1x11 Front Ring alignment

Oddjob

Merry fucking Xmas to you assholes
I spend so much time using a 2x setup on my commuter I rarely forget to drop to small ring.

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EsPeGe

Likes Bikes and Dirt
I've got the 46T shimano cassettes on both of my rigs and have had a 46T OneUp extender and generally not had this issue. The only times it did happen was when my cable tension wasn't right after a few months. I don't want to be patronizing but have you checked that all your teeth on the 46tT aren't damaged? A burr here or there would certainly cause that and that part of the cassette is pretty exposed. Also I've started to check my HiLo limit screws with the chain off the bike and no cable connected. I've found it is way more accurate way to get them set correctly. Again I'm probably telling you something you've already checked or know, if so please disregard.
 

mtb101

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so had some time to compare old bike with 1x11 11-46 and new bike, if you run a straight edge from front ring to rear cog, new bike hits cog 4 and old bike hits cog 5 (further up cassette), so there you go, that's the reason.

the new bike front ring alignment isn't hitting the cassette in the middle more to the outside and of course when in 46 the chain line is too extreme that back pedaling causes the chain to travel down cassette

now to remove the spacer from the press fit and move it over to the other side, maybe no spacer required, will see.
 

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EsPeGe

Likes Bikes and Dirt
so had some time to compare old bike with 1x11 11-46 and new bike, if you run a straight edge from front ring to rear cog, new bike hits cog 4 and old bike hits cog 5 (further up cassette), so there you go, that's the reason.

the new bike front ring alignment isn't hitting the cassette in the middle more to the outside and of course when in 46 the chain line is too extreme that back pedaling causes the chain to travel down cassette

now to remove the spacer from the press fit and move it over to the other side, maybe no spacer required, will see.
So how do you know you've got the straight edge parallel with the bike's centre line? I would think it's pretty hard to get it lined up? Are you eye balling or measuring from somewhere? I'm shortly setting up a new bike and knowing how you do this will be handy. The frame is boost but has a chainline of 50mm. The XT cranks I'm getting are 50.4 so I may have to space the chainring in .4mm. That said does anyone think .4mm will be an issue?

Cheers Scott.
 

schred

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Imo eyeballing the chainline relative to the sprockets and wheel is easy enough, the chain is nice and long and my eyeball error is less than the width of the sprockets so I'm confident i can tell which gear is most aligned with the chainring. Otherwise stringline off the chainring could work, but really you'd have to ask why.
 

mtb101

Likes Bikes and Dirt
So how do you know you've got the straight edge parallel with the bike's centre line? I would think it's pretty hard to get it lined up? Are you eye balling or measuring from somewhere? I'm shortly setting up a new bike and knowing how you do this will be handy. The frame is boost but has a chainline of 50mm. The XT cranks I'm getting are 50.4 so I may have to space the chainring in .4mm. That said does anyone think .4mm will be an issue?

Cheers Scott.
I clamp the straight edge (some alloy tube) onto the front ring and then of course see which cog it lines up with on rear, I have a cx 1,11, training bike 1,10, the old xtc 1,11 in pic, all fine when back pedaling, the trick is to hit the middle of the cassette when lining up the front ring. the one on new bike is just a bit out.
 

EsPeGe

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I clamp the straight edge (some alloy tube) onto the front ring and then of course see which cog it lines up with on rear, I have a cx 1,11, training bike 1,10, the old xtc 1,11 in pic, all fine when back pedaling, the trick is to hit the middle of the cassette when lining up the front ring. the one on new bike is just a bit out.
Yeah good idea, I'll give the clamp thing a go if I have any chainline related issues.

Cheers
 

mtb101

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when you're fangin it over all sorts of stuff, this test is a good start to know you have the alignment right. you want to hold the gear you've selected no matter what you're doing with your pedaling, etc.
 

mtb101

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update, I removed what looks like a 2.5 mm spacer from the drive side to the other side and what do you know, no chain crawling down the cassette when back pedaling when in 46, just shows sometimes the factory and the mechanic get it wrong, mechanic said that's how they are I knew it must have been the spacer. brand new bike and I don't like stuff not working how it should so now I just ride in peace.
 

goobags

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Without reading the whole thread, wouldn’t that effectively move your pedals to the non Drive side by 5mm as the entire crank has moved? Surely spacing the chainring itself is the way to do it


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mtb101

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so spacer was on the press-fit bottom bracket cup on drive side (between cup and frame), removing that moved the press-fit bb in by 2.5 which moves the front chain ring in by 2.5 which means the chain has less angle or a less extreme line when up in the 46, as you back pedal the lesser line means the chain won't run down the cassette.

the spacers needs to be there to maintain the overall width of the bb for the crankset so the space is the same overall just 2.5 over on the non-drive side.

hope that makes sense I've now got to convert these carbon wheels to tubeless, amazing how heavy the factory tubes are.
 

Nambra

Definitely should have gone to specsavers
Good to hear you got it sorted. I can recall both Giants I owned having that same spacer on the drive side too, although they were 2x10 setups with 11-36 cassettes, so chain drop in reverse wasn't an issue anyway.

I'm assuming your new bike is boost, with Shimano boost cranks? If so, the chain ring will already be 3mm further out, and the BB spacer adds another 2.5mm. Clearly too much offset for the extended range cassette.
 

mtb101

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^ yes that's right boost it is, bikes at 10.4 kg after going tubeless, (XTC Advanced 29er 1 2017) happy days.
 

The Duckmeister

Has a juicy midrange
Good to hear you got it sorted. I can recall both Giants I owned having that same spacer on the drive side too, although they were 2x10 setups with 11-36 cassettes, so chain drop in reverse wasn't an issue anyway.

I'm assuming your new bike is boost, with Shimano boost cranks? If so, the chain ring will already be 3mm further out, and the BB spacer adds another 2.5mm. Clearly too much offset for the extended range cassette.
The reason for the spacer is some frames have a 92mm wide shell, others have a 89.5mm shell (why? who knows), and the cranks are designed for a total bottom bracket assembled width of 96mm (92mm shell + 2mm flange on each bearing housing). Therefore a 89.5mm shell needs a spacer to fill the remaining 2.5mm, otherwise the cranks will float laterally. Traditionally the spacer has been fitted to the drive side in something of a throwback to threaded bottom brackets with outboard bearings which catered for the possibility of fitting a BB-mounted front derailleur or chainguide, so always had a spacer on the driveside in the absence of such an attachment. Given that a press-fit shell is too wide for such an attachment, it's less relevant which side the spacer, if required, goes on.

Boost spacing doesn't really come into play here. The extra 3mm offset at the chainring is to match the 3mm outboard offset of the cassette compared to a Q/R or 142mm T/A rear end, so the relative chainline remains the same, the whole lot is just shifted 3mm to the right. Coming back to a point I made earlier in this thread, the 11-sp. cassette is wider than 8,9 & 10-sp, with the extra width fiitted inboard. That results in greater chain deflection on low gear compared to an 8, 9 or 10-sp. drivetrain.
 

mtb101

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duck you work in the bike industry do Giant release advisories on this kind of stuff? if you have any new giants 1x11s in shop can you confirm they have spacer? just interested to know.
 
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