I've got a Rondo Ruut.

Two wheelsets
(1) 650b with 2.1inch tyres for the Gravel rides (and road rides...I often ride these on the road)
(2) 700c with 32mm tyres for the road (and light gravel rides)

I have one cassette that I swap between the two. Takes me 2-3min. I could have different cassettes fixed to each rear wheel I suppose but I haven't gotten there yet.

Running 1x....42 up front
10-42 on the rear.

I haven't run out of gearing on the road yet. Spinning up to 120rpm in a road race but fine to hang with the bunch.

If I did get a bigger chain ring up front I might need a longer chain but then I'd just have two chains in my workshop and swap them out as needed.

Sold my roadbike when I built this one and I've never been happier. The only riding it can't answer for me is the really rough MTB stuff.

I have a racing cassettes on my racing wheels and training cassettes on my training wheels. I have a race chain that goes on when the race wheels go on. As for the training wheels the cassettes are cheaper models and I replace them as I do the training chain when they are worn out.

There's best practice and there's 'here's what works for me with no complaints.' This is the latter.

I think I'm at 8 or 9 wheelsets for two identical CX bikes. Smallest cassette is 11-28. One has an 11-40. The Shimano RX800-GS (Ultegra, clutch, longer cage) is ideally set up for the 11-40 cassette, but has been flawless this year with a handful of 11-28 and 11-32 cassettes for CX racing. Previously, I was using regular short and long cage 105 or Ultegra rear deraillers up to 11-34. Wolf Tooth extender when I wanted the 11-40. It didn't shift very well on the small cassettes, so it was basically only used for the 11-40 until I ripped off another derailleur last January and bought the new clutched version with higher capacity.

I have 5-6 chains for those bikes too. They get rotated every couple hundred miles or terrible conditions event. Whichever comes first. Most are sized for 11-32 and work just fine with anything 11-28 through 11-34. I use a different (longer) chain for the 11-40. I think the 11-34 wheelset was used with the 11-40 chain a few times over the summer.

I really can't think of any problems. If you use too long of a chain, dropping the chain is more common. The newer clutched derailleurs help with that. I have seen it on bikes sized for a 10-42 cassette that are suddenly using a 11-28, going downhill fast and a bunch of excess chain bouncing around the small tooth on the cassette suddenly launches wraps around the crank or bottom bracket.

There's no real reason to use the same cassette gearing for your purely hypothetical situation if you can use a new Shimano Ultegra or GRX (or Sram long cage) clutched rear derailler made for a bigger cassette. I wouldn't go smaller than an 11-28 cassette on your skinny tire wheels. It's pretty hard to go bigger than a 40 or 42 tooth cassette on the other wheels.

I've got a Sequoia with 3 wheelsets.
650b w/2.1 knobbies and 11-40
700c carbon 40mm rims w/32 Pro One 11-34
700c grails w/38 G-one 11-36

respectively use them for:
gnar
road
gravel

I use the same chain for all. It's sized one link smaller than what ideally it should be for the 40t but i'm good about not cross chaining (not sure if you are 1x-ing it or not). Also good about replacing it before the chainchecker falls in the hole.

Currently in an n-1 phase and this is my "project 1 bike." Commuting, road, gravel, fully rigid mtb. So far so good.

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36 kona qualifiers 2006-'23 - 3 Kona Podiums - 4 OA IM AG wins - 5 IM AG wins - 18 70.3 AG wins
I ka nana no a 'ike -- by observing, one learns | Kulia i ka nu'u -- strive for excellence
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