Zwift Sticky Draft Investigation

Zwift Sticky Draft Investigation

Ever since I started Zwifting – in 2015 after a broken collarbone – I’ve been interested in the draft, and how we could make Zwift feel more like riding in the real world.

I even raised a support request after my first month, asking if it would be possible to adjust the resistance on smart trainers according to the draft as well as according to the terrain. Feeling the terrain is great, but as a trackie myself, feeling the draft is almost more important than feeling the terrain for total immersion in the game.

Editor’s note: interestingly enough, Zwift Insider also published an opinion piece on the topic of “feeling the draft” back in September 2019

I envisaged a new generation of smart trainers that replicate the speed in the virtual world rather than the gradient – the Tacx NEO has the perfect hardware to do this.

5 years later, I’m finally building this for myself – I’m converting my rollers to run at the speed of my avatar in Zwift – like a rolling road – rather than simply adjusting resistance for gradient which is what I currently have. I’ll then be able to feel every change in speed in Zwift, rather than only seeing and hearing it.

Testing the Draft

So how good is Zwift’s modeling of speed, and what can I expect to feel? For a lone rider, it’s fantastic! I did some analysis a couple of years ago to reverse estimate the model, and then compare actual rider speeds with the speeds from my model. I got to a very close match – enough to show that Zwift uses standard equations sensibly applied.

But what about the draft? I’ve always been bothered by two things. First: the weird effects in medium-paced group rides, where you have to concentrate to not ride off the front of the bunch while it’s challenging to stay on the back. Second: the dreaded sticky draft! For me, the sticky draft is a real enjoyment killer – you find someone to ride with at a good challenging pace, and are rolling along together nicely. But then you overtake a group, and one of you gets stuck, and that nice partnership is over.

So, I wanted to see what the sticky draft actually looks like…

I set up a dashboard displaying power and speed of the rider I am watching, picked a faster rider to watch, and waited for them to overtake a group – and I saw this:

The rider’s speed was varying nicely according to power and terrain (this should feel great on my rolling road) then bang! – at 14:15:44 they instantly lost about 3km/h when they reached a slower group.

I watched a few more riders, and could see this pattern happening again and again…

So I set up a more scientific experiment – fixed power on a flat road to rule out gradient changes. Here’s a video of a test rider holding 250W through Ocean Boulevard – the flattest bit of road in Zwift, where we can expect to find lots of riders/groups to overtake – together with the live dashboard:

There’s a lot of interesting stuff to see here.

On a flat road at 250W, this rider will end up at a solo speed around 37.6km/h.

First (00:01) we see that doing a u-turn immediately drops your speed to about 24km/h. (I also noticed there’s a similar effect going round the Buckingham Place u-turn on London – so it turns out that Zwift can force dropping speed for corners!)

Then we roll down the slope to the underwater section, taking a couple of small knocks on the way (00:30 and 00:37) – but let’s not worry about these – there are bigger ones to come.

A little dip at the bottom of the slope, and then from 00:58 we’re on the flat, and our speed should converge on around 37.6km/h, except where lifted by drafting.

We see some really nice examples of drafting working exactly as you hope it would: speed curving upwards as you get closer and closer to the rider in front, and then as you pass, resuming the decay towards the 37.6km/h solo speed.

And then bang! At 2:10 we hit the rider in front, and instantly drop from 40.76 to 38.74km/h, and then half a second later, another bump down to 37.65 km/h. This looks like a classic sticky draft – but there’s a bigger one coming that we’ll look at in more detail:

We carry on passing riders with drafting working as expected as we pass small groups:

And then the biggest hit is at 3:10, where we drop from 41.50 to 38.12 km/h.

Here are my logs for this big hit – the Zwift client is sending around 5 updates per second to the server – and between two of these updates – in less than 0.2s – we have lost 3.37 km/h.

