The Ultimate SB20 Troubleshooting Guide

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Here are the most common SB20 problems based on Stages support postings and social media:

  1. Power Meters
  2. Wireless Connections (Mostly Zwift and Stages Cycling app)
  3. Resistance Issues
  4. Drive Belt (Tension and Alignment)
  5. Shifter Buttons
  6. Clicks and Noises
  7. Flywheel Concerns
  8. Crank Smoothness
  9. Settings and customizations
With this list in mind, here is my summary covering the most common problems I have helped people resolve since 2021.  

See the FAQ for additional details on how this list was compiled.

YOUR FEEDBACK IS REQUESTED 

If you have additional information or experiences, please share in the comments.


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SB20 TROUBLESHOOTING


This section lists 21 different problem descriptions with links to common causes and suggested solutions.

1. Sudden Drop in Resistance


Resistance is normal until more power (force) is applied.  Resistance suddenly reduces - sometimes to zero.

Possible Causes

See SB20 - Resistance Failure for a discussion of related problems. 

2. Power Readings are Wrong

Power readings are too low for a given effort.  Speed in Zwift is slower than it should be.

Possible Causes

The most common issue is batteries.  See Stages Power Meter Battery Tips. 

🔬 Related: Nearly depleted batteries can affect readings. Surprise!  It is not as bad as you might think.  See Batteries and SB20 Power Meters.

Your power meters may need to be calibrated. See SB20 - Measuring Torque Against Factory Specifications and Comparing Power Meters with ZwiftPower.

⚠️ Power meter failures do happen. Keep in mind, both rarely fail at the same time. It is important to isolate failures. The SB20 works flawlessly with a single power meter. Don't assume both are broken. See SB20 - Power Meter Failure.  


3. 100% Resistance / Shifters Don't Work

Start pedalling. Resistance suddenly rises to maximum and stays there. Shifting gears often does not change things. Resistance stays at 100%


Possible Causes

See SB20 - Resistance Failure for a discussion of related problems. 

There is a small chance that your shifters are having issues. See SB20 - Shifter Failure.
  

4. Can't Connect to Zwift (or other apps)

The Stages Bike is not shown for Cadence, Power Source or Resistance. Power meter cranks may or may not be shown if you start pedalling.

Possible Causes

Wireless network interference can affect connections to apps like Zwift or the Stages Cycling app. See: Better Wireless Communication 👈 and SB20 - Dropping Connections!

Zwift has bugs that prevent some SB20 riders from connecting. See SB20 Not shown in Zwift and SB20 - Can't Connect to Zwift.

Turning your bike off regularly can also help.  See SB20 - Won't Connect with Wireless!.

Worst case ☹️ : The Upper PCB controls communication. It may have failed . See SB20 - Upper or Lower PCB Failure.


5. Data Dropouts


Speed and movement in Zwift suddenly stops and then occasionally returns. Blocks of data in associated .fit file are missing.

Possible Causes

Wireless network interference can affect connections to apps like Zwift or the Stages Cycling app. See: Better Wireless Communication 👈,  SB20 - Dropping Connections! and Indoor Riding - ANT+ and Bluetooth.

Turning your bike off regularly can also help.  See SB20 - Won't Connect with Wireless!.


6. Resistance is Erratic

Start pedalling. Resistance suddenly rises and falls randomly. Shifting gears still works.

Possible Causes

Here are some basic resistance debugging tips: SB20 - Bike Resistance Issues.

The controller boards in the SB20 manage resistance changes - particularly when using apps like Zwift .  The Upper and Lower PCBs both play a part. See SB20 - Upper or Lower PCB Failure.

The optical sensor in the flywheel occasionally fails. See SB20 - Flywheel Bearing Replacement > Optical Sensor. 


7. Poor Shifting Performance 


Some shifter button presses are missed. Some single presses result in multiple gear changes. Could also include: some buttons no longer work.   

Possible Causes

Misbehaving and broken shifter buttons are common. See SB20 - Shifter Failure.


8. Clicking Noises 


Clicking noises are a common complaint.  This includes clicks and grinding noise that occur when pedalling or coasting.

Possible Causes

There are many culprits. See SB20 - Clicking and Rubbing Noises. 


9. Stages Bike Not Shown for Resistance in Zwift



The Stages Bike is shown for Cadence and Power Source on the Zwift Paired Devices page.. It is not shown for Resistance. The power meter cranks may or may not be shown when you start pedalling. The bike works fine with the Stages Cycling app.

