Should there be no chain contact with front derailleur no matter what gear?
 

Should it be possible to adjust the front derailleur so that there's not even slight brushing contact audible while pedaling no matter what gear?

Yes, that is a true statement. However that not how everything goes. One may have cranks that have sway, and/or flex on the strokes. One may need to coldset the rings or the spider for even rotational clearance.

Frame flex can happen but that usually can be cleared with shifter trim.

I wouldn't say "no matter what gear." Cross-chaining may induce chain rub. Which is--personally--one of the several reasons why I don't do it.

Yes, and unicorns...

This could be a matter of priorities. I raced and still have some race expectations of my shifting. No, it doesn't have to be as fast. But dropped chains from hasty upshifts or downshifts up front? Well I leaned decades ago that those happened most often when on the extreme cog corresponding to that chainring. Ie - when on the small cog and shifting inner/middle to large chainrings or large cog and shifting to the inner chainring, That a simple solution was to set the limit screw to a touch of rub when in my highest or lowest possible gear.

I set my bikes up with no rub. First dropped chain and that limit screw comes in say a 1/4 turn. Repeat if necessary. Now, this is all for friction shifting and on most of my bikes, using the old, narrow SunTour front derailleur, often with the cage narrowed further with a shorter bolt at the bottom. (Better, quicker shifts to the inner ring on triples and again, fewer chain drops.)

Edit: My experience is almost entirely with friction shifting and I have never had brifters.

I haven't (at least yet) owned or ridden a 1x system. But on my 3 x 9 road bike, don't think it's possible. The bike shifts great, is quiet in most gear combos, but even well tuned, some combos will have the chain rubbing the derailleur cage. There are enough combos that those specific combos can easily be avoided. Not a problem (for me).

Yes, this is what you want to achieve and it is indeed achievable. Well maybe not if you are in your larger/smaller front ring and the opposite smaller/larger cog on the back, but that's on you.

1. Check your derailleur hanger alignment; if it is off no amount of other adjustments will fix things across the entire range.
2. Check your chain line; too long/short an axle could be putting your chain at the wrong position, forcing unnecessary steep angles.
3. Check your rear derailleur, they do get bent.
4. Adjust your limits on the front derailleur so you have enough movement.
5. Non index friction shifters let you put that derailleur in whatever position you like.

It'd be real nice if that were true, but I don't think it always is. Especially when you get into 11 speeds on the rear. While for the perfectly designed and built bike it might be true, but probably not all bikes are perfect in all the ways they need to be perfect.

Trim helps quite a bit. If you don't know about trim, then you should learn about it. And don't forget to take trim out when you go back the other way if you don't make a front shift.

The bike I have with microshifters lets me make very small adjustments to take the rubbing out.

It is not possible on all bikes and set ups. I have 2 different 2X bikes, 10 and 11 speed, that I can trim to hit all gears with no front dr rub. I have another that I have never been able to get to that point. I can set it so either the lowest or highest will clear no matter the front ring, but not both at the same time. The one I cannot stop the rub has a braze on mount, the other 2 are clamp on. Maybe being able to adjust the angle a bit makes a difference. I keep it so I can hit the smallest cog with the big ring, and the biggest cog with the little ring. Just to throw this in, one bike I went to a 1 X 12 set up, 44 front with 11-34 rear, no worries about the non existent front DR. I have to say, I really like it.

With 2 chain rings, it is possible in most situations. With triples, no.

Despite all the talk I hear about modern drivetrains having enough room to eliminate rubbing in cross chaining situations, I can not seem to adjust my FD in such a way. Doesn't matter though because hearing the rubbing tells me I'm cross chaining and I don't like doing that anyway.

In some instances, you can fit chainring bolt spacers to move the outer chainring outward to eliminate rub. The spacers are very thin washers (.5 mm or 1 mm thick) that go between the ring and the crank arm.

Which can lead to the chain getting stuck between chainrings.

I don't know why people go to such lengths to make their bicycles cross chain into gear combos they already have elsewhere.

I haven't run a 1x system either, but guaranteed there should be no front derailleur rub with the chain.

On occasion, we agree!

I don't get any derailleur rub with the 2 x 11 GRX drivetrain on my gravel bike, but I do get chain rub on the large chainring when I shift to the smallest cog and the small chainring. Reminds me not to do that

Wouldn't that keep the chain from rubbing the other chainring, but make the derailleur cage rub even worse?

Agreed

A silent front derailleur... Ahhhh...

One of the benefits of using non-indexed friction shifters...

Or indexed shifting, used correctly.

I have 10 year old first gen SRAM Rival. No trim. Never rubs because I don't ride in crossovers.

My Campagnolo Athena triple has a trim position for cross chaining. It's essentially a half shift toward the bigger chainring. It's a click when the shift lever is moved about half way.

(My Di2 has auto trim, a front derailleur small movement when the rear reaches two different mid cogs. Nice!)

Ideally, it should be possible, although the extreme gear combinations (small front ring, small rear sprocket, large front ring, large rear sprocket) may be a problem, but those combinations are best avoided, anyway. With friction shifting, it's generally possible to trim the front derailleur to eliminate scraping, but not all indexed front shifting setups allow for this.

Depends...
On older drivetrains...9 speed and down...you can 'generally' eliminate chain rub induced sound but then again not always...depends on the setup of the front derailleur...it is correctly adjusted, etc. Also depends on the gear you are in...a lot of chain rub comes from cross chaining and that is a user caused situation.
As the gears increase cross chaining seems to be more prevalent and as the front derailleur cage becomes more narrow chain rub becomes more common...see the little plasticy insert Shimano uses...reduces the sound of metal on metal chain rub when cross chaining...brilliant isn't it lol...

+1 on that. Or wearing a gouge in the chainring arm.

to the OP I'd suggest looking closely at your derailleur alignment - out plate should be parallel with the big ring.

/markp

I've got a triple (nine speed). Sometimes, for fun (!), I run through every possible combination, including small-small and big-big. I can get them all without chain rub, though I have to use trim on some combinations. But in normal cycling I don't get any chain rub, and I don't have to use trim either.