zPower: Don't be a "Flier"

(J eff) #181

Think of it this way.  Using zpower is just taking a guess at your power.  As an example, would you be happy if you were selling/buying gold at a store and the guy picks up a weight, then picks up the gold and says, it feels about the same.  Hell zpower is probably even worse.

Zpower is better than nothing, but it’s going to be off by a lot.



(Liam) #182

@Paul McCombes

“I’d suggest preventing winning a jersey/acheivements if you are on a trial - I’m hoping the current crop of edopers will find other mischief for free rather than pay to be a clown, so less free booty is less incentive.”

I was thinking the same thing!! Will recommend this now!!

(Paul McCombes) #183

@ Jeff Hirsch Think of it this way.  Using zpower is just taking a guess at your power.

No it isn’t - it is making a calculation, just like a power meter (which also have errors and inaccuracies). The accuracy of the answer depends on the quality of the data from the sensors, the quality of the kit, and the diligence of the setup. For example an Garmin Vector power meter needs calibrated but it also needs installed with a torque wrench. Torque wrenches also need calibrated - how many of the Garmin Vector’s being used do you reckon have been installed with a properly calibrated torque wrench)? Would you be happy buying your gold from a guy whose scale wasn’t calibrated?

(Jon) #184

I’ve been trying to stay away from this thread as I truly think it has run its course but Paul’s comment above has summed it up for me.  

PM’s are a relatively new innovation in cycling and they are used to measure an individuals power for training and pacing reasons and not really for comparing yourself against others (How many pros publicise their FTP?).  I’m sure many people have bought PM’s, installed them on their bikes and simply believed in the numbers they are seeing without question.  That in itself is OK as the numbers will be consistent so are valid.  

This is the same for zPower.  If people are using Zwift as a training tool it doesn’t matter if someone is pushing 6w/kg for entire laps as long as when they do their FTP the calculation is based upon those numbers.  If they are racing on Zwift then you only have to look at the lengths that the race organisers go to to validate the riders to realise that the people flying will soon need to understand that they either don’t race or they work out their setup to make it more accurate.  If people are then only concerned about the achievements, the Jerseys and the Strava segments then I would suggest they are using Zwift for the wrong reasons.

And on that note, I’m out!


At least until the next post infuriates me anyway.






(J eff) #185

No it isn’t - it is making a calculation, just like a power meter (which also have errors and inaccuracies). The accuracy of the answer depends on the quality of the data from the sensors, the quality of the kit, and the diligence of the setup.


What exactly is that formula?  The only sensors it has since it doesn’t have a strain gauge is speed and cadence.  Converting that to wattage requires knowing the exact resistance and that is being guessed.  Even on my CT I can’t with any reliability set the press on force exactly the same every time.  PMs if properly calibrated (using known weights) can be both accurate and precise.

Zpower may be great as a training tool (better than nothing I suppose).

Don’t get me wrong, real PMs don’t solve all problems with racing in Zwift as there is nothing that verifies the weight input by riders.  

The reason you can’t use a PM for a real life race is there are still too many variables that determine speed besides power, and some of them are not easy (or practical) to measure continuously.

(Paul McCombes) #186

What exactly is that formula? 

It is P = (5.244820) * S + (0.019168) * S^3 (P = Power in Watts, S = Speed in mph).


(Ben Crone) #187

Come on Paul, if you’re going to make up formulae at least try and get the correct units!

(J eff) #188

Based on that formula, no matter what the press on force you end up with the same wattage for the same speed.  If that is truly the “formula” it would be no wonder folks can crank out 400+ watts at their resting heart rate.

(Will I Am Adams) #189

I am not even  sure  of the point you are trying to argue -  but suffice it to  say don’t  try to  tell anyone that  the  power  based training interface with Zwift  is  equally inaccurate  as  Zpower and  any other non -power based interfaces.  That’s  BS dude.

Power is the most accurate measure of   effort and  work.  I  have a computrainer and  I  assure you my  powers reading are  dead on and by the  way its incredibly simple to set up.

95% of the  ridiculous performances I  see on  Zwift are  non-power based  trainers.  Its  a simple  fact  - they  are not  as  accurate, they are far  harder to  set up and  frankly I  don’t  want to  ride with  that  group.

That same  group seems to  want to argue that them riding at 8-10 watts/ kg  for   extended periods is  valid - its a  joke.

(Alison Kubota [Vision] CVR) #190

Why do so many of you lump two different problems as one?  Zpower inaccuracy is one issue while the opportunity to cheat (cranking down the manual trainer resistance, knowingly using the wrong trainer like rollers with zpower, etc.). 8-10 w/kg is an opportunity to cheat issue.  Guy whose power curve is off by 20w is an inaccuracy problem (and maybe their actual power is higher than what power reports).  If you’re angry about the latter, then whining about the former doesn’t make sense.

(Jon) #191

Ha ha, I’m back.

I’m not sure the above post is aimed at my last comment but if it is then you clearly don’t understand what a power meter is for.

