JanMM

Intermittent shifting issues starting last Fall on our Screamer. with about 8200 miles. Pedaling motion froze after shifting to little ring but not always immediately. Sometimes seemed associated with a rear shift. First happened - several times - during Day 2 of October's Hilly Hundred. Caused us to walk up a few hills. Didn't figure out the cause till a week ago - after having replaced the main chain and cassette earlier this Winter. That didn't fix it. After that , had same problem on a small hill a couple of weeks ago on a rare day with OK weather. Disconcerting but again able to stop upright. Finally after putting bike back up on stand and doing some shifting saw classic chain suck on the little ring. The Dimension 28t that replaced the original 30t after a few hundred miles had pretty beat up teeth - we had abused it grinding up lots of hills. Today put on the original low mileage FSA inner ring along with new FSA middle/outer 39/50 combo. All seemed good riding around the neighborhood in between this afternoon's rainstorms. Hope to be able to try it out better tomorrow.

PMK

Have also seen where bikes were upgraded in the number of rear cassette gearing, but the inner front chainring was left on and was unfortunately too wide for the chain.

In short, a narrower chain on the wider front chainwheel can promote chain suck. Then again, possibly the worn chainwheel was simply the cause. Especially if the wear created burrs on the teeth, widening the chainwheel.

JanMM

9-speed chain on 9 or 9/10 ring. Definite burrs on teeth.
Small ring that sees a relatively large amount of climbing miles probably should be inspected and changed out appropriately. (We don't hesitate to use the small ring.)

ReidH

You may want to look for a stainless or titanium chainring for the smallest ring. Not many teeth to carry the load.

JanMM

Good idea.

Carbonfiberboy 

You can also file off the burrs, which will extend ring life somewhat. But I've said the heck with it now and just pop on a new middle ring. It's always the middle ring, never anything else on our bike. The other thing which will work for a long time is calling the shift and hitting the granny ring early. When you call it, stoker stops all pedal pressure. When you feel stoker let off, you let off too and then shift down. This is obviously harder to do after you've committed to the climb in the wrong ring, but this method works then too. In that situation, I usually call "Spin up!", then the shift call.

It's easier upshifting from the granny that way, too. Chainsuck is pretty much always stoker pressure.

We have a SS granny. I doubt it'll ever wear. Nice that the granny only needs to be a plain ring, no ramps or pins, so anything with the right bolt circle works.

jethro00

Carbonfiberboy, where were you 1.5 years ago when we got our DaVinci Grand Junction? We experienced chain suck when we tried to go to the big ring or the granny ring. That was not fun. We have learned, just as you say, that the stoker has to stop pedaling before we go to the big ring. We don't have steep hills where we ride. So, we have not tried the granny ring in ages.

Alcanbrad

The wear shown in the picture is indicative of a very worn chain. As a chain wears the link to link spacing increases and wears the gear teeth as in the picture.

Replace the gears and not the chain, the stretched chain will prematurely wear the teeth (I am using teeth to mean chain rings and/or cassette).

Replace the chain and not the the worn gears and you risk the chain slipping over the teeth when under high power (which is no bueno).

My recommendation is to replace all the rings, the cassette and the chain and if you don’t already have a chain stretch measuring tool, get one and replace the chain when it reaches the “worn” state. You will experience better shifting performance and get longer life from your drivetrain.

JanMM

About 8,200 miles on the bike - replaced the three rings yesterday. The small ring had maybe 7,500 miles. The middle and big were original. Chain has been replaced several times including this Winter. Same with cassette. Shifting seemed good on an eight mile ride today with a couple of mild hills.

PMK

Simply, after seeing the photo, the inner chainring is worn out. No big deal, it happens.

Often, as you do get miles on the drivetrain, it is a good visual inspection looking for burrs on the chainwheel teeth. With a touch of care, and a sharp file, you can invert the entire bike, and while turning the crank backwards, simply let the file lessen or remove the burrs. Positioning the chain on the big ring can allow filing the outer edge.

No, this will not make the chainwheel last any longer, but can save a nasty chain suck that can damage the frame or be impossible to release short of loosening a crank.

Not that it matters, we run a 4x up front, with great granny a steel Shimano mountain chainwheel. The other 3 are higher quality Race Face on RF cranks. Seldom use great granny, but when needed, it is nice to have.

gracehowler

One thing I have learned, the hard way: inspect, those rings and chains wear out!
R&J

JanMM

Yep, I was very negligent in not regularly taking a close look at the rings - especially the little one.