As promised in last week’s episode, this Tech Talk covers a few additional chain-drop, chainline and front derailleur issues raised by readers in our Comments section. As a reminder, a few weeks back, in Issue 732 of RBR Newsletter, I wrote about helping a friend diagnose and solve his chain-drop issue. We’ve received some excellent comments on these topics in the weeks since. So, I’ll share a few of the most insightful ones and add a few more tips.
Front Derailleurs are Just Plain Difficult to Adjust
First, an important point to appreciate is that front derailleurs may be one of the hardest things on a bicycle to adjust perfectly. I say this because as a bicycle shop service manager, I found that it was always among the most challenging things for new mechanics to learn and master. Some could never get it right and would have me do the final fine-tuning for them.
What makes it so difficult is how front derailleurs mount to frames. It’s nothing like the rear derailleur that simply bolts on and is automatically in the optimum position (assuming the dropout and derailleur hanger are aligned).
Instead, the front derailleur can be positioned in an almost infinite number of positions – even when mounted to a braze-on on the frame. Even if you understand the basics of front derailleur adjustment, it’s easy to make it too high, too low or angle it incorrectly. And, if you do any of these things, it won’t shift properly, if at all.
One of the challenges is being able to see what’s going on and to determine what change is needed to solve whatever adjustment issue you’re experiencing. That’s because, judging the gaps between the chain and the front derailleur cage (both sides), and also the gaps between the cage and the chainrings can be difficult. But if you can’t see it or recognize that something’s misaligned, you can’t correct the problem.
To help, here’s an excellent tutorial from Park Tool. Their photo above shows how slight changes in the derailleur angle can mess up the shifting.
And Now For Your Comments
Chuck Davis made a great point about chain drop: that it can be caused by operator error, too. He said, “failing to trim when you’re on the big chainring and on the largest cogs lets the front derailleur take a full swing at an enhanced chain angle. And that can cause the chain to come off.”
That’s absolutely correct. As you shift up onto the largest cassette cogs, the chain angle increases to the extreme. If you decide to shift to the smaller chainring when your chain is angled like this, it’s almost asking for the chain to come off. Ideally, you would realize you’re in a gear that’s creating a risky chain angle and shift to a smaller cog to improve the chain angle. Then you can safely shift to the smaller chainring.
Chain rub or chain drop, those are his options
JeffDH explained, “My problem with chain drop is that if I adjust the limit screw so that the chain NEVER drops, then in the outside cassette gears the chain rubs on the derailleur cage. This happens both with the large cog/small chainring and small cog/large chainring. But, if I adjust the limit screws 1/4 turn in/out so that the chain doesn’t rub on the derailleur cage, I will occasionally drop the chain, especially if I shift the front when the rear is already in the last couple cogs on that side of the cassette.”
These symptoms, where you either have chain rubbing or chain drop usually indicate that the derailleur cage angle isn’t aligned correctly with the chainrings. If it’s angled even slightly wrong, it will rub and/or can throw the chain. So, I would check closely by sighting from above. If you systematically shift into all of your gears one by one and look at the alignment of the cage, you should be able to see which way it’s off and how to change its angle to fix the problem. (The above photo clearly shows how the angle can be off either way, in A and B, and correctly aligned, in C.)
A worn chainring can throw the chain, too
Larry K. pointed out that “worn chainrings can cause the chain to drop when backpedaling, too. I had one that did that even though the teeth weren’t hooked enough to cause skipping. The teeth were worn to a point, however, and that seemed to be the cause of the unshipping – especially when the chain wasn’t in the middle range of the cogs. Chain drop might occur when pedaling as well but I have an inside chain retainer on my bike so it never did so for me.”
With modern chainrings it can be hard to visually spot a worn ring since so many have different shaped teeth to optimize shifting. Larry mentions hooked teeth, referring to how teeth that are symmetrically peaked when new, take on a wave-like hook with enough miles.
