Stages SB20 - Drive Belt Adjustments

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 STAGES SB20 DRIVE BELT ADJUSTMENT 

Stages includes belt adjustment tips in their support note on fixing SB20 noises:  Flywheel Making Noise. Several people have mentioned these instructions are incomplete. I’ll try to help.

I wish this process was easier. Good news: With practice, you can complete all adjustments in less than 30 minutes.



TWO GOALS

Adjusting the drive belt accomplishes two things:

  • Align the belt to ride as much as possible in the centre of the drive cogs. This reduces friction and positions the front axle perpendicular to the drive belt. Don’t be too worried about this step. The SB20 manufacturing tolerances aren’t perfect. Getting the front drive wheel roughly aligned and generally perpendicular is about all we can expect to achieve.
  • Get belt tension right. Optimal tension means quieter running and no slipping during hard efforts. For most of us, this is a trial-and-error process.You want tight but not too tight. For me, this is measured as a 1 cm deflection when pushing down hard near the front cog. More on this later.

SIMPLIFIED BELT ADJUSTMENT STEPS

Here is the simplest way I have found to adjust the drive belt without removing the side covers. 

Note: Removing the drive-side cover makes it easier to assess belt tension. These instructions don’t require removal of either side cover.

1. DRIVE-SIDE FRONT COVER REMOVAL



Remove the two forward-facing 3 mm hex bolts. Pull the front cover forward. 

Some enthusiastic wiggling while pushing toward the flywheel is often needed to get this cover to slide off.

2. NON-DRIVE-SIDE FRONT COVERS (2) REMOVAL


Remove the back panel first. Unscrew the two side-facing 3 mm hex bolts. Pull the front cover toward the back. 

Remove the front panel next. Unscrew the two side-facing 3 mm hex bolts. The lower bolt can be hard to reach (Hint: I don’t replace this bolt when reassembling). You may need to push fairly hard - up and to the left - to get this panel to slide off.

3. BELT ALIGNMENT



I do alignment first by moving only the drive-side half of the front axle. You want to get the belt to ride in the centre of the front cog as much as possible. Loosen the 14 mm axle bolt. Turn the front-facing 7mm nut clockwise to move the belt to the right. Turn the nut counter-clockwise to move the belt to the left. 

You may need to tap the axle nut with a mallet to encourage the axle to move backward (after a counter-clockwise turn). Leave the 14mm axle bolt loose for the next step

4. BELT TENSION


Tension is adjusted by moving both sides of the front axle together. 

Goal: You want the belt to deflect about 12 mm when pushing hard near the front cog. 

Loosen the 14 mm non-drive axle bolt. Both axle bolts should now be loose.

 ⚠️ You must also loosen the vertical 6mm bolt behind the non-drive axle bolt. 

Turn both front-facing 7mm nuts clockwise to increase belt tension. Turn both nuts counter-clockwise to reduce belt tension. You may need to tap each axle nut with a mallet to encourage both sides of the axle to move backward (after a counter-clockwise turn).

From the Stages support page:
"A loose belt will have a slack feeling when pedaling from stationary, and a too-tight belt will make a lot of ambient noise when pedaling hard. The tension of the belt can be checked by hand under the plastic belt guards. There should be about 1/2'' or 12-15 mm of deflection near the sprocket. Adjust this nut and check the feel of the bike until you are satisfied."

That’s it! The belt should now be aligned and properly tensioned. 

FINISHING UP

You must now:

  • Tighten both 14 mm axle bolts. I torque these bolts to around 50 nm. In other words, you push fairly hard. Stages says just 30 Nm. My axle slips when torqued that low. Industry standards for this size bolt are 50-90 Nm depending on steel used. Use your best judgement.
  • Tighten the vertical 6 mm bolt behind non-drive axle bolt. Torque is about 20 nm. For me, that is medium-tight.
  • Replace non-drive-side front cover followed by the back cover.
  • Replace drive-side front cover.


What do you think? Will you try doing this? 

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One more thing: Is a slack belt an advantage?

Answer: Yes - but only for other bikes!!!

Slack is not desirable or beneficial with the SB20 but is for most other indoor bikes. 

With smart bikes and trainers: You get easier pedalling for the same watts when you loosen the belt. That's because power is measured (estimated actually) at the flywheel. These bikes let you "cheat" by reducing drive train resistance after power has been estimated 🤷‍♂️.

The SB20 is different. Power is measured at the cranks. You are given credit for any additional drivetrain resistance by generating more watts. Slack or tight belt does not matter. You get the correct number of watts 🔬.

Comments

  1. BjörnNovember 6, 2023 at 9:45 AM

    Thanks for your effort putting together such a great post!
    I was wondering if you could help me with an issue here. After loosening the bolts I can pretty easy adjust so that I get, what I think, is a good belt tension. It's when I start tightening the bolts the issues starts. The non-drive side is no problem, but as soon as I start to tighten the drive side bolt the flywheel moves forward and tightens the belt tension again. Any hints on how to tighten the bolt and make sure the flywheel doesn't move at the same time. Any tips would be highly appreciated.

    Thanks!

    ReplyDelete
    Replies
    1. CraigNovember 16, 2023 at 8:38 PM

      Hey Björn. Try this.

      1. Get the tension correct with both axle nuts loose.
      2. On the non-drive side, loosen the front-facing retaining bolt by a full turn (counter clockwise).
      3. Tap non-drive-side axle with a mallet (described in post) to nudge the non-drive axle backward.
      4. Tighten non-drive axle nut.
      5. Tap drive-side axle with a mallet to make sure it has not moved forward.
      6. Tighten drive axle nut.

      Keep repeating 1-6 until tension and alignment is correct.

      Note about belt alignment: The drive cogs are not manufactured with super-high precision. Alignment can drift to one side after a day or so. This happens on my bike. I just settle with partial alignment but good tension.

      Delete

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