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 @ 273W steady
- Segment time: 9:32.1
- Speed: 44.4 kph
- The wattage required to sit behind the front rider is much lower in PD4. PD3 required 313W, while PD4 only required 273W!
- In a TTT situation with all riders taking equal pulls on the front, each rider would average 304.8W (compared to 335W with PD3). That means the hybrid format results in nearly the same average wattage as the 400W single file test, while being a much easier formation to hold!
Let’s answer the two questions we stated at the top of the page:
Is road bike power savings in the draft with Pack Dynamics v4 different than the savings with Pack Dyamics v3?
Absolutely! Here’s a table showing approximate power savings with PD3 and PD4 based on your position in a TTT group of 4 riders:
Why is there so much more savings with PD4? Because PD4 uses double-draft, so the draft effect is stronger than PD3.
Do our findings with PD4 tests using road bikes back up our findings with TT frames and PD4?
Yes. The power savings table above very closely matches what we found for TT frames with PD4.
Additionally, we saw the same anomaly with the “churn” (test 1) being faster in PD4 than it was in PD3, both with road bikes and TT bikes.
While PD4’s auto-braking is supposed to help stop riders from accidentally moving up and into the wind, our churning pack of 300W riders held steady power, so auto-braking never kicked in. That meant they got a bit of a double-draft slingshot from behind the front rider, then shot into the wind momentarily before slowing and being replaced by the next slingshotting rider. We believe this accounts for the faster speed of the churn group in PD4.
What It All Means
For road racers on Zwift (vs TT), Zwift’s new pack dynamics should result in races that more closely reflect IRL racing.
Double-draft is enabled for all races (since it’s built into PD4), so the draft is delivering more power savings than before.
Additionally, with autobraking and other changes accidental churn is decreased on the front of packs, keeping pack speeds a bit lower and forcing riders to be more intentional if they want to take a turn on the front.
These changes should lead to more breakaway possibilities, as smart breakaway-loving riders can get more rest in the draft, and work together to stay away from the slightly slowed pack once a breakaway is established.
Got comments or questions? Share below!
Just looking at the numbers I think they’ve made things worse. The churn is the issue. IRL if 4 identical people ride at 300W, then they are riding beside each other. But in PD4 the churn is such that this group will go as fast as a single rider (or small group) at 350W (used to be something like 320W?). This breaks racing. Why would you attack if not a single person in the group has to work to catch you? If no one attacks, breaks don’t form. Zwift doesn’t seem able to get rid of the churn, my guess… Read more »
You have to break away, create a gap. Same as real life, preferably a coordinated attack with a few riders to share the burden.
Wasn’t another goal to make catching packs at least possible if you get temporarily dropped?
The point is that once you have that gap the pack can catch you easily. No one in the pack has to outwork the break. IRL someone in the pack has to put out a higher wattage than the break in order to catch.
IRL you can attack as a single rider. And if it looks promising someone will join. In zwift, nothing looks promising until there is a big enough break. So co-ordination before hand becomes key.
The churn in PD4 at least looks like it is much, much less. When you ride in a group now you don’t see riders surfing right to left in the pack as they all try to sit second wheel. I interpret a single rider going the same speed as a pack being pulled by someone as an absolute incentive for breakaways. You can’t just go to the front and up your output to do it because you’ll just drag the pack with you. If you do it aggressively though, get clear of the pack, and then settle into a maintainable… Read more »
That’s not what the numbers are showing though. The Test 1 speed is the same as the Test 3 speed. So for Test 1, no one is doing 350 W yet they catch the break
Test 1 doesn’t trigger autobraking, since there’s no decrease in power vs 10-second average. In a race scenario in PD4, there’s no chance the pack is all pedaling away at the exact same power at the exact same time for any period of time. Churn is absolutely reduced in PD4 in practice, and Test 1 in this article doesn’t accurately
Ah, interesting! Thanks for pointing that out. I’d be curious if the autobraking is enough to drop the speed to the Test 2 time though. Since that would be the expected speed of a pack with someone on the front at 300W.
