Graupel731

My trek fx front derailleur appears to be rubbing against the "chain guide" (don't know the technical name"). Especially if I'm riding in the smaller rear cogs (e.g., 2-5, 2-6, etc.). Can the guide be adjusted - my quick and low knowledge regarding bike mechanics leave me hesitant.

FBinNY 

Is the cage (the part the chain runs through) of the front derailleur rubbing something on the crank? Or is the chain rubbing on the inside of the cage in certain gear combinations?

Either can usually be corrected by making adjustments, but the specific answer depends on a better explanation of the problem.

Before reposting, you might search for some free tutorials for "how to adjust a front derailleur" or similar and review them to get a sense of what you need to do.

escarpment

by chain guide do you mean the plastic piece on the outside of the crank? whats commonly refereed to as a bash guard. if so than no. If the chain guide is a plastic piece on the inside than probably.

but those are technically there to keep your chain from slipping

Graupel731

Alright, will do!

FBinNY: Yep, the chain in certain gear combinations (specifically 2-5, 2-6, etc. where 2 is the 2nd or medium cog on the FD) is rubbing on the inside of the cage of the FD. From Sheldon brown's website (https://sheldonbrown.com/creaks.html), I couldn't find a match to the problem per say. Also, further reading (https://sheldonbrown.com/derailer-adjustment.html) makes it sound like an adjustment to the FD shouldn't be made in haste unless i'm sure the RD is not the culprit.

Hmm..

Graupel731

Well, I took it to the LBS and they took a look at it. From his explanation, because it's a compact crank/triple crank, you may hear it rub at combinations 2-5, 2-6, etc. and that I should then change to a "higher gear" (e.g., from 2-6 to 3-6 then 3-5). Like, think of it as a signal?

Thoughts?

My understanding was that with the FD derailleur, the chain will only touch the cage while shifting.

cny-bikeman

The chain is at an angle when going from a more inner chainwheel to a smaller rear cog. It's still a fairly high gear, and will tend to rub due to the angle. You just need to observe what the chain looks like as it is in different combinations to understand why it rubs on the cage in certain combinations. Sometimes the left shift lever allows you to move the derailleur (trim) part way to prevent rubbing. It's bad practice to ride cross chain with the small cog in the rear due to both angle and high wear.

Finally, as to what the bike shop folks said, the gear ratios with the chainwheels in the front overlap. So if you have rubbing on a combination with the middle chainwheel you can probably get about the same "feel" with a larger chainwheel and larger cog - for example 48 front, 17 rear is close to the same ratio as 38 front, 14 rear. So if you "double-shift" by moving to a larger rear cog and a larger chainwheel you avoid the cross-chain and rubbing. You can find lots of info on using gears and shifting to help you understand, but it's easier to find someone in person to help you if you can. Of course it is possible that the derailleur can be misadjusted, but presumably the shop checked that.

tahoeeddie

i agree with cny-bikeman. it sounds like your problem is more with cross-chaining (how you are riding your gears), rather than a mechanical issue.
although, it is possible that you may need some simple (but tedious) fine tuning of your front derailleur. i recently had to do that for mine when it came back from the shop for an install of new cranks/chainrings. depending on your bike, you may or may not be able to fine tune that. for my bike i have a barrel adjuster for the front derailleur.