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 in regard to 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.
Last week, Zwift announced the rollout of Pack Dynamics 4.0 game-wide. How would this impact TTT races? There was only one way to find out, so we set up a private test event, booted up 4 Zwift PCs, pulled the TT frames out of the garage, and did several test laps of Tempus Fugit. The results of these tests are summarized below.
Test Goals
We set out to answer three questions with these tests:
- Is the power savings in the draft with Pack Dynamics v4 different than the savings with Pack Dyamics v3?
- Is the game’s positioning of TTT riders noticeably different with PD4 compared to PD3?
- Do PD4’s modified pack dynamics result in different overall speeds in small churning packs?
Test Parameters and Methodology
All test riders were set to 183cm height, 75kg weight, and rode Zwift TT frames with ZIPP 808 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, 4.4 miles long) which could be used to measure the speeds of each test formation precisely.
The ever-helpful James Bailey at Zwift HQ flipped the switch on our event so our TT bikes could draft each other.
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 9:40.5
- Speed: 43.8 kph
Notably, the segment time with Pack Dynamics v3 was 9:53! So even though there’s less churning happening in PD4, somehow this pack moved faster.
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 @230W, Rider 3 @ 210W, Rider 4 @ 190W
- Segment time: 10:08.9
- Speed: 41.7 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 23.3%, 30%, and 36.6% – 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 232.5W. With PD3, the average wattage for the same group speed was 247W!
- Test 2’s segment time was almost 29 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 @266W, Rider 3 @ 247W, Rider 4 @ 229W
- Segment time: 9:36.9
- Speed: 44.1 kph
Notes:
- Riders received power savings of 24%, 29.5%, and 34.9% (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 273 (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 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 @299W, Rider 3 @ 273W, Rider 4 @ 256W
- Segment time: 9:08.2
- Speed: 46.4 kph
Notes:
- Riders received power savings of 25.3%, 31.8%, and 35% (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 307 (compared to 325W 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 @274W steady
- Segment time: 9:06
- Speed: 46.6 kph
Notes:
- The wattage required to sit behind the front rider is much lower in PD4. PD3 required 319W, while PD4 only required 274W!
- In a TTT situation with all riders taking equal pulls on the front, each rider would average 306W (compared to 339W with PD3). That means the hybrid format results in (essentially) the same average wattage as the 400W single file test, while being a much easier formation to hold!
Conclusions
Let’s answer the two questions we stated at the top of the page:
Is the 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:
| Position | PD3 | PD4 |
| 2 | 17% | 24% |
| 3 | 25% | 30% |
| 4 | 30% | 35% |
Why is there so much more savings with PD4? Because PD4 uses double-draft, so the draft effect is stronger than PD3.
Is the game’s positioning of TTT riders noticeably different with PD4 compared to PD3?
Yes. This doesn’t really show up in our test numbers, but what we saw is a lot less forward/backward movement of riders, and less of the “slingshot” effect of boosting your speed by coming around the front rider and heading to the front of the group.
Riders doing lower power numbers than the front rider would sometimes start to come around the front rider, but once they hit the wind (with their front wheel roughly equal to the pulling rider’s front wheel) their speed would decrease and they would drop back without ever being fully on the front.
Do PD4’s modified pack dynamics result in different overall speeds in small churning packs?
Also yes! Our first test of 4 riders holding 300W resulted in a significantly faster time than the same test with PD3. This is surprising, given PD4’s reduced churn on the front. We have two theories as to why this is happening:
- One of the stated goals of PD4 is to “Make breakaways have a slightly better chance of sticking if the attackers work well together.” Perhaps Zwift is giving a speed boost to smaller packs of riders? UPDATE: Zwift HQ assures us this is not the case.
- Somehow the increased “double-draft” effect is still causing small speed boosts as riders rotate to the front.
Single File or Hybrid Formation?
Clearly “The Churn” is not a good TTT formation. So what’s better – the single file formation, or the “hybrid” approach? With PD3, our 400W tests showed that single file was the most efficient approach since the average power needed was 14W lower compared to hybrid.
But with PD4, the single file and hybrid approaches delivered the same average wattage in our 400W tests! So go with either formation – the important thing is that your front rider hits their power/speed targets.
The good news is, with PD4 it’s easier than ever to hold your desired position in the pack. So whether you’re shooting for the single file or hybrid approach, your TTT team will be able to stay in formation more than ever.
Let’s Break Records!
Released in September 2022, the Cadex Tri frame trimmed 4.5s off a 50-minute flat course compared to the previous fastest frame. Now PD4 appears to give even more speed advantages to small churning groups while increasing the draft so riders can rest more between pulls.
This means Zwifters should be able to set TTT records now, more than ever. Ride on!
Your Comments
Got comments or questions? Share below!
Nicely done. I suspect the reason that the churn is faster with PD4 is simply due to the new criteria for pack control aren’t met. Essentially, you have to be signaling your intent to slow by letting off power, when moving faster than the rider in front of you. It’s a bit more complicated, but effectively your test bots at 300W aren’t ever letting off power, and are now churning with double draft. It should be the same impact as if churning in double draft under PD3.
Yeah, it’s that letting off a bit of power so you don’t create a gap that worries me that I’ll get hit with an autobrake in a TTT. This is especially true for me as a heavier guy coming to the front with momentum. We tend to have our heavy guys hang out in the back of the hybrid bunch when not pulling so that sticky draft doesn’t prevent the lighter guys from being able to get through us to the front when it’s their turn – this (along with me creating gaps due to sticky draft just by falling… Read more »
Very cool.
Interesting testing. As a note, I think James said PD4 is 1.5x draft, not double draft.
