Basic Guide To Road Bike Tires And Tubes
At first glance, you may think a bike tire is a bike tire. They are round. They are rubber. They help get you down the road. But the reality is that tires utilize some of the most advanced technology in the cycling industry. Unique rubber compounds, strategic tread patterns and the recent push toward tubeless technology are just part of the diverse and complex tire story. But before we dive into the complex details, it helps to understand some of the basics.
First off, there are two basic tire types, road and mountain. Generally, road bike tires have smoother tread, a larger diameter and a narrower width. These factors conspire to make them more efficient on paved surfaces. Mountain bike tires, on the other hand, are generally wider with knobby tread, making them more sure-footed on dirt trails, but slower on smooth surfaces.
In the world of road tires, there are two fundamental tire designs, the commonly used hook-bead clincher and the lesser used tubular. The hook-bead clincher class also includes the increasingly popular tubeless hook-bead clincher. More on what this all means later. First some tire basics.
In an ideal world, all tires would be light, puncture proof, durable, aerodynamic, roll efficiently and maintain traction on all surfaces. Unfortunately that tire does not and cannot exist. But by tweaking certain tire characteristics, you can create tires that will do many things pretty well or some specific things very well.
For example, a light, high performance road tire saves weight from the bike’s biggest moving parts (wheels) and will accelerate like a jack rabbit. But it will only last for about 1,000 miles before needing to be replaced. Conversely a durable long-lasting tire has more hard rubber that resists wear, but that resistant material makes it heavier and may reduce cornering traction.
Along the same lines, high pressure, smooth, narrow road tires roll more efficiently than a wider, softer mountain bike tires. But that same smooth tire will slip and slide on loose surfaces. And a knobby mountain tire will gobble up rough trail, but will be less efficient when things smooth out. You get the idea.
Modern road tires are made up of two main components, a casing and a tread. All hook-bead clinchers also have beads.
The fabric foundation of the tire is called the casing. It is constructed to resist stretching while remaining flexibility. This allows the tire to hold its basic shape while conforming to road surfaces. It is made of plies that are layered on top of each other. More layers mean more wear and puncture resistance, but heavier tires. A common way to boost puncture resistance without adding weight is to place a tough, cut resistance belt, usually Kevlar, under the tread. This helps prevent flats but also makes the tire more expensive and heavier.
Most modern tire casings are made of nylon, but polyamide, cotton and aramid (Kevlar) alone or in various combinations are also sometimes used. The size of the threads used in the plies effects the handling and durability of the tire. Thread size is called thread count and is noted as threads per inch or TPI.
High TPI Casing: A TPI of over 100 indicates very fine threads that make a thin but supple casing. Thin, supple casings conform better to the riding surface for improved traction. Racers will appreciate the improved handling. High TPI tires are also usually lighter, which improves efficiency and acceleration. The fine tight weaves of high TPI casings are more resistant to certain types of punctures. However the thinner casings are more prone to sidewall cuts, and high TPI tires are usually more expensive and less durable.
Low TPI Casing: Low TPI (60TPI and less) tires have thicker more durable casings that are ideal for training and commuting. The thicker casings are more resistant to cuts, meaning low TPI tires are generally more durable and cheaper. But that thicker sidewall means they’ll be heavier and slower.
The part of the tire that contacts the ground is called the tread. Depending on the tire and its intend purpose, the tread is designed to maximize traction, durability, puncture resistance, aerodynamics and/or rolling efficiency. Tire engineers wrestle with balancing these requirements, knowing full well that no tire can do all things well.
A tourist wants durability and puncture resistance more than low rolling resistance. A racer wants superior grip and low resistance more than durability. A time trialist wants aerodynamics and low rolling resistance more than puncture resistance. And that’s the problem: How do you balance the characteristics you want in a tire? Tire engineers are concerned with three aspects of the tread: compound, tread pattern and shape.
Compound: Most tire treads are made of butyl or natural rubber that often includes additives such as carbon black, Kevlar or silicon. These additives improve specific tire characteristics. Some tires incorporate multiple tread compounds. For instance dual-compound tires have a tougher compound in the middle for straight-line durability and a stickier but less durable compound on the sides for security in sharp turns.
Carbon black compounds are typically more durable, longer wearing, and more accepting of abuse like poor storage and use on resistance trainers. But typically they are not as sticky and have poorer traction. Silica and other synthetic compounds are typically grippier and have better rolling resistance, but are less durable.
Tread Pattern: Treads range from smooth and slick to knobby. Smooth treads are intended for on-road use, where any tread pattern or knobs will diminish what is already a very small contact area. This is especially true on narrower race or training tires. Very wide street tires might benefit from an inverted tread or stippling to avoid hydroplaning in wet weather.
The bead is one of the two steel or Kevlar cables that are folded into the inside edges of the tire casing of modern hook bead clinchers. In a practical, non-scientific sense, the beads do not stretch. This quality keeps the tire from blowing off the rim even at the highest air pressures. Beads can be made of steel or of flexible, foldable aramid cables. Both have advantages and disadvantages.
Kevlar Bead: Also known as folding bead, these make the tire lighter, saving 50-70 grams over the same tire with a steel cable bead. This also makes the tire foldable for easier transport and storage. The downside is that they are more expensive, and more difficult to install because of the floppy, flexible bead.
Wire Bead: Also known as steel beads, these hold their shape better for easier mounting, are less expensive, and make a good choice for use on trainers or as a training tire. The downside is that they are typically heavier.
Now that we have some of the basics covered, it’s time to delve into tire types. Here’s a breakdown of key categories.
Hook-Bead Clinchers: These are made to fit on modern rims that have inward projecting ridges at the top of the rim walls. Many older rims had smooth flanges. These hooked edges grab the tire just above the bulge of the bead and hold it securely allowing for higher tire pressure and the use of a wide range of tire widths on a single rim. Standard clinchers are available in more sizes, shapes, brands and tread patterns than tubulars, and are generally lighter (even with the tube) than their tubeless cousins.
Other advantages of traditional clincher tires include the fact that they work with all appropriately sized rims, are usually cheaper for a given tire, and are easier to install. The primary detractor is that they lack the supple ride quality of tubular or tubeless tires, and are more susceptible to pinch-flat punctures.
Tubeless Hook-Bead Clinchers: These are very similar to hook-bead clinchers, but they have a stiffer and more prominent bead that allows an air tight seal when used with tubeless specific rims or a standard rim adapted to be tubeless. Tubeless clinchers are designed to be used without tubes, but can be used on