Mountain Bike Tire Design Explained (Size, Compounds, Casings)
Modern mountain bike tires can offer an amazing grip by using the latest casings and construction technologies. These can be pretty damn confusing and hard to keep up with the trends. Especially when you don’t wear tires down at least once a year and stay in the loop.
It’s not that there is a clear right or wrong tire, nor is there an ultimate best tire ever. There are just lots of different options out there for you to dig through to find the perfect package for you. The technologies, sizes, and rubber compounds you can choose from are so niched down that there is something available for every imaginable bike and riding style.
How a Mountain Bike Tire is Constructed
A bicycle tire may look innocent enough, all black and rubbery. But far from it. It’s not even made solely from rubber, let alone only one type of rubber. A modern mountain bike tire is just as high tech as the rest of the bike and technology is constantly improving and adapting to new demands on the trail.
Let’s start with the only part of the tire actually touching the rim. You’ve got the tire bead on either side of the tire, the tire casing holding it all together, the tire pattern on the top – that’s the bit that keeps you connected to the ground – and then the rubber sidewalls on either side. Printed on the sidewall is all the information about the tire model, like name, sizing, and even things like the rubber compounds and casing important for the tire’s uses. Read all about how to read and understand MTB tire labels here.
With the basics covered, follow me down the rabbit hole for a deep dive into the fine details about mountain bike tire technology and what all that means for you on the trail.
A simple way of looking at tire construction is the following split into two major parts:
- Tire Tread Pattern made of different Rubber Compounds sitting on top of …
- … the Casing made from cloth plies, which includes the Beading, Sidewall and Puncture Protection, that is determining tire size.
Let’s go through them one by one, starting with the only part that is actually attached to the rest of the bike: the two beads, sealing tire and rim.
The tire beads are what hold the tire on the rim. As the only part of the tire actually touching the rim, beadings are important for a tire to get right. There are different beading materials like steel, Kevlar and aramid that affect the handling in slightly different manners.
Thankfully most manufacturers seem to have this nailed these days.
Wire beads vs folding tires
There are basically two types of beads in a mountain bike tire: steel and kevlar beads. Both can be tubeless, but it is uncommon for wire bead tires.
Wire or steel beadings were used for heavy-duty downhill tires, and are still seen on some cheaper end tires. Metal material is used to reinforce the contact area with the rim for the tire to be able to handle high-impact riding while keeping a perfect fit.
A steel or wire bead tire cannot be folded. Only tires with Kevlar or aramid beads can be foldable tires. The reason is that when the metal in the beading is folded, it remains bent and cannot seal to the rim anymore.
Usually, it’s the higher-end tires that have Kevlar or aramid beads on them. These can be folding beads, also called folding tires. Dual-ply casings tend to be not foldable, even with Kevlar beads. You can clearly make those out in your local bike shop. Those are the ones curled up in their packaging as opposed to hanging around as a full tire-shaped circle.
Other than the weight, there is nothing wrong with steel beads – except if you try to get your tire on or off the rim. Rigid beads tend to require extra effort, patience, and good technique on a tire change.
In my estimation, there isn’t a good reason anymore to go with a steel bead tire. Even for Downhill, they don’t work noticeably better than modern folding tires. The rigidity and durability of dual-ply casings and protective inserts (within the casing or in the tire) are all you need when smashing down some park laps.
But we’re just on the surface. More on tire beads here. On to the next part of the tire.
When talking about tires and their characteristics, tire pressures and tread patterns come to mind. They are instrumental to the way the tire (and therefore your bike) handles on the trail. Casings may be the dark horse here, fundamental for any tire.
Understanding the basics to be able to selecting the optimal casing option for your riding style can vastly increase your performance and joy out on the trail. Especially when you experience unwanted characteristics like unreliable grip or reliable punctures the casing may be the issue. That, or maybe your tire pressure is off.
A tire casing is the main body of the tire and where the tire tread sits on top of. It’s constructed of one or two layers of plies of nylon cloth covered in rubber. The tire casing acts as the fundamental structure of the tire, giving it its shape, stability, flexibility and puncture protection.
As you can see in the illustration above, the tire casing is smack dab in the middle of it all. It is surrounded by other parts, even woven into it, that all rely on the casing as a supporting structure. It joins the two sections of beading, that sit on the rim itself, together. The tire tread, the bit that grips to the dirt, sits right on top. The sidewalls are the home of another feature: puncture protection. And on them is all the information you need to know about your tire, but deciphering the labels on an MTB tire is a whole other story.
