Bug/Cheat: Wattage without pedaling


Month ago I created topic that something strange with zwift. I was not really sure what it is, but after last race I can say that the root cause of the bug was found:

My initial topic: : https://forums.zwift.com/t/power-data-is-totally-incorrect-are-you-serious-zwift
I found the same report ~1y ago: Power Output When I Stop Pedaling
and the same ~2y ago: Race Cheating

Yesterday I shared results of my investigation in our local chat and after it most of the guys were able to finish in top of A-cat using this bug!

Protocol to reproduce is quite simple: Better to do it out of saddle: increase rotation, push the pedal hard (1 stroke of sprint) and stop pedaling immediately. You will find the zwift does not drop power immediately - your power output will be the last high value for ~3 more seconds (more on android). … relax during these 3-5+ seconds, repeat again (not necessary to sprint very hard to extract quite good advantage from it).

Even if you do not use the bug, you can try to catch the group - sprint far away from group - and you will catch it without pedaling. Someone during race mentioned that something wrong with draft - It feels exactly the same, but it is not draft problem. The worst case - you can repeat this bug all race long.

By the way - the problem affects not zwift only - most of the head-units affected: SRM, Android, Bolt (less than others). Right now I can show very high numbers in strava outdoors.

Everything was calibrated, and recorded from the same SRM on 4 devices, you can find the final protocol extracted from fit files. Bolt do the same - but drops power much faster - it is better, probably Zwift can fix it this way.

Also, it is easy to understand why it was necessary - to approximate power if you have ant+ drops, but it is a serious bug and cheat, even if you do not know about it - it can increase your power.


Just to be sure about calibration on zwift-side, checked Log.txt and it is full of “NEW Calibration offset = X” with X from 520 to 530 - which is correct value for my SRM offset.

Thanks for the report. I’ll have the team take a look at this ASAP.

Please fix this issue. I used to love Zwift. After discovering their was a bug that increased my output numbers, zwift became much less interesting for some reason.

Thank you Alexander for digging into it more deeply than I had a year ago!

this shouldn’t spoil your enjoyment though, as far as I can see this is something you have to try and do so just don’t do it.

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It is better to fix, because stop pedalling sometimes is not unusuall in race.

Chris, I can definitely go out of my way to avoid doing it. But, in my experience, it occurs without actively trying to do it. All it takes is to stop pedaling after a strong effort. If I stand up to pedal hard and catch a group or get up a climb, and then stop pedaling, I will get a free 3-4 seconds of sustained power anywhere from 300 - 1000 W. For me, this happens every time I stop pedaling after a strong effort. To avoid doing it, I have to consciously continue to soft pedal while resting after a strong effort, and this is not natural for me.

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i’m not saying they shouldn’t fix it just that it seems more like a problem of people trying to cheat (not you but others may exploit it) than something that overly adversely affects a users ride in most cases

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as I said, not saying they shouldn’t fix it just that for 99% of people it won’t be an issue unless they try to do it

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Graph shows technique being exploited. Bar graphs show improvement since he started using technique.

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one thing that I do not understand is the physics of it.
Ok, lets say someone wants to ride at constant 500 watts for a while.
So he goes for 500watts and stops for 3-5 seconds. As described above.
The wattage stays for 3-5 seconds. The rider not pedaling for 3-5 seconds. But what happens after those 3-5 seconds, the wheel is not turning at full speed (power meter on the pedals) and the rider need to bring back from 0 to 500 again. And lets say not from 0…from 200watts. Still big effort. And again, only 3-5 seconds, so in order to keep the momentum he needs to start at second 2 in order to be again at 500watts at second 5. Correct?
…or I just didnt got the whole bug issue?..


I think that wheel rotation does not matter in Zwift at all - the only source of information for zwift is the power. Bike and bike-wheel has inertia, but bike-pedals inertia is quite negligible. You can do 300-500w in a couple of strokes. So, you are doing work for 3sec and 3s zwift supports your power - you are doing 1/2 of real work. It is very good visible in attached document in averages.

Real life or wheel or trainer inertia is not applicable to zwift - it calculates it is own speed/acceleration/inertia.

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Very interesting.
So, this bug could actually work only with pedas powemeters? Correct?
Since, if I’m not wrong, the integrated into smart trainer powermeters are dependent on the wheel.

It is interesting question, I did not dig into it.

I do not think that smarttrainers have the same problem like pedals => do not transmit power if not rotation, because they are on the rear-hub which always rotates.

On another side - I am not sure how smarttrainer calculate power - if some of them do it from measure voltage of generator - in this case it could be the problem with inertia - it will add some numbers to zwift. but I do not think it is very correct to measure cycling-power that way - maybe on the first smarttrainers did it. All of it just an assumption. I do not use smarttrainer like a source of power - I will check it later.

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Am I reading that I can game Zwift by pedaling, in effect, a cadence of 20 RPM or so? Would sustaining that cadence be pleasant?

This is watt bike.

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Took a closer look at some discussions on other sites about the same issue. Apparently, this is something known among Zwift riders and people use it during the races, improving their in-game FTP etc…
Actually, I do not really mind what they do, as long as Zwift has in place auto ranging of categories by FTP or latest results. This way, at some point, all the cheaters will go up to some topest group A++++ where they could compete in the new pedaling technique ))

We are so on the same page here. 100%. Once you reach A+ level you have to jump thru all the hoops to stay racing.

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I cannot agree with you, because I did not cheat, but found the bug. And right now - I am not so sure if I can count all times when I sprinted to catch the group in front.

If you cheat all the time - it is not a question, but you can reproduce this cheat during race even without knowing it - and it would help you to stay in group.


I’m not sure I understand this. Looking at OPs original docs file are the times in yellow where there is no power being applied but there is still power being displayed. It looks like on the Wahoo bolt results that it is showing a 3 second average so that’s why it quickly drops power over 3 seconds. Zwift and Android ( I presume this is Zwift running on Android) seem to be maintaining the last power max for 2 or 3 seconds (perhaps a method of maintaining power in the case of signal dropouts). The SRM, well I don’t know what the SRM is doing but it looks very wrong.

I can’t really check this as I use a stages PM which seems to be one of the devices unaffected so my test in Zwift looked more like the Wahoo Bolt results, a bit of power still being displayed after stopping pedaling due to the 3 second averaging but then I lose power when I start pedaling again due to the 3 second averaging.

I think you understood everything correct. Except that I recorded on Zwift-PC, not android. Also, I suppose that SRM is doing something like 0.9*prev_pwr, or something like this, not exact, but close.

Even bolt is not correct - but it is much better than anything else + no reasons to do any sprints even on bolt numbers - constant power would be better.

The only correct numbers is in “theoretical” column. If Zwift would not want to drop power immediately (and it is possible to understand, because it is possible to lost wireless packet, probably some people with radio interference will complain), in the case - it is possible to apply “bolt” solution, because if wahoo uses it and it means that it is acceptable for most users.