Zwift and Flux2 - not communicating correctly?

General Discussion
1

Hi

I sure could use some help.

I’m not sure my Flux 2 and Zwift are communicating correctly.

Let me explain

I’ve been a cyclist for many many years

I ride indoors regularly.

Details:

  • I originally had a Magura mag trainer (certified by Zwift) and hooked up to Zwift.

– I felt the numbers I was receiving in Zwift were correct (speed, effort, HR, Watts)

  • So one day I went and biked up Alpe D’huez (the one in France) – I did it in XX minutes

  • Shortly after I returned home I did Alpe D’Zwift – I did it in almost the same amount of time

  • I then took a friend to Alpe D’huez and we did it in YY minutes (fun ride - not a race ride)

  • Shortly after I returned home I did Alpe D’Zwift and I did it in XX minutes again

Then - my significant other gifted me a Flux 2.

  • I did all the normal setup things

  • I then decided to try Alpe D’Zwift to see if there was a difference… this is where it all went south.

— I couldn’t complete the climb. seriously, I could barely move the cranks. I think my cadence was something like “03”

— I must not have calibrated it correctly, so I calibrated it, and calibrated it again and…

— I tried it again, I made it 1/2 way and couldn’t do it - I was soooo exhausted there was no way I was going to complete the ride

Recently I found a setting in the app for something like - resistance level. settings are “off” to “max”

So I turned the Resistance to “off”

  • I tried Alpe D’Zwift with this setting - I was able to make it to the top in 2 times XX

If that’s not enough, another thing recently happened

  • I adjusted the resistance level to 75%

  • I joined a workout

– the workout was going to do some FTP stuff.

  • At some points in the ride the ride leader said to do a cadence of 95, The best I could do was 30. Seriously 30.

  • Then at another point in the ride we were going downhill at “-4%” and again, I could only do a cadence of 40. It was SOOOOOOO hard that I felt like I was going uphill of 22%

  • Additionally, my avatar kept up with the group and told me I was riding at 23mph. How in the world could I be doing 23mph when only doing a cadence of 30 and it felt like I was climbing a WALL.

Anyway

I have since turned off the resistance again – I just can’t push that hard for any length of time.

I have calibrated the unit almost every ride and I get the same results.

OH - and the kicker is:

  • I know my outside Watts are XYZ

  • On the Magura connected to Zwift my watts were similar (not exact but similar)

  • once I got the Flux2 - my watts dropped by 65%

  • my outside / on the road watts are still at XYZ

  • It might not seem like a big deal but i’m now in Category “D” and struggle seriously struggling to complete the races.

For extra info:

  • The summer before receiving the Flux 2 I had an opportunity to do some training throughout the alps in Italy, Switzerland and France. So I know what a “hill” feels like.

Thanks for listening - Any suggestions / recommendations are much appreciated.

My setup:

  • Flux 2 communicating to iPad (current ios)

  • App on iPad should be most current

  • Ipad within reach when on bike

  • I’ve used this setup in different places (my current apartment, my previous apartment, and my basement, and a garage).

  • I have used it using Cell service, and Wifi and a very very strong Wifi.

  • Used 2 different bikes, Gravel with compact crank setup and a Road bike with standard road setup.

My background:

  • I’ve gone through multiple wind trainers and a few mag trainers and rollers

  • I used and owned multiple computrainers

2

Hi @Jam_Jamboree welcome back to Zwift forums.

Shuji at Zwift HQ here. Your experience moving from a mag trainer + speed sensor setup to a smart trainer with an inbuilt power meter is 100% understandable. As far as I can tell by looking at your server logs - your trainer is communicating to Zwift as expected.

The speed sensor method is using an estimated power curve, and not measuring your actual watts you’re putting out. That estimated power is far less accurate, and almost always estimates rather higher than actual. A 65% drop sounds like a lot, but not if you see my comment below about your FTP being set in the 400’s.

With a mag trainer where resistance is manually controlled, you will not feel resistance change automatically. The time you set on a route like Alpe du Zwift with 7% - 14% pitches will not be the same once you switch to a controllable smart trainer that makes you feel those hills.

Your FTP is currently set in the mid-400’s, probably because you had been using an inaccurate classic trainer setup. An FTP number that high is appropriate for an elite pro racer. Think about that when a warmup for pros feels like hitting a wall to you.

Manually adjust your FTP much lower - say 100 - and try the same structured workout. That might be way too easy, and if so - bump it up by 20 until you can those wattage targets feel challenging, but doable. Then - consider taking an FTP test that will measure your current level of fitness more accurately. I recommend The Grade - the most fun doing something that’s inherently challenging.

Welcome to the world of training with power. I started indoor training on turbo trainers and rollers in the `80’s . Doing structured workouts in ERG mode will help you learn for example that 100 watts is an easy spin, you can hold 120 all day, 250 for 5 minutes, and so on. Everyone’s numbers will vary as you gain or lose fitness, but if you pay attention to what your power output feels like, you’ll be better served than worrying about your average speed in game in a certain gear combination, or how much time it takes to cover X distance in Zwift vs outdoors.

3

Thanks for the feedback.
Here is what I did today. I set my FTP to 100, I then set the resistance level to about 75%.
I then chose to ride up Alpe D’Zwift. It was very hard, so about 15min in I changed the resistance level to about 50%, still at that I did not make it to the top. I turned around at about 1hr and I still had 3ish miles to go.

You mentioned an FTP of 400 is for an elite pro athlete — Yup.

I get that the mag trainer is not exact, however Zwift “certified it”.

Can you help me explain this one:
I can ride Alpe D’huez in XX min
On my mag trainer I almost match the time on Alpe D’zwift
On the Flux2 it takes me twice as long to climb Alpe Dzwift, and like today - I gave up with 3miles to go after I reset my FTP to 100 and set the resistance to 50%.

I appreciate that the logs are showing all is communicating, however - there is something going on.

4

Do you have this ride recorded on Strava to show your VAM and you can calculate the Power you did…why use XX just write the time it took you to do it.

5

I do not use strava (not regularly).
Exact time – no need for exact time, It will only get people distracted from the question.

6

Was this a free ride, or did you do a workout in ERG mode?

Changing your FTP value in Zwift has no effect on free rides and is only used by workouts. In workouts you don’t feel the gradient because your workout is determining the power target and the trainer sets the resistance based on your cadence in order to meet that power target.

I assume this was a free ride, since changing Trainer Difficulty (which is only for free rides, and affects the gradient that you feel but not your speed up that gradient) seems to have made a difference.

7

YES - Free ride.
you said <>
my thoughts: that’s exactly what I thought. That’s a leading reason I’m so confused by the issue I’m having.