The tire casing and the two beads are the foundation of the tire. No matter how good the rubber compounds are, if you don’t get the basics right, it’s simply not going to handle well and you will end up with an unreliable tire.
What TPI on a tire means
TPI stands for threads per square inch, meaning, how many threads are in one square inch of cloth the bike tire casing is made of. These are commonly nylon or cotton threads. The higher the TPI number, the smaller the individual threads are, making the tire more compliant and comfortable to ride.
Bike tires used to be manufactured from cotton thread back in the day. Some high-end road tires still are because of the ride quality that only cotton can offer. A major downside of cotton thread used in a tire, that has to endure a lot of abuse, is – you might have guessed it – durability. This is why bike tire manufacturing has moved into using nylon thread. With these nylon threads, you tended to get 60 and 120 threads per inch on a tire casing. Up to 320 TPI is not uncommon in road cycling because there they use much thinner threads to produce a tire that is as lightweight as possible while still somewhat comfortable to ride on hard concrete.
Single-ply and dual-ply
Tire ply is a term that refers to the casing construction method. Most tire brands offer mountain bike tires in single-ply or dual-ply tire casings. What this refers to is simply the number of plies of cloth used in the casing construction. It doesn’t say anything about the cloth itself, only that it’s folded over itself to create a dual-ply casing.
So, there is singly ply, which is typically used on lighter tires. Cross Country and Trail tires are all about minimizing rotational weight and tires with only a single ply casing are definitely lighter. The downside of a single ply tire compared to a dual ply is simply the fact that it’s far less puncture-resistant.
A dual ply tire is much thicker in comparison. You can actually see and feel this yourself when the tire is deflated, or even better when it’s off the rim. A dual ply will keep its general shape without folding over. It’s a very tough, thick tire and exactly what you’ll want for gravity-oriented biking like Downhill and Freeride. That more rigid structure also tends to make it harder to get onto the rim in some cases. The downside of dual ply is that they weigh more.
Some manufacturers have found ways to strike the middle ground between single ply and dual ply. Sounds like exactly what you want to have on an Enduro bike. They do this by making their, lighter, softer single ply casings more resistant by putting some extra armor into the sidewalls or even around the entire surface of the casing.
In our example, the casing’s puncture protection or flat-resistant armor is indicated by the little square that says “EXO+ Protection”. Tire casing protection refers to the added layers the manufacturer weaves in between the cloth of the tire casing when is being manufactured.
Manufacturers put protection in the sidewalls because when you’re riding your tires squishes together, pushing the sidewall further out, making it prone to hit rocks and roots on the trail. That’s the EXO part, colored green in the picture below.
All the tire brands are doing something like this and calling it something strong-sounding like: EXO, MaxxShield, Kevlar Composite, Silkshield, MaxxProtect for Maxxis, or Raceguard, Double Defense, Dualguard for Schwalbe, or Hardshell, DuraSkin for Continental. You get the idea.
There is also the lighter EXO Protection sidewall armor, that protects only the sidewalls. For additional protection you need on hard-hitting downhill tires, there’s more armor available. That would be EXO+, which comes in with the regular EXO layer in addition to their “silk shield” technology.
This thinner protective layer runs from the bead on one sidewall all the way up, under the tread, and down to the bead on the other side. Again, that’s another layer woven into the tire casing combined with the sidewall protection. Again, most manufacturers do something very similar but call it differently.
Let’s get into it with a supposedly easy topic. The dimensions are clearly labeled on any tire by number combinations as 27.5×2.4 or 29×2.5 and so on. These measurements are the outer tire diameter in inches and the tire width in inches.
You can count on that piece of information to be always printed on any bike tire’s sidewall, even in the same format.
Why tire size matters on a mountain bike
MTB tire size affects handling over rough terrain and when cornering, as well as rolling resistance. Bigger mountain bike wheels have higher pedal efficiency and handle better over obstacles. Smaller wheels on the other hand are more agile and handle better in corners. The common sizes 27.5″ and 29″ are equally viable, based on the intended use.
