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There is currently a choice of rim widths ("mouth sizes") that following the tables I found on the web would pass for my 2.35" (27.5" diameter) tires. In general the tables seem quite liberal, assuming a wide range of width would work.

Assuming it is the same tire, would it be easier, more difficult or makes no difference to mount it on a wider rim vs more narrow? I have a rogue rim difficult to mount and suspect maybe there is some extreme mismatch of some important parameter.

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    In my personal experience, for road bikes it’s much easier with wider rims (>17mm internal width instead of 13mm)
    – Michael
    Mar 30, 2022 at 7:36
  • @nightrider have you tried feeling around the rim for any kind of burr or sharp edge? It could be that some light sanding and gentle polishing could give you the difference needed to ease the tyre's fitting, without making any significant difference to the strength of the rim. Same goes for the tyre - sometimes there's a mold line or sprue left over that could be getting in your way.
    – Criggie ♦
    Mar 30, 2022 at 7:53
  • @nightrider another option is to grab some fine measuring tools like an internal micrometer, or maybe a vernier caliper, and compare your front and rear rim's internal measurements. From memory you said the rear causes issues but the front is easy by comparison.
    – Criggie ♦
    Mar 30, 2022 at 7:54

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A wider rim (meaning the internal distance) will allow a deeper valley, so the tyre bead can settle further into the rim on the far side from where you're levering.

So yes a wider internal rim width would be easier to get the same tyre on/off.

The external rim width for aerodynamics should be about 105% of the tyre's maximum width, to reduce the airflow splitting from the surface and becoming turbulent. This is much more of a road thing.

An off-road tyre will be much wider that the rim externally, partially to shield the rim from the surface and partially because offroad tyres are enormous.

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    Good explanation. One thing to Add: wider rim widths are trending for road wheels, and with that a little more of a challenge when mounting a tubeless (tubeless-ready) tire on a wider road rim. Mounting being the operative word here and interpreted as not jut getting the tire beads into the channel of the rim, but including getting the beads seated on the rim and inflated. Still doable, but you have to bring your A-game (for inflation and bead-seating) more as the rim width gets wider.
    – Ted Hohl
    May 18, 2022 at 21:33

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