Zwift world physics: w/kg no longer the primary driver of movement?


(Aaron Deutsch - BMTR) #1

Updated to the new Mac client this morning and the power seems off and I can’t quite pinpoint what the improvement was supposed to be, if any.

There was a group ahead of me, in which the leader was pulling 3.5w/kg in the front. I was chasing at 4.7w/kg and not gaining ground. We were on the flats.

Climbing the Col clockwise I was working my tail off trying to gain ground on riders ahead of me who were also pushing less watts/kg and it would take almost the entire climb to catch them

It is no easier to stick in the draft than before

Coasting downhill seems different, but I’m too new to the clockwise direction to say for sure

If there has been a new change, and if it is more ‘realistic’ I think it might be detracting from the game element. It’s a tough challenge to mix real world and virtual world and make it compelling, fun and just “real” enough.


(... Teako (TV5)) #2

Yes, something definitely different. They are also controlling the Kickr. Perhaps getting ready to release the workouts, but the entire experience has changed. Seemed we went back to an older release where I’m in my biggest gear and my Kickr is screaming and my wattage is minimal. There were many complaints…we could do a training session in Trainer Road and ride the island, now we can’t do that either. Please update quickly…the warm weather hitting and you will find many will brave the cold vs. being frustrated on the island with power not working correctly. Also have friends riding and their power goes to zero, then back up, making it impossible to ride together. They need to smooth the power changes, maybe delay the update unless the user increases power by a greater % like a sprint or breakaway. They have their work ahead of them…but I know the Kickr experience was much better going c clockwise then the way it is now.


(Aaron Deutsch - BMTR) #3

Good point on kit. For Zwift HQ: I’m on a CycleOps Fluid2 with Stages for power/cadence and Garmin for speed and ANT+.


(Alan Hamilton - MRC) #4

Not a fan of today’s update for two reasons:

  1. I was riding beside someone on a flat section but needed to push about 0.5 w/kg more than he was pushing to stay even with him. Similarly I was drafting behind him and was pushing the same w/k without overtaking.
  2. Zwift now grabs control of my KICKR every 20-30 seconds so I can’t use my iPhone to control the KICKR. Pretty sure this will help the people who had problems with Zwift losing the KICKR link, but it sucks for me personally. I used KICKR’s resistance mode to be able to easily ride/race with and draft off others, but now it’s really hard to maintain a consistent w/kg on uphills or downhills. And I always get dropped on downhills even in my 53-11. And KICKR’s erg mode was great for training, but that’s gone bye-bye too. And although I didn’t confirm it, I’m pretty sure I won’t be able to use TrainerRoad and Zwift together either.

Sure hope they add an “opt out” mode for the new KICKR feature or I’ll be seeing a lot less of the island.


(Christopher Pallotta) #5

I’m using Zwift with a power meter and Kickr. Haven’t tried the new update yet, but will tonight and report back. I’ve never ridden on Zwift while controlling the Kickr with another app, so I don’t think the changes will affect me.

If you guys have a Kickr and a power meter, I would suggest connecting your Kickr to the app you want to use for resistance control, and connecting your power meter to Zwift.

I’ve used my Kickr on Zwift both ways: (connecting to Kickr/connecting to power meter) and it works fine either way. Naturally, when connecting with the power meter, the Kickr is not in simulation mode, though, and does not vary the resistance.

Just a side note, Alan: I saw that you mentioned your concern about using the Kickr in Zwift in another post. In my experience, having Zwift control the Kickr works great and I don’t notice the issues you mentioned about keeping up with other non-Kickr riders.

Also, I joined MRC this year, hopefully I’ll see you on the real roads soon!


(Jeremy Fand-TV5) #6

i think it was a simple programming change - the code has some Ant+ out call that tells the kickr about an elevation change. I assume it used to be a simple algo that took the gradient of the hill and added some percentage to resistance. The odd thing about that algo was when i used my phone and wahoo fitness app to control the kickr and simply went to level mode, i felt changes in elevation, but they were muted. If it were a percent addition, i should have felt a more significant increase to my base power. With the NEW UPDATE it seems that everytime the wahoo kickr receives info about an elevation change it also get a reset command that puts the power back under control of Zwift. ANNOYING.

