Chain rubbing inside of large ring
 

Progress has been made on a vintage build for a friend. Having decided on an updated set of wheels, I cold set the frame to an 8-speed dropout spacing and just got the shifting system cables done. With this I noticed the chain rubs distinctly on the large ring while in the smallest rear cog. Although this is normal for some, I like to minimize shifting of the front derailleur and therefore prefer to exhaust the full range of gears with the smaller ring before shifting up in front. As such, I would like to eliminate this condition. I first took a look at the chainline and the bottom bracket spindle length seems spot on for a double according to sheldon brown with the mid-line of the two rings being about 44mm from the center of the seat tube. Then I facetiously considered how if I cold set the rear triangle a millimeter left of center, I probably wouldn't be having this issue. I've also heard of spacers for the drive side bottom cup, but am unsure if this would leave me with too few threads for the locknut on the non-drive side. I suppose I could replace the nice loose-ball bottom bracket with a cheap sealed-cartridge BB of a slightly longer length, but does anyone have experience swapping an extraneous spindle into an existing set of cups with success regarding the races meshing properly? Two other options would be slipping in 5 thin chainring spacers between the crank and the middle chainring, or limiting the rear derailleur out of the smallest/highest cog, although this would negate the cold set altogether, that is, if I had a 7-speed wheel in the first place.

So, what chain is on there?

Make sure the rear triangle (dropouts) is centered along the frame axis (I understand you've done that already).
Measure both the front and the rear chainline, see if they are matched. My explanation how if you need it: link.
Problem you have could be caused by front chainline being smaller than the rear chainline.

Riding small/small combo causes more mechanical losses due to chain being at a sharper angle, and, since fewer teeth are involved, causes faster drivetrain wear. I understand using that in a racing situation, but wouldn't call it a good practice.

Slaninar makes excellent points about the small-small combo. It also can cause the chain to bounce on and chip that pretty right chainstay. You can't change the chainline in front or rear without making the alignment in the large-large combo worse, and I doubt a 1 mm diff is going to resolve the issue anyway. Finally, the times when a rider will get down to the small-small and then not shift to the large chainwheel will be minimal, and as there is overlap between the two ranges there's likely a combo on the large ring that is close in ratio to the small-small. If one is going to shift to the large chainwheel anyway there is no savings in waiting until the small cog to do so.

What cranks are they, what length BB spindle do you have and what size is the chain? Those look like older cranks, you should be able to look them up on Velobase and see what spindle they require.

Now I used an 8 speed chain on 10sp chainrings once and had to add extra 0.6mm chairing spacers behind the big ring to stop the rubbing.

To answer the replacing the spindle question, I do it all the time at the co-op I work at. I've never heard of a bearing problem after a transplant.

you are shifting wrong (cross-chaining) and attempt to overcome that with hardware adjustments. 2 remedies:
1. shift correctly (shift front on large chainring before going to small rear cog), this is the way it is designed and the cheapest solution applied by billions
2. convert to 1x drivetrain since you don't seem to like front shifting

Overthinking may have occurred.;) Since this bike is for a friend, what are the chances he will share your aversion to using the gears properly? He will most likely (and should be) perfectly happy with it as is. To paraphrase Shimano instructions, if it rubs when you are cross chained, don't use that combo.

If your front derailleur has sufficient throw there should be no issue in shimming a ring to eliminate chain rub; I have done it successfully. I get the arguments against cross-chaining and do not do it myself, but some folks are happier if they can use all of the combinations.

Limiting the RD out of the smallest cog would be an unacceptable hack.

I'd try the thin chainring bolt spacers between the crank spider and small ring unless the bottom bracket is due for a repack anyway. It would worsen the chainline slightly for the small-small combo, but you have a good chance of improving, if not eliminating, the rattle.

Could you have reversed the spindle when it was out for service?

I wouldn't say I am shifting improperly as this would be the method with only one front chainring, though I can see how leveraging the chain against cogs with more teeth would put less wear on the drivetrain over time. I usually don't encounter enough long downhills to necessitate shifting to the larger ring, and with my shifters on the downtube, I have become accustomed to keeping my left hand on the bars while sparing my right for the shifting.

This bike for a novice rider and therefore I would like it to have as few restrictions as possible. I have tried 'transplanting' foreign spindles into existing cups and have not been able to adjust them properly; there are standards for the thread pitch and diameter, but I think the diameter of the race from different models/manufacturers can vary and therefore do not guarantee a proper mesh.



I know it's a completely egregious solution, but I am leaning toward tweaking the rear triangle slightly to the left, partly because this how I found it before the cold set. It is currently centered, measuring the same distance from the seat tube to a thin cord strung around the headtube between the two rear dropouts. But since it only rubs whilst in the one smallest cog, I figure the adjustment would be minimal and unnoticeable. The rear wheel can also be rotated slightly counter-clockwise (from above) to compensate.


Then although the chainring to seat tube distance and spindle length seems to be spot on according to sheldon brown's specs for double cranks, it does seem a bit close to the chainstay and so will try to dig up a slightly longer spindle and hope it meshes, but if not would consider going with the former fix. I have pictures comparing the range of the chainline and a pic of the proximity of the crank to the chainstay.

Here's another thought: how often is your novice friend actually going to shift into the big ring? Maybe it could be swapped for a smaller size that doesn't rub, or left off entirely until such time as they find themselves needing it. They might even appreciate the simplicity of only having one chainring that they don't need to shift.

Say it any way you want -- it's still cross chaining and the drivetrain was not made to do that. See photographic proof above.