Possible Causes

 Zwift has several long-standing bugs that occasionally prevent SB20 riders from connecting.  See SB20 Not Shown in Zwift and  SB20 - Can't Connect to Zwift. 



10. Loud Clunking Noise when Sprinting Hard



Loud clattering or clunking noise when doing hard sprints.  Power levels are suddenly lower than expected

Possible Causes

Most common: Your drive belt is loose and jumps cogs. It needs to be adjusted. See SB20 - Drive Belt Adjustments (2025).  

Your drive belt could also have missing teeth or small tears that will lead to complete failure. See SB20 - Drive Belt Replacement.

You could also be suffering from minor noises related to other components.  See SB20 - Clicking and Rubbing Noises.


11. Whistling Noise when Coasting 


When pedalling in a moderate gear, everything feels right.  You hear a slight electronic whistling / whining noise when coasting. It stops as the flywheel slows down.

Possible Causes

✅  This is normal! It is the SB20 electronic brake doing it job. 

🔬 You may not hear this these electronic sounds because flywheel noise drowns it out. If so, you could be experiencing early flywheel bearing issues. See SB20 - Flywheel Bearing Failure

 

12. Flywheel Grinding and Clicking Noises 

The flywheel should be silent. As the flywheel ages, you may hear slight grinding noises. You may also feel increased vibration and rumbling. You may be detecting higher flywheel heat than in the past.   

Possible Causes

If rumbling is connected to pedalling only, it could be a poorly adjusted drive belt.  See SB20 - Drive Belt Adjustments (2025).  

Worst case ☹️ : Flywheel bearings could be beginning to fail. See SB20 - Flywheel Bearing Failure. 


13. Erg Mode is Erratic


Erg mode is a special bike function that keeps power constant no matter how fast you pedal.  Here's a description of how it works: What is Erg Mode and Why Can it Suck?

Hitting power targets for efforts less than 30 seconds do not necessarily work on the SB20 as many riders expect. Longer efforts should be smooth with accurate regulation of power,

Possible Causes

When Erg mode is not smooth, it can point to a power meter problem. See SB20 - Power Meter Failure.  

The controller boards can also be responsible for poor Erg mode behavior.  See SB20 - Upper or Lower PCB Failure.


14. Nothing Moves in Zwift


Rider does not move in Zwift. No power readings are shown. No movement is detected.

Possible Causes

Zwift has bugs! Make sure you restart Zwift and your SB20 regularly.  See On/Off switch & Wireless Charger,  SB20 - Restart and be Happy and SB20 - Won't Connect with Wireless!.

Review how you are connecting to Zwift: SB20 - How to Pick a Zwift Power Source

Power = Speed in Zwift.  A power meter could be misbehaving. See SB20 - Power Meter Failure.  


15. No Resistance, No Shifting - Bike Seems to be Dead


Nothing works. The bike appears to be dead.

Possible Causes

Shifter button failures can cause the SB20 not start up. See SB20 - Won't Connect with Wireless!.

Checking Power Supply is a good idea. See SB20 - Power Supply Failure.

Worst case ☹️ : The Upper PCB controls main bike functions. It may have failed . See SB20 - Upper or Lower PCB Failure.

 

16. Metallic Scraping Noise when Pedalling

Your hear a metallic scraping noise near the flywheel. Only when pedalling. 

Possible Causes

The drive cogs can rub against one of the cover fasteners. See SB20 - Clicking and Rubbing Noises. 


17. Flywheel Gets Very Hot After only a Few Minutes


Flywheel heat is normal.  You have noticed it is higher than normal.

Possible Causes

Excessive heat is a sign of early bearing problems. See SB20 - Flywheel Bearing Failure. 

  

18. Cannot connect to Zwift but can connect to Stages Cycling App 


The SB20 is not shown on the Zwift Paired Device pages. You cannot connect. You can connect to the Stages Cycling app.

Possible Causes

This rules out Upper PCB problems. You are likely experiencing one of the Zwift bugs that affects the SB20.  See SB20 Not shown in Zwift and  SB20 - Can't Connect to Zwift.

Turning your bike off regularly can also help.  See SB20 - Won't Connect with Wireless!.


19. PC / Mac No Longer Connects 


You can no longer connect to Zwift on a PC or Mac.

Possible Causes

Many PC/Mac riders use an ANT+ dongle.  It is worth trying to use Bluetooth if you are having issues.  Conversely, it is worth experimenting with an inexpensive ANT+ dongle if you are having Bluetooth problems. 


