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Discussion Starter · #1 ·
I just installed a Wolftooth direct mount 34 on to my Scalpel 29er. The riding in my area tends to be made up of long climbs and long tricky descents so I spend a majority of my time in me two lowest cogs. I'm thinking that it makes more sense for my chain line to be optimized for those gears to reduce wear and friction when climbing. Seems to me that extra drag from a poor angle would be less of an issue in my 10 and 12 than my 36 and 42. Thoughts?
 

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That is exactly how I run my chain line. I just adjust chain line inward a few mm's, probably just short of one full cog inward. No scientific data to show that is when the most wear takes place, but that where all the grinding happens for me.
 

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Discussion Starter · #3 ·
Nice to have that confirmed. I have the bb30 short spindle version. The long spindle (GXP) version will push my chain ring 6mm inboard.
 

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Trail Tire TV on blogger
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6MM might be a bit much, but yes, moving inward will help make the drive train last longer if you use those gears the most/hardest.

just have to make sure your cranks don't hit the stays..
 

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Discussion Starter · #6 ·
Thanks guys. Rather than get a new ring with the 6mm difference I wonder if there is a way to space the ring itself. The only issue that I can see is that the ring is a direct mount and needs to interface with the pattern on my XO crank. Perhaps I can get away with a small washer and still have plenty of contact for the spider.
 

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Thanks guys. Rather than get a new ring with the 6mm difference I wonder if there is a way to space the ring itself. The only issue that I can see is that the ring is a direct mount and needs to interface with the pattern on my XO crank. Perhaps I can get away with a small washer and still have plenty of contact for the spider.
I would recommend messing around with the spider/crank interface. Get the correct direct mount or spider/chain ring if the chain line is off with the current. That being said I used direct mount wolftooth chainring made for GXP on my pf 30 BB crankset and it was fine. It actually put the chain ring slightly inward already. For 30mm BB buy the Wheels manufacturing shims. Various sizes to adjust chain line as needed.
 

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EVnut
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Can I just hop in here with my chain line woes? I have my first 1x11 setup, and I'm astonished at how far off the chain line is... by design! I am running the new Race Face SL crank and matching press-in BB. It is set up for 51 mm chain line. There is no adjustment. The ring is offset to the inside slightly. And I've now determined that the ring should be offset to the inside MUCH more, but Race Face doesn't see why I have a problem.

Here's what I wrote up to chat with the fine folks who build the drive train, and who build the bike. I'm somewhat surprised to find that nobody else seems to care... or even notice this. I'd love to hear your input and/or any solutions!
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The Issue
My Ibis Ripley running 1x11 with Race Face Next SL crank (current version with DM ring) is specified for, and measures at 51 mm from center line to chain ring. The rear (middle gear of the cluster) measures out to a ~42 mm chain line. This means that when the chain is straight, it falls between gear eight and nine - not on gear six where it belongs. There are two main problems with the chain line being biased toward the “high gear,” outboard end of the cluster in this manner:

  1. During highest torque riding (climbing in the lowest gear) the chain is at it’s maximum deflection, creating extra noise, inefficiency and wear.
  2. When in lowest gear, the chain derails when backpedaling (if the rider levels the crank arms to launch from a stop in the middle of a climb, or to keep the cranks out of rocks, etc)

The Measurements
51 mm chain line at the chainring. (Bike centerline, to center of chainring.)
142 mm rear axle. So rear centerline to end of axle = 71 mm

The Math
To find where 51mm from the centerline is in the rear, I'll take the centerline to axle-end measurement, and subtract the centerline to chainring measurement. I’ll then measure that distance in from the axle end to find where a straight chain would land on the cluster.

Centerline to the axle end is 71 mm. And 71 mm-51 mm (centerline to chainring) = 20 mm. I measured 20 mm in from the end of the axle, and that puts the chain on the outboard face of gear eight. So a straight chain ends up between gear eight and nine. The chain currently must move almost eight gears inboard, and only three gears outboard.

The Fix (that nobody seems interested in producing)
Offset the chain ring to the inside to match the center of the cluster.
Cog thickness 1.6mm.
Spacing between cogs 2.2mm
Center to center = 2.2 (spacing) + 1.6 (two halves of a cog) = 3.8mm. For perfect chain line, the chain ring should move inboard the distance of two cogs (center to center) plus half the thickness of a cog. 7.6 + 0.8 = 8.4mm. My math says that moving the chain ring 8.4mm inboard gives us a straight chain line. I’m happy to round it up to ten (I’d rather have the chain line inboard toward the lower gears anyway).

There are no physical barriers to moving the chainring inboard 10 mm. In fact, that still leaves the chain outboard of the inside face of my chain stays, so there is no interference with the tire. The chainrings simply need more inside offset. No, I will not be shoving my crank off-center by 8-10 mm in order to solve this. The solution is either a way to shim the factory chain rings (not likely) or to offer larger offset in the chain rings you make for direct mount. For max clearance, I’d be OK if the larger chain rings are left at minimum inboard offset. But there is no reason for the 30T and smaller rings to suffer bad chain line as well.

In the included image, the steel rule is projecting the axle end, and the plastic rule is measuring inboard by 20 mm to find that a straight chain will hit just outboard of gear eight.
 

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You're not the only one. I asked a similar question to Tehan from Absolute black over on the Oval chainring forum. Their direct mount ring has a chainline of 50mm, whereas Sram uses 49mm, so i wanted to know why they had a worse chainline.
He kept telling me that 50mm was perfect.

Sheldon Brown has the ideal chainline for an MTB at 47.5mm. However from your calculations, it seems like 42.6mm is the perfect chainline.

