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Zwift vs. TR erg modes
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Just did a workout in zwift erg mode for the first time. I typically use TR when I want to do an erg type workout and zwift when I just want to do a more freeform ride. Zwift seemed to do a much better job of 'controlling' my trainer (Kickr) than TR does. The power on a hard interval seems to level out quicker and there was less variability. Anyone else have a similar experience? All of my firmware and software versions are up to date
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Re: Zwift vs. TR erg modes [jsoderman] [ In reply to ]
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i use both pieces of software for the same reasons, but im on a tacx neo.

ERG mode responsiveness seems to be the same with either software for me.

2018 Schedule: Texas Half Ironman April 8 // Tri Cap Tex, May 28 // Cypress, TX Sprint July 29 // Kemah, TX Olympic October 21
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Re: Zwift vs. TR erg modes [jsoderman] [ In reply to ]
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I wonder if what you are feeling could be an artifact of the variable "trainer difficulty" setting in Zwift. Ie, your Zwift has a lower effective trainer difficulty level then TR.

Pushing that slider leftwards effectively softens simulated grades and might make your impression of ERG being smoother. If you push the slider right it might make resistance more true to grade. The downside is it should make you shift more and can really add resistance quickly when you hit a hill - and sometimes if you let cadence drop at the same time, the requested torque really adds up (for your set watts) and can you can really get out of rhythm and take a while for the watts to settle out. Perhaps you are feeling this difference in TR?
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Re: Zwift vs. TR erg modes [rdubs] [ In reply to ]
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The slider only affects "Grade" mode - when you are out riding around what we transmit as the actual % of the (virtual) road grade. The slider goes from 0 - 100%. So if it's the middle, the grade we send to the trainer is half (50%) of what is actually displayed on screen. So if you're climbing the radio tower and you see 14%, we'll tell the trainer that it's actually 7%. You can adjust this so we will tell the trainer it's a full 14% (all the way to the right) or that it's more like 1.4% (all the way to the left; I think we will always transmit that it's SOME gradient). Trainers typically are "heavy," so the 50% grade actually feels more realistic (for most people) than if we actually transmitted the exact value on screen. But it's personal, which is why we allow you to adjust that slider to suit your preferences.

But this is totally separate from ERG mode, which is only used for workouts to send the trainer the actual power and the prescribed power target so it can adjust resistance. There is some algorithmic work here that could result in a difference between Zwift and TR. Obviously, I do not know the exact nature of what TR does here, so I can't directly compare how our approach might differ.


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Re: Zwift vs. TR erg modes [Rappstar] [ In reply to ]
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Sorry Mr. Rappstar, I know this is your baby. Poor wording on my part, reading my post above clearly yields more confusion then the analogy helps. I actually know ERG/workout doesn't involve the slider bar per se, but what I meant was since we know zwift (or any program) allows for a variable simulated resistance load "ramp", perhaps the zwift workout mode calls for an effective "lower" resistance ramp compared to the setting on TR - akin to the slider being moved leftwards on Zwift non-erg.

More succinctly, just as you said - perhaps there is some difference between the two programs in how a requested increase in torque is applied to achieve a given wattage delta, similar to how moving the slider bar feels within zwift non-erg mode. So yes, an algorithmic difference. Or calibration.

While I have you, there is one related question I have had for a while - is there a difference in how ERG changes resistsance in 3sec vs 1sec wattage reporting?

Thanks for the great program.
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Re: Zwift vs. TR erg modes [rdubs] [ In reply to ]
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rdubs wrote:
While I have you, there is one related question I have had for a while - is there a difference in how ERG changes resistsance in 3sec vs 1sec wattage reporting?

Thanks for the great program.

I don't know off the top of my head; I'll check and report back.


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Re: Zwift vs. TR erg modes [rdubs] [ In reply to ]
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Nope, no difference; it's just visual.


"Non est ad astra mollis e terris via." - Seneca | rappstar.com | FB - Rappstar Racing | IG - @rappstar | Game Designer @ Zwift

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Re: Zwift vs. TR erg modes [Rappstar] [ In reply to ]
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Cool -thanks.
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Re: Zwift vs. TR erg modes [Rappstar] [ In reply to ]
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Yikes I’ve been riding with my slider all the way to the right for my Tacx Neo. No wonder I seem to really suffer on the hills more than usual.
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Re: Zwift vs. TR erg modes [jsoderman] [ In reply to ]
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jsoderman wrote:
Just did a workout in zwift erg mode for the first time. I typically use TR when I want to do an erg type workout and zwift when I just want to do a more freeform ride. Zwift seemed to do a much better job of 'controlling' my trainer (Kickr) than TR does. The power on a hard interval seems to level out quicker and there was less variability. Anyone else have a similar experience? All of my firmware and software versions are up to date

Unless power match is used it is completely up to the trainer how to maintain prescribed power. There is one thing here though. KICKR actually supports 2 versions of ANT based control protocol: standard ANT FE-C and also their own proprietary version that was introduced way before ANT FE-C came in to existence. For whatever underlying reasons there might be but the native protocol responds to commands faster (I tested it on our own Veloreality software). So we support both protocols and let customer to choose either. Maybe (big maybe) if Zwift by default uses "native" protocol and TR goes for ANT FE-C it could in theory lead to that impression you have.