With tire width, it’s similar but not entirely the same. The wider a tire, the better it is over the rough stuff, but the less efficient it is. The opposite is true for narrow tires, but more on that further down. Let’s get cracking with wheel sizes first.
The range of dimensions you can actually mount on the wheel is dictated by the rim width and rim diameter. This takes a lot of guesswork out of the equation for you as the bike manufacturer provided you with the wheel dimension that best suits the bike’s intended use.
Let’s talk about these letters and numbers on the sidewall of every MTB tire. Let’s stick to our example: 27.5 x 2.4 WT. I think you already know what 27.5 stands for. It’s the outer tire diameter in inches. That means it’s a 27,5-inch tire in diameter.
The standard mountain bike tire diameters are 27.5″ and 29″. Opposite to tire width, the larger tire has more pedal efficiency, and better handling over rough terrain while the smaller wheel is more nimble and agile (also more clearance before your butt touches the rear wheel when you’re hanging off the back on a steep downhill).
Easy as that. There is more to it, but that’s the need to know.
Optimal rim width
Rim width is in fact crucial to the tire profile. Only the optimal rim width, which a tire is designed for, gives it the shape it needs to work properly. Stans NoTubes have a very illustrative comparison of what happens if you run the same size tire on different rim widths on their website.
In the middle, you’ve got a tire that’s mounted on the rim width it’s designed for. This is how the profile of a tire on a rim should ideally look for it to be able to perform optimally in all its characteristics. It can absorb the most force laterally as well as vertically while conforming to the ground the best. The tread pattern has a good, sharp edge to it to dig in on a lean angle, while it’s still round enough to make the transition from center tread to the side knobs.
On the right of that, you got the bell shape on a too wide rim. With the tire pressing against the ground, it’s going to take more of a square shape with no real transition as the entire tread, including the shoulder tread is touching the ground all at once.
And on the left the lightbulb on a too narrow rim. The shoulder knobs are actually sticking out almost 90 degrees to the side and the tire tread can’t do its job properly anymore. On top of that, there is a drastic loss of stability from so much tire volume with the tire beadings sitting so close together.
This is why it’s quite important to factor in rim width as much as tire size. You want to have the recommended rim and tire widths go together for the best-performing wheel. Here are the recommended internal rim widths for the common tire sizes in each MTB discipline:
|MTB Discipline||Tire Width in inches||Internal Rim Width in Millimeters|
|Gravel||1.8 in||19mm – 25 mm|
|Cross Country||1.9 in – 2.1 in||19mm – 25 mm|
|Trail||2.3 in – 2.4 in||25 mm – 30 mm|
|Enduro||2.3 in – 2.5 in||25 mm – 30 mm|
|Downhill||2.4 in – 2.6 in||30 mm|
|Plus-Size||2.7 in – 3.0 in||30 mm – 35mm|
|Fatbike||> 3.0 in||> 40 mm|
Optimal tire width for MTB
While most mountain bike disciplines, regardless of the type of riding, have trended towards 29″ wheels from Cross Country to Downhill, the real difference-maker in terms of dimension is the tire width. Only looking at tire width there is a clear preference for narrow tires when energy efficiency and rolling speed are favored. The more gravity-oriented disciplines like Enduro and Downhill generally use wider tires with trail bikes in between to take advantage of both worlds.
Leaning into extra-wide tire dimensions are plus-size tires, that can get wider and bigger than regular frames can accommodate. Fat tires are in a league of their own, needing a fat bike to be designed entirely around those huge rubber whoppers.
There is a window between the minimum and maximum tire widths viable for the rim width you got:
|Mountain Bike Discipline||Optimal Tire Width|
|Cross Country||2.0 inches|
|All Mountain or Trail||2.3 inches|
|Enduro MTB||2.4 inches|
|Downhill MTB||2.5 inches|
In mountain biking, rear tires are usually the same width as front tires, or 0.1 inches more narrow in order to roll a little faster. Especially on uphill sections, the weight distribution to the rear wheel increases its resistance in relation to the front wheel. This can be mitigated by higher pressures, low profile tread patterns or narrower widths.
I personally prefer predictable grip over rolling resistance and always run both my tires in the same dimensions. The only difference is the tires’ tread pattern on my Enduro bike, which is more aggressive in the front, and easier rolling in the rear for those uphill pedals. On my downhill bike, I see no real reason to run different tire dimensions or tread patterns. They are always the same tires front and rear.
