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I have Hope rims Enduro rims, 23mm internal. If I'm rightly informed this limits to 2.4ish tyres?
Enough for work and play, or should I go wider? Longitude MKI frame, so should take plus-sized up to about 3" on a 29" wheel although I don't plan to ditch the 2X anytime soon.
*Hope Tech Enduro rims
I've got Velocity Blunt 35s, though they're some years old now, I'm sure you can still get them. Wide enough for ghetto-tubelessed 3" but also fine down to 1.9"
Hope rims always seem heavy and narrow (I know there are newer ones but they are still heavy). I'd be looking elsewhere. Hunt xc would be a good choice but not sure if they do qr front and rear you need? If you want plus tyres then I would say a minimum 30mm inner, with 35mm+ being better.
If you want plus tyres then I would say a minimum 30mm inner, with 35mm+ being better.
Not sure if I do require plus tyres, or whether 2.4 will be enough as all-rounder, or if they will fit the rims I already have?
Currently running Race King 2.2s, which are ok/pretty good for the riding I do - but would like a bit more cushion for the pushin' tbh.

Just how much more is ... too much more? Looking to fit mudflaps.
If it;s rigid, just go for a fatter front. I've got a 26er with 2.4 on Crest on the rear, 3" on a hugo on the front. Similar ona rigid 29er, but 27mm internal rear rim.
Works really nicely. You get comfort and grip from the front, lower rolling resistance and clearance for 2x on the rear. Compromise is you're missing out on traction for scrabbly stuff from the back, but that might not be much of an issue for you.
Clink
Hunt xc would be a good choice but not sure if they do qr front and rear you need?
Hunt do QR, and they very kindly include the skewers with them too.
Before I sold the frame set, I was running 29x2.35 Big Apples on my 2018 Longitude. Plenty room on the frame/fork but never checked the chain rings (2x). I've now gone for 25mm WTB Tough rims with the same tyres on a Big Bro frame set
I use ARC 35 rims on my rigid 29er with a maxxis ardent 2.4 rear and Nobby Nic 2.6 front. Wide rims are great, let you run lower pressures (good on a rigid) and the tire won't feel rubbish in corners. Also will let you put 3 inch tires on later or you can put big apples on it if you are going to be on the road a lot.