Training with power is all about training at the right levels and nothing to do with what the number is.  It doesn’t matter whether your power meter is showing 200w or 2kw as long as if for the same effort you put in each time reads the same number.

The number only becomes important in Zwift when it is the only sensible metric they can use to compare one rider against another.

I’m assuming you also have a PM to verify the accuracy of your Computrainer?  Otherwise, how could you be so sure of its accuracy?  Have you had your PM calibrated? How?  What against?

5% of the ridiculous rides you have seen are valid and based on power?

Where are these people claiming that 8-10w/kg over an extended period is valid?  I’ve been on Zwift since March/April (and in the FB groups) and haven’t witnessed this?

Are you a troll?

Cheers, Jon. 


(Jon) #192

Not your post Alison, kudos to that.  It just took me a long time to write mine.

(Alison Kubota [Vision] CVR) #193


not directed at you.  Totally agree that for training, doesn’t matter at all, since the target levels are % of FTP so using a Zwift generated FTP to feed the Zwift training FTP cancels out the error.  People should be keeping track of different FTPs anyways, outdoor power meter FTP, trainer power meter FTP, trainer zPower FTP, etc, since there is likely to be differences between them all.

(Jon) #194

Will I Am Adams,  

Fancy sharing a link to your strava profile?   Interested to see why this is upsetting you so much.

This is me.  https://www.strava.com/athletes/1120497



(Will I Am Adams) #195


Troll? - please - Maybe you  should  stay away form this post.  Are you in 3rd grade?

For you and Alison - the original thread centered on the  issue of  what  appears to be   people  either  gaming the  system (cheating) intentionally or  unintentionally - it  doesn’t matter as  the discussion was that this  seems to  be many more of  these performances with non-power based trainers and  whether they  should  be  competing for  jerseys or  riding with   groups of  similar vs. riding and  racing  all together.

You both should understand that the Zwift program uses the  riders watts/kg to  determine  speed - so  regardless of all the   stuff you are both  talking  about that has some truth -  yet   irrelevant to the discussion that the  non-power based trainers rider   seem to  dominate the leaderboards and for whatever reason the  TdF level efforts.   We  are not talking about training.

I contend that this is probably the inaccuracy of  reliably setting up the  non-power based interface.  Surely  you  don’t think the  coincidence is that the non-power  based riders are  just  all a  professional level.

I   think Zwift  should  separate the  groups let the powerbased  people compete  together and the non-powerbased compete together until its  sorted.

(Alison Kubota [Vision] CVR) #196

We already know that those zpower flyers are flyers.  But I don’t think zwift is listening to any of this anymore.  Maybe the squeakiest wheel doesn’t get the grease in this cases.  Maybe it’s more about a calculation to maximize revenue and overall happiness, not to maximize the happiness of the extremes.  But I have to say I sometimes get a minor chuckle reading vitriolic threads.

(Jon) #197

I think you’re right, maybe I should stay away.  After all it’s just going round in circles.

Every constructive comment posted is met with the now familiar cry of ‘just separate the leaderboards as I have a PM/Smart Trainer so why should I have to put up with people who don’t’

Every comment suggesting that this doesn’t fix the problem is met with ‘but these people don’t take their training seriously because they haven’t got a PM/Smart Trainer so why should I have to ride with them, just separate the leaderboards’

Every comment suggesting that the playing field still won’t be level due to the inaccuracies and variations from one PM/Smart Trainer to another is met with ‘but it’s only a few watts out, just separate the leaderboards’.

Every suggestion that even people with a PM/Smart Trainer could be gaming the system is met with ‘why would they do that, they have invested in their training, just separate the leaderboards’.

In essence, there are people trying to help find solutions for all and there are people just happy to keep on suggesting the same old ‘quick fix’ for themselves.  And you wonder why I questioned whether you are a troll?

Oh, and I left school quite some time ago.  In fact about the same time I stopped worrying about if someone was cheating to beat me in a computer game.

(Ben Crone) #198

This thread makes me laugh. Jon you are no better than Will, neither of you can see things from the others perspective. If anything, your position is slightly worse because you’re too quick to disregard the importance of one of Zwift’s core aspects: competition.


(Jon) #199


I can see things from Will’s perspective and I have also conceded that splitting the leader boards is necessary.  

It does not however fix the problem for people who don’t have power meters or smart trainers who want to compete.  That has been my standpoint all along.

Zwift have also said they are going to split the leader boards so it’s a done deal yet this thread keeps getting resurrected.

I do however admit to venting somewhat in frustration and I’m sure that myself and Will can agree to disagree on how they banish fliers (believe me I want this as well) and I certainly will try to stay away from this thread from now on. 



(Yancy Fry) #200

I like Zwift and have used it for almost the entire beta. But I wont be signing up until this is fixed. It’s sad since it is a good training tool, but the frustration of coming in second place to z-power riders with bogus power constantly is too annoying.