I will put my bike with a SRM power meter on the Kickr for a ride tomorrow and that will let me drive the kickr from one machine and simply use Zwift to capture the power numbers coming off the SRM. In other words - one machine for output and one for input.
Would be nice if Zwift gave us that control.


(Alan Hamilton - MRC) #7

@Chris: Some day the snowbanks will not be as high as an elephant’s thigh and I will ride outside again! Hope to meet you out there soon.

Regarding Zwift controlling KICKR and keeping up with other riders, it is very apparent if you are cresting the first steep section of the hill with other riders producing around 4 w/kg. As the gradient falls quickly from 9% to a negative gradient you have to flip up to your biggest gear and increase cadence significantly to produce the same amount of power you were easily producing on the hill. Most of the time a good sized gap opens to the riders in front who are able to keep producing a smooth 4 W/kg as they crest the hill. Before I learned how to use the iPhone to control the KICKR I had to prevent getting gapped by accelerating before the top of the hill to gap the other riders before I lost the ability to generate power. Not something I liked doing, but it was better than always chasing them.


(Jeremy Fand-TV5) #8

Just a suggestion - Zwift should provide a input for starting power / base power for kickr… So start out in your smallest gear and set power to 100 and then ride. What happens to me with my kickr is my lowest gears only generate 20-40watts, which means for me to go to 500+ watts i must spin out my top gear. Outside of all the shifting that has to take place to ride on the island, the wahoo kickr is spinning like mad and making all that noise.


(Christopher Pallotta) #9

Alan, I now understand better what you’re noticing. That makes sense, as in the real world it’s also difficult to keep the same power (as going up) once cresting a hill and things flatten out. I prefer the more realistic feel using the Kickr this way in Zwift, but can see the advantage of holding the power more consistently by forgoing the simulation.


(Jonathan Pait (X)) #10

Hmmmmm, I was actually about to pull the pin on a KICKR purchase, but now I’m not so sure. Most of the comments I read with disappointment with Zwift come from KICKR users. I’ve been enjoying myself on my dumb CycleOps Fluid 2 using a Quarq power meter. Are you guys basically saying that when it comes to Zwift I would be better off staying with what I have?


(David Sack 50+) #11

I have a Kickr and love it. I’m no racer, just trying to get in shape and the variability on the ride makes all the difference. I’m not worried about getting jerseys (maybe a little) or keeping up on the hills (not to say I don’t try) but I love the fact that it feels real to me. To each their own.


(Christopher Pallotta) #12

Jonathan, no, that’s definitely not my stance. I love the Kickr and it’s going to give you the most realistic feel on Zwift as it will adjust the resistance automatically. Zwift still need to work some things out on their end to “level the playing field” for all riders, though.

I will say, though, that my #1 beef with the Kickr is that, in my experience, it tends to overstate power by about 30 watts. I and others have written extensively about this on the Slowtwitch forums. Some have had better luck and claim their Kickrs are accurate compared to their power meters.

There is a workaround to the problem which I’ve discovered and detailed on the forum (I’m Krispy 2014) and a software fix is in the works which you can also read about on the forum. By using my workaround, I’ve been able to calibrate my Kickr to very closely match my SRM power meter. I’m not sure if it’s allowed to publish links here, but you can read more by going to the Slowtwitch forums and searching for “controlling the Kickr via external power meter.”

If you don’t have a power meter to confirm the Kickr’s power readings, then it will be hard to tell if yours is reading power accurately. That may not matter, as it still should be consistent workout-to-workout. You’ll also get the great “road feel” that the Kickr offers.

But, as is the case with all the “dumb trainers” using estimated power your new Kickr may not be what would be considered “accurate” compared to a real power meter.


