Derailleur, Cassette and Chainrings
 

Hello to every one! I have a vintage road frame and i want to customize it with new components. I am looking to put a rear mountain bike cassette (11-46 or bigger) and road bike chainrings at the front. BUT, i think there is no derailleur with such a capacity to fit both so big cassette at rear and also big chainring at front (34-52 for example). Also, i saw that there are chainrings with 58 and 60 teeth. Are they worth it? What i want is to have a road bike and climbing even the most sharp slope. What can i do? What do you suggest? (custom derailleur cage for example, or an other groupset, or... whatever)

Thank you for your time!

First thing to do is to measure the space between the rear dropouts. Much older bikes might be 120, 30+-year old might be 126. Somewhere near the early 90s brought 130 mm, and most MTBs are 135 or 142 or whatever the new "Boost" and "Boost Plus" and "Only buy our parts" standards are.

I think, but i'm not sure at all, that this space is 130. I will measure it when i can because i dont have the frame here now. But after that?

Consider a triple crank instead.
The joy of riding something exotic, unique, tend to fade really fast when you have to hunt down or pay for one of those rare and/or expensive parts AGAIN.
Really big rings are primarily a benefit for small wheeled bicycles.
And for those who are either anatomical freaks thriving on low cadences, or like playing Russian Roulette with their knees.
Or some other specialty application.

I don't think that there are any rear derailleurs that are officially spec'd to do what you're asking. The S-Ride Over Long Cage rear derailleurs (like this) come close, and would probably do the job. Shimano's 2x gravel derailleurs (like the RD-RX810) are only spec'd for 11-34 or 11-36 cassettes, but they have a huge b-screw adjustment and can handle much larger cassettes surprisingly well, and might be an option as well.

You might end up with somewhat baulky shifting in the small cogs, though. And if you do the usual "big-big plus 1 inch" chain sizing, expect the drivetrain to go slack when in the small ring and the smallest cogs, since you'll be exceeding the derailleur's chain wrap. When you pair 11-46 cassettes with road 2x cranksets, you're getting into the territory of things that "can be made to work", but should not be expected to work as cleanly as the certified combinations.

Why are you looking into super-large chainrings?

Agree that if your goal is to handle the steepest climbs, consider getting a triple crankset along with a more typical road cassette (12-34).

Yeah. Selection of triples is thin for 11-speed or whatever, but an old-school wide-range touring triple isn't necessarily a bad option for mostly having a road drivetrain but with some bonus climbing gears.

Like the 3x8 on my gravel bike:
48-38-24
11-13-15-18-21-24-28-32

https://i.imgur.com/oUFqt3q.png

It gives me a 113" top gear (a bit higher than what Eddy Merckx raced on) and a 19" bottom gear (lower than anything officially supported by most current "gravel" drivetrains). The cassette has wide steps, but the two larger chainrings do a good job of 1.5-stepping it, so there are tight shifts available in most situations where I'd want them. And the cheapo RD-T4000 handles it very well.

It is hard to build a real "do-everything" bike .... there are just too many things a bike can do.

If the steepest climbs you want to climb are paved, 8,9,or 10-speed triples should be great---just what @HTupolev suggests.

No reason you can't use an 8.9. or 10-speed FD with an 11-cog cassette either .... the derailleur cage will be a little wider than necessary abut that is no problem. You might have to mix-and match brifters---unless you go with bar-ends.

Yo also need to be realistic about how fast you want to go and really will go.

I think a 50-34 with 11-28 setup at 90 rom delivers 33 mph on the flat---but how long can most people honestly spin 90 rpm with a 50x11? And do they spin out (pedal so fast they rock and wobble)? Unless you are addicted to doing 45 mph downhill, I'd suggest smaller chain rings (48,36,24 is about perfect IMO .... I use 48-38-28 with 14-34 and can get up a lot of hills, and I am old, fat, and weak.) If you really spend a lot of time going 35 mph on the flats, okay .... and if you also need to climb 15% grades on those same rides .... but I think most people could use what HTupelov suggested and be fine.

You could probably get an 11-34 or 11-36---24x36, the problem would be not falling over because you will be going so slow.

The only
possible reason you’d want a 58 or 60 tooth big ring would be on a time trial bike and then only if you’re monster strong, and are gearing for a course with a lot of downhill downwind.

Even then super big chainrings are going away with the availability of 10 and 11 tooth rear gogs.

A 58 tooth big ring is the exact opposite of what you want to accomplish the goal of gearing to climb anything

Thank you all for your advices and your time. I understand what you suggest and i will build the bike, following your instructions about the gearset.