Unfortunately your solutions could result in actually encouraging a novice rider to use the small-small combo excessively, possibly most of the time, as it's too much trouble to shift the front - or even the rear. Then you will be in the position of explaining to her why her chain and small cog wore out so quickly. If you offset the rear triangle you will also be blessing her with a bike that may veer to one side if ridden no hands. Unless you re-dish the wheel she may also wonder why her wheel is not centered, or why the brakes don't hit the rim at the same time. I already spoke to the problem of making the large chainwheel with larger cogs chainline worse. Of course if you properly align the dropouts with each other after resetting the triangle the cogs will no longer be in the same plane at the chainwheels. But if, after asking for advice you choose to ignore both the better solutions offered and the counsel to reconsider encouraging that combo, then damn the torpedoes.

Look at the first picture showing the chain zig-zagging and tell us again how this is not improper shifting.
Your problem of not wanting to take hands from handlebar has been resolved with the invention of handlebar shifters.
The problem here is the rider (or the friend of the rider)

Looking back at the chainline pics, I think a longer spindle is all it needs -- a couple mm would do the job.

What brand of cranks/BCD are you using?

Many of the modern cranks have the two rings offset in opposite directions, which helps with cross-chaining on a bike that was originally designed for 5 gears on a 126mm rear-end.

So, perhaps by replacing your chainrings with 9/10 speed rings would help.

You might also try using a 9 speed chain that is slightly narrower on the outside, but without a significant change between the plates.

I agree with others, cross-chaining should be discouraged. It usually doesn't hurt much, but if one hears it rubbing, then it is time to shift.

So, what chain is on there?

Sounds like a lot of screwing around to avoid using the lever that is 1 inch from the right one, which you can even use your right hand to shift.

On most rolling rides the front shifting provides a more useful shift than going up and down the rear cogs.

Maybe the "novice" can learn to use the gears properly. If not, how about not bothering with a road bike and just getting and upright with an internal 3 speed? I don't understand putting someone on a specialized road racing bicycle and then discouraging them from using it properly.

With one front chainring that chainring would generally be larger, so that you would be in the smallest cog only when going quite fast. More recent 1x drive trains have 10 or 11 gears, not only 5 or 6, so wear is more evenly spread out. In addition your rear cogs are further out for the small chainring and further in for the large one than they would be for a 1x.

Quote:

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Originally Posted by joedab (Post 20092489)

...though I can see how leveraging the chain against cogs with more teeth would put less wear on the drivetrain over time.

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Yes, it would, because one is putting just as much pressure on the chain, but the chain is engaging many fewer teeth per mile, both front and rear, it will wear about twice as fast on the small ring as it will on a similar gear ratio with the large ring, and the small cog will wear much faster as well, especially if it is an 11 tooth.

Quote:

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Originally Posted by joedab (Post 20092489)

I usually don't encounter enough long downhills to necessitate shifting to the larger ring...

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..and that is a problem because that means you are riding the small cog far too often, just to avoid the "necessity" of shifting to the large chainwheel.

Quote:

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Originally Posted by joedab (Post 20092489)

and with my shifters on the downtube, I have become accustomed to keeping my left hand on the bars while sparing my right for the shifting.

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...but it's not your bike, so your habits are not at issue.

Quote:

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Originally Posted by joedab (Post 20092489)

This bike for a novice rider and therefore I would like it to have as few restrictions as possible.

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You are restricting the life of her drive train, and her knowledge of how to properly ride a multispeed bike.

Quote:

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Originally Posted by joedab (Post 20092489)

I have tried 'transplanting' foreign spindles into existing cups and have not been able to adjust them properly; there are standards for the thread pitch and diameter, but I think the diameter of the race from different models/manufacturers can vary and therefore do not guarantee a proper mesh.

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You are mistaken in almost all cases on that point.

Lower-end bikes in the old days very typically used over-length spindles so that beginners who ended up riding with both levers slammed forward would not encounter noisy transmission.
It was fairly typical for a percentage of beginners to ride their road bikes this way at all times, since the grinding noises of shifting signaled to them that they were doing something wrong, or because the friction adjustment screws had lost tension after some period of service.
Many such riders were loath to ride one-handed even for the time it took to friction-shift gears!

While I myself (for my own use) have changed many such spindles to a shorter length (or an effectively shorter length via a symmetric cartridge bb), I can understand why the bike makers in those days did what they did, and why someone (as the case here) might want to do the same.
Many of us here are old roadies, who by habit use the big ring for 90% of their riding, but it seems this bike's rider likely presents the opposite case.

So a longer spindle can be used, just a millimeter or two will compensate for the chain angling of perhaps a full two or three cog spacings in back since the longer crank chainline is far more local to the critical position along the length of the chain's upper and lower runs than is the cassette!

Crank bearings with space for 11 balls all have the same bearing track diameter, and differences in the load path angle is in all cases plenty close enough for smooth running, as smooth as the bearing surfaces are in any case. So find a spindle with same ISO taper as the original, or use a length compensation of 2.5mm shorter off of each end to use a JIS spindle, and add a millimeter to the driveside end. Can you not just add a 1mm spacer under the driveside cup flange?
You will need to get the final driveside spindle projection length correct by whatever means, and will have to use a spindle with the same width between races, but you seem up for this bit of experimentation. Better yet, try a couple of cheap cartridge bb's and perhaps save considerable time!
Lastly you will want to apply a very thick chainstay covering and be certain your derailer is tensioning the chain sufficiently.

I agree there are riders who just have no interest in using the big ring, I've repaired bikes where all riding was done with both levers slammed forward and have even seen the small threaded cog split open from such use. But it took a good while for this to happen, and the rider was obviously getting plenty of use from their bike.


I would consider putting a thumb shifter on the top of the bars for such a rider to at least feel safe while acquainting themself with the shifting process, but there is some value in letting a rider learn the art of friction shifting instead of dumbing the process down for them completely with a click-shifter.