When I ordered a Torker unicycle from Amazon on a whim about a month ago, I received one with a fairly knobby tire that was 2.125 inches wide. Now that I can ride 50+ yards at a time, I’m wondering if a narrower or smoother tire will make riding easier or not. I ride mainly on the street or an inline rink. What are the differences between how the tires respond? Thanks
thinner tyres are easier for road use once you have got used to them, you will probably feel a bit wobbly because you are used to a thicker one. if your not going to be doing any hopping or drops then a thinner tyre would be a better idea 
Pump it up.
At higher pressure you will get less resistance from the tire. (It also becomes a bit harder to control, as does a very narrow tire.)
Try it and see if you like it.
Scott
You may want a Hookworm for road use. I like it on my 24" KH.
Carey
When I was learning, I learned on a really crappy uni with a really skinny low pressure tire. The result was that it was really grabby when making turns. O hated this, so I bought a new high pressure tire that was also skinny, and it helped me a lot. I preferred to have a tire with less friction with the ground because it became easier to make small fast adjustments, as I was really unstable.
I agree with Ereksonj. The high PSI tire is very very responsive. To the point of becoming difficult. Except for my 36er, I prefer to ride at 100 PSI or greater. After you become familiar with the feel, the difficulty goes away. I would suggest high pressure for advanced riders only. But, check it out. You might like it.