20. Grinding Noises near Cranks 

You hear grinding noises around the bottom bracket.

Possible Causes

Rumbling noises can be associated with a poorly adjusted drive belt.  See SB20 - Drive Belt Adjustments (2025) and SB20 - Drive Belt Replacement.  

Worst case ☹️ : The bottom bracket is starting to fail. See SB20 - Bottom Bracket Failure.


21. SB20 Configuration Keeps Changing 

SB20 changes keep getting lost. Cranks power meter change are saved inconsistently.

Possible Causes

Bike Settings are saved in the Stages Cycling app. Power meter settings are saved in the cranks themselves.  Here's how to save settings with greater reliability: SB20 - Saving Settings.


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Component Repair and Maintenance

This section describes how to improve or repair major SB20 components.

SB20 - Drive Belt Adjustments (2025)

SB20 - Bike Resistance Issues

SB20 Not shown in Zwift

SB20 - Can't Connect to Zwift

SB20 - Won't Connect with Wireless!

SB20 - Flywheel Bearing Failure

SB20 - Clicking and Rubbing Noises

SB20 - Power Supply Failure

SB20 - Upper or Lower PCB Failure

How to Pick a Zwift Power Source

SB20 - Drive Belt Replacement

SB20 - Shifter Failure

Better Wireless Communication

SB20 - Dropping Connections!

Stages Power Meter Battery Tips

Batteries and SB20 Power Meters

SB20 - Measuring Torque Against Factory Specifications

Comparing Power Meters with ZwiftPower

SB20 - Drive Belt Replacement











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FAQ

Frequently asked questions...

Q: Did you use AI for this list?

A: Sparingly. In addition to the problem list at the top of the page, I got a good list showing components that fail most often:
  1. Power Meters (Left/Right Cranks)
  2. Bike Control and Wireless (Upper PCB) 
  3. Shifters (Buttons and Wiring)
  4. Resistance Control System (Electromagnetic Brake + Lower PCB)
  5. Flywheel Bearings
  6. Wiring Harnesses & Internal Connectors
  7. Crank Bearings (Bottom Bracket)

The results from ChatGPT Pro, Google Gemini and Perplexity.ai were otherwise very poor. Some problem descriptions were OK but suggested solutions were downright awful. It appears the Stages SB20 is not well understood by AI.  

Answers often described problems and solutions related to smart trainers. Nuances, like built-in power meters and lack of worldwide Stages servicing after bankruptcy, were completely missed. Solutions like "do a spin-down calibration" or "align the moving magnets in the electronic brake servo-motor" were completely incorrect. 

In the end, I used the above AI services to get lists of problems and then used my own experience writing PedalSmart.Blog augmented by social media links and numerous on-line discussion threads.   

Summary: I used AI to get a ranked lists of problems. AI solutions for SB20 problems were TERRIBLE.  I used my own content for everything else.


Q: What do you think about Stages Support?

A: Stages support is excellent.  They offer good advice and will even sell replacement parts at a discount.  The problem is: the SB20 parts inventory is shrinking. Things like drive belts and PM battery compartment covers are no longer available. How long will other parts last? Your guess is as good as mine.

Stages support people are dedicated and knowledgeable. They respond to Support Tickets quickly. The information they share is invaluable. Unfortunately, Stages no longer offers service people to do repairs. We must do repairs on our own - or we must find people who can do the work.

My primary goal with this blog is to show SB20 owners that they can fix their own bikes. The work is not always easy.  With the exception of repairing crank power meters*, I have been able to service and repair every major SB20 component.

*Repairing power meters is not always essential. The SB20 has two of them. Both rarely fail at the same time.  The SB20 works nearly 100% with just a single power meter. Many people don't know this.


Q: Why does your bike need so many repairs?

A: It doesn't. Every repair I have shown since 2021 has been motivated by:
  1. I like to show people how to fix things. Maintaining and overhauling my bike has been driven by curiosity. I have never had a major component failure. I have enough confidence in the SB20 build quality that I am comfortable taking things apart just to see how they work. I am 99% certain I can put things back as good or better than before.

  2. I like to improve on designs when I can. I think components like the flywheel and shifter buttons have some limitations. I feel that things like moisture infiltration are a potential problem. I thought the lack of gear display was a big enough problem that I wrote my own GearView iOS App. 

    After owning my bike for several years, I continue to believe the SB20 is easy to fix.

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