2021-01-02 14:02:57,077 INFO speed 40304760 power 250
2021-01-02 14:02:57,280 INFO speed 40368648 power 250
2021-01-02 14:02:57,484 INFO speed 40435204 power 250
2021-01-02 14:02:57,670 INFO speed 40501076 power 250
2021-01-02 14:02:57,890 INFO speed 40578068 power 250
2021-01-02 14:02:58,076 INFO speed 40655804 power 250
2021-01-02 14:02:58,280 INFO speed 40737588 power 250
2021-01-02 14:02:58,480 INFO speed 40813260 power 250
2021-01-02 14:02:58,681 INFO speed 40895832 power 250
2021-01-02 14:02:58,880 INFO speed 41000124 power 250
2021-01-02 14:02:59,067 INFO speed 41087960 power 250
2021-01-02 14:02:59,270 INFO speed 41212560 power 250
2021-01-02 14:02:59,473 INFO speed 41352544 power 250
2021-01-02 14:02:59,676 INFO speed 41499440 power 250
2021-01-02 14:02:59,865 INFO speed 38126480 power 250
2021-01-02 14:03:00,087 INFO speed 37877664 power 250
2021-01-02 14:03:00,274 INFO speed 37946692 power 250
2021-01-02 14:03:00,477 INFO speed 38015924 power 250
2021-01-02 14:03:00,694 INFO speed 38094700 power 250
2021-01-02 14:03:00,868 INFO speed 38163176 power 250
2021-01-02 14:03:01,072 INFO speed 38229232 power 250
2021-01-02 14:03:01,274 INFO speed 38297072 power 250
2021-01-02 14:03:01,475 INFO speed 38383356 power 250
2021-01-02 14:03:01,680 INFO speed 38463896 power 250
2021-01-02 14:03:01,865 INFO speed 38525808 power 250
2021-01-02 14:03:02,082 INFO speed 38592660 power 250
2021-01-02 14:03:02,283 INFO speed 38656560 power 250
2021-01-02 14:03:02,468 INFO speed 38718224 power 250
2021-01-02 14:03:02,671 INFO speed 38783208 power 250
2021-01-02 14:03:02,876 INFO speed 38818664 power 250

In energy terms, this is an instant loss of at least 678 J (calculated from the rider weight – we will in fact have lost more than this for the weight of the bike and the spinning wheels).

If we then add say 50 Watts, it will take nearly 16 seconds to regain this lost energy, i.e. just to get back to the speed we should have been at. And we’ll be falling behind nearly 1 metre every second at first. So after say 5 seconds we’ll be nearly 5 metres behind the riders we were with, outside their draft, and still needing another 10 seconds at increased power to get back up to speed, let alone to catch up again.

So I think this explains why the sticky draft feels like it does. It feels like you suddenly get pinned to a slower rider, and then struggle to escape them. I think in fact you get hit once to their speed, and you are then struggling to get back up to speed  – rather than struggling to escape them. And in some cases, you may get more than one hit, like at 2:10.

A Bug, or a Feature?

But why is this happening? To me it looks like it’s either a bug – albeit a long-standing one – or it’s a slightly crude feature put in place to work around some other difficulty in modeling drafting.

If it is a bug, ‘fixing’ it might have other unintended consequences.

The draft is a complex area – knowing who is in the front row of the bunch and should be taking the wind, and who is sheltered and should be getting maximum draft benefit is not easy when each game client needs to work this out from slightly delayed updates from other clients.

In the real world, riders can’t go full gas when they are in the wheels, but in Zwift they can – we need some kind of mechanism to stop the body of a bunch going faster than the front row – otherwise the bunch will accelerate to unrealistic speeds – but we still need to allow riders to move up and rotate at the front.

It doesn’t feel like instantly taking 3 or 4 km/h from a rider is the best solution here – it feels like it would be better to put more riders effectively in the wind. For example, putting you in the wind as soon as you are moving up on a rider you were drafting – and this would help you stay in the draft. Then you could sit in a bunch, but have to work hard to move up. Though no doubt this would introduce its own problems, and a lot of experimentation and tuning would be needed.

It’s the kind of challenge I love to get involved in, especially understanding the knock-on consequences. I’d love the opportunity to get involved in solving this one!

Share Your Thoughts

What are your thoughts on the sticky draft? Is it working the way it must due to a lack of braking/steering, or could something be improved? Share your comments below!

