Except during the unfortunate event of a crash, your tires are the ONLY part of your bike that actually touch the trail. Everything you do atop your bike, from churning the pedals, to body position, and weight distribution, translates down to the tires. You can do everything else right, but the wrong set of skins can thwart your efforts like nothing else. A proper set of tires that suits your riding style and the terrain you ride most often provides arguably the best cost-to-performance ratio of all bike upgrades.
A dropper post is right up there as well. If you're washing out on corners or slipping during steep climbs and you've already eliminated crappy technique from the equation, take a look at what tires you're running. If you're on a tubeless setup, blow off a couple psi and see if that helps. Rock hard tires are a thing of the past. Still all over the place and you're absolutely sure you don't just suck at riding a bike? Seriously, it's the tires.
As quickly as mountain bike technology evolves, we've become conditioned to think that shiny, lighter, more expensive, carbon fibery things are the key to enhanced riding performance that will make us faster than the next guy. With their lack of moving parts and propensity for the color black, tires lack shelf appeal. Proper size and lowest price are often the only purchase considerations for many riders. This needs to change.
Think about that time you cracked your skull on the icy sidewalk outside your office building because you were wearing hard-soled wingtips instead of your deep-lugged winter boots. Or remember that mid-November dump that made for a harrowing drive to the ski resort because you hadn't switched over to your snow tires yet? A good set of tires can instantly make your "OK" bike handle like a top-of-the-line race machine. The wrong set of tires can turn an $8000 enduro bike into something you'd hesitate to take out onto the bike path. So, ready to pull the trigger on some new rubber for your ride? Keep reading!
We'll start with the basics. It is imperative that you purchase a tire that will fit your wheel. Tire companies make the same model tire in a variety of sizes. Your buddy told you all about what tire he thinks is the one to buy, but you'll need more information than that. Luckily, it's probably right in front of your face.
Wheels are the metal things (or carbon if you're fancy) that your tires are mounted to. Tires are made of rubber and are the subject at hand. To avoid the mechanics at the local bike shop making fun of you after you leave, know the difference. Also, know they're probably making fun of you regardless. Mountain bike tires come in three different sizes; 26-inch (get with the program already), 27.5-inch also known as 650b if you want to trick the shop guy into thinking you know what you're talking about, and 29-inch. If you already have a tire on your wheel but aren't sure of the wheel size, it's the first number in this example: 27.5 X 2.3. If you only have the wheel, it's likely printed on there somewhere.
While a 26-inch tire won't work on a 29-inch wheel, you have some wiggle room with the second number after the "x" in the above example. This number represents the width in inches of the tire. Typically, mountain bike tire widths will range from 1.6 to 2.5 inches. Values of 2.6 inches and above are the realm of "plus" or "fat" bike tires.
Generally speaking, narrower tires will roll fast and are typically oriented towards cross-country riding. They won't perform nearly as well in rough and loose conditions. As an extreme example, imagine putting road bike tires on a mountain bike and riding your favorite downhill trail. Conversely, the increased contact patch provided by wider tires will increase grip and traction and will be more stable when moving fast over very rough terrain. It's always a good idea to check with the bike and/or fork manufacturer to see the maximum width tire that can safely be run on your particular bike. A too wide tire can rub against the suspension fork crown causing excessive wear and jeopardizing your safety.
Short of actually riding a tire, just looking at a tire's tread can give you a decent sense of how it might perform. Big, widely spaced knobs will bite into wet soil and shed mud well. Small, tightly spaced nubs will roll fast and provide lots of contact on hard packed soil or rock slabs. The knobs that run down the center of the tire provide traction during pedaling and braking, while the lugs on the sides of the tire engage during turns to provide grip and stability. The rest of the 'tweeners provide a smooth transition when the bike is leaned into turns and brought back upright. You'll notice the leading edge of many of the knobs are ramped to reduce rolling resistance. The direction of rotation is typically marked on the tire's sidewall.
There are a number of proprietary rubber compounds out there and each manufacturer will claim theirs is undeniably the best. The hardness of rubber, or durometer, is measured in Shore A, which is abbreviated with a small a. On this scale of 1-100, soft tires are somewhere around 45a and hard tires up to 70a. Often times, a particular model tire is available in different rubber compounds. Generally, tires made from softer rubber will provide exceptional grip, but tend to wear out much faster, especially when ridden on pavement.
Even with great trail access right from our office in South Lake Tahoe, we still put plenty of miles on pavement just getting to our daily rides. If you're the type that rides from your doorstep, a harder durometer tire may be a good choice. Save the soft stuff for racing. Conversely, if you're a shuttle-bunny adverse to pedaling uphill that typically burns more dinosaurs than calories driving your bike around, softer tires may be a good bet. To combat the issue a bit, manufacturers often use dual, or even triple rubber compounds in the same tire. Harder rubbers are used on the middle knobs and softer rubbers for the side knobs. This provides a good balance of grip and durability.
Front and Rear
While plenty of riders choose a matched pair of tires for both wheels, we feel there is good argument to run a different tire for each. Many tires have been optimized for use on either the front or back wheel, although you're likely to see some riders out on the trail riding them otherwise.
The front tire is responsible for cornering and needs to respond appropriately to the forces translated to it in order to remain on your intended line. A wider front tire will also help you stay on course, as more of the tire is in contact with obstacles, and will deflect less than a narrower tire. Front tires often feature directional knobs to improve rolling resistance. A front tire does not suffer as much drag and therefore it is common to see riders elect a big knobby tire up front and a smoother looking tire for the rear. In fact, many riders simply run worn-out front tires as rear tires. We feel differences in tread pattern and knob spacing make a rear specific tire a better bet, but alas, it's not the worst option and easier on the wallet. You'll wear through a rear tire faster though, so the timing is kinda funky for this approach.Rear tires
A rear tire typically has horizontal knobs running across the tire. Much like the track on a snowmobile, these knobs provide traction and prevent the rear wheel from spinning under large pedaling forces such as when climbing a loose hill.
There's a lot more technology going on in a tire than it appears. Did anyone else get scolded by their parents for leaving 20-foot skid marks on the driveway by locking up that coaster brake at top speed on your first bike? Well, after an afternoon of driveway graffiti skid school, you might have succeeded in wearing a rear tire down to the "threads." Those nylon strands you managed to expose form the casing of a tire.
Just like those Egyptian cotton sheets, tires have a thread count too. Measured in tpi (threads per inch), usually the higher the thread count, the lighter the tire because less rubber is required to fill the matrix created by the casing. More isn't always better though, as a higher tpi, although lighter, can make for a weaker sidewall. Various types of reinforcement are added to tires in order to beef up sidewall and tread puncture resistance.
Sometimes just an additional "ply" of nylon casing is used to reinforce a tire. Materials such as Kevlar can be used as well to reinforce sidewalls and make a tire more robust, although the rolling efficiency of the tire may be altered. "Belting" incorporates strips of material under the tire tread to increase puncture resistance. A full cap of material can run from bead to bead to provide protection across the entire tire. As rim internal diameters grow and allow riders to run lower and lower tire pressures, tire beads must be reinforced to insure an air tight seal and prevent "burping."
Tubeless or Tubed
We ran everything tubeless for this test. There's no argument anymore. Tubeless is the way to go. You can ride super gnarly terrain faster because you don't have to stop every 20 minutes to change a pinch-flat. Low tire pressures allow for a huge contact patch that increases grip and lets you clean obstacles your tympany-tight-tubed tires would have glanced off of. Instead of filling your hydration pack with tubes and patch kits, ski-strap a single tube to your frame, strap on your fanny pack and go pedal!