I direct your attention to post 13. 11 speed cassettes aren’t anything magical. Large cogs on the rear have been around since the 80s when Suntour offered a freewheel with a 38 tooth cog. Granted, larger rear cogs have become more available more recently but those can be used with a triple just as easily as with a two ring set up. The triple, as I showed in post 13, has more choices when it comes to gear selection and an easier to ride shift pattern.

As to exceeding the rear derailer’s capacity, that’s difficult to do. My touring bike I used for the example in post 13 has an old gray XTR rear derailer on it. I am using a RoadLink so that it works with the 36 tooth cog but that isn’t a problem. Additionally, I do have to run a bit longer chain which can be problematic on cogs smaller than the 20 tooth cog but that’s not really much of a problem since I usually shift up to the middle ring before I get to that size cog.

I also have a mountain bike with a triple…yea, I’m old school…with an 10 speed 11-40 cassette and a 20 tooth inner chainring. It uses a 10 speed SRAM XO rear derailer that has a larger tooth capacity than the XTR. I also have an 11-42 tooth cassette with works as well. There’s not much out there that can match that range. A 1x can get lower but the high suffers even with a 10 tooth cog on the cassette. A 50/34 double with an 11-50 would get close but the gaps in the shift pattern are really bad.

And if you can run a double with an 11-50, I can run a triple with the same cassette, although a 20/40 combination doesn’t really need to be much lower. It’s a pretty slow speed.