Will the revised Pack Dynamics only apply to races though? I think this whole thread/discussion needs to make it clear that PD applies across the board so will affect Group Rides and Robo Pacers at all levels.
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In which case it matters a lot less how accurate that zFTP number is. Most people do the intro workout for ride #1 (I assume? could be completely wrong) in which case it really doesn’t matter how wrong the “first ride no-zFTP” factor is.
Quoting for additional emphasis, in case the bold text didn’t do it.
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I saw it and I disagree with its exclusion. So weird that I keep getting the impression that the “fix” has been determined and all that’s left is fiddling with the details.
Any consideration to my suggestion to figure out how to make the dynamics work with bots at 0w descending the alpe before moving on to making it work with powered riders? I’m guessing not as “reduction of X% power from the last Y seconds” wouldn’t work there.
Except that using zFTP is absolutely off the table?
I think that there is a difference between easing-off and taking it easy, I think zFTP would only be a gauge of the second but it is the first that is important for micro-managing group position and the range of power change needed will depend on the situation. A group on a 2% uphill might see many people over their zFTP just to stay with the group and riders won’t need to drop power by much to avoid moving up.
Having said that, if a rider does not want to hit the front but does so and is still easing-off then they are making it harder on themselves to avoid being dropped if the group is very fast and compact. These PD4 changes might help that both by reducing the group speed but also teaching us to be extra careful about hitting the front and getting braked when we don’t want to.
Edit: on the 0W descending - a power check threshold slightly above the last 3s average would do this, though need to be careful not to cause sticky draft if the threshold is too high but the breaking force could be made a function of the power difference.
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Using zFTP was never on the table. For the reasons already discussed and other technical reasons related with how the whole Zwift software stack works (that I won’t go into detail).
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Will be interesting to see if this will work…To engage Auto-braking do all 4 rules need to apply at the same time?
I really have a hard time with that rebuttal about lighter riders having an “advantage” uphill. There is no inherent advantage for lighter riders. It all comes down to WKG, which is a function of training. I know light riders that can’t climb worth a damn because they don’t have a good power-to-weight ratio.
Now I understand as riders get heavier, they start to approach an asymptote of the maximum power-to-weight ratio that can be reasonably held for extended periods of time. If you want to call that an “advantage,” I suppose you can make a weak argument to that point. However, that’s physics and that’s the real world. Disproportionately favoring heavier riders with unrealistic descending speeds because it makes it “fair,” is a beyond ridiculous contention. Go race in the real world; no one will put a motor on your bike at the top of a hill so that you can catch up to a rider that drops you by 4 minutes on a climb.
I’m not saying heavier riders should have NO advantage on descents. Physics favors heavier riders downhill, that’s a fact, but not indiscriminately, as seen on Zwift. I’m certainly not saying the physics model would be easy, I mean, let’s face it, no one can push 5WKG on a descent of -8% without the magic of the Zwift model and/or trainer difficulty settings…
Perhaps the right answer is to evaluate the correct terminal velocity that could reasonably be achieved on the descents in the game, then accelerate riders to that terminal velocity relative to their weight. It would be predictable and irrespective of group size. A lighter rider could then put in a larger effort to reach that terminal velocity as fast as or faster than a heavier rider that is putting in less relative effort or coasting. Even if both riders coast, the gap should theoretically reach a certain point and stop expanding (unlike the current state). It would be as close to real life as I think the game could get without being able to account for things like descending skill and CdA.
I do not think Zwift ever will (or should) perfectly represent the real road, but being this unrealistic on descents while producing relatively reasonable representation on other terrains, is a gap that I would like to see closed.
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Your comments above make me wonder WHY heavier riders have an advantage on the downhill… is it the added mass allows them to carry kinetic energy through the group? Just like in real life, everything falls at the same speed when you remove air resistance so… I guess I’m unclear as to the relationship of mass to gradient in zwift (thinking of the anvil here) the why is key I think.
Could it be mass to cda instead?
For the sake of discussion and understanding… not to be adversarial, this is very interesting imho…
I’m pretty sure there IS and inherent advantage to lighter riders, especially as wind resistance drops and the grade increases… it’s the relative power to weight as you said but there is an ideal ratio there. This wouldn’t hold as true on shorter climbs where a larger riders power and speed are able to overcome that but at a certain point that advantage reverses.