(Jeremy Fand-TV5) #13

The issue with the kickr is not that it does not work well with Zwift, the issue is that Zwift has yet to make itself work well withe the Kickr. What i mean is that the kickr is a very powerful training tool whose features are not fully used by Zwift - YET. Many complaints about the kickr on zwift stem from the desire to have the kickr structure your ride. If you are trying to do a structured interval workout at a target power, you can either use your power meter to target your effort, OR you can use the kickr to control that effort - the kickr forces you to ride at a certain power if you so desire. For example, i wanted to ride 7min long intervals today with some rest in between. On the road, or on a power meter only based set up, I would be looking at the power number coming off the metering of my effort and try to control it with my body. With the kickr (or computrainer) I can have the kickr hold me at that precise target power for that interval length (and i dont have to think about it, but simply have my legs do the work).So now go the Zwift Island and I can do that interval workout by pushing hard for one full lap and then resting on the next with perhaps some pushes on the hill or sprints. With the kickr I can ride that full interval lap at a targeted power - say 350 watts. The terrain then becomes irrelevant to my effort = meaning i dont feel the change in elevation. BUT with that steady watts/Kg, my speed will change based on the terrain.
Bottom line - if you are training with power, the kickr gives you added tools and control over how you train. Zwift will clearly get up to speed with this and offer controls to enable full use of the range of possibilities that the kickr allows.
My complaint is that Zwift has the base power set too low for the Kickr at the moment. What that means is that my lower gearing has me barely pushing 50 watts, and i spin out my top gearing when sprinting or climbing at anything over 300-400 watts. I simply cannot do 1000 watt sprints on zwift the way they configured the Kickr interface. That needs to change to satisfy the kickr users.


(Alan Hamilton - MRC) #14

@ Jonathan Pait: I would also recommend the KICKR. My only issue is a temporary one that will be solved in the next couple of weeks by an update to Zwift that will allow the user to configure how Zwift deals with the KICKR. (See post in Feature Requests about “opting out” for details.)


(Jonathan Pait (X)) #15

Thanks all for the feedback. I am really only interested in the KICKR for its ability to have Zwift control its resistance. Since I already have a power meter with which I am very satisfied. For power training, I would primarily use that unit.

Your answers help me better understand the pros-cons. Does sound like the KICKR is a pretty cool device. Hmmmm…


(Alan Hamilton - MRC) #16

@ Jeremy Fand: Good idea. And while they’re at it…

I would love to have a dial that would reduce the KICKR’s reported wattage by X%. It reports wattages that are higher than what my legs are actually producing. I’d like to be able to tune it to match what I get out of my PowerTap in the real world.


(Matt Sharpe) #17

As a KICKR user, things felt very different for me tonight as well. The entire experience felt sluggish and unresponsive. I have no problem with Zwift making the resistance more difficult, but not at the expense of variation, which I’ve found to be the most appealing thing about riding on the island. Tonight I felt practically the same resistance going up the KOM hill as I did going downhill on the other side of the island. And the 9% portions felt about the same as the 3-5% parts of the climb. Perhaps I’m missing something?

Here’s the best feedback I can give in regards to the latest update: I’ve done more than a dozen rides since I got my invite a couple of weeks ago and they’ve all been an hour or longer with the longest more than 3 hours. Tonight I was over it after 45 minutes.


(Christopher Pallotta) #18

Matt, I used the Kickr tonight with the upgraded Zwift and my experience was opposite yours. Definitely felt plenty of variation in resistance. Make sure your Kickr didn’t slip out of sim mode by restarting everything. That can cause the issue you’re describing.


(David Sack 50+) #19

After the latest update mine was fine for 7 laps and then went to dumb mode for the last three. Repared, used Wahoo fitness to force into SIM…nothing would work. Used Wahoo fitness after my ride and it controlled SIM mode just fine. Not sure what was up. Will try again tonight.


(Matt Sharpe) #20

I tried going to the Wahoo app and switching to Sim mode after my first lap. I’ve had previous success with that process, but last night it didn’t seem to make a difference. Perhaps I’ll have better luck tonight.