SB20 - Drive Belt Replacement

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SB20 drive belts don't break very often.  When they do, installing a new belt is quick and easy.

The most difficult task is finding a replacement a belt. 

The Stages web site no longer lists drive belts for sale.  Fortunately, standard Gates Manufacturing belts fit the SB20.


How to Replace

Here's the video.



SB20 Drive Belt Attributes

Here are the attributes of the SB20 drive belt:  

Tooth Shape: Curvilinear
Tooth Pitch: 8 mm
Tooth Count: 200
Pitch Length: 1600 mm (8 mm pitch x 200 teeth)
Belt Width: 9 mm
Tooth Depth: 4 mm
Belt Thickness: 7 mm

Orignal Manufacturer: Gates

The GT 8 mm tooth pitch means this is a timing belt and not a bicycle belt.  No big deal. Just don't look for bike belts.



The Gates catalogue shows no GT belt with 8 mm tooth pitch having a 9 mm belt width. This means the Stages OEM belt was a custom belt.

Closest match is a 12 mm wide belt. That's good.  A 12 mm belt fits comfortably in the 20 mm wide Stages drive cogs. 

Summary: A 12 mm wide drive belt fits the SB20. It will be more durable than the 9 mm OEM belt.  Just keep it aligned.


Understanding Gates Part Numbers

Here's how to decode a Gates belt part number.



Poly Chain GT is the name for the Gates product line described as 'Carbon-polyester belt with curvilinear tooth profile'.  GT Version 2 was used with the SB20.  A newer Version 3 has since been released. Version 2 and 3 are functionally compatible. 

Tooth Pitch is the space between teeth centers in mm. 8 mm is needed for the SB20.

Pitch Length is Tooth Pitch x Number of Teeth. The SB20 has 200 teeth. This means Pitch Length is 1600.

Belt Width is the belt casing width in mm.  A 9 mm wide belt was originally used with the SB20. 12 mm is the thinnest standard Gates belt width available for GT 8 mm tooth pitch.   

Gates Standard Belt Part Numbers

The following standard Gates belts are compatible with the SB20:

Poly Chain GT2 or GT3 denoted as 8MGT-1600-12 

If you can find a custom 8MGT-1600-9 or 8MGT-1600-10 belt, it will also fit. 

Other Manufacturers Equivalents

Other companies make compatible timing belts.

CONTINENTAL Conti® Synchrochain Carbon Timing Belt: Continental CTD-8M-1600-12

OPTIBELT ZR Timing Belt: Optibelt ZR-8M-1600-12

Ordering a Replacement Belt

Timing belts from Gates and other manufacturers are typically sold via independent suppliers and distributors.  Do a search by part number and verify that delivery is possible to your country.  

Here are some North American distributor links to get you started:



FWIW: I bought a Gates GT2  8MGT-1600-12 belt on eBay for $30.  See it in the video.

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Replacement Steps

Here's how to replace a drive belt.

Difficulty


Replacing the belt is fairly easy.  You will need to remove the flywheel.  That's the only tricky step.



I rate difficulty to be 5 out of 10.

 
Tools Required


  • 8 mm hex driver with extension
  • 7 mm hex socket
  • 14 mm wrench
  • 3 and 5 mm hex keys
  • Small Phillips screwdriver


Remove Covers




Remove the two non-drive side front covers and the main drive side cover.



Prepare Flywheel for Removal



Loosen the 8 mm vertical hex bolt

Slide the belt off the crank cogs.

Lower PCB and Brake Stay




Remove the four connectors and then the Lower PCB.

Remove the brake stay.


Loosen Axle Bolts



Loosen both axle nuts. You can leave the bolts and tensioners attached since we are only removing the flywheel to make room for belt replacement. 


Remove Flywheel



Support the flywheel.  I use a wooden board and towel.  See SB20 - Flywheel Cog and Axle Bearing Service  for more details.

Slide off the flywheel.

Replace Belt

You can now remove the original belt.



I am replacing the 9 mm wide custom OEM belt with a standard 12 mm belt.

Install New Belt


Insert the new belt and slide the flywheel into the frame



Align the tensioners on both sides of the axle.

Spin the new belt onto the crank cogs.

Brake Stay and Lower PCB



Replace brake stay and tighten its two hex bolts.

Replace the Lower PCB and its 4 connectors.

Adjust New Belt

See Stages SB20 - Drive Belt Adjustments (2025) for details on setting belt tension and alignment

Tighten Axle 



After completing belt adjustments, tighten the drive side axle nut followed by the non-drive side nut.

Tighten the vertical hex bolt.

See SB20 - Flywheel Cog and Axle Bearing Service  for more details.


Replace Covers




Replace the plastic covers.  See SB20 - Flywheel Cog and Axle Bearing Service  for more details.


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FAQ

Q: Why did Stages use a custom 9 mm wide belt instead of a standard 12 mm belt?

A:  Stages designers were likely concerned that poorly aligned belts would ride improperly on the crank cogs.



A thinner belt is less likely to hang over the edge of the cogs. 

🔬 This alignment error can happen if:

1. The frame was built outside of manufacturing tolerances (rare)
2. The flywheel has been serviced and reassembled incorrectly (hopefully rare).

If you do flywheel maintenance with care and take the time to align your drive belt, there should be no problems using any belt from 9 to 12 mm wide. 

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