I ordered the Nimbus 24 inch MUni. I want to get a road tire for it while I am learning. The unicycle comes with a 24x3 tire. Is it okay to use a 24x2.5? Someone recommended the Hookworm, but I only found it in a 24x2.5 size. Thanks.
Heather
A 2.5 inch tire is just fine for most purposes.
Good luck with the learning process! If you search this forum you will find loads of tips for beginners.
Also, there are a number of riders all over the Bay Area. If you’d like to get in touch with us, sign up on Corbin’s mailing list at http://lists.bluetreesoft.com/mailman/listinfo/muni and shoot us a message.
If you want a road tire and want a 24x3 there is the Kenda flame and the Electra Fattie-O. I have the latter on on my cruiser bike now and it is a great tire. I have one on order that should be in within a couple of days for my Nimbus 24 MUni. Once I get it installed I will get a pic up.
Just go for the hookworm. You won’t ever regret it. 
I’ve heard someone put a 2.5" Hookworm (63.5mm) on a 65 mm wide Large Marge rim and it worked great. So going by that, you could theoretically put on a 1.65" tire on the Nimbus rim. But I don’t think I’d put on anything narrower than 1.95".
For the road I like this Specialized tire. It’s long lasting stiffish sidewalls, light weight, thorn resistant and cheap (I got mine for $14 a year ago).