The basis of any bike tire is its casing, which gives it its shape and is fundamental for riding characteristics.

A tire casing is the main body of the tire where the tire tread sits on top of. It’s constructed of nylon cloth covered in latex.

The tire casing (often just referred to as sidewalls) acts as the tire’s fundamental structure, giving it its stability and puncture protection.

Tire Structure & Technology

As you can see in the illustration above, every part of a bike tire connects to the tire casing.

At each end there are tire beadings, that sit on the rim itself. The tire tread, the bit that grips to the dirt, sits right on top.

The sidewalls (the sides of the casing) often have puncture protection woven into them.

Now, let’s see how the casing actually matters for riding.

Casing Construction

TPI

A tire casing is made of individual nylon threads woven together. The thicker the threads, the stiffer the casing.

Stiff, thick casings are great for stability and puncture protection. But thinner casings are lighter and more comfortable.

TPI, a label found on tires’ sidewalls, describes how thin the threads are and how many are used in one square inch of nylon cloth

TPI stands for threads per square inch.

The higher the TPI number, the smaller the individual threads are. Which makes the tire casing more compliant, thinner and softer.

bike tire casing cloth texture
On the inside of a tire, you can make out the texture of the casing’s cloth. This is a 120 TPI casing.

120 TPI and 60 TPI are the most common casing options you can choose from in mountain bike tires.

Related article: Bike tire TPI explained

Single-ply and dual-ply

Tire ply is a term that also refers to the casing construction method. Meaning if the nylon cloth is folded over itself to create a dual-ply casing.

Singly ply is typically used on lighter tires for Cross Country and Trail. 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 (like Maxxis DoubleDown) is much thicker in comparison. Exactly what you’ll want for gravity-oriented biking like Downhill and Freeride.

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.

That increased sidewall stiffness of a dual ply helps the handling of the tire in aggressive cornering situations where folding and wallowing can become an issue. It’s also a big help in puncture protection.

Puncture Protection Armor

MTB tire manufacturers make their, lighter, softer single-ply casings more resistant by putting some extra armor into the casing.

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. It also helps with pinch flats (snake bites).

Another level is an insert running over the entire casing from bead to bead. This helps with sharp rocks punching through the top tire profile.

Maxxis Exo Protection Explained
Maxxis EXO+ Protection inserts woven into the tire’s casing.

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.

If you ride aggressively with heavy hits, save yourself time, money and your patience by going for a heavy-duty tire casing at least in the rear of your bike.

And remember:

Thin rubber feels great, but offers minimal protection.

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