I don't have it memorized, but it's in the dealer manual on Shimano website

 

One on the drive side is normal.

 

Yes, one 2.5mm spacer on the driveside for 73mm shell widths.

68mm shells require all three, one spacer on each side plus the 2.5mm driveside spacer.

 

Yes, one 2.5mm spacer on the driveside for 73mm shell widths.

Thanks for confirming! What I find strange is that the recommendation seems to focus solely on shell width but doesn't mention rear spacing, say 135 mm vs 148 mm.

73 mm shell and 148 mm spacing should logically need to push the chainring 6.5 mm (148-135=13. 13÷2=6.5) further out to center the chainring on the cassette.

Or is this extra needed offset handled by the crankset?

 

BB width and rear hub width are unrelated. There are no boost-BB-s.

Cranksets or chainrings are different for boost and non-boost wheels.

And one correction to your math. 135mm hub is quick release type. Same hub in thru axle configuration is 142mm. So the difference in chainline between boost and non-noost is (148-132)/2=3mm.

 

Cranksets or chainrings are different for boost and non-boost wheels.

the difference in chainline between boost and non-noost is (148-132)/2=3mm.

Thanks for setting facts straight!

 

When all is fitted correctly as recomended the actual chainline quoted for your crankset will be accurate at 52mm.

Thanks! But I just noted something. This fc-m7000-11-b1, which I thought was a 1x crankset, actually has mounting holes for two chainrings. Only one of them can accurate for 52 mm chainline. As someone noted in another thread:

it has two sets of holes which is why i am confused. it is the asymmetrical 96/64 bolt pattern. the spec for the crank only lists the 96, but it has holes for the 64 too.

Someone replied:

You would get much better chainline with 64BCD chainring.

Can that really be correct? I bought a 32t 96 bcd chainring for it. If it is correct I guess I should remove the single 2.5 mm spacer on the drive side to move the chainring further inwards.

EDIT: OP reported back that:

1. the slx 1x crankset still has two sets of bolt holes. not sure why, but confirmed this is the case at the bike shop. so the crankset i received is the correct crankset.
2. further research, even with the 1x, the chainring is not centered. its between cog 5 and 6, not on cog 6.

But I don't know if that was a boost spaced bike with 73 mm BB shell.

 

Thanks! But I just noted something. This fc-m7000-11-b1, which I thought was a 1x crankset, actually has mounting holes for two chainrings. Only one of them can accurate for 52 mm chainline. As someone noted in another thread:


Someone replied:


Can that really be correct? I bought a 32t 96 bcd chainring for it. If it is correct I guess I should remove the single 2.5 mm spacer on the drive side to move the chainring further inwards.

EDIT: OP reported back that:


But I don't know if that was a boost spaced bike with 73 mm BB shell.

m7000/m8000 used the same crank for 1x and 2x. there is no difference. b1 is boost spacing, which is in the crank, vs offset in the rings.

 

I have the manual on my phone to use asap, Chris king follow Shimano spacers for xtr m9120

 

Mine also has another set of 64bcd bolt holes too. It's definately a 49mm (technically 48.8) chainline based on the 96bcd chainring mounting point. I also measured it as accurately as I could with a digital vernier gauge.

I'm running this on a 148 Boost bike because it slightly favours the low end of my 11 speed cassette more.

52mm is basically the 'safe' standard chainline for Boost bikes so there's no worries about chains hitting wide tyre shoulder knobbles or chainring teeth clearance on slightly wider chainstays for Boost frames.


Newer style direct mount Shimano cranksets also share the common 52mm Boost chainline which they state is still suitable for both Boost and non Boost bikes.

Again the shell width is irrelevant because a 68mm shell has one 2.5mm spacer on each side to effectively make it 73mm plus one 2.5mm driveside spacer anyway.

You could put the driveside spacer on the non driveside instead to alter chainline but that obviously offsets the whole crankset rather than just the chainring.

 

Someone replied:

...

Can that really be correct? I bought a 32t 96 bcd chainring for it. If it is correct I guess I should remove the single 2.5 mm spacer on the drive side to move the chainring further inwards.

