Tires- Where the Rubber Meets the Road

When determining the type of tire system that is needed for a given application, it is critical to first understand the intended use, including the types of surfaces that the tire will be used on. For example, will this be a road or off-road application? What type of wheel will be used? Will the performance KPIs (Key Performance Indicators) be based on rolling resistance, handling, durability, protection, or some combination of these factors? Next, the individual components of system will need to be reviewed, to recognize how the materials and processes work with each other. Depending on the intended use, specific materials are chosen, and construction methods are employed to produce the desired outcome. Finally, comparing the benefits of each system will serve to set performance goals, from which the system can be built around. Simply put, tire system shave evolved to overcome challenges that cyclist have found themselves in need of conquering. In each example, individual systems will have benefits that define the whole, and combine both the consideration of the intended use as well as production methods to serve a purpose that is unique to the system. In the course of this white paper we will cover these topics and equip the reader with detailed descriptions and key characteristics to quickly differentiate between tire types and systems commonly found in the marketplace, as well as the benefits of each. In all examples, we will be using pneumatic(air-filled) tire types, as these are most common, and have historically given the highest level of performance.

In essence, a tire is made up of three main components: tread pattern, tread compound, and casing. The tire then relies on either an innertube to hold air, or in some cases may use a tubeless style casing, once mounted on the wheel. Each part plays a key role in how the tire system is assembled, as well as how they perform within their intended use. When a tire model is produced, the name typically refers to the tread pattern. This is a bit unfair to the compound and casing, which do much of the work, but as the tread is the most obvious visual feature, it has become the standard in identifying the model. In simple terms, the tread pattern of a tire is designed for the terrain of the intended use, and developed to reach
specific goals in this setting. Whatever the goal, we must first define what makes the tire perform well in the conditions it will be used in.

The term “fast” is not universal. For example, a tread that will be used in a time trial on pavement will be designed for low rolling resistance as the top key performance indicator (KPI). In contrast, a tread designed for downhill mountain bike racing in muddy conditions will have a completely different set of performance criteria. In both examples, the key performance indicators reduce time between the start and finish lines, so they are both equally “fast” in their intended use environments. Speed is just one example of a KPI that is considered during the tread design phase. Others may include abrasion resistance, ultimate mileage, maximum load, etc. Whichever KPIs happen to be on the list during tread design, the system (as a whole) must be considered, and perhaps nothing effects a tread design quite like the compound itself. The compound is the very substance the tread design is composed of, and is typically made from either natural rubber, synthetic rubber, or a blend of the two. Occasionally other substances are added to the formula, to enhance specific characteristics of the compound itself. One example is Graphene, which
has been proven by Vittoria to reduce rolling resistance, decrease abrasion, and increase wet weather grip. Silica is also a popular additive, which can be used to decrease rolling resistance. Other brands, like Continental, refer to their secret formula as Black Chili, without disclosing the ingredients. Regardless of the formulation, the compound must work in concert with the tread and casing to achieve the desired outcome. The composition of the compound can change the way a tread design works in practical applications, as the elastomeric properties of the rubber will have a large effect on the flex and wear of the tread.
In road racing applications, Vittoria has found that the properties of the compound, combined with the thickness of the tread can have as much an effect on the rolling resistance as the casing itself. This is notable, as the road surface is quite uniform, which helps to isolate the effect of outside influences on data, clarifying the performance traits. One way of manipulating how the compound and casing work together is by layering multiple compounds on the casing. Maxxis is famous for using three compounds in their 3C formulation, while Vittoria pioneered the use of 4 separate compounds on a single casing. In both cases, the base of the tread can be made more robust, stable, and firm, while the surface of the tread can be made softer to increase grip. This is especially useful in off-road applications, where a “knobby” style tread is more common, where each tread block stands alone, devoid of surrounding support. Layered compounds help the tread block resist tearing at the base
while under load, despite the use of a soft surface compound. Also worth considering is the random nature of the intended use (off-road) surface, where roots, rocks, and multiple dirt types are evident. In this case, the compound must allow the tread block to deform enough
to produce grip but simultaneously balance durability, while returning the least amount of rolling resistance possible. A tall order indeed, and a prime example of how compound and tread work in unison.

In these examples, the definition of performance is directly tied to the scenario in which the Tire is used and cannot be defined universally across categories. Speed is just one measure and is always relative. Often, depending on use, durability will be the key defining factor of the tread, especially when increased mileage is paramount. For example, this is common in Tires that are intended for more utilitarian purposes, such as in the city/commuter category, or in high load scenarios in e-bike applications. Regardless of the intended use, or measures of performance, one thing is constant - the tread and compound rely heavily on the casing to achieve the goals of the system. In comparing various tire system types, the casing is perhaps the most defining feature.There as on is,the casing type will define how the tire is affixed to the wheel, as well as how it holds air. Virtually any tread pattern or compound can be applied to the casing types we define below, making the casing the foundation of tire construction. For this reason, we will focus on casing as the key differentiator when comparing types of tire systems. The casing will dictate the type of rim the tire can be mounted on, and whether the tire will require an inner tube for use. This not only provides the structure of the system, but is also tasked
with balancing durability and rolling resistance simultaneously, which is no easy task. In a broad categorization, casings typically fall under one of two classifications: clincher style or tubular constructions.

In both style casings,pressurized air serves as a spring to al-low for a certain amount of deformation, which provides the ability to fine tune the performance of the system.
Both style casings feature some common elements, such as casing materials,and hardware such as valves. Both are available in sizes that share an outer circumference that is consistent per size, which allows users compatibility as well as the freedom to choose between systems on a given bicycle. From a material perspective, bicycle tire casings are most commonly made from nylon cloth, but in higher end applications, cotton cloth is also quite popular.

Regardless of material, casings are assembled using a system of layered cloth, which are fused together, most often in a bias-ply layout. Bias-ply is when the threads of the first layer of material run perpendicular (90-degrees) to the next layer of cloth. These layers together form one complete layer (or “ply”) of material in the Tire. This bias-ply pattern is then cut, so the direction of threads within both layers sits at a 45-degree angle to the direction of rotation. Doing so produces a long lasting and predictable performing tire. Bias-ply differs from “radial” construction, which is typically found in automotive use.Radial construction uses a much different bias angle, which approaches 90-degrees to the direction of rotation. This type of construction has benefits in terms of straight-line impacts, and potentially lower rolling resistance. While rare, radial-ply bicycle tires have been produced, but typically are not as well suited for the lightweight system and dynamic demands of bicycle applications, as advantages in rolling resistance are often negated by diminished handling and wear patterns. With both clincher and tubular casing styles, the two most common valves are Schrader style (as used in most auto-motive applications), and Presta valves, which are also known colloquially as “French” style valves. When used on an innertube (within a clincher application), either style valve will be molded into the tube structure, and the valve will exit the rim via a valve hole. The Schrader valve has an advantage in familiarity, as well as an internal spring which closes the valve. The Presta valve offers simplicity, as well as security with a threaded valve closure. Also, the Presta uses a smaller valve hole, which is beneficial on narrow rims. When used in a tubeless configuration, the valve will resemble a Presta valve shape, but will employ a conically shaped seat which is placed into the valve hole in the rim and tightened down via an external valve nut. During inflation, air will be sent directly into the tubeless tire casing, as there is no innertube in this system. Tubeless valves are designed to prevent air loss through the valve hole, while allowing a familiar method of inflation for the user. As we’ve seen, tubular and clincher construction share many of the same traits, despite being quite different in construction. Now that we have the common attributes out of the way, let’s dive deeper into what makes each system unique.