This is kind of hard to judge, so what you could do is snap a close-up photo of your chainrings with your phone and then use it for reference when you think your rings are wearing out and shifting poorly. Or, if you keep some new replacement rings on hand, a surefire way to gauge wear is to hold the new rings right next to your old ones to compare the tooth profiles.
Steve’s chainline tip
Finally, Steve Andruski mentioned, “Park Tools made the CLG-1 and CLG-2 chainline gauges. They are both now discontinued, but there’s still an extensive article about chainline on the Park website.”
Thanks a lot, Steve and everyone else who commented. Here’s to smooth shifting and chains that stay on! If you’ve got more tips related to these topics, let’s hear them in the Comments below the Newsletter version of this article.
My bicycle has Campagnolo Record 10 components, and I make no assertions about having the front derailleur perfectly adjusted. When the chain is clean and properly lubricated, the chain rarely drops. However, when the chain’s lubricant becomes dirty, it begins to occasionally drop to either the inside or outside. I try to keep the chain properly lubricated, based primarily on mileage. However, mileage is not always the best metric, and I pragmatically consider the chain-drop characteristic a feature to notify me the chain is in need of lubrication.
Bob Eltgroth says
I use a Stein chainlink checker.
I installed a K-Edge chain catcher on both my wife’s bike and mine, never dropped a chain since.
Brian Nystrom says
I agree with the comment about chain watchers and I do use them on my road bikes. However, they should not be used as a substitute for proper front derailleur alignment. Oddly, I don’t need them on my off-road bikes (‘cross, MTB and fat), as the MTB front derailleurs that I use on these bikes have large inner cage plates that make them almost unnecessary.
It’s also important to understand why and where a chain is coming off. The article explains common shifting-related issues for road bikes, where the chain comes off of the top of the chainring, but there are other reasons why this happens.
Bouncing around on rough roads or terrain, can obviously cause the chain to drop. Another issue which is more common off-road occurs when dismounting the bike. When getting off in a hurry, most people tend to unclip and backpedal a quarter turn or so with the foot that’s still clipped in. Combined withthe bouncing or flopping to one side that may occur during an awkward dismount, the backpedal motion can cause the chain to come off of the bottom of the chainring. This is especially common with ‘cross bikes which typically use road bike front derailleurs.
If caught immediately, this can often be remedied by pedaling forward, but continued backpedaling may result in a nasty chain jam. This is why MTBs designed for more aggressive pursuits have chain guides that cover the bottom of the chainring, too.
Mark Pemburn says
If dealing with afront derailleur for a double is tricky, a triple can be a bit nightmarish. Both of my bikes—a Cannondale MTB and an older Trek road bike—feature triples. I never had the chain spill on the Cannondale (which has a 7-speed), but after acquiring the Trek recently (with a 10), I found myself having to stop frequently to replace the chain when shifting down on a climb. Your advice from a couple of weeks ago saved the day for me: shift to the small ring _before_ going to the biggest cog. If I find myself on the big cog, then hit a steeper section, I shift up one or two on the rear, and then drop to the small ring. No spill. Thanks!
Greg Przybyl says
On our recumbent tandem where easing up when shifting on the front is not always easy to do, add to that 14 feet of drive chain to move on a triple up front, shifts to granny were always, ahhh, adventuresome. Due to the frame style chain watchers wouldn’t work. But then the hostel shoppe made the Volae GrannyGuard which has made us very very very happy. It bolts onto the inner side of the granny gear to prevent the chain from dropping off. Did I say it made us very very happy?
I’m experiencing chain drops when starting from a standstill, uphill, while on the largest chainring and mid to small cogs on the cassette. The chain will drop at the front, to the outside of the bike.
I am quite sure that chain angle can’t be the problem, Also, the bike is pretty much brand new (500km) and has very recently been adjusted by the bike shop mechanics to deal with any play that may have come with use after the initial setup.
Is there such a thing as starting on too heavy a gear from a standstill that would cause the chain to drop? I am not shifting gears while putting heavy pressure on this sub-ideal gear. I do not intentionally start on a heavy gear when going uphill but it happens in cases where i will suddenly have to brake or make a u-turn