That someone was me 49mm chainline for non-boost and 52mm chainline for boost are both wider than the center of cassette. For more clearance on tires and chainstays. I was running 45mm chainline on non-boost frame with good results. I rarely needed the 11t cog, but used the 46t a lot.

The problem with 96/64BCD Shimano cranks is that the bolt holes are not at 90 degrees to each other. There are very few 64BCD narrow-wide chainrings with such bolt pattern. IIRC I found one manufacturer that made smaller round chainrings that fit and non made oval. So you are stuck with 96BCD chainrings.

You can try to put the spacer on the non-drive side and see if the chain clears the chainstay and tire. It will give you are better chainline. On my new bike it didn't and I'm running 52mm now.

Newer style direct mount Shimano cranksets also share the common 52mm Boost chainline which they state is still suitable for both Boost and non Boost bikes.

This is a lie from Shimano side. 52mm chainline on non-boost is horrible. Fortunately Garbaruk makes direct mount Shimano chainrings with increased offset for non-boost bikes. Great company.

 

Arnea, yes, it's a lie that's why my next crankset will probably be an M7100 with an aftermarket 6mm offset chainring if I can't source old style non Boost crankset for sale in future.

 

Your Apex 1 derailleur will work horribly with a 2x.

Gotcha!

Yes it's a "lazy solution".

Thanks for confirming their laziness.

 

Thanks for confirming their laziness.

Not lazy at all. Intelligent. Why make special cranks for 1x. That's stupid. Direct mount at that time was also still a gamble. Remember shimano had done direct mount all the way back in 1996 but gave up on it by the 2000s. To them it made much more sense to stick with tried and true integrated spiders when they were still expecting people to run 36, 38 and even 40 t rings in both 1x and 2x. With 12s and then 29er becoming norm that all changed and people rarely run larger than 32t. 2x was now almost entirely gone so direct mount made the most sense.

When looking at the decisions of shimano (moreso than sram) you need to remember that the needs of niche mountain biking in general are a TINY fraction of their business. They have to be ultra conservative when it comes to any new trends as product development takes year, or even decades to perfect. Once that niche becomes a clear mainstream direction, they will jump on.

 

Diameter of 28t chainring is too small. Mounting bolts would interfere with teeth.

If you are heavy and weak then you sure need 26t and 28t chainrings Not a common thing though.

 

I have an older Shimano manual that contains requirements for the frame builders. It has this diagram:

According to Shimano 92mm bb shell is asymmetric and 89.5mm is symmetric. With 2.5mm spacer on later both are asymmetric. Cranks are built with opposite asymmetry so that crankarms on both sides are same distance from the bike center.

 

I have an older Shimano manual that contains requirements for the frame builders. It has this diagram... According to Shimano 92mm bb shell is asymmetric and 89.5mm is symmetric. With 2.5mm spacer on later both are asymmetric. Cranks are built with opposite asymmetry so that crankarms on both sides are same distance from the bike center.

Very interesting. Looks like I was wrong about the BB shell always being symmetric. This also explains why my 89.2mm BB shell was symmetric when I measured it.

Looking at the diagram, the 89.2mm BB shell is symmetric, so the spacer will offset the BB by +2.5mm on the DS. Consequently, the DS crank must be offset by -2.5mm to keep everything centered.

On the other hand, there is no spacer on the 92mm BB shell. To compensate for the cranks being offset by -2.5mm, that must mean the 92mm BB shell is offset by +2.5mm on the DS.

So confusing... What happens if you use a non-Shimano crank? Will that throw everything out of wack?

 

Thanks. I had been trying to find that fricken thing, haha.

And to the question of why the spacer even exists: it is to allow adjustment for the edge cases where your frame is not built in the "standard" way shimano expects - either on purpose, or because of sloppy QC.

 

Bike build OCD kicking in… What currently available boost cranksets from Shimano does not have an extra (unadvertised) chainring that causes an offset in relation to the cassette?

Preferably compatible with my 4 bolt SLX FC-M7000-1 SM-CRM70 chainring. But not a huge deal if I need to go direct mount. I’m preferably looking at the cheaper end of the spectrum (Deore, SLX).

What seems to be Shimano’s plan going forward? Phasing out 4 bolt? They still seem to be selling cranksets with it.

