Derailleur Adjustments Can't Eliminate Chain Rub/ Front Derailleur Cage Possibly Bent
 

I'm a newbie, but I've done hours of research to attempt to improve the shifting on a used Jamis Ventura A2 I just purchased (chainrings 50/34 and cassette 11-32T)

Should it be possible to adjust the derailleurs so that the chain doesn't rub on the side of the front derailleur cage in any of the chainring/cog combos? Even in big chainring/big cog or small chainring/small cog? (I know cross-chaining should be avoided)

I ask because, no matter what I do, I can't eliminate chain rub in the biggest/smallest cogs. The chain rubs on the inside of the front derailleur cage when on the biggest cog, and it rubs on the outside of the front derailleur cage when on the smallest cog.

I question whether the front derailleur cage is bent (narrower than it should be). It's extremely difficult to shift to the big chainring. If I make adjustments so it is easier to shift to the large chainring, the chain rubs on the inside of the front derailleur cage in every single other gear.

I can't find any information about front derailleur cage widths, but when I measure mine on the inside of the plates, it is 1 cm (or possibly 9 mm) towards the front. I measured cage widths on four other bikes in our garage, and they were all about 1.25 cm.

Possibly you know this already but if not, there is a thing called "trim" which is a half-shift of the shift lever which slightly moves the derailleur over to stop the rubbing without shifting to the next chainring. It feels like a soft click compared to the other clicks.

Are you certain that you have it aligned perfectly parallel over the large chain ring (or small if that's easier for you to see) and within 2mm from the large ring when positioned over it. You should be able to eliminate all chain rub unless you're in the large up front and the large in the rear or vice versa (small to small). That is not always possible (rarely). My clamp-on FDR moved once on my favorite road bike and took me a while to figure out what happened, but it caused exactly what you're describing. Good luck,

Yes and no.

The problem arises because of the mix of wide cassettes and short chainstays. This means that there's a big difference in chain position within the FD cage, depending on which end of the cassette you're using.

The obvious solution would have been a wider cage, but that would worsen shifting.

So, some FD levers have 2 clicks for the outer ring, and you shift that half click to trim as nneeded. Others may not trim, and you simply avoid the problem combinations.

Or you learn to live with chain rub. Yes, it does wear the cage and will eventually go through the chrome and the steel under it faster. Eventually you will have to replace the derailleur if you use the rubbing gear combos enough. Chain rub isn't a matter that requires attention. Everything works just fine while the rub is happening. I raced long ago on a bike with a very narrow cage that we used to further narrow with a crescent wrench to speed up shifting. Rode sometimes for miles not noticing the rub. About every two years I replaced my FD because I has created deep grooves in the cages. Never affected my rides or races.

Yes, it might be bent. Top down pictures help.

What the above posters have said. But I've always figured even with perfect derailleur and adjustment, it can be just the way mechanical stuff works sometimes: there are limits in which it works well. In this case, not big-big or small-small. There's really no reason to use those combos, just don't use them. I can't give you specific examples, but over the years with various drive trains and bike frames, I've had derailleurs that rub in the extreme cross chaining. I've adjusted as best I can and then just chalked it up to it being the way it is, it seems logical, and I don't bother chasing it down or obsessing over it.

Some FD cages rub and some don't. I've learned to not cross-chain, but I've also manually widened a FD cage or two to somewhat mitigate this issue.

Usually, yes. It starts with setup and mounting of the derailleur. I've found it easiest for this when a hanger is not used and the derailleur clamps to the seat tube.

I've found it near impossible to remove all chain rub when the bb shell is not faced perfectly and an on-frame hanger is used. The hanger limits the derailleur mount. A poorly aligned bb shell will cause chainring wobble.

Remember, you must trim the front derailleur when shifting the rear!

How would that cause anything to wobble?

Proper installation of the FD contributes to good performance.
1. Outside plate should be parallel to the large
2. 1mm clearance of the bottom edge of the cage plate from the teeth of the large ring
3. Limit screws should be adjusted for large ring/small sprocket and small ring/large sprocket
4 proper cable tension.

Large/large and small/small with rub is normal, as stated above. It can vary. I have more rub on older drive trains then newer ones. The Campy Record 10V on the De Rosa is nearly imperceptible but it has a plastic insert on the outside of the cage.
https://live.staticflickr.com/65535/...13365d07_b.jpgP1050183 on Flickr

The 2x7 Nuovo Record on the Colnago is very noisy in x-chain configuration.
https://live.staticflickr.com/5488/1...a3e17a7d_b.jpgDrivetrain on Flickr

Can't say for sure, but I think the flexibility of a narrow chain along with chain stay length are major contributors along with cage width..

