Riding Beacon Hill in Spokane, WA
This is a guide for choosing the best tire for your mountain bike. Too many riders obsess over lightweight frames and top-dollar components while ignoring the all-important tire. Tires connect your bike to the trail. They set the limit for how hard you can corner, accelerate, and brake. Changing a tire can completely change the way a bike handles. It pays to invest some time and money into finding the best tire for your setup.
The best starting point for choosing a tire is to ask the other riders at your favorite trails which tires they prefer. Local bike shop employees are usually helpful as well. Online opinions and reviews in forums are useful, but unless you’re browsing forums for your particular region you may end up with tire recommendations that are sub-optimal for your local trail conditions.
I typically go through 8 tires or more per season, and I keep a stack of different tires in my garage to swap out depending on the trail, the weather, or if I just want to try something new. Through trial and error I’ve learned what to look for in a tire, and what to avoid. Here are the most important things to look for:
1. Tire Width
Wider tires tend to grip better during cornering and over rough terrain, at the expensive of increased rolling resistance and weight. Wider tires will also float better in sandy conditions and are much more resistant to pinch flats when riding over sharp rocks or off of drops. For moderately rocky cross-country use, the sweet spot is between 2.0″ and 2.3″. If you primarily ride smooth hardpack or travel at a leisurely pace, choose a 2.0″ or even a 1.8″ tire. Likewise, if you tend to corner hard on the downhill and ride rough terrain, lean toward a 2.3″ tire. For downhill mountain biking where pedaling efficiency is less of an issue, look for a tire between 2.3″ and 2.6″. Tires up to 3.0″ wide are available, but rolling resistance becomes very significant past 2.6″.
The front tire is typically subjected to more cornering forces than the rear tire. Likewise, the rear tire is usually loaded with more weight while pedaling. Consider using a wider tire in the front with a slightly narrower tire in the back to get the cornering benefits of a wider tire with the rolling resistance advantages of a narrower tire in the rear. I’ve had good luck with a 2.5″ tire up front with a 2.3″ tire in the rear on my downhill bike.
Also note that widths are approximate. I’ve got a 2.3″ tire which measures 2.5″ wide with my calipers, and a 2.4″ tire which is actually only 2.25″ wide. Make sure that your frame and fork have enough clearance to support the width of the tire. Maximum tire sizes are listed in the owner’s manual. If you ride through mud often, allow for even more tire clearance to keep mud from building up between the tire and frame.
2. Compound (a.k.a. Durometer)
42/40a compound tire. Left: Brand new. Middle: Used as a rear tire for four days of downhill. Right: Used as a front tire for four days of downhill.
The hardness of the tire’s rubber compound dictates how soft and sticky a tire is. Softer compounds grip better at the expense of shorter tire life. Likewise, a harder tire will last longer but have less traction. Softer compounds also have a higher rolling resistance because the softer rubber absorbs more energy as it conforms to the ground.
Hardness is measured by the tire’s durometer with higher numbers indicating a harder compound. A standard cross-country tire will have a durometer around 60a (the ‘a’ is omitted by some manufacturers) and will last for one to three seasons of moderate weekend riding. A 50a compound will provide noticeably more grip under cornering and braking, but might last only one season. 40a and 42a tires are the softest available compounds and will provide the most traction, but plan on replacing these tires at least twice a season. Some tires are available with a 70a compound for the ultimate longevity, but these are only really useful if you’re riding on pavement or the smoothest off-road trails.
The rear tire will wear faster than the front tire due to higher loading, braking, pedaling, and sliding forces it sees. Consider using one step harder of a compound in the rear to minimize this effect with little impact on overall performance. Riders who slide the rear end a lot will definitely want to avoid soft 40a and 42a compound tires in the rear. If you do use the same tires front and rear, rotate your tires halfway through the season to get the most life out of the set.
Foreground: Soft 42a tire (ab)used as a rear tire. Background: Same tire, brand new
Multi-compound tires can be the best compromise of the above factors. Maxxis’ 3C tires use a hard base rubber for lower rolling resistance with softer compounds on the surface and for the side knobs for better grip. For example, a 70/42/40 compound tire would have a 70a hardness base rubber under the surface, with 42a center knobs and 40a side knobs for the best cornering. From my experience, they tend to last about as long as a 42a tire with the slightly better cornering of a 40a tire.