MTB Tread Patterns
Now to the sexy part of mountain bike tires that actually digs into the ground to produce traction where slick tires would have limited grip. This allows MTBs to be ridden in various terrains like dirt, loose soil, mud, rocks, sand, and snow. There are optimal thread options based on conditions and riding style.
The tread on a tire is essentially what keeps you rubber-side down when you’re riding. There’re lots of different tire tread patterns out there to suit all sorts of riding styles and riding conditions as well as mountain bike disciplines. You’re not going to want a semi-slick tire on a downhill bike, nor do you want aggressive knobs on a cross country bike. Just as bikes, tires have very specific applications.
The best MTB tire tread pattern
There is no right or wrong approach to tire choice, nor is there the ultimate best tire. There are a lot of options out there. Whatever tread is most suitable for your preferred type of riding, it’s most important to keep your tires predictable. An overall predictable tire is preferable to one that’s good in one situation and horrible in another.
Predictability is the king of all the tire characteristics.
How tread profiles are designed
Let’s break down the features within tire tread so you can understand what you need to look for to pick the right tire.
The central part of a tire really does affect the way a bike can handle off-road – especially under acceleration and deceleration. How the central ridge behaves has huge implications on rolling resistance, which is key for disciplines like Cross Country.
When looking at MTB tire tread patterns, think of the very distinct pedal designs on motocross tires – especially the sand tires which kind of look like a steam boat’s pedal wheel. The whole point is to literally cut into the terrain and propel the bike forward. Digging into the dirt is also what helps you generate maximum braking resistance on downhill sections. Even with the best, most powerful brakes you still need to connect that to the braking surface through the wheels and tires.
At the shoulder of the tire are the outside edges. This section of the tire is designed to cut into the dirt to give you good grip when on a lean angle or a cambered section, not unlike the edges on skis or snowboards. The key to a good shoulder is the transition from center tread to that shoulder.
If the tire is too square-shaped because of a too wide rim or too narrow tire, there is no transition from upright into a lean angle. Instead, you’re on the tire’s edge straight away. Similarly, if the tire shape is too round because of a too narrow rim or too wide tire, you’re diminishing the tire’s capability because there is less of an edge to cut into the dirt. More on optimal rim and tire widths here.
Looking at a very pronounced tread, you can clearly see how it is designed to interact with the ground:
This is really important and why aggressive mountain bike tires do have such defined shoulder patterns. There are also tires with a less aggressive, more rounded profile. These are commonly used for Cross Country, where rolling resistance is key and not so much raw grip.
The different types of MTB tread patterns
With all the variability and possibilities tire manufacturers can implement in their tire designs, there are clear categories mountain bike tires fit into. They are marketed that way to help in buying decisions and keep all the options organized. There is of course overlap between all of those, but here are the many types of tread patterns MTB tires.
Semi-slick MTB tires are what you would expect with that name. They have a center tread that is as low as possible while technically still being mountain bike tires. They offer the best rolling resistance while still having an actual tread pattern. The side knobs are usually much more pronounced in comparisonand are there for traction on a lean angle. Those are usually mounted on MTBs with primarily urban use.
One example for more of a Cross Country tire are the Maxxis Rekons I had on my Trail bike years ago. The idea was to have the best pedaling efficiency uphill for my days out on the trails. Turns out, leaning that far into rolling speed came at the cost of predictable traction on any surface except hard-packed dirt. This is also the case for any kind of loose surface uphill. Spinning tires are kind of a killer for rolling speed.
At the opposite extreme are full-on mud tires. The tread pattern on a mud tire like this Schwalbe Magic Mary is very open and has got a very deep tread. Again, very similar to motocross tires that need all the grip they can get on loose soil by cutting deep into the ground. Accordingly, on firm ground, those tall rubber knobs squirm around quite a lot compared to a low-profile tire like a semi-slick. The comparison is not unlike that between an off-road jeep tire and the low-profile slick on a sports car.
All Mountain & Enduro
The in-between variant of a mountain bike tire would be something like a Maxxis Minion DHR, which is an aggressive tire designed for rear wheel use. It’s very commonly used in Trail, Enduro, and Downhill on both front and rear wheels because of its broad window of optimal conditions. So it strikes a balance between acceleration traction and rolling resistance. As you can see, everything is a lot lower. That means on hard trails it’s not going to squirm around and remain feeling very predictable.