Now when a triple is in consideration, the FD is often a different design. The Campy FD example in the following pic has a "step" on the inside plate near the bottom. Hard to see in the pic but it is there.
https://live.staticflickr.com/65535/...366e666e_b.jpgP1030407 , on Flickr

I know there isn't clearance for the ring in this picture. This condition is what alerted me to realize I had a triple FD instead of a double. It ended up on the Pinarello. Another way you can id the difference is to look at the "arm" with Record stenciled on it Note the location of the "D" relative to the limit screw.

Look up the Shimano instructions for your derailleur. Shimano There will be a picture that shows which combos will rub. It's normal to have two or more with current components.

Consider that the rub as a reminder that you are in a gear combo that you shouldn't ride in for extended periods of time. However , are you aware of how to use the trim as another person ask?

Though some bikes will always rub regardless due to things about their design that put the chain in a slightly different angle coming off of the rings going to the rear cogs.

I tried to post photos and I'm too new to the forum 😅 Said I need to create ten posts first lol

Thank you for the reminder! I intuitively knew about this, but didn't know what it was called. Sometimes I feel like it does help, sometimes not. I will have to pay more attention and remember to try this when I'm having chain rub issues.

Just put them on an image hosting website and paste the link as text. Imgur works fine.

There are tons of excellent and active threads to get involved in and you can get 10 posts easily. Nothing really funny on that front, it is a very useful tool to prevent spam and also encourage people to use the forum rather than treating it like a search engine.

https://www.bicycling.com/bikes-gear...a-comp-review/

Sora usually works without cage rub, IMO...

i'd be highly suspect of it being due to misalignment or damage....
and i'm not seeing any mention of Bottom Bracket BEARING Play.. Is there Any BB Bearing looseness or roughness?

Thank you for your response! There are no issues with the BB.

I wish I could send a photo of the FD cage, but need to make ten posts first lol.

I took the bike out for a ride yesterday, and it rode/shifted much quieter and smoother than it had been originally.

Currently, there's some chain rubbing while cross-chaining, but also when on big chainring/smallest cog (not very intense at least) and also on small chainring/biggest 2-3 cogs.

To quote myself in case you missed it:

Hopefully you get involved and we can easily see those pictures and you will have the satisfaction of being a part of a neat community of folks who enjoy bikes in some form or another.

First, when you said big and small, you are referring to physical size, rather than whether it is easier or harder to pedal, right? You did not specify how many speeds the RD and cassette are. For example, Shimano documentation indicates that the 3 or 4 physically smallest cog of an 11 speed cassette cannot be used with the small chain ring without rubbing.

It sounds like your FD is not properly adjusted. What is the specific model of your FD? In my case, Shimano FD-5800, I got better results from following the steps in the Shimano dealer manual rather than the Park Tool video.

The chain will always be noisier at an angle than when perfectly straight. If you mount the bike on a work stand and pedal and shift, do you see or hear any actual rubbing between the chain and the FD cage, or is it just noisy? Also, have you checked whether the chain is worn?

It's been a couple of days since you originally posted. Heck, many of us comment more than 10 times per day! Stick your nose into threads that interest you and make comments or questions. Get on it, mara777 !! ;)

That said, when I was kind of new to FD adjusting, I would chase adjustments around and get frustrated. Then I learned that it works really well to completely disconnect the derailleur from the cable and completely re-adjust it starting from step one in the manufacturer's guidelines: alignment, height, limit screws, cable attachment and tension. Everything, not skipping any step. You won't overlook anything and might get some insights that help you do minor tweaks in the future.

Yep. Following the mfg instructions is especially important with current Shimano FD. :foo:

Ok I should be able to post photos now. I don't know if this is what you are looking for? Maybe the cage isn't aligned perfectly parallel to the chainrings, but it's kind of hard to tell since the plates aren't perfectly straight from front to back? Currently, I have it adjusted so that there is very minor chain rub on the outside when I'm on the large chainring/smallest cog, but there is a bit more rub on the inside when I'm on the 2-3 largest cogs using either chainring. I believe the chain only rubs at the very front of the cage (when it rubs on the outside plate and on the inside plate).


https://cimg7.ibsrv.net/gimg/bikefor...8c5638c07.jpeg
https://cimg8.ibsrv.net/gimg/bikefor...371587f20.jpeg
https://cimg9.ibsrv.net/gimg/bikefor...faa7d108c.jpeg

It would have been nice to see the back 2/3 of the cage without the top of derailleur blocking the view, but it doesn't look like anything is bent.

Find the longest straight section of outer cage plate and use that part to align with the chainring. Do it when the cage is in the low cog so that outer place is right over the outer chainring.