What’s in a Tire? All About Casings and Compounds

Closeup view of the front end of a bike with a Teravail tire mounted between the fork.

One way to elevate your ride experience is to choose tires with compounds and casings that are suited to your riding style and terrain. If you’re not sure how to do that, we asked our product team the most common questions about these key parts of a tire, so you can learn how they affect performance.

What is a rubber compound?

Tire treads contain multiple types of rubber. Some are from natural sources like latex, and some are oil-based synthetic rubber. We mix these rubbers with additives that create a compound. Some additives, like carbon black, improve tires' resistance to wear and UV degradation. Others, like silica, increase tread flexibility and traction in slick conditions. We use these ingredients and others to customize each tire's compound for an intended use.

What makes a rubber compound soft or hard?

All bicycle tires go through a vulcanization process, also known as curing. In this process, the factory adds heat to the rubber compound, and its molecules start to connect in a process called cross-linking. These molecular bonds add structure to the rubber. By adding fillers, like oil, to the compound, polymer scientists can influence this cross-linking to control elasticity, hardness, and other attributes.

Choosing Your Compound

What are some advantages of choosing a softer rubber compound?

Softer rubbers conform to the terrain. This increases the amount of the tire in contact with the ground, which boosts traction and grip. Softer compounds also do a great job of maintaining contact; they take longer to rebound when riding over irregular or uneven surfaces, allowing riders to maintain grip and stability.

Diagram showing a how pressure affects a tire tread with a soft rubber compound.

What are some potential drawbacks of choosing a softer rubber compound?

Softer compounds increase rolling resistance, which can slow you down in scenarios where you don’t need additional grip for cornering traction. Softer compounds also tend to wear down faster and weigh a bit more.

What are some advantages of choosing a harder rubber compound?

Harder compounds tend to last longer and roll faster, as long as they’re paired with the appropriate tread pattern and trail conditions within the tire's traction limits.

Diagram that shows how pressure affects a tire tread with a hard rubber compound.

What are some potential drawbacks of choosing a harder rubber compound?

A fast-rebounding harder rubber can be overwhelmed by uneven terrain or high-speed use. Therefore, we typically use a softer compound on the shoulders of our trail tires and throughout the entire tread of our most aggressive tread patterns.

When shopping for tires, how might someone tell whether a tire has a harder or softer compound?

Tire brands often label their compounds and offer a variety of rubber selections for specific tread and casing combinations (we label ours “Fast” and “Grip” compounds, for example). You can get a general feel for a compound's hardness by using your hand to push down on tread rubber. This is not totally representative, but it gives you a quick indication. The next time you are in a shop, try pushing on the shoulder or center lugs of a few tires. You can quickly differentiate between a 60a-durometer trail compound and a 45a-durometer DH compound.

“The next time you are in a shop, try pushing on the shoulder or center lugs of a few tires. You can quickly differentiate between a 60a-durometer trail compound and a 45a-durometer DH compound.”

Can you provide more detail on Teravail’s “Fast” compound?

We use the Fast compound designation in our road, gravel, and trail product categories. This compound's high abrasion resistance and puncture protection are critical in gravel conditions. The 60a-durometer Fast compound supports our tread patterns' mechanical grip and sustained life, especially in our gravel range designed to deliver reliable grip on variable gravel terrain. We also offer a Fast compound on some constructions of our trail tires; these often have a dual compound. In dual-compound constructions, we use 60a-durometer base rubber for the center of the tire for the same fast-rolling reliability as our gravel product. Some trail tires use a softer, 52a-durometer rubber on the shoulders for slower rebound and sustained contact when cornering.

A cyclist rides on a gravel road. The focus is on the front of the bike.

Can you provide more detail on Teravail’s “Grip” compound?

Our Grip compound is exclusive to our off-road line and aggressive trail tires. The Grip compound has a foundation of 52a-durometer rubber in the center of the contact patch and soft 45–48a-durometer rubber on the shoulder lugs. Our goal with this compound is to boost grip through sustained contact and controlled slow rebound as riders navigate high-speed, high-impact conditions.

A cyclist hovers over the edge of a rocky descent. The focus is on the rear of the bike from below.

How do you decide whether a tire should use the “Fast” or “Grip” compound?

We design our tread patterns, casing configurations, and compounds to elevate a focused experience. In the gravel category, we understand that durability, mechanical grip, and low rolling resistance promote the ride experience for various rides and use cases. We know that the consistency of our 60a-durometer fast compound excels in a wide variety of gravel terrain, so we use it for all gravel-focused designs.

A mountain biker banks a turn and catches air over a rock on a mountain trail.

Trail riding is more nuanced due to the wide variety of terrain and riding styles, larger casing volumes, and tread features. We look at each tread design's intended use and conduct back-to-back testing to validate our compound selection. Typically, the compound choice is intuitive; our cross-country-oriented tread designs might use the Fast compound, while our downhill-capable treads benefit from the Grip compound.

“Typically, the compound choice is intuitive; our cross-country-oriented tread designs might use the Fast compound, while our downhill-capable treads benefit from the Grip compound.”

In some cases, we offer both Grip and Fast Compound offerings for flexibility as you mix and match offerings and refine your ride experience. We are always tuning the rubber selections within the Fast and Grip compounds to improve the focused ride experience based on rider feedback and laboratory testing.

Tire Casing Introduction

What does the term “casing” describe?