About The Author

Pete Buckney

Pete lives in London, UK and can often be found going round in circles at Herne Hill Velodrome, or out in the Kent countryside with Penge CC. His day job is CTO at a financial services company. He’s been Zwifting since breaking a collarbone in the summer of 2015, and in addition to riding, he enjoys applying his programming and inventing skills - he’s currently converting a set of standard rollers into a powered rolling road that will run at the same speed as his avatar in Zwift. Pete’s wife Zoe and two kids ages 14 and 9 can all also be found on Zwift from time to time.

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Jozsi
Jozsi
11 days ago

Yes, it is a hated “feature” , if the speed difference is within 3-4km/h between me and the rider front of me, sometimes i stucked behind him/her instead of overtake (without steering wheel it’s sucks) . If You go with B partner and riding with 47-48km/h on Tempus, when You are the end of the bunch and the bunch is overtaking with this speed the hundreds of riders there, sometimes the B Brevet is stucking behind to one of them (if the speed difference is similar 3-4km/h, if more, my experience is it doesnt happen) I dont know it is… Read more »

A.Hofmann
A.Hofmann (@ahofmann)
11 days ago

Pretty sure the sticky draft is a “feature”. I imagine it was designed for newer riders to prevent you from accidentally passing the rider you are intentionally drafting, so that they can hold the draft line easier. While I’m sure that works fine in internal testing with a couple of riders, it surely doesn’t work that way in real game. Its also my biggest gripe with Zwift currently as I do a lot of solo riding and its real annoying to be riding along at a nice speed only to have Zwift force you to slow down because it decided… Read more »

ScottyP
ScottyP
10 days ago
Reply to  A.Hofmann

Or the other challenge of approaching a slower rider who sees you coming and intentionally increases their output so they can grab your wheel but you end up stuck behind them. I see this a lot when I’m riding solo.

Eric Schlange
Top Member
Eric Schlange (@eschlange)
10 days ago
Reply to  A.Hofmann

You could always turn it off by riding a TT bike!

Mick Such
Mick Such
11 days ago

I hate sticky draft. As you say going great in a bunch, then normally at the bottom of a slight incline, bang sticky draft on a slower rider. Tried dropping back a bit, tried pedalling like mad, tried sprinting, all seem to have issues with getting past this rider n rejoining the group.
It’s just weird how it seems to effect some riders and not others.
I believe it has to do with the Wkg your producing being same as the sticky rider.
It’s annoying, but hey ho, that’s zwift. 🤔

Stu
Stu
11 days ago

I wondered this same thing when attempting to ride my fastest time up Alpe du Zwift. Is it better to ride without anybody on the course? When riding uphill you don’t get the draft benefit but do seem to get stuck behind riders riding a little slower than you. It seems like you need to kick past them. Maybe the draft should only be sticky for the person being passed. As you ride up to someone you get the benefit but the rider you are passing has the opportunity to stick to you rather than you to them. But as… Read more »

Hummel
Hummel
11 days ago

Great article! I *hate* the sticky draft. It’s the worst feature in Zwift. I bought a Sterzo steering unit to steer away from sticky draft. RGT virtual cycling does not use sticky drafting. It’s much more realistic. The downside is it takes a bit of skill to draft in RGT. I think the issue is there is no braking in these program so you can’t feather the brakes or move slightly out of the draft when the drafter gains on the person pulling. one question I have for Pete, have you been able to measure a difference in sticky draft… Read more »

Sticky Buns
Sticky Buns
10 days ago
Reply to  Hummel

Some races use double draft which likely makes sticky draft a tad less sticky. Also the pace is generally higher on average, and you’re less apt to come up behind someone doing 3-4 km/h less than you (at least consistently like you would in free riding).

I’ve experienced sticky draft before but had no idea it has such an impact on speed. Kudos to the author for dredging up more details on it!

naan
naan
8 days ago
Reply to  Pete Buckney

Racing is where it makes an actual difference, otherwise it is a minor annoyance at most. You don’t need to be passing a group, even a single rider can mess it up big time. It can be anything from hitting a wall in a sprint if you don’t (over)commit early enough to getting dropped because the rider in front of you opens a gap and you have to make a burst or two to first escape the sticky draft and then close the gap (same thing when rejoining the pack from behind and trying not to get stuck behind the… Read more »

Wheezy Wheels
Wheezy Wheels (@richardneil)
10 days ago

Good examination of the Zwift draft. It would be very interesting to compare with RGT drafting. My feeling is that RGT is more like IRL – not perfect but better, especially cornering.