I think however that most likely it is just an impression.

http://veloreality.com
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Re: Zwift vs. TR erg modes [kostya416] [ In reply to ]
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kostya416 wrote:
jsoderman wrote:
Just did a workout in zwift erg mode for the first time. I typically use TR when I want to do an erg type workout and zwift when I just want to do a more freeform ride. Zwift seemed to do a much better job of 'controlling' my trainer (Kickr) than TR does. The power on a hard interval seems to level out quicker and there was less variability. Anyone else have a similar experience? All of my firmware and software versions are up to date

Unless power match is used it is completely up to the trainer how to maintain prescribed power. There is one thing here though. KICKR actually supports 2 versions of ANT based control protocol: standard ANT FE-C and also their own proprietary version that was introduced way before ANT FE-C came in to existence. For whatever underlying reasons there might be but the native protocol responds to commands faster (I tested it on our own Veloreality software). So we support both protocols and let customer to choose either. Maybe (big maybe) if Zwift by default uses "native" protocol and TR goes for ANT FE-C it could in theory lead to that impression you have.

I think however that most likely it is just an impression.

We allow(ed) users to select either "native" or FE-C, but we are slowly but surely deprecating "native" in favor of the (more reliable) FE-C connection.


"Non est ad astra mollis e terris via." - Seneca | rappstar.com | FB - Rappstar Racing | IG - @rappstar | Game Designer @ Zwift

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Re: Zwift vs. TR erg modes [jsoderman] [ In reply to ]
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This is a much more sophisticated Q than might first appear. Let's say that you're recovering at 100 W and about to do an interval at 200 W. The trainer *always* compares your power output relative to the target power (setpoint) and uses an algorithm to modify the resistance to get you to the target/setpoint. This is called control theory and is used in many situations that are not so obvious. The simplest is to increase the resistance in proportion to the difference between the actual power and the target power. The rate at which the resistance changes is typically this difference multiplied by a proportioning factor. TMI, I know, but here's the take home: if the proportioning factor is too 'stiff' the system is underdamped and your delivered power will increase rapidly, pass the target and then recover back to the target. If the factor is too 'slack' the system is overdamped and you will require a long time to achieve the target. I have a Tacx Vortex Smart and it's clear to me that an update about a year ago made the control much more 'stiff' than previously. I'll be at 100 W, have the target change to 200 W and my power will spike to, I dunno, 350 W before returning to 200 W. The behaviour was far more damped previously - but the downside is for short intervals, you could never reach the target wattage before the interval was over. So, it would be no surprise that TR and Zwift use different algorithms to control the dynamics when the target and the actual powers are different. In 'cruising' at constant power, the differences are small and different approaches to control are not so noticeable. But when you have a step change of 100's of W, the system dynamics are discernible.
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Re: Zwift vs. TR erg modes [jsoderman] [ In reply to ]
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My 2 cents: TR is light years ahead of Zwift in erg mode.

If you're just doing long periods at XXX watts, there's no difference between them.

If you're doing highly variable workouts, especially with intervals < 30 seconds, zwift is quickly left behind. It takes far too long to ramp to the required power and doesn't hold it there particularly well.

The proof is in the pudding here - it's almost impossible to achieve the planned average power of short intervals in zwift.
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Re: Zwift vs. TR erg modes [n_bens] [ In reply to ]
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This depends on your trainer as well. I did a comparison to see how different trainers react to short sprints type intervals and there was an obvious difference between them. I should have more on that hopefully soon.


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Re: Zwift vs. TR erg modes [giorgitd] [ In reply to ]
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giorgitd wrote:
This is a much more sophisticated Q than might first appear. Let's say that you're recovering at 100 W and about to do an interval at 200 W. The trainer *always* compares your power output relative to the target power (setpoint) and uses an algorithm to modify the resistance to get you to the target/setpoint. This is called control theory and is used in many situations that are not so obvious. The simplest is to increase the resistance in proportion to the difference between the actual power and the target power. The rate at which the resistance changes is typically this difference multiplied by a proportioning factor. TMI, I know, but here's the take home: if the proportioning factor is too 'stiff' the system is underdamped and your delivered power will increase rapidly, pass the target and then recover back to the target. If the factor is too 'slack' the system is overdamped and you will require a long time to achieve the target. I have a Tacx Vortex Smart and it's clear to me that an update about a year ago made the control much more 'stiff' than previously. I'll be at 100 W, have the target change to 200 W and my power will spike to, I dunno, 350 W before returning to 200 W. The behaviour was far more damped previously - but the downside is for short intervals, you could never reach the target wattage before the interval was over. So, it would be no surprise that TR and Zwift use different algorithms to control the dynamics when the target and the actual powers are different. In 'cruising' at constant power, the differences are small and different approaches to control are not so noticeable. But when you have a step change of 100's of W, the system dynamics are discernible.

