Why front derailleur is rubbing crank arm?

Question

Last week I realized that when I am on the big ring, crank arm touches front derailleur slightly. If I try to fix that with limit screw, then chain does the same (if I am on rear smallest gear). So it seems that there is not enough space between chain and crank arm for my front derailleur and I can't understand why.

My front derailleur is 1.5-2mm above from big ring and it is quite parallel to it. There is no bent or damage on front derailleur.

My components are;

Ultegra r8000 front and rear derailleur
Cassette 11-32T (shimano 105)
Ultegra chain
Ultegra r8000 crank set (52-36)
Bike is Canyon Endurace Al (components were ultegra 6800 few months ago)

So if you have any idea about how to fix it or what is the problem here I would like to learn.

By the way I have right arm only Stages Gen 3 power meter on crankset, but it seems irrelevant to me.

FD out most
FD outmost 2
Best adjustment possible

Swifty · Accepted Answer

I have a similar issue with my Shimano 5700 50-34 crankset and band-on derailleur, see telltale scratches in photo below from before I noticed and solved the problem. I don't know the provenance of my derailleur, it came second hand with the frame years ago, so I'm not sure why it should happen, but can share what I did.

Normal adjustments of the front derailleur weren't helping; with the derailleur aligned straight ahead, the outer plate would always catch the crank. If the high limit was tight enough to prevent this contact, it was too tight to allow the derailleur movement to the big ring.

So I struck a balance between high limit position and derailleur alignment. The tail of the derailleur is tucked just slightly inboard than I would normally align the FD, while the high limit is set so that the outer plate just doesn't contact the crank. I worked iteratively, angling the derailleur slightly, then checking the cable tension and the high limit vs rubbing the crank, then starting all over again if it wasn't right (patience). This was a few years ago and the derailleur operates fine in either direction, it is only skewed inboard a little bit.

Hopefully you can set up your derailleur with a little care and a little creativity to try something similar. Remember to have the rear derailleur set up correctly (limits included) before working on the front. Yours would be slightly more involved than mine because you have the newer design with the support screw and is a braze on. Then again, using the support screw to your advantage might allow you to be pretty precise in your adjustments.

No cables on the bike at the mo unfortunately, but you might see how the alignment is just slightly skewed in this photo - it is subtle!

Carel · Answer

Pic 1 shows that the outside plate of the FD is unnecessarily far out. It should just be a hair away from the chain when in big front and rear small. You'll have to adjust the limit screw quarter turn by quarter turn, so that the chain climbs on the big ring and does not rub against the outer plate. Also the outer plate should be parallel to the big ring.

On some bikes this adjustment can be a fiddly process requiring lots of patience. Also on YouTube check the videos from several pages like GCN or Park Tool.

Why front derailleur is rubbing crank arm?

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