James
James
8 days ago
Reply to  Pete Buckney

Definitely try RGT! It’s not as polished as Zwift, but resistance is based on speed. I use my trainer at 0% in Zwift, since it feels so artificial. In RGT, I actually enjoy riding with resistance.

Mark
Mark
10 days ago

The “sticky draft” is the most annoying feature riding Zwift. It’s most frustrating when you’re working with a group and your avatar suddenly drops 4 km/h to “stick” to the draft of a slower rider your group is passing.

anderfo
anderfo
10 days ago

so…does the energy disappear there, or do you give it to the rider you’re stuck behind? 🙂

Hummel
Hummel
10 days ago
Reply to  anderfo

I believe it just disappears.

ScottyP
ScottyP
10 days ago

Thanks Pete. Excellent research and good stimulus for thought.

RvdB
RvdB
10 days ago

I hate the sticky draft, as far as i know they introduced this to make draft easier.

Rick Hellard
Rick Hellard
10 days ago

A very good synopsis. I find it especially frustrating in meet ups with the keep together function on. It is almost impossible to get past the back of the group. As one of the stronger riders, and often the leader, being stuck at the back is hard on my ego.

I just want my output to reflex position in the group. Nothing more. Nothing less.

Dan Connelly
10 days ago

The underlying phenomenon is that it takes some finesse to ride past people IRL. You can’t just blast thru them. The energy loss from sticky draft could be avoided by approaching riders ahead gradually, then accelerating past, which is what one would need to do IRL if the road is crowded. The problem with Zwift is it has only a crude model of rider positions so it can’t detect if you would have a clean passing line. RGT does keep track of whether there’s a clean passing line. If not, it requires your avatar to brake, wasting energy if you… Read more »

CJ Weseman
CJ Weseman
10 days ago

Should just be a button “pass mode” and “draft mode” toggle on when you want to pass and it kicks you out in the wind and disables sticky draft.

Darryl Ketter
Darryl Ketter
10 days ago

I have definitely experienced this, and it has cost me dearly in group events wherein I got stuck behind a slower rider that our group overtook. I got unhitched, dropped five metres, and could not get back on. I have even tried to charge slower riders that we are passing so as not to get stuck, but the effort and timing needed is hard to gauge due to the effect of “sticky watts”.. I use a Neo Smart trainer.

Gil_SantaMaria
Gil_SantaMaria
10 days ago
Reply to  Darryl Ketter

This happened to me during a race. I lost the front group because I got stuck behind a slower user

Andrew
Andrew
10 days ago

It’s a particular issue/bug when you come up behind a Heavy rider, even in TTT we were finding it hard to pass our 110kg teammate without hitting 4.5w/kg, and that was in Cat D!!

Gil_SantaMaria
Gil_SantaMaria
10 days ago

I thought that the sticky draft only happened to me. To climb the Alpe du Zwift with the sticky draft is desperate. Getting stuck behind other users makes it more difficult. I think this is a bug This is annoying

M. Plumleigh
M. Plumleigh
10 days ago

Funny, I hadn’t really paid attention to this until very recently in a couple of 2-man meetups this week! My buddy and I would be motoring along until we hit a small group of riders and bam, it’s like hitting a wall. Instead of rolling past, one or both of us would get “stuck” for a bit.

LUIS
LUIS
10 days ago

I HATE THE STICKY DRAFT!!! HHHAAATTTTEEEEE IIIIIITTTTTTTTT!!!!!!!!!!!!!!

Jeremy barnes
Jeremy barnes
10 days ago

Stick draft sucks. You come upon someone just a couple wkg more and then stuck!. You have to generate a lot more to pass. On a climb this is very tough.