I’m not sure double draft was ever technically 2x the draft effect. My guess is, whatever they’re using now is what was called double draft previously (since that’s what ZHQ has told me).
I checked with James as I noticed he was online just now as I was reading this, and apparently yes PD4 uses 1.5Draft compared to “standard draft” pre-PD4, and there’s now no such thing as “Double Draft” for events anymore (dammit, I was hoping for double double draft haha!)
I have read the same (1,5x) and “Test 5 Hybrid” shows the confirmation : with PD3 you needed 319W to follow the 400W rider in front, so ~20% draft effect … with PD4 you only need 274W to follow, it’s ~30% draft effect now, so the ~1,5x effect than before … these are great news for the weaker riders in a team … many thx Eric for testing to understand the game 🤗 side note : I’m really surprised depending the results … I expected much slower times because “less churning” and “decreasing pack speed” were 2 main goals for… Read more »
With actual people (and not bots), I wonder if the new PD4 does mean that it’s more important than ever to be sitting 2nd wheel (regardless of hybrid vs paceline) when you’re going to be pulling next. The big fear with PD4 and TTTs is that, if you’re not 2nd in line when your turn comes (and especially if you’re at the back of a bunch in the hybrid), you put on some power to get to the front, but you ease up a touch before you get their so you don’t make a gap. PD4 then interprets this as… Read more »
If you’re easing before you pass the front rider, I’d say you’re making for a slow TTT rotation anyway!
Have you raced a TTT with PD4 yet? I’ve heard good reviews…
I didn’t get a chnace to do our Thursday TTT with OMG last week, but the reviews were stellar afterward. On Saturday I got to ride with a teammate for the 149k France Classic Fondo. We did a 2-man TTT for the last 40k. The best part of the new PD4 is the auto-braking feature which basically restricts wheel overlap when you are drafting. Makes it much easier, especially when you’re rolling 6+ in a TTT and overlap will push the guy in front out of his draft.
Ooh that does sound nice. A big problem I’ve had in TTs is I’ll be waiting to pull next in the 2 slot and an overanxious person in the 3 slot will decide to fight me for the puller’s wheel and then I’m essentially out in the draft for the previous person’s pull and mine and am working against the wind twice as long as I should.
As a big person with a lot of momentum, I tend to let up about the time I’m even with the puller or sometimes a touch before, if I was all the way at the back of the bunch and pushing hard to get to the front, or else I’ll create a big gap. I was right behind them, I just have to click to one cog smaller in the rear, keep my cadence the same and I roll through them and take over. If I was sitting at the back (something we sometimes do if there are really light… Read more »
That seems like a valid concern. I’ve noticed, or created in my mind, a problem with moving from the front row of a group to the front rider in a group. It hasn’t been as noticeable at race pace but the other night I was riding with the D pace bot as a warm-up before my race. I wanted to put in a few hard efforts so I rolled to the front row, everyone riding along at a leisurely <=2.0 w/kg, and I bumped my power up to about 4.3 w/kg. Rather than pulling away from the pack I found… Read more »
Sounds a lot like riding outside. 😁
I’d like to see a comparison of the TT bikes vs. the Tron bike in a TTT setting. It’s still not obvious to me that TTT bikes are faster.
Well… they are. By a BIG margin. 😁
But we might do a road bike drafting test just to see the numbers.
We had a three guest riders from OTR join our OMG TTT one Thursday. I think all 3 of them didn’t know the right time for our start so they barely made the pens in time and forgot to change their bikes. They all struggled! In fact, 2 of them fell off after about 1/4 of the course and the 3rd (a Tron) we just kept in the back of the paceline while the TT bikes did the work.
Thanks for posting the info on PD4 Eric. I’ve followed this since your earlier posts and how it relates to TTT. These are fantastic ‘lab’ results. They are an effective way to demonstrate changes Zwift makes in dynamics to better understand them. But…what would be more relevant to those of us who race TTT, is ‘meaningful’ results. We know that watts, weight, and height affect draft. All 4 of your riders are 183cm height, 75kg weight, and race at ~300w. Rarely would Zwift TTT teams would all be the same height and weight. More realistically, heights and weights would vary… Read more »
Hi Elaine, That is exactly what I do retrospectively with my Power Planner, to give you all individual powers. However, I can tell you that the Times that people get (I am usually pretty acurate) are determined by the AVERAGE of a team by and large, assuming that you are all at least doing roughly similar turns, or variable turns based on the power planner. Zwift is looking at the overal cohesion of a team and whilst I am sure there are vagueries, by and large comparing Average Team physiologies is enough to tell the difference. I vary my stated… Read more »
This PD4 comes with an update 1.34.00
Possible that not everyone get it? I had no update since announcement. I’m a Captain of a TTT Team. After reading this new test i would like to use it 😉 Thx 🙋♂️
No, PD4 is a server-side thing, so everyone has the same PD4 even if they didn’t install the update (which is a good thing, since the update is rolling out in stages!)
I thought TT bikes dont have Draft?
Read the intro paragraphs 🙂
1️⃣🗄🏆
Now if only you could do one of the test runs at about 225 Watts which might be within my capabilities, haha 🙂
I really don’t understand why they say they want to give breakway riders a chance, then slap on double draft. Makes absolutely no sense to me. Double draft makes it way harder for a solo rider to break away, as evidenced by the crazy power savings during test 2. Based on the results of this, it will now be even harder than before for a solo rider to break away..? Complete opposite of the intention, no?
Finally somebody gets it. The churn is and always has been the downfall. Essentially a break of 4 will require exceptionally high over / under intervals to have any chance of success. This churn is in no way realistic.