ok so i have a nimbus 20" trials unicycle. i was wondering if its possible to turn that into a freestyle unicycle by getting like a smaller tire (i know it still has to fit the 20" wheel) or something.
so i was wondering if i could do that, or would it really make a difference?? can i use a trials for freestyle? 
… thanks!
oh and can i use a trials for street? thanks a lot!
and exuse me for my ignorance…
Trials unis are almost identical to street unis, so sure.
Only a trials tire will fit a trials rim.
oh ok thank you! what about just replacing the whole wheel but keeping the frame?
You probably wouldn’t have to replace the hub. You would just need a regular 20" rim with the same number of holes as the hub and maybe longer spokes. Most freestyle tires are thin enough that they will still fit in the frame.
Only problem is you end up with lots of tire clearance.
check out the KH flat unicycle.
As you can see with a relatively wide tire (2.1) you still end up with more space between the crown and tire than most freestyle unicycles but it is by no means horrible.
I would leave your trials wheelset how it is and build a completely new wheel for freestyle. The only part you use twice is the hub and it is nice to be able to switch back if you want.
You could save some money by using a cotterless hub with bearing shims to fit your frame.