 

Preferably compatible with my 4 bolt SLX FC-M7000-1 SM-CRM70 chainring. But not a huge deal if I need to go direct mount.

I used the SLX M7000-1 crankset and a Wolftooth Shimano-compatible chainring for a 1x12 conversion. Shimano claims the chainline is 50.4 mm, and that's just about where I measured it. This was on a non-boost frame.

To tweak the chainline inboard, I switched my 2.5mm BB spacer to the NDS. This has worked just fine. Another alternative would have been to add some 2.2mm spacers to the chainring bolts. You can find these in bags of 4 or 5 spacers if you look around, for example here.

 

I thought this was covered already. The is NO offset. A shimano 11s 1x ring will be in the right spot for 1x. A shimano 2x 11s ring will be in the right spot for 2x. There are no aftermarket cranks that use the shimano asym bolt pattern, and even if there were, they would be identical.

4 bolt was phased out like 6 years ago when 11s was phased out of the higher end groups. 12s uses direct mount as does deore 11 and 10.

 

I thought this was covered already.

Sorry, I have some trouble following all the windings in this rabbit hole!

A shimano 11s 1x ring will be in the right spot for 1x.

You’re saying the SLX FC-M7000-1 SM-CRM70 1x11 speed chainring should be centered in relation to the cassette with the SLX FC-M7000-11-B1 crankset? Visually it doesn’t look like there’s any inward offset to center this 96 bcd chainring between the 96 and 64 bcd chainring mounting points, so to speak.

The following post seems to support that:

1. the slx 1x crankset still has two sets of bolt holes. not sure why, but confirmed this is the case at the bike shop. so the crankset i received is the correct crankset.

2. further research, even with the 1x, the chainring is not centered. its between cog 5 and 6, not on cog 6.

 

chainring should be centered

I said correct chainline. It should not ever be centered. It is always bIassed outward. As the other guy says, its sorta a floating variable subject to some debate, but one thing it never is is on centre with the cassette.

 

"Standard" chainlines (49mm for non-boost, 52mm for boost) have never been centered on cassette. They have always been little bit outwards. Also, for 2x cranks the "chainline" is defined as average of two chainlines - on small and big gear. Chain is never on that position in reality. I would say that there is no such thing as "correct" chainline. Some chainlines improve performance on big cogs, some on small ones, usually there are technical limitations how far inboard you can go. Pretty desperate situation for OCD people I would say

If you are looking for 24mm spindle cranks my recommendation is Shimano SLX 7100. It is most futureproof, comes also in 165mm crank length, same weight as XT, but cheaper. Shimano provides you with 52mm, 55mm and 56.5mm chainline options. Garbaruk makes offset chainrings that allow to reduce it by ~3-3.4mm, so with 52mm cranks you will get decent chainline for non-boost frames as well.

Raceface Aeffect R is another good option - same weight as SLX, direct mount. I haven't checked it, but I believe that chainring availability for Cinch interface might be better. I.e. chainrings with bigger offset etc. With Shimano direct mount you are at the mercy of Garbaruk if you want smaller chainline. They are great company though and seem to do well so I personally do not worry about this.

 

If you are looking for 24mm spindle cranks my recommendation is Shimano SLX 7100. It is most futureproof, comes also in 165mm crank length, same weight as XT, but cheaper.

Thanks for the recommendation! Gotta say their take on “direct mount” is interesting. The chainring does not seem to mount directly. Now we have eight screws instead of four (like it used to be) and a direct mount interface. 😄 I understand I could get a Garbaruk ring that is truly direct mount… But still!

 

I would say that there is no such thing as "correct" chainline. Some chainlines improve performance on big cogs, some on small ones, usually there are technical limitations how far inboard you can go. Pretty desperate situation for OCD people I would say

its sorta a floating variable subject to some debate, but one thing it never is is on centre with the cassette.

Argh! Thanks for your teachings y’all! I accept defeat, but I’m also interested in why it wouldn’t/shouldn’t be centered. The most stressed position on the cassette with my derailleurs has been the largest 46t cog. Seems it wouldn’t be easier to get a clean use of that cog if the chainline is outside of the center of the cassette. Is it a tire clearance thing?

 

Because that's actually the least likely to derail from being off axis.
The geometry of these things are very carefully thought out.