Purposeful weight adjustments impact on CE

I lead some group rides in the Club context (and previously in MeetUps) where we would purposefully make weight adjustments to make it so riders of different fitness levels could ride together. The typical example was for everyone to adjust their weight to artificially to create a 4 wkg FTP. This made everyone’s relative effort similar.

The question is: what effect would this have on riders’ CE category for public events? What weight would Zwift use to calculate zFTP and zMAP?

This will impact the calculation.

Best to create a meetup with the keep together option.

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It would be better to have fast, stronger riders use a heavier less aero bike.
IRL, to keep a group together, some riders just have to ride slower.

There is also the rubber band or ride ahead and circle back.

Changing wt will mess with CE.

I thought that changing weight did not affect CE (for more than a day) because the CE calculation was based on watts with the conversion to W/kg redone every day according to the current weight. So while it could perhaps mess up a rider for one day it would have no lasting effects.

Contrast with the ZP system where the calculation in W/kg is performed for the event and the answer then used for up to 90 days.

There’s been a lot of discussion on the way weight changes can be used to retrospectively change category with the CE system which takes advantage of this algorithm.

You can look at the data on your profile to understand (after the fact) whether an effort has affected your CE data. Go to zwift.com, My Feed, My Profile, More Info. There you can see the dates for each PB that they have included in the calculation. That helps narrow down which rides mattered in terms of categorization.

I think this is the important thread you need to read.

FWIW this is the key section which I believe applies to the question you asked.

“The weight used for category enforcement calculations in watts/kg (using zFTP and zMAP) will be determined by the average weight of all weights that were in effect at the moment that certain key peak power values of the power curve were set (within the last 60 days).”

The way I read this - Changing your weight will only effect your CE category if the ride, where your weight has been ‘artificially’ changed, results in an improvement in one or more of your 4 key peak power values. Your changed weight will not effect CE category calculation if you do not produce a new peak power value.


There are 8 power values revealed on the profile, so I assume (?) a change in any of those could have some effect on the CE curve… Maybe someone from Zwift can clarify.

Yes. That’s perfectly clear already.

There are 8. I used 4 above as I took it from more information in the linked post.

“The key durations of time that we examine are:

  • 3 min.
  • 5 min.
  • 12 min.
  • 20 min.

As an example, Zwifter X set their peak power records for various times as follows:

3 min. : 400w at 70kg on 23rd of October

5 min. : 380w at 72kg on 13th of November

12 min. : 340w at 73kg on 14th of November

20 min. : 320 at 73kg on 14th of November

The weight that will be used on the present day (e.g: 10th of December) will be 72kg (average of the 4 weights)”

I’m not saying it is definitely just these 4 but I do think their examples might suggest just these 4 ?

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Yes, it would seem that the answer is “don’t set any peak power records” with a tweaked weight.


Actually, this is not a good solution for when you have “throw-down” or “game-on” sections within such rides.

Bike selection is too blunt an instrument to level riders. We tried that first.

But in that case the stronger riders should just slow down to ride with the rest. Changing weight will make it unfair in a throw down section.

What are you saying? The whole point of a “throw-down” is to go hard, slowing down to ride together is something completely different.

Also, what do you mean “Changing weight will make it unfair”? How is it unfair to intentionally slow down faster riders and speed up slower riders?

This was an effective solution to normalize a group with disparate fitness levels, I don’t understand why you want to tell me it doesn’t work or not to do it. My post was about whether this could be done w/o negatively affecting participating riders with regards to CE calculations.

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Change height instead of weight.

Height has an effect on CdA so will affect rider speed on flat or small gradients but it is not used for CE. Only problem is you’d need to tweak the height settings a few times to get the desired results because it’s not a simple w/kg calculation.

Ideally it sounds like you need Zwift to create a separate “handicap” option to equalize riders of different abilities. It would be good to see that happen for racing purposes too. But it won’t happen so I wouldn’t hold my breath waiting.

Just seeing your post made me wonder if it’s possible for racers to change their height on the fly in Companion app, reducing it in the start pen and then changing it back to normal just before the race end?

This should have been stopped as it was the issue Luciano called out and got shadow banned for.

Riders weight & height should be locked once in the pen post the fix applied… plus it should show in ZP if it changes.

Though, the amount of bugs that reappear who knows if it is currently blocked and if it will remain that way.

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It’s been suggested before, that is, the idea of a speed bias setting that would allow your speed to reflect a power value less than you’re really exerting (but not more). Basically a way to handicap yourself so you could go as hard as you want in an event that would otherwise be too easy for you.

Did you miss this?

Bad recollection it seems, I thought it was all about weight changes during races, not height changes too.