As we all know, a bicycle is useless without a fully pumped tire, or the tire itself. The tire is an essential part of a bike as it provides a gripping surface for traction, as well as serving as a cushion for the wheels.
As simple as a tire may appear, it takes lots of selection and processes before it comes to modern innovation. Let’s take a look at how it was developed and modernized.
This article will tell us how are bike tires made.
Table of Contents
The Birth of the Modern Tires
The process of vulcanization was discovered by accident in 1839 by an American inventor, Charles Goodyear. Vulcanization is the process of strengthening rubber which involves the formation of cross-links between long rubber molecules to achieve improved characteristics and traits.
While experimenting with a mixture of india rubber and sulfur, Goodyear accidentally dropped the mixture on a hot stove. A chemical reaction occurred and instead of melting, the mixture hardened to form a lump. A few trials with this mixture later, he was able to replicate the hardened qualities to sheets of rubber.
While it might seem like a simple rubber hoop, the development of a bike tire involves high-tech machinery, the latest manufacturing techniques, and labor-intensive craftsmanship. Let’s take a glimpse of the overall process of how a bike tare is made.
Step 1. Selecting Raw Materials
Rubber is the primary raw material used in producing bicycle tires. It can be natural or synthetic.
Natural rubber can be extracted from the bark of the rubber tree, Hevea Brasiliensis. A milky liquid is extracted from the barks and mixed with acids that cause the rubber to solidify.
To squeeze out excess water and form the rubber into sheets, high pressure is applied to the sheets. They are then dried in tall smokehouses, pressed into stacks, and shipped to tire factories around the world for shaping.
Synthetic rubbers are derived from the polymers found in crude oil.
Choosing a Balance of Characteristics
Before the creation of modern rubber, scientists had gone through numerous experiments to get the perfect measurement of components to make a durable tire. The following are traits that were taken into consideration to create the perfect bicycle tire:
- Aerodynamics and running performance for a road tire
- Elasticity for a mountain bike tire
- Durability and longevity for a touring tire
- Surface adhesion for maximum wet weather performance
- Density and dampening for a commuting tire
Step 2: Mixing & Extruding
The ingredients are then mixed using an internal mixer, known as a Banbury mixer.
The Mixing Process
Bales of rubber are kneaded inside a chamber by two rotors. These rotors are kneading at variable rotations per minute while being heated at 338°F. While being kneaded, other ingredients are added to obtain the desired traits discussed earlier.
The Extrusion Process
Once the materials are uniformly incorporated, a dough-like consistency rubber exits the machine through a release hatch at the bottom of the chamber and is sheeted out like a pastry into a thick, continuous layer by rollers, known as a slap.
Step 3: Tread & Sidewall Formation
The slap that is meant for the sidewalls of the tire is covered with plastic sheeting and rolled further. On the other hand, the thread slap (the part that comes into direct contact with the ground) is cut into long, narrow strips.
The narrow strips are fed into an extruder and heated again to achieve optimal durability. Once the heated strips become doughy again, it is sent to a revolving screw that applies sheer force. It is then sent to a machine that cuts and forms it to become thicker in the center and thinner on the sides. This characteristic improves the resistance to wear.
The tread rubber is eventually submerged in water to cool and to set its shape. It is dipped in an anti-tack compound like powdered mica, talc, or different water-based formulas, to allow for release or separation after storage. The long tread line is then wound onto spools with a fabric separator between each layer to prevent unwanted adhesion.
The same process is done with sidewall slaps, wrapped around a spool separated by fabric sheets, and dried. These cases are then called “books” and can be used in production for later use.
Step 4: Carcass Creation
The carcass, also known as the casing, is perhaps the most essential part of a bike tire since it acts as the underlying framework and determines its shape. It also determines how the tire will conform to surface irregularities, together with its rolling resistance.
Here’s the process on how it is made:
Fabric Mesh Creation
A nylon textile yarn is twisted together. Yards of bundled nylon are treated with chemicals to promote bonding with rubber, which results in a grid pattern.
The yarn is stored in a monitored storage area where temperature and humidity levels are carefully observed since both of these factors can impact its tensile levels.
Fabric Mesh Application
Consequently, webbing is passed through hot rollers at a 45-degree angle. This will permanently bond the tire casing and the webbing through a process called calendering. This defines a tire’s shape and provides it with a great deal of support.
Before a webbing yarn is used, the density needs to be measured in threads per inch (TPI). It refers to the number of threads contained in one square inch of the casing.
The lower the TPI (usually < 80), the larger gauge threads and more rubber it needs, resulting in heavier and more rigid tires. The higher the TPI of a casing mesh (> 100), the less rubber and finer threads it has resulting in greater strength, lighter weight, better flexibility, and improved suppleness.
In addition to the mixing process, the yarn’s structure can have an impact on a tire’s performance. Very fine casing material makes the tire smoother and protects the carcass from punctures while a coarser fabric is more cut-resistant and makes the tire more robust.
Cutting & Assembly
After the application of the mesh, casing rubber proceeds into a cutting station where blades silence it into pre-measured strips. Typically, multiple strips are needed to construct a single tire.
After the assembly, these casing strips are wound into spools with a fabric backing to prevent sticking. They can be stored for future use or can be used immediately.
If the strips are used immediately, raw tread rubber is added to the carcass by wrapping a layer around the drum to firmly stick it down. The tread thickness is also a significant contributor to a tire’s quality characteristics.
Bead Creation & Insertion
A wrapping machine then bundles steel or kevlar fibers and twists them together to form rings, known as tire’s beads. These beads will be covered in a thin layer of protective rubber.
A specially trained employee then inserts the beads on each side by hand while the casing is already wound up around a metal spool. The strength provided by these beads will help hold the tire onto the rim while it is inflated with air.
A piece of machinery simultaneously folds the casing’s rubber over both beads. If additional puncture protection is required, a Kevlar strip is added to the rubber as well.
Step 5: ‘Green’ Tires
The extruded rubber for the tire’s sidewalls is glued in place, then the tread is placed in between the sidewalls. With all the layers in place, the tire is removed from the building machine and can now be called a green tire.
Green Tire Vulcanization
The green tire is placed inside a mold over a tubular bladder. It is sealed while steam is being pumped into the bladder like a balloon while being heated up to 356°F for about three to six minutes. This process is done to achieve two goals:
- The high pressure forces the rubber of the tire against the sides of the mold, giving a negative impression of the tread. Think of it like a waffle iron for a bike tire.
- The heat applied during the vulcanization process fuses all of the tire’s layers at a molecular level, resulting in a hardened and elasticized rubber.
Step 6: Quality and Safety Testing
Finally, the tire is removed from the mold and is hanged to cool. After cooling, each tire is inspected for flaws such as bubbles, voids, or misalignments, either by a specially trained employee or with x-rays and visualizing the results on a screen.
It is also a standard procedure for one tire from each batch to undergo in-depth quality control testing. It may involve one or more of the following:
- Spinning the tire against a metal wheel until it goes bald to simulate long-distance travels (usually after thousands of miles). Sensors will automatically record and report if the tire remains balanced.
- Simulating a metal wheel with a large bump to mimic hitting a curb several thousand times in a row.
- Applying high pressure onto one or more sharp metal studs, which examines a tire’s puncture resistance.
It’s easy to overlook the technology and manufacturing processes involved in the development and production of every tire that rolls under your bicycle.
The next time you go for a ride, take a brief moment to marvel the many decades of progress associated with the innovations and improvements in making a bicycle tire to make sure you have the smoothest ride possible.