The only reason I can figure out is that due to bigger tires and chainstays, the industry moved the chainline further out to so that chainrings would fit without interfering with chainstays. However in many cases, as you found out, this clearly isn't and issue, and i'd suggest that it is less of an issue with 1 x setups.

Since I have a pressfit BB, the only way i have to adjust chainline is to use chainring spacers. But I'd like do with a lighter direct mount setup - but this leaves me stuck with a poor chainline.

I think the Industry just expects people not to notice, and reap the benefits of increased sales due to excessive drivetrain wear.
 

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EVnut
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Thanks, xcabary -

If nothing else it feels good to have some empathy. I'm just amazed that my googling has turned up NOTHING on this subject. There are a few "adjust your BB" comments, but honestly, there just seems to be no concern about this out in the wilds. You can use chainring spacers? I *WISH* I could. But there's just not enough mounting surface to move the thing over as much as it should be. The Race Face rings have offset. I just can't help but wonder why they don't put the proper amount of offset in them. It's cheaper and uses less material to offset less... but that's the only advantage I can come up with. I've spoken to them about this, and they simply don't care. Their test is: Does it work? Yes or no?

I won't claim to know what the perfect chain line might be. Or even if there is one. I only know what we all know - that a proper chain line puts the chain at the middle of the cassette when the chain is straight! I wouldn't be complaining if the chain line were cheated inboard, so there was less cross in the lower gears. But this seems to be the worst of all worlds. Cross the chain the most for the highest-torque application.
 

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As far as I'm aware, some bike manufacturers including cannondale, have offset their chainstays a few mm to make the chainline better, but this requires the rear wheel to be redished, but I'd see that as a small price to pay for a better chainline. It also makes the wheel stiffer due to more even spoke tension.

One thing puzzles me. There's a a new axle system coming out called boost 148, which is a new standard for rear axles (6mm wider), this will push the cassette out 3mm - which should improve chainline. However, Sram are also going to make a new spider to go with the the new chainline, 3mm wider than their standard one...?

Clearly no one at Sram thinks that there is a Chainline issue.
 

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EVnut
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Certainly on my particular bike, there is no need to mess with the chain stays or the rear wheel. Plenty of room before I hit the inner plane of my chain stays.

When I look at my old 26" mtn bike with a 3x9, the granny ring puts the chain inboard of the chainstay anyway. Certainly not ideal when I'm also shifted into the inboard cog at the rear, but also not a show-stopper since this is all low-speed stuff with that gear selection.

I'm happy to sign off on tire chain-suck if that's the concern. But I really don't think it is. They just don't care. The chain ring is somewhere within the cluster width. Good enough!

I tuned up my initial post to (I hope) make it a bit more clear.
 

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I believe that some time ago - about 10 years, I noticed it when I switched to an external threaded BB, the chainline was increased on MTBs, due to bigger down tubes on bikes, to allow the front deraileur to work properly (bigger tubes prevented it moving in properly)

I think the standard mtb chainset chainline went from 47.5 to 50mm.

With 1x setups, this isn't necessary now, but we seem to be stuck with this legacy, and the engineers at Sram / Race Face don't seem to care or have noticed the poor chainline issues (if you search for XX1 sprocket wear - you get plenty of threads of people talking about the issue)

The main reason I hear is chainstay clearance, but surely this is only an issue with bigger chainrings. With direct mount chainrings, why not make small rings with 45 - 47 mm chainline, and keep the bigger ones at 49 - 50mm?
 

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I'll take a DM ring with a narrower chain line. I can hear the front ring when I'm in the larger cogs. I think there is a member here that wore out a Wolf Tooth ring in 500 miles? The sides of the teeth looked smooth.
 

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EVnut
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The main reason I hear is chainstay clearance, but surely this is only an issue with bigger chainrings. With direct mount chainrings, why not make small rings with 45 - 47 mm chainline, and keep the bigger ones at 49 - 50mm?
I hadn't even heard THIS reason before. I guess that would make some sense. But on a 29'er... who's using big rings? Uh... nobody.

Yeah, I can see the concern. Now we just need the component folks to see the reality.
 

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dadamamabooboo
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This chainline thing also affects us 2x'ers as well. I've been running a hybrid 2x + bash for a while and recently switched from a 3x to 2x fd (I'm pretty much all sram x9) in an effort to improve my shifting a little. But I run a 20/36 so that jump speaks for itself in terms of optimum shifting..it's not recommended of course and in practice took a bit of patient tweaking to run well.

But, like many of us I'm sure, I was interested to explore the vaunted 'dedicated 2x crankset'. Woohoo..so it's gonna be better than a hybrid 2x/bash right? Eh..no. Why did they decide to create a worse chainline? They've got a chainline dead center between them, right where the middle ring is on a triple. Why not have moved it a few mm's inboard centered around the inner ring? I've had to experiment with 'angling' the fd to try and eliminate chatter against the cage, and pretty much 'split the difference' between having a quiet 10 and a noisy 1st, or vice versa..so I just have a little chatter on both extremes.

I raised a question on this recently, asking what 'precisely' accounts for the physical diff's between 2x and 3x cranks, and apparently it's all in the spider thickness. I'd like an aftermarket to make maybe some 'universal' spider variants that could effectively move these chainlines inboard at least a few mm's..it'd make a world of diff on my bike. like many of you others, chainstay clearance isn't even close to a problem on my frame.

sucks to hear this is a pia on 1x as well. sorry for a 2x hijack guys, just struck a chord.
 

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Indeed, so will I! Who's going to make them for us? this can't be hard to do. It just takes somebody who cares.
I'd say try Tehan on the Absolute Black chainring thread, but he'll probably just tell you that no one wants a narrower chainline, and that 50mm is perfect.

Makes me think I should go into business and start making chainrings myself.
 
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