OP here. Thanks everyone for the well though out replies. I think this is what I was looking for. Some, but not all of the time on TR I'll be doing a longer interval and for the first 30sec or so it will have me ride under my target power. It usually 'figures it out' after just a bit and I'm ok for the remainder of the interval. Not a huge deal on a 20 ftp interval, but on a 3 minute VO2 interval, it's can make me under power significantly. I wonder if my kickr is 'slack' to use girogitd's terms.
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Re: Zwift vs. TR erg modes [jsoderman] [ In reply to ]
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jsoderman wrote:
Zwift seemed to do a much better job of 'controlling' my trainer (Kickr) than TR does. The power on a hard interval seems to level out quicker and there was less variability. Anyone else have a similar experience? All of my firmware and software versions are up to date

Well, I had exactly the same impression until lately. I've used Trainerroad for several years and last autumn started also with Zwift (using Elite Drivo and Mac mini). I've always had the feeling that Trainerroad erg mode is like riding in the sand and somehow very unnatural - so starting from some point I did not like to use erg mode in Trainerroad anymore.The first impression with Zwift was that Zwift erg mode was far superior feeling and yes, much less waiving and variability. I also like very much the Zwift erg mode feature how it shuts erg mode automatically off/on if you stop pedaling. In Trainerroad one has to wait when Drivo resets it and this takes some time. But there was one important difference in my Trainerroad and Zwift setups - namely Zwift connection was via Bluetooth and Trainerroad via Ant+FEC. From curiosity I recently tried Trainerroad erg mode via Bluetooth and somehow it feeled quite better than what I remembered from the past. I must repeat this to be sure, but maybe the Bluetooth connection is more error-proof, less dropped packages etc. Also I don't know exactly but maybe ANT+FEC updates info between trainer and software max 1 time per second, as BLuetooth can have higher rates?
Last edited by: Tr3: Feb 5, 18 15:46
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Re: Zwift vs. TR erg modes [jsoderman] [ In reply to ]
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This is a timely topic as I do some product testing for Kinetic and I've been comparing the ERG behavior between programs, primarily Zwift and Trainerroad. My experience there is that the reported power tends to "wag" around a bit more with Zwift and presents some challenges with steep increases in power. Comparatively on TR the transitions felt more natural (easier to keep on top of the gearing to avoid a low cadence death spin) and the power figure was much more steady and true to the target.

I'm doing some testing in the weeks ahead with Bluetooth over FTMS (not yet supported by Zwift) and it will be interesting to see how it all comes together.
Last edited by: dgran: Feb 13, 18 13:33
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Re: Zwift vs. TR erg modes [Tr3] [ In reply to ]
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Tr3 wrote:
jsoderman wrote:
Zwift seemed to do a much better job of 'controlling' my trainer (Kickr) than TR does. The power on a hard interval seems to level out quicker and there was less variability. Anyone else have a similar experience? All of my firmware and software versions are up to date

Well, I had exactly the same impression until lately. I've used Trainerroad for several years and last autumn started also with Zwift (using Elite Drivo and Mac mini). I've always had the feeling that Trainerroad erg mode is like riding in the sand and somehow very unnatural - so starting from some point I did not like to use erg mode in Trainerroad anymore.The first impression with Zwift was that Zwift erg mode was far superior feeling and yes, much less waiving and variability. I also like very much the Zwift erg mode feature how it shuts erg mode automatically off/on if you stop pedaling. In Trainerroad one has to wait when Drivo resets it and this takes some time. But there was one important difference in my Trainerroad and Zwift setups - namely Zwift connection was via Bluetooth and Trainerroad via Ant+FEC. From curiosity I recently tried Trainerroad erg mode via Bluetooth and somehow it feeled quite better than what I remembered from the past. I must repeat this to be sure, but maybe the Bluetooth connection is more error-proof, less dropped packages etc. Also I don't know exactly but maybe ANT+FEC updates info between trainer and software max 1 time per second, as BLuetooth can have higher rates?

Exactly (what you wrote that I put in bold). BLE is always better for ERG mode because it can be higher frequency. ANT is a 1Hz signal. BLE can be much faster, though it's up to individual manufacturers how frequently they actually choose to transmit data packets. But the standard transmission rate for BLE is virtually always higher than 1Hz, which means your trainer can update faster.


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