Tight/loose spots in chain when cycling crank
 

I'm sure this has been discussed before ad nausea but here goes...

I've read that a tight/loose chain is not necessarily a problem unless the chain falls off. Always tighten the chain to the tightest spot so that the chain isn't too tight. Ok, so I do all of that but what actually causes this?

I'm guessing variances in the chain ring and/or crank arms? Maybe the crank and chain ring are not quite 100% concentric. Maybe the sprocket is a little out of round also, but I wouldn't think this would cause quite as much as a crank that is out.

Anyone care to weigh-in on this with wisdom on what the cause(s) are and any Pro tips?

IMO it's mostly the chainring. All the ones I ran would have a pretty bad tight spot but then I bought some Wabi Pro/Andel Deluxe cranks and the ring is perfectly round with even tension all around. Sadly you can't buy those rings individually.

It's usually an out-of-round chainring, but a wonky cog and/or freehub body can contribute. Narrow-wide chainring teeth can help chain retention, but unless it's really bad, a loose spot alone shouldn't throw the chain.

Cranks and chainrings for derailleur bikes don't need to be perfectly concentric, and QC is applied accordingly.

If you want good concentricity, buy fixed-gear/single-speed parts with a good reputation. :thumb:

Unfortunately, that's no guarantee. My current White Industries ENO cog and chainring have the worst loose/tight spots I've ever had. They musta made them on a Friday.


EDIT/UPDATE: See post #19.

Hmm, that's disappointing. You've ruled out the crank?

I'd be inclined to make some noise, for the price of WI stuff. My FG is cobbled together from old junk, so I have no one to complain to. :lol:

Yes. Same old cranks with a new 38T chainring. They changed the tooth profile to narrow/wide, and their usually flawless machining seems to have suffered.

EDIT: see post #19.

If you haven't, you should read and study Sheldon Brown's technique to address the issue. It is in the following link:

https://www.sheldonbrown.com/no-derailers.html

Read all of the info, but the section titled "Minimizing Chain Slack" gives method Sheldon recommends to minimize the problem.

I bought the chain ring from Wabi as it matches the old one. It is actually pretty darn close to concentric.

Not sure if anyone else has tried this and it just dawned on me to give it a try:
I got it to run even more evenly by loosening the chain ring bolts to a little tighter than finger tight and rotated the crank to find the high/low spots then softly bumped the chain ring with a rubber mallet, then tightened the chain ring bolts. It helped. A few trial and errors and it's running pretty evenly.

That's the Sheldon Brown method mentioned by TugaDude. It doesn't work with spline-mount chainrings, however.

Thats good troubleshooting!

every chainring, cog, crank, frame combo i've owned has had this to a varying degree. never had it cause an issue while riding.

I know this is prolly wrong, but I have always suspected one contributing factor might be the chainring/cog tooth numbers. I've tried a few different combinations (46/15 - 48/19 and in between) and they seem to differ in the amount of stiff/loose variation.But I'm not a good enough mechanic or mathematician to explain the issue.

It is my experience that no matter what one does, more budget-friendly chainrings are going to be wonky along with their budget-friendly cog when it comes to variations in chain tension... Though the fixed-gear drivetrain (and secondly the single-speed) is so efficient that any slop should be taken in stride and looked upon with pride.

However, when first implementing a professional-level fixed-gear drivetrain on my own, I still felt a little more variation in tension than I had expected from something so 'finely tuned' and was unnerved. In contemplation on this conundrum, I remembered a piece of advice that was given from an old messenger/mechanic in Minneapolis years ago:

Install the chainring with slight finger-tightness on the bolts and put the drivetrain in maximum tension, to the point of binding (i.e. pull the rear wheel out of the ends as far as possible) and run it through a few cycles: Thus absolutely centering the chainring on the crank arm. Then, after tightening the chainring bolts and properly tensioning your chain, one will find their drivetrain in near-perfect harmony. It works a charm :)

Reach out to Lynette or anyone at WI and they should be able to help you. They are super nice and if things are not right you should allow them the chance to make it right. Narrow Wide with 1x1 and the wrong chain could be an issue but I would still see what they can do.

Yes, I haven't done that, and I should. Thanks for prompting me to reach out.

+1

Yes to both quotes. Derailleur bikes have absolutely no need for tight roundness tolerances, In fact, a slightly wonky circle probably improves front shifting. And close tolerances cost money. On fix gears it matters.

I've done most of my fix gear riding on 110 BCD cranksets. I can generally get the chain slack to never tight and never falling off but not always. By contrast, my Sugino 75 is a joy. Yes there is a little variation but so little I can do wheel flips blown out at the top of a major climb and get the slack every time. Several years ago I set my namesake bike up fixed with three 110 BCD chainrings. Bought MOJO 1/8" rings and have been very impressed. Crankset is an old Sugino. AT? GT? Decent but by no means of 75v quality. Setting chain slack takes more attention but is not bad. Another thought - I seem to have had better luck with roundness and slack issues since I went to 1/8" everything, Now the makers of the 1/8" rings know it's going to be ridden fixed (or single speed with the same issues to a less critical degree).,

I don't have data but I am pretty certain that the cranksets themselves have tolerance issues, not just the chainrings. And it may be the tolerances on the four flats for a square taper BB. The spindle too might be a little off. And I could imagine the fit between them changing a little over a few removals and replacements.

These observations are all from experience; 20,000 miles on the velodrome quality 75 and about 90,000 miles on various adopted road cranksets.

Great suggestion! Too many times I see folks on this and other non-bike forums discussing quality issues but they never seem to let the manufacturer in on it.

I worked for a global manufacturer and I can't tell you how many times I was disappointed to find a customer who said "Yeah, over the years I've had issues with some of your company's products, but I just figured out a way to make them work". Two things wrong with that statement. First, by us not knowing, we had no ability to "fix" whatever was broken. Perhaps it was specific to this customer, but chances are it was just an issue with the product. Would have been good to know. Second, the customer indicated that they found ways to work around the limitations of the product. It would have helped to know what those methods were. Manufacturers learn a lot from their customers in the field. Feedback is priceless.

So my recommendation is when anyone has a problem with a product and it just didn't meet your expectations, go ahead and reach out to the manufacturer. You'll likely be doing them and yourself a favor.

Further inspection reveals that it's not an out-of-round chainring after all, but appears to be either a bottom bracket or freewheel issue.

My apologies to WI.