I have a 26" wheelset with a 42mm wide Nimbus Dominator rim. I don’t think this size will accommodate fat bike tires but I’m wondering what the largest size it will accommodate. I’m thinking about trying the Origin8 Captiv-8er UL 26 x 3.5" but have only seen this in the wild on a larger rim. Does anyone have experience trying something wider than the 26x3" Duro Wildfire Leopard on a Dominator rim? I’m planning to ride this as a wheelset so it doesn’t have to fit in a frame.
IMHO, you’re not going to get anything larger than a Gazz (3") to work on a D2 rim. I’ve little experience with fatbikes, but from what I’ve seen, their tyres aren’t as stiff as your average uni tyre, necessitating a wider rim for support.
Even if you could get a 3.8" tyre to mount (and stay mounted) on a D2, I doubt it would ride very well. Part of the reasoning behind chosing wide rims on unis is to stretch the tyre out for a squarer profile.
I tend to disagree. According to MTBR forum, running a 47mm rim with fat tires in the 26x4.0 range is possible and works. Remember than 47mm is already plenty wide by MTB standards.
However, I agree that fat tires are used to their full potential with wide rims (65mm and wider) but I am sure that it will make for a rideable uni. It won’t be that much worse than anybody riding a 30mm rim with a Duro 26x3.0 
I was planning to get a fat tire for my 24 with a Koxx-one 47mm rim… I am very interested Waaalrus by your experience. And if it doesn’t work, we can split the cost of an Oregon 
Thanks for your feedback! I went ahead and pulled the trigger since I could pay for it with my Amazon points. It’s a worthwhile gamble just to see what it’s like. As I said I’m just planning to ride the wheelset and a worse ride may be better for my purposes (ankle exercise) anyway. As long as it stays on the rim I’ll be good.
With a “skinny” rim you change some of the characteristics of the fat tire and what you can get away with.
A fat tire on a skinnier rim would have to be used at a higher pressure than the same tire on a wider rim to keep the tire from folding etc. With the higher pressure and rounder profile you loose some of the cushion and float that the fat tire provides but you will get a easier to steer and more precise wheel. In fact it should result in a wheel similar to riding a heavy 29" wheel with a moderately wide tire on a wide rim without the risk of rim strikes and pinch flats.
Though I don’t feel it is ideal for unicycles a tire twice as wide as the rim is pretty normal in the mountain bike world and I don’t think you will run into any major problems.
Let us know what you think, i am always curious about people perceptions of gear when they stray from the “norm”.
Mmmmf! Mmmmf!
removes foot from mouth
I guess you’re right there…
That said, who rides a Duro on a 30mm rim?
I second that. All this talk of fat wheels makes me want to buy one.
I got Origin8 Captiv-8er UL 26 x 3.5" tire today and was pleasantly surprised to find it just fit into a 26" Oracle frame.
I rode it for a short time at high pressure and found it to be a lot of fun. It felt more sensitive to balance changes but worked fine when I kept to a more rigid posture like I use when I ride my freewheels. I just sent my 26" Nimbus muni frame off to get a disc tab welded on so I can’t see how well the tire fits that frame for a couple weeks. It seems like it’s going to be perfect to ride as an ultimate wheel.
I went on an 8 mile ride on this tire which included 3 miles of riding in a river bed with sand and loose rocks. I’ve tried this area before on my Duro Leopard and found it to be mostly impassable. I can ride sections where the sand is firmer and the rocks are tighter together but not this part right in the middle of the river bed. On the Captiv-8er it look a little pressure experimentation to find the right amount but once I did I was able to ride fairly well although it was still slow going in the loosest stuff. Best of all it was fun! I rode back on a trail I ride a lot on my freewheels with Leopards and I pumped the tire back up. It floated over a couple soft sections I normally have to grind out but I was almost constantly wrestling the tire to get it to go straight. With the narrower (42mm) rim the tire is very sensitive to any camber including the constantly changing camber of this trail. It works fine in soft sections and when a road/trail is level laterally but is a struggle otherwise. I’m interested to see how this experience compares to a 24x4" tire on a Large Marge (65mm) rim.