When I first started trail riding just for the sake of riding I never really gave much thought to my tires. Back in those days I had a Kawasaki KLR 650, you know the "Swiss Army Knife of Motorcycles". It was big and heavy and generally a pig, but it was street legal and I could ride it on trails. I was of the opinion that as longs the threads weren't showing I was still good. Well, many years later I have changed my mind on that particular subject. Maybe it was the multiple times I found myself going the wrong direction up a hill, like sideways or backwards, maybe it was the ridicule at the staging area, maybe age and experience. After thousands of miles off-road riding on a variety of bikes I am a firm believer in good tires, and not just any old tires, but tires that are designed for the terrain you are riding.
Before you start rolling your eyes and thinking this article is about converting you to a particular brand, stop and relax. I realize when you start talking tires with people it can be allot like talking religion or politics. So I will avoid talking brands and focus more on types of tires.
The first thing you have to know is the terrain you primarily ride. I have talked to people that choose their tires and tubes because they are concerned about weight. That's all fine and good if you are a track rider and you are doing big jumps and so on. But if you are a trail rider weight is only really an issue if you have pick the bike up off the ground. Here in Sunny Central Washington, we have more than our fair share of rocks, in most cases very sharp rocks. Which means that the wrong tire choice can result in a short day and lost money. Just like truck and car tires, motorcycle tires come in a variety of thicknesses known as a "ply". A ply is essentially how many layers of rubber were used to create the tire. The more ply's a tire has the the thicker it is and the more it weighs. Also, dirt bike tires can be DOT approved or not, meaning they are legal to use on the road. Typically speaking a DOT tire is going to use a harder compound and stiffer sidewall, also called the carcass. The good thing about these types of tires is that they last longer than average and are less prone to getting a pinch flat. The downside is you generally are sacrificing traction/grip since the tire is not able to flex as much.
A rough rule of thumb when choosing a tire is the harder the terrain the thicker the tire. If you are primarily riding sand and mud without many rocks, then a softer tire is a good choice for you. Lots of grip and the tire will last a reasonable amount of miles. If you are a Central Washington rider you can still run the soft tires, but be prepared to replace them often and be sure you carry a tire repair kit in your pack.
Some other things to consider when choosing tires are tubes, or whether or not you want to run a Tubeliss system. Personally, I run a Tubeliss, but if you don't want to go to the extra expense I recommend always running a heavy duty/extreme duty tube. The heavier tubes will be less prone to pinch flats and will last longer overall.
Finally, the last thing to consider is your tire pressure. The heavier duty the tire and tube the lower you can run your tire pressure. Keep in mind, dirt-bike tires are terrible at higher pressure, anything above 15 pounds is like riding on marbles. When I run a tubed tire I typically keep my pressure somewhere between 10 and 14 lbs. depending on where I am riding and how fast I think I will be going. When riding single track in the mountains I run a lower pressure, generally this type of riding is slower and more technical so you want the tire to flex as much as possible. But, when riding the desert, either outside of Mattawa or the Desert 100 I run a higher pressure since riding speeds are much faster and the terrain makes a pinch flat a real possibility.
Having a good tires can be the difference between having an enjoyable day on your bike and a day that makes you wonder why in the world you bought a motorcycle in the first place. Personally I have a very strong cheap gene and hate having to replace a tire before I can see the cords, but I have ended up on the ground or getting my butt kicked on some scrabbly hill enough times to realize that cheaper is not always better.