I hate to compare IRL to zwift… it’s not the same but… As a shorter rider i can generally descend pretty fast with my lower cda…
From a physics standpoint, it gets a little obtuse, but at a very high level, it comes down to drag force. A heavier rider has a stronger pull of gravity and can overcome the drag force/air resistance than a lighter rider. The objects are not in free fall, so the acceleration function is different. In a gross oversimplification, the frontal area of a rider in this function is squared when calculating the acceleration and the mass is cubed. Those two variables will be different from rider to rider e.g. putting an 800 lb man on a bike against a 130 lb man in an aero tuck but accounting for the normative range of cyclists, weight will trump raw CdA if both riders are proportionately aero and have the same descending ability.\
With respect to your comment about climbing, keeping watts per kilogram constant, the heavier rider can actually has an advantage uphill because the raw wattage is higher. Of course, this varies by grade because rolling resistance then becomes a larger component in the equation, but if there was no upper limit to human capability in terms of strength to weight on the bike, we wouldn’t be discussing advantages for lighter riders. Both would have advantages at varying grades if WKG is equal.
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I’m with you all the way on this for the vast majority of Zwift courses (as a mediocre C-cat weighing 57 kg @ 175 cm) 
And conveniently, no one really wants to talk about the “advantage” heavier riders have on flat roads… 
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I think what I’m trying to articulate is not coming through clearly, I agree with the hard physics of it, no problem there.
There is a component to this that I’m having trouble articulating and I’m not completely sure how to lol.
I think it’s something like the effort of a smaller person relative to their max capacity is more effective on climbs than on flats where overall higher watts are more effective. I’m sure there are more articulate people out there that know what I mean but are able to break it down better haha.
Regarding zFTP or other similar metrics, it would seem odd and unfair to me if two physically identical avatars behaving in precisely the same manner would get treated differently (with one being abruptly slowed down, and the other not) purely based on some assessment of the rider’s physiologies being different.
That said the 5% thing seems highly unsatisfactory to me. Is this a one-off instantaneous assessment, ie the power is assessed at the moment when the draft drops and the autobrake decision is made. It seems highly unreliable and likely to feel very arbitrary, judging from how my power number fluctuates in normal riding.
IRL descending when you start getting up to elite amateur racing and higher there’s accelerative power that really hurts lightweight riders - to get up to the greatest possible speed as quickly as possible before tucking and also to maintain momentum if the descent has spots where it levels out. It’s a sprint to get into the tuck at the highest speed possible.
Once in tucks, it’s the aero, but you could be gapped well and good before that. An explosive 138lb-148lb rider can easily gap a group of much bigger riders with a lot more absolute power but poor acceleration and then tuck at a higher speed and more aero (smaller frontal area) and they’ll never catch up on the descent (but maybe on the flats later). A true lightweight climber might crest a huge climb minutes ahead of a chase group but enter the tuck many km/h slower and lose ground at every point on the descent where they have to burst the power to maintain momentum, but it would be a fight to catch not a formality. If Zwift could eventually model something just somewhat more reflective of reality, well that would be great!
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My thinking with it is that the intent is “the rider is going easier → disrupt passing via auto brake” and so “easier” is going to depend on the individual rider. The only instance “fairness” is going to matter is in a race, and with cat enforcement everyone in the same race is going to have similar capabilities. I’m genuinely unconcerned about the edge case of some level 2 racer without a good zFTP value disrupting a race.
But David said that they aren’t capable of applying it in-game. Maybe they should check with the Sauce guy since he’s able to globally determine bunch sizes through basically-packet-sniffing whereas Zwift guys say it’s not possible to determine group sizes.
I’m very near the point of moving away from Zwift due to constantly getting dropped on descents regardless of what watts I output. I weigh 56kg I’ve lost count of the races / group rides that have been ruined by losing touch with a group on a descent. I’ve tried everything I’m convinced the physics for descending are nothing like IRL and greatly favour weight. I always start to fall back once descending I’ve tried super tucking, sprints etc etc however once I start to fall back it doesn’t matter what I do the end result is the same. I posted prior that descending in Zwift needs to be looked at / adjusted however the comments I generally receive are I should break away from group on the KOM however if that was possible I would still get caught and passed on the descent with no chance of attaching myself to the group. One other request I’ve asked to be changed is trainer difficulty for declines to be locked regardless what trainer difficulty setting is used for inclines.
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In a race this morning coming down off Titans I got in a break (not through being super fast or aggressive, just by virtue of having an anvil). Three of us were away from the group by a fair margin. As soon as the anvils wore off the pack came roaring up on us and I was barely able to sprint hard enough to hang onto the back, and almost got dropped - purely as a result of ending up in a break out front. Definitely an eye-opening experience and something that needs to be addressed.
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