Try calling UDC (free call), and asking.
From the look of it, the rim is not big enough for that muni tyre. You may be able to fit it on there, but it would fold a lot - but of course you are best of actually calling UDC and asking, as tattooedbandit said.
I’m thinking it might be better to go for the the Numbus ISIS trials 20 now and save up and get a better 24" maybe 26" for Muni and moderate distances:D . I still have my self-repaired “ebay 24” if im going for “longish”(not very long) rides. 
I’m going to ring around today but it would greatly help if anyone could tell me of any shops that sell unis in Sydney??? I know heaps of people here are from heaps of different places but i have seen a few Sydneys:)
Quick resppnse would be appreciated:D 
Thanks for all the advice guys
I’ve just bought a Nimbus 20" Trials with all my Bday money:D
You guys were right and helped a lot
Ill try and give an update when i get it:)
Cheers,
Sam
Is it the one with the ISIS hub samsta???
I think you made the right choice. ENJOY!
see the post 2 above yours.
ok, i’m a little dissapointed 
not in what you bought, but that you didn’t get a proper explanation, while trials can be done on a 24" a 19" is ideal, and more likely to be comfortable in the long run.
quax and torker make good unis too… for an up and coming rider.
Well it turns out that on the day i ordered this uni uni.au.com got 3 orders but only had 2 of them
I was the last to order and they are offering me this one for the same price as the Nimbus
What should I do?
Does the Qu-ax 20 have ISIS?
Cheers,
Sam 
Bugger about them selling out, the Nimbus ISIS on UDC Australia is real cheap! I paid $450 for mine in New Zealand. I wouldn’t buy that Qu-ax for $340 Australian dollars, it’s not really set up for trials. They even state “Although this is called a trials unicycle it does not have the large volume tyre that other trials unicycles have so is only useful for beginners and lightweight use. It is not suitable for serious jumping as only has lightweight ISIS hub and cranks, for extreme jumping look at our unicycles with splined hubs”. As you get better you’ll end up bending/breaking stuff. I’m not really familiar with Qu-ax uni’s though.
Unfortunately UDC usually takes a few months to restock. You could keep checking ebay for ISIS trials uni’s. I know that muzzle is selling a good nimbus with KH hub and KH/onza 06 cranks. Not sure how much it’d cost to ship from New Zealand though?
Here’s a link to the trademe auction: Trade Me
I may be wrong as i don’t really know about Qu-Ax, but I think the one with the yellow hub is much stronger, although a little heavier. It’s the $475 one. Perhaps ask for the $60 difference they are offering and then pay the extra $75.
Like I said though, I don’t really know about Qu-Ax so maybe somone else will be able to help better.
I’ve got a 24" qu-ax. It’s pretty much bomb-proof.
But you’ll need to change the pedals and the saddle on the stock model. Maybe you should ask your udc if they can change them before you buy it for a small additional price.
Just… don’t get it.
Today I rang again, knowing that I didnt want the $400 one and negotiated and came out with this uni for the price of the Nimbus ($340)
I’m pretty happy with the deal as the uni is a mountain and trials, what I was looking for originally
I hope you like it, it’s 6.55kg so hopefully it never breaks! 145mm cranks are quite long, but yeah… not a bad uni for $340 australian.
Well done Samsta, that’s some nice negotiating. $135 saving. Kinda wish i’d ordered one too now.
Just got my Qu-ax 20:D
Tis an absolute beast:D
I’ve put it all together but still need to cut the seat post
Any tips for this?
Just use a hacksaw or a pipe cutter if you have one. Just cut it down little by little to make sure that you don’t cut it too far.
don’t forget to bevel the bottom end of the seatpost if you can. use something abrasive such as sandpaper, a file, or some type of a grinder, ive even used a dremel. the idea is to remove the burr (rough edge left by cutting) so the seat post slides smoothly into the frame. this is not neccesary, but it does add a nice, proffesional touch 
OH YEAH! Thanks OneWheelLess. I forgot to say that. Inside and out too. A file works best. I guess I assumed people automatically do it like I do.