3. Bead (Wire vs. Foldable, Steel vs. Kevlar)
The bead is the inner edge of the tire that holds the tire to the wheel. This edge is either wire reinforced (steel) or foldable (Kevlar or Aramidd). Foldable beads are about 50 grams lighter and allow the tire to be folded up. Tires with steel beads cannot be folded up, but hold up slightly better under heavy downhill riding.
I always run foldable tires on my cross country and all mountain setups, but after a few bad experiences on my downhill bike I stick to steel bead tires for downhill. Most downhill tires are only available with a wire bead anyway.
4. Number of Plies (1-Ply vs. 2-Ply)
The casing (internal structure) of a tire is a nylon cloth wrapped from one bead to the other. A single ply tire has one layer of nylon fabric, while a dual ply tire has two layers for additional durability at the expense of additional weight. Single ply tires are generally fine for cross country, but for all mountain or downhill riding you will definitely need a dual ply tire. Some 2-ply tires have an additional butyl rubber insert sandwiched between the plies in the sidewalls for even more pinch-flat resistance.
5. Threads per Inch (TPI)
A tire’s thread per inch count refers to how many nylon threads cross through one inch of a single ply of the casing. Lower TPI tires have larger individual nylon threads while higher TPI tires have smaller, more tightly woven threads. High TPI tires have less rolling resistance and weigh less due to the smaller threads, but the thinner weave is more easily damaged than a lower TPI tire. A TPI of 60 is best for downhill and all mountain, and a TPI of 120 is fine for lighter cross country.
Tire weight is proportional to width and durability. A super strong wide downhill tire can weigh up to 1.4kg (3.1lbs) while some narrow, paper-thin, race-only cross country tires can weigh as little as 285g (0.6lbs). I wouldn’t recommend super-light tires for any use (even racing), but if your riding is limited to cross-country on smooth trails a 450g tire can be strong enough . For all-mountain, anything less than 600g is probably not as durable as I would like. Downhill tires start at around 1kg, but the extra weight is a small price to pay for the added durability.
As long as you’re picking an appropriate class of tire for your bike and riding style, it’s not worth obsessing over a difference of a few 100g between tires. It is interesting to note, however, that the weight of a tire has almost twice as much influence on your bike’s inertia than any non-wheel parts of your bike. When you accelerate or brake, you are not only fighting the linear inertia of your tires, but also the rotational inertia of the tire as well. Usually this effect is too small to notice, but it’s an interesting fact nonetheless.
7. Knob Pattern
The tread pattern and knob locations can provide insight into how the tire will handle, but these are very difficult to read. Trying a tire out for a few days is the only way to truly know how a tire will handle, but there are a few guidelines you can use to judge a tire:
- Tread patterns with lengthwise-overlapping knobs will have a lower rolling resistance because they maintain a smoother contact between the road and the tire as it rolls
- Knobs with ramped leading edges in the center of the tire have a lower rolling resistance
- Widely spaced knobs will shed dirt and mud better at the expense of higher rolling resistance
- Knobs with channels cut through the center have more edges and therefore grip more, but wear faster than solid knobs
- Patterns with a large gap between the center knobs and side knobs can require more leaning in corners to get a solid bite but grip better under hard cornering
8. Tubes vs. Tubeless
Tubeless mountain bike tire setups have become more popular recently due to their lighter weight and self-healing properties when used with an appropriate sealant. A tubeless setup requires either special UST wheels which are airtight, or standard wheels modified with an additional strip of rubber to be airtight. I’m not a big fan of the modified wheel approach but many people have no issues with it. A UST wheel can in theory be used with a UST tire without additional liquid sealant, but the added protection of a sealant is definitely worth it. Any other tire or wheel combination will absolutely require a liquid latex sealant inside of the tire, as standard tires are not actually 100% airtight and their bead is not designed to form an airtight seal with the wheel.
Perhaps the biggest advantage of a tubeless setup is the ability to run very low pressures without worrying about pinch flatting a tube. A tubeless setup with sealant will also seal any tiny punctures from thorns automatically. The downsides are the additional cost of UST wheels and tires and the added difficulties of mounting a tubeless tire. (Hint: Use a lot of soapy water on the rim first!) Also, sealants are messy and dry out over time, requiring refills every 1-2 months for maximum effectiveness. Always carry a spare tube and tire levers anyway in case your tire is punctured with a hole too large for the sealant to properly seal.