A tire’s casing is the structure that supports the tread cap and connects the tire to the bead, anchoring the system to the rim while keeping the system airtight. The casing may include inserts and layers intended to provide stiffness, impact resistance, and improve the tire's longevity.

What layers make up the casing? How do those layers affect performance?

We construct our casings out of nylon threads. The quantity of these threads varies among constructions; most tubeless-ready tires are 60 or 120 threads per inch (TPI). A lower-TPI casing uses fewer, coarser threads, while a higher TPI uses more, finer threads. These threads are coated with casing rubber and configured into layers called plies. These plies are combined with other components to create the structure of a tire. The ply count varies by construction as designers balance the casing structure and weight to tune the system.

Diagram that illustrates the difference between a course weave casing and a tight weave casing.

You might also find reinforcement layers for sidewall and puncture protection. These layers, often made of nylon, use an application-specific configuration and TPI. For example, sidewall protection is usually coarser than the material used in a casing ply, as it is intended to protect from lacerations and provide additional stiffness.

Some tires use an additional rubber insert that sits above the tire bead in a wedge shape. This wedge of rubber is an apex wedge or a butyl insert, and it provides an additional layer of defense against impacts and sustained loads.

All casings also contain two tire beads. This material (usually high-tensile aramid) is folded within the casing ply. The beads mate with the rim and their fit is critical for reliability, especially for tubeless tires since the bead acts as a sealing surface.

Finally, a thin layer of nylon, known as a chafer, is added to the outside of the tire near the bead to protect against wear.

A cyclist on a forested mountain bike trail rounds a corner.

Choosing Your Casing

Can you tell us about Teravail’s “Light & Supple” casing?

Our Light & Supple casings use a one-ply, 60 TPI configuration without additional sidewall or puncture protection. We’ve found that the structure of the 60 TPI casing provides a reliable tubeless seal while protecting the tire from light trail debris and impacts.

What are some of the advantages of the Light & Supple casing?

Removing the additional layers of protection makes the casing lighter and more compliant. This allows the tread to conform to the terrain, providing both grip and ride comfort.

What are some potential reasons the Light & Supple casing might not be the right choice?

It’s not a great choice if you frequently ride sharp, rocky terrain or have a loaded or touring bike. The Light & Supple casing will be more susceptible to punctures and sidewall cuts and offer less stability when cornering on a heavy bike.

When would you recommend that someone opt for the Light & Supple casing?

When riding road, gravel, or XC and trail-riding in regions with limited sharp rocks, the benefits of the Light & Supple casing’s reduced rotating weight and additional compliance likely outweigh the risks. If you are unsure about the risk of punctures or sidewall cuts in your area, chat with your bike shop or local ride groups.

Illustrated diagram of the light and supple casing on Teravail's Warwick tire.

Can you tell us about Teravail’s “Durable” casing?

Our Durable casing uses the same foundation as the Light & Supple casing but includes layers of sidewall and puncture protection.

What are some of the advantages of the Durable casing?

Our durable casing provides additional protection against cuts and punctures, but those layers of protection also reinforce its structure. The result is stiffness that prevents squirming when riding at lower tire pressures or initiating hard corners.

What are some potential reasons the Durable casing might not be the right choice?

If you live in a region without many trail hazards and your riding style doesn't involve heavy loads or high-speed impacts, you might prefer to save weight and stick to the Light & Supple casing.

When would you recommend that someone opt for the Durable casing?

I recommend the Durable casing to anyone planning an extended ride through uncharted or variable terrain and those who live in regions notorious for eating up tires. It’s also an excellent choice for loaded or touring applications or riders who enjoy descending at high speeds, as the structure of the Durable casing provides additional stability and control while allowing for a broader operational range of tire pressures without squirming.

IIlustrated diagram of the Durable casing on Teravail's Cannonball tire.

Can you tell us about Teravail’s “Ultra Durable” casing option?

This tire is beastly! In addition to the ingredients used in the standard Durable casing, it uses a supplemental half-ply of 120 TPI casing and an apex wedge above the bead. This produces a reliable configuration for technical routes and high speeds.

What are some of the advantages of the Ultra Durable casing?

With unmatched sidewall stiffness and targeted sidewall and puncture protection zones, this tire is the go-to for those who prioritize stability and reliability.

What are some potential reasons the Ultra Durable casing might not be the right choice?

The additional material in this casing comes with a weight penalty and adds extra stiffness to the wheel system. If your riding style or terrain doesn’t require this level of protection, opt for a lighter-weight casing that will provide the appropriate flexibility and responsiveness for general trail riding.

When would you recommend that someone opt for the Ultra Durable casing?

The Ultra Durable casing delivers if your focus is descending at high speeds and maintaining control through jagged rocks and high-gravity corners.

Illustrated diagram of the Ultra Durable casing on the Teravail Kessel tire.

What sets Teravail tires apart when it comes to compound and casing?

Teravail is a younger tire brand that we built around the emerging gravel scene as tubeless-ready tires gained popularity. By supporting journeys on extended gravel routes like the Great Divide Mountain Bike Route, we learned firsthand that the reliability of a tubeless casing is a top priority, and we focused on casing reliability over minimizing weight. Though we offer each of our tires in multiple casing weights, we shy away from paper-thin race-day casings. Instead, we opt for the reliable tubeless setup of our standard one-ply 60 TPI casing. This design approach came from our gravel background, but we’ve kept this focus on tubeless reliability and durability in our road and off-road categories.