Harold
Harold
10 days ago

Sticky is just blocking. It is the biggest Zwift buzzkill. You ride with a group and get blocked by a slower rider, sometimes never rejoining your group. Hate. It. With. A. Passion.

Stephen
10 days ago

Does steering help?
IRL one would steer around a slower group

Alex
Alex
10 days ago
Reply to  Stephen

Yes steering does help. I’ve had the Elite Sterzo Smart Steering Block for about a month now and I’ve enjoyed every ride since. No more yelling at the TV and Zwift for me. LOL Also that offroad course is challenging and fun.

Hummel
Hummel
10 days ago
Reply to  Stephen

yes, I have a Sterzo. You can steer around people. It generally does not work in events though, but for free riding it works. It’s the only reason I bought it.

Roger Persson
Roger Persson
10 days ago

This is a thing and must be no 1 priority to solve. Zwift is growing and this is a downer, bummer and a DRAG…😀

Richard Gate
Richard Gate
10 days ago

I think the answer could be quite simple. How about an overtake button, either on the companion app, or using the buttons on smart bikes, or a Bluetooth button as recently demonstrated on Zwift insider. This would turn off the sticky draft for a set length of time, put the rider back in the wind and hey presto!

Dupytrens
Dupytrens
10 days ago

I was demoralised when I got stuck overtaking a team in the TTT, after doing my turn, I hit the group when I was at the back of mine, got stuck, it took so much effort to get out the team had gone.

Ben F
Ben F
10 days ago

It would be interesting to see how bad it is between different weight groups, and at different w/kg’s for example a 60/70/80/90 kg rider riding at 2/3/4 w/kg and see which is more prone to the stick draft, from reading this and watching zwift. My thoughts are that the lighter riders are more prone to stick draft than bigger riders . Would be interesting to see if that’s true

Ole
Ole
9 days ago
Reply to  Ben F

Lighter riders have less mass in motion and would be more easily sucked into the draft of a rider. This is how it works IRL. It would be interesting to know if it works this way in Zwift as well.

Matthias
Matthias
8 days ago
Reply to  Ben F

I’m a light rider (<60kg) and never saw the sticky draft. To me the assumption that the effect is baed on a W/kg difference sounds likely because I always have to put out significant more W/kg for the same speed as the average riders.

Deb Momeyer
Deb Momeyer (@deb-momeyer)
5 days ago
Reply to  Matthias

same… I’m 55kg and my w/kg are higher than others to maintain same pace/speed. Very challenging on descents…physics!!

TeePee
TeePee
10 days ago

Its a game, who cares?

Eric Schlange
Top Member
Eric Schlange (@eschlange)
8 days ago
Reply to  TeePee

I do. Pete does. And apparently you do, because you’re reading the post! 😉

TeePee
TeePee
8 days ago
Reply to  Eric Schlange

I’m that bored in lockdown, I have little else to do but to read everything I can.

Art Vandelay
Art Vandelay
9 days ago

Yes, sticky draft is a serious issue. Can’t really draft up steep hills but you sure can lose 20% of your speed ‘drafting off slower riders. The only way around it is to attack when you overtake slower riders. Hard to do when you’re at your limit. Another issue is losing the draft in sharp turns. The best example is the switchbacks on the French map. Even when in a blob I don’t stay in the blob and don’t draft AT ALL. Have to attack and put out 50% more power than the blob just to stay in the blob.… Read more »

Ole
Ole
9 days ago

The worst about the sticky draft is when you are racing and the field is splitting up. A few seconds ago you were sitting comfortably at the back. Suddenly you realize that the rider in front of you is making a gap. Before you know it, you are stuck in the sticky draft of the rider that made the gap and sees the front riding into the horizon. It requires too much to both get out of the sticky draft and then bridge up. The race is over.

ArtV
ArtV
8 days ago
Reply to  Ole

Agree with this. Getting stuck behind someone that is letting a gap open is VERY frustrating.

Ole
Ole
7 days ago
Reply to  ArtV

Especially when you are caught in the sticky draft 😤

Terry
Terry
9 days ago

Great analysis!

have you done any work on what difference in wattage is required so the stickiness is non existent or reduced?

