FWIW- I've used Cyclone and Cyclone MII FDs on 28-38/42/46-48/50/52 triples.

when pushing the limits or beyond, subtle things matter. Consider seat tube angle, (the slacker the better as it lowers the trailing end of the front derailleur in relation to the chain stay.

I've pushed a lot of front derailleurs, mostly SunTour. I've run 52-42-28 the past 40 years. My FW/cassettes were not big, 13-19, 12-21.

Running a Cyclone or the like with that wide range triple, the chain drags on the bushing at the rear of the cage. I replaced the bushing with a stack of tiny washers so the contact was steel on steel, low friction and the bolt is protected (maybe only for the next 500 miles, but that is 500 miles of pure climbing ) I also used to make the stack narrower than the bushing for more positive shifting. Yes, a lot more adjusting to do to avoid rub but rub never mattered a whole lot for those relatively few miles and I always had friction shifting so I could eliminate it any time i wanted.

I now run a Dura-Ace triple FD (new circa 2010) on my best bike. As much as it pains me to say this, it is the best shifting FD I've ever run.

Ben

Thank you. It took a moment to process the concept, but I think I get it. Makes sense to me anyway. But let's check...

The more a seat tube is angled backwards, the lower the tail end of the FD cage sits in relation to the the chainraings, and so it doesn't have to pick up or lower a chain as much as it would if it were positioned directly above the bottom bracket. Correct?

In this case, the frame in consideration has a fairly upright seat tube geometry. Eisentraut touring frame with a 55 cm seat tube, and 54 cm top tube. Seems that in this regard, and without knowing the exact angle of this seat tube, the frame itself may present further challenge on a Vx front derailleur already tasked with a wider gear tooth differential than its designed for.

Funny, I have a 7803 FD and it's explicitly the WORST FD I've ever used.

Of course- the caveat is that I wasn't using it with a "modern" triple- so no ramps or pins. But those things are optimized for EXACTLY what they're designed for.

(these links are both individual posts)

The Golden Boy's Trek 720 Re-Re-Re-Rebuild

The Golden Boy's Trek 720 Re-Re-Re-Rebuild

yes, longer the chain stay the better too.
Reminds me that one of the Japanese companies, Suntour? on one of the front mechanisms sold a cage extender that screwed on to the tail end, for wide range triples... I want to say it was an early Cyclone option, been a long time.

It's not the lack of pins that causes modern front derailers to struggle with vintage or aftermarket cranksets, but rather it is that these modern front derailers have inner-plate "step" features that are designed to work (only) with a specific tooth-count difference between the large and middle ring.

As for vintage front derailer's capacities, it seems that if the crank is a triple, then the capacity might actually be a little better in terms of vertical clearances, owing to the additional vertical (as well as horizontal) cage travel.
And whether or not one might use the small ring and small cogs at the same time might also impact the effective capacity.

The trick is to use the smallest outer ring you can tolerate. (Easy for me, since I'm a spinner who is happy with a top gear of 50/14 or 46/13, or even 49/14 or 45/13.)

I run a 48-40-28 1.5-step-plus-granny on my mountain bike, with SunTour XC front derailleur and 12-28 8-speed cassette in back, and it works like a champ. I can substitute a 24T inner chainring, but to use it I have to be very careful when executing 24-40 upshifts. Fortunately, I am old school enough that I never shifted under load to begin with, but this really reinforces good gear changing habits.