There is no in-between with full-on downhill tires like the Maxxis Assegai. This one in particular is designed for racing purposes and it shows. Everything about it is exaggerated for maximum traction. Weight is of little concern as long as these tires do their job digging into the ground. There is a wild mix of various shapes and sizes both in the lugs of the center tread as well as in the shoulder knobs to perform on all kinds of obstacles.
A bike tire compound is the rubber material the tread pattern and sidewall are made of. Single, dual, and triple compounds are common for mountain bike tires, that need to perform in various conditions. Handling differences between rubber compounds are more pronounced the harder or wetter a surface is.
While the actual tread pattern of a tire is the only part of a bike actually touching the ground, it’s the rubber compounds that determine what is perceived as traction on the trail. Tire compounds are what the actual tread pattern is made out of. Every rubber compound consists of natural and synthetic rubbers among other ingredients.
Four properties, in particular, are very important in a modern mountain bike tire compound:
- rolling resistance
A single tire can’t actually excel in all at once since these demands are contradictory: a very soft tire with high damping always suffers from higher abrasion. Similarly, a tire with a lot of grip will never excel with the lowest rolling resistance.
So, a single compound can never provide the answer to everything. Because of that, there are a lot of different compounds of rubber available.
The best MTB tire compounds
Optimal compound selection depends heavily depend on the intended riding style and conditions. This is why there can never be one ultimate tire compound. But tires are designed and built for very specific purposes. Finding what tire compound fits your riding best can be overwhelming. Even reading the sidewall of your tire is a puzzle. Which is a shame, because the compound selection is among the most important decisions on a bike tire.
I compiled a list of every relevant MTB tire compound made in 2022 by the major bike tire manufacturers. These are the recommended mountain bike tire compounds for your riding discipline in one table.
Single compound, dual compound, triple compound … quadruple compound?
By using rubber technologies, manufacturers can really fine-tune a tire’s behavior to the type of riding and riding conditions. And so can you as a rider. Two different tires in terms of compounds on one bike is in fact very common. Since there’s generally more weight on the rear wheel on a mountain bike due to body position, riders prefer to have a stiffer, durable and faster rolling tire in the rear.
Under braking, it’s the opposite, when weight shifts forward. Since the vast majority of actual braking performance comes from the front wheel, the grip in the rear is less important. The same goes for cornering. Front tire slip is hard to recover from, as opposed to rear-wheel sliding.
The idea is to put the grippy compound where it meets the ground, the longer-lasting compound in the middle, and the hard compound at the bottom for support.
Single compound (1C)
Single compounds are actually rare on mountain bike tires and more common on road, gravel and commuter bikes. How it handles and under what conditions it performs best is based on the firmness of the individual compound used. For example, a commuter tire would have to be the most durable and firmest. A mountain bike tire, that has to conform to uneven or wet terrain has to be the softest. A tire for hard-pack conditions would have to be somewhere in the middle.
Dual compound (2C)
These are the most common in mountain bike tires, used by every relevant tire manufacturer, and provide all the most important characteristics.
Dual layer compound means the tire tread is made up of two different layers of rubber on top of each other. There’s the stiffer base layer, that provides support for the knobs to push against, durability and puncture resistance. And the actual compound digging into the dirt is a softer variant, that conforms to the ground better but is also less durable.
On dual tread compounds, instead of the common base layer, the center and shoulder areas are entirely made out of different rubbers. This allows the tire to have low rolling resistance, high braking traction and more durability. Still, the softer side provides the grip and control while cornering.
Triple compound (3C)
Triple compound bike tires combine both of the dual compound versions with a firm, durable base layer and varying layers on the center tread and shoulder tread. The softest slow-rebound rubber compounds are used to offer cornering traction, medium compounds on the center surface for a compromise between traction and durability, and a hard base layer beneath the entire tread for support and puncture protection.
Quadruple compound (4C)
Their 4C is basically a dual tread compound … doubled.
What I mean by that is the center tread and shoulder tread are different rubbers. But each area is not made out of one compound, but two. Here’s what this means in the illustration:
- Soft and grippy
- Firm and durable
- Firm and durable
- Soft but puncture resistant
The soft layer number 4 is what’s unusual compared to the other compound variations.