I’ve been riding zwift since 2015, and my unscientific observation is that you need to be at 1w/kg higher than the rider you are trying to pass to get by without getting “stuck”

I don’t see them ever fixing this when they either can’t or won’t fix the user interface and user experience issues.

Max Krause
Max Krause
8 days ago

I think parts of it is the “lanes” Zwift has. You see that in steering… there are multiple different lanes on the same street. I guess the “weak blows” come when there is few riders, and you just steer in a different lane and overtake. You will get the “full wind” whenever changing the lane. Now if the pac is big enough, all “Lanes” are occupied, and THIS IS when you will be reduced to group speed, because you “ride into a moving wall” and first have to drill to that wall to pass… A solution there would be to… Read more »

Chopkins
Chopkins
7 days ago

Could the stickiness be due to the desire of Zwift to rotate rider position within the blob if they are all running at the same WKG? In a group, I feel I am either moving to the back or to the front at all times.

ScooterD79
ScooterD79
7 days ago

Thanks for looking into this. As a mediocre A rider I often find myself hanging on the back in full suffer mode, I’m also a relatively light (64kg). I have never been able to understand why I was often getting sucked off the back while putting out higher watts then everybody and really struggling to move up. At least now I know it is only partly me…

Does it happen more to some people then others?

Mark
Mark
6 days ago

I remember when it was brought in a few years ago. In Zwift it was impossible for riders to stay close together when they wanted to ride together. Zwift UI was not (and still is not) good / responsive enough like it is in other online games. It’s approximate rather than instant and accurate. For example, if I ride with my girlfriend on Zwift, I can see myself on the left of the road on my screen; and I’m on the right on her screen. And I can be just ahead on my screen and just behind on hers. So… Read more »

Deb Momeyer
Deb Momeyer (@deb-momeyer)
5 days ago

Thoughts on Pace Partener riding? I enjoy the concept but either fall behind and get completely dropped or far ahead and get dropped off the group. Very frustrating.
It does not seem to matter how much harder I try to catch up or completely stop my avatar when ahead.

James Annan
James Annan
5 days ago

How do you get 700J from 50W at 3.5s?

James Annan
James Annan
3 days ago
Reply to  Pete Buckney

Thanks! Glad to know I understand what your calculation is 🙂

DJB
DJB
3 days ago

Pete…love your work on this and attention to detail. Any tgoughts on Stuck Draft being compounded when you come up on a TT rider while you are on a non-TT? I was just racing a crit where a number of riders forgot to change off TT’s and on numerous occasions I would hit a TT rider at the back of the group battling to stay on without the advantage of draft and when I hit their back wheel it was like I hit a brick wall. It then took a good effort to get by and once I did I… Read more »

DJB
DJB
3 days ago
Reply to  DJB

*sticky draft but maybe in this case it should be called Stuck Draft 😅

Steve Jones
Steve Jones
3 days ago

I recently went up the ADZ for the tour de zwift stage 3. I took it steady to the bottom and hit the bottom of the climb in about 200th position. I finished the climb in 33rd (and a PB 🙂 ).

My question is, on the way up i was constantly “getting stuck” behind other riders going slower. Would I have been faster riding it solo? It was really bugging me making me feel like I was constantly being slowed down.

Maybe I could do a test of my own at the same power/setup and find out 🤔

Thanks!

David Pearson
2 days ago

I agree, I don’t like the fact it nerfs your speed as your approach a slower bunch. If anything it should increase your speed a bit as in a draft illegal triathlon you can still gain an advantage by approaching a rider you intend to pass in the slipstream before you overtake… even if you are going slowly.

David Pearson
2 days ago
Reply to  David Pearson

they are going slowly*

C Flan
C Flan
19 hours ago

Wondering about the effect in TTTs. Often have a problem passing the lead rider when it’s my turn to pull – have to put in a big dig that’s unnecessary. I think the best way is for the lead rider to literally stop pedalling for a second and allow himself to drop back, but I can’t convince my teammates to do this – they’ll soft pedal, but not enough and I still have to put in a big effort, while the previous leader will slot back in 3rd place and block others.

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