Increase chainline with spacers?

[Nics]

I want to increase the front chainline. Using a longer axle is not an option (because I already have that longer axle). What's also not an option is to put spacers between the spindle and the chainrings because it's "direct mount" (the big and small rung and the spindle are all one CNC'd piece).

So Im asking myself whether I could use spacers to increase the front chainline and by how much I could increase the chainline this way.

I have a Rotor Aldhu 2x crankset (30mm axle diameter). Rotor sells a spacer set but I don't know whether that is to fine tune the chainline or whether it is for "filling gaps" (I don't know what that means but it is hinted at here: https://rotoramerica.com/products/m...JgKGRf8rESrc8rJ_sFXzltts-Whlm_uNsrbwKrora-NQi).

I also heard that the amount of spacers might interfere with the preload which sounds a bit like increasing chainline is limited by how much the spacers impact preload.

(min 2m50sec) seems to indicate that I could use spacers between the frame and the bottom bracket. True? Does that have any downsides? And how much chainline increase could I get this way?

 

[BikeGremlin]

I want to increase the front chainline. Using a longer axle is not an option (because I already have that longer axle). What's also not an option is to put spacers between the spindle and the chainrings because it's "direct mount" (the big and small rung and the spindle are all one CNC'd piece).

So Im asking myself whether I could use spacers to increase the front chainline and by how much I could increase the chainline this way.

I have a Rotor Aldhu 2x crankset (30mm axle diameter). Rotor sells a spacer set but I don't know whether that is to fine tune the chainline or whether it is for "filling gaps" (I don't know what that means but it is hinted at here: https://rotoramerica.com/products/m...JgKGRf8rESrc8rJ_sFXzltts-Whlm_uNsrbwKrora-NQi).

I also heard that the amount of spacers might interfere with the preload which sounds a bit like increasing chainline is limited by how much the spacers impact preload.

(min 2m50sec) seems to indicate that I could use spacers between the frame and the bottom bracket. True? Does that have any downsides? And how much chainline increase could I get this way?

Hi Nics,

That's a good question. I've discussed that in the video linked below.

If you swap spacers from left to right (and vice-versa), without adding or removing any spacers altogether (completely), you can get the optimal crank arm engagement, as the total stack width remains the same.

Just, keep this in mind:

• For systems with a front derailleur, moving the right chainring too far out or too close in can make it impossible for the front derailleur to shift properly (it has a limited range of motion outwards and inwards).
• Crank arm (and hence pedal) symmetry will be affected (the right pedal may be further out from the frame's longitudinal axis compared to the left pedal - and vice-versa, depending on which spacer is moved to the opposite side). This is nothing you notice when riding so unless it's extreme (5+ mm) it should not be a problem, but worth checking just to be sure.
• Make sure that cups have enough engagement (I would say at least 7 mm of thread engaged - but I haven't measured it yet to give 100% exact numbers).

Relja

 

[Nics]

Hi Nics,

That's a good question. I've discussed that in the video linked below.

If you swap spacers from left to right (and vice-versa), without adding or removing any spacers altogether (completely), you can get the optimal crank arm engagement, as the total stack width remains the same.

Just, keep this in mind:

• For systems with a front derailleur, moving the right chainring too far out or too close in can make it impossible for the front derailleur to shift properly (it has a limited range of motion outwards and inwards).
• Crank arm (and hence pedal) symmetry will be affected (the right pedal may be further out from the frame's longitudinal axis compared to the left pedal - and vice-versa, depending on which spacer is moved to the opposite side). This is nothing you notice when riding so unless it's extreme (5+ mm) it should not be a problem, but worth checking just to be sure.
• Make sure that cups have enough engagement (I would say at least 7 mm of thread engaged - but I haven't measured it yet to give 100% exact numbers).

Relja

I watched the video. Can I conclude from your video, that you can increase the chainline by 2.5 mm while keeping the pedal symmetry? Does that also apply to my crankset?

My Rotor crankset allows to separate both cranks from the chainrings (not like with the Shimano in your video where the chainrings are permanently attached to the left crank). Does that make a difference?

 

[BikeGremlin]

I watched the video. Can I conclude from your video, that you can increase the chainline by 2.5 mm while keeping the pedal symmetry? Does that also apply to my crankset?

My Rotor crankset allows to separate both cranks from the chainrings (not like with the Shimano in your video where the chainrings are permanently attached to the left crank). Does that make a difference?

Pretty much. Let me explain it in a bit more detail (with the important nuances), just to be safe.

For Hollowtech II (and similar) cranks, there is some room to go wider or narrower in terms of total shell + spacers + cups width (I discuss that in the section "How to check if it's all good" at about 24 to 27 minutes).

The total "wiggle" room is about +-2 mm from the middle setting so to say.

If you want to keep the symmetry unnafected, you can add one 2 mm spacer on each side, and end up with a 4 mm wider setup in total.

A more realistic scenario is that when you set it up as "default recommendation", your left crank will be close to the middle of the "wiggle hole" (as shown in the above- mentioned video section). So, you will only have a max of about 2 mm room for increasing width (i.e. you'll have room for only one 1 mm spacer on each side max).

On the other hand, if you forfeit the exact symmetry (or if the "default setting" puts the left crank further out compared to the righ crank), then you can add about 2 or 2.5 mm of spacers only to the right hand side (the engagement hole is there to let you know if the total width is too narrow or too wide for proper left crank engagement and preload).

Relja

 

[Nics]

One feedback: your YouTube video is great but people who are looking for ways to adjust their front chainline with spacers won't find it. If the video had the word "chainline" in it, it would be more valuable because more people would find it.
And it seems that your advice not only applies to Shimano Hollowtech, right?

 

[BikeGremlin]

One feedback: your YouTube video is great but people who are looking for ways to adjust their front chainline with spacers won't find it. If the video had the word "chainline" in it, it would be more valuable because more people would find it.
And it seems that your advice not only applies to Shimano Hollowtech, right?

Thanks for the suggestion - I've edited the title and the video's description.

Regarding the advice: I try to make it as universal as reasonably possible, without ommiting to note any important specifics (gotchas, caveats).