Well, doing a handful of races with PD4 I personally feel it’s harder than before even if the speed is suposed to be dlower and the draft suposed to be better
I agree. It also doesn’t help that Zwift’s zFTP categorization now allows former As into the B races. Things are being torn asunder by these stronger riders, and the former blob is now a stung-out line of debris falling away from a burning meteor.
You paint a vivid picture, sir!
If Double Draft is part of PD4, would it be more accurate just to call it “regular draft” at this point? Under what scenario would the former regular (half draft) be used?
One thing I’ve observed is that the van power up is pretty ineffective in packs with double draft. Is that my imagination or part of the design? If the latter, does that mean it’s always a bit useless in packs now?
I don’t think this is specific to PD4. After using Sauce, I’ve realized Draft Boost doesn’t work the way I always assumed it did. If you are already in a large pack and receiving “optimal” drafting, the draft boost seems to provide no additional benefit. Where it seems to really help is when you are maybe second in a line and not at optimal draft.
I’d only really felt the lack of any advantage in double draft events though. For normal draft, it at least felt like a bit of a break.
But from what you say, this certainly means that the van is pretty useless in all packs.
Please experiment with new tests (script based / auto it/ etc) where riders change watts and do a real rotation. Like pulling 1min at 300watt then 1min 200watt then 1min 220 watt then 1min 240 watt then again 320watt … and repeat all over again … would be nice to see a video how that unfolds and what fine tuning is needed to keep a nice paceline!
The numbers really surprises me!! I’ve experienced the opposite. For example, with PD3 I was able to follow Constance with around 250 watts average (I weigh in at 72 kilograms). With PD4 I need to do at least 280-290 watts average! I’m a level 60 rider so maybe I’m to used to PD3 and my “game skills” doesn’t apply very well with PD4? What do you guys think?
Also, the average speed seems to be quite a bit higher with PD4. On a flat route with PD3 it was always 44-45 km/h. Now with PD4 on a flat route it’s more like around 47 km/h. Why is that?
Hey Tony, good questions! I’ve noticed similar experiences when racing in a pack. The overall efforts seemed higher to me. In my case, it also seemed like the speed was a bit lower. I’ve quite used to PD3 as well, so thought my experience with that system might be changing how I experience PD4 compared to a regular Zwifter, though. I would guess that the effect of PD4 on a group of riders in a race or pacer group is different than the effect of PD4 in a TTT team. Effectively, a TTT is like a breakaway, so making a… Read more »
I noticed that group rides I do regularly were suddenly harder with PD4. Had a harder time staying in the pack (even the middle … even with very large packs). Noticed my watts/kg during the ride and final avg watts at the end of the same rides/courses are getting a bit higher (out of necessity apparently).
Thanks for the study. I have 2 questions:
Yes, 300W is way more than enough to hold on, when everyone else is doing 300W as well. No problem.
PD4 is rolled out game-wide.
Does it mean we should opt for road bikes instead of TT bikes during the TTT ?
TT bikes are still fastest when drafting is enabled for them. If there is no drafting then TT bike as always. If you are free riding, then it depends on how much draft you think you will be getting as to the bike you choose.
My experience doesn’t match the numbers and I don’t know how much it’s me being more out of form now then min March or how much it’s PD4. But my experience is that races are much harder now. My theory is that it’s so much harder to move up the pack. Previously you did three hard revs and you moved up the entire pack on cruise control. Maintaining position through an even effort was hard. So position control was very much small burst, cruise, small burst, cruise. Now it’s not possible to move up more then a few places by… Read more »
That’s exactly how I experiencing PD4 as well! And I agree, it’s not a bad thing even though I found it a bit easier to perform well in races with PD3 😉
Interesting – so unlike PD3 the saving here for Road bikes and much higher than the with TT bikes. 4% lower power required in positions 2 and 3 … any thoughts on why?
The changes theyve made make solo attacks/breakaways tougher.
I think a break away pack is slightly easier, in the races I’ve seen so far 2&3s have a chance, more the merrier but solo is incredibly difficult.
You list Average power for Tests 2/3/4 but NOT Normalized Power. This is somewhat misleading and not what the group of riders would “feel” . Those numbers must be included for completeness.