I purchased a 29 in unicycle with a street tire. I have been riding it since April. I ride mostly on streets and a rail trail with small stones probably 1/4 in diameter. I have probably put 75 miles on it total. My tire already is down to the thread in spots. Is this normal?
Mike Adams
No, it isn’t normal. What aren’t you telling us?
Tire type? Air pressure? Riding on a belt sander?
Tires come in many varying degrees of durability and grip, and some seem designed more for looks than for function. I’ve noticed the yellow 20" qu-ax tires perish very fast when left to the elements.
If you turn around on the spot without moving forwards a lot it will wear tires fast, and less pressure will also perhaps encourage wear as low psi grips more and high psi turns easier.
If there are two spots which are more worn than others, you can rotate your tire 90 degrees, or move your cranks if you happen to be doing maintenance. This will prolong the life slightly but it sounds like time to experiment with a different tire. I’m tempted to try a hybrid tire on my 29er with lots of small knobs, I use the Kenda nevegal 700x55c it came with. I have a unicycle with 700x28c too but it gets neglected due to the 36" being faster.
The best way to get a long lasting tire- get a 36" 
I’ve far less punctures since switching.
Are you a wobbly rider? Is it a grippy race tire? Are you running low PSI?
Wobbling on pavement, especially hot pavement will probably wear a tire more than any other riding.
A grippy tire will wear much faster than a touring/training tire.
Low pressure will also contribute to faster wearing, especially when turning on pavement.
75 miles seems like a really short wear life though, even if you are doing all three. I have had tires on bikes last over 2000km and done over 1000km on my 36" and the wear is barely noticeable.
Silly question
Did you remember to rotate your tire?
yes, that’s how I learnt that even with one wheel you still have to rotate your tire! Especially beginners, I think, need to rotate tires often.
I slide the tire around about 90 degrees every four or five months to even out the wear.
First tire on my 24 lasted 6 months, the second one is still going strong after 14 months 
Now is when you go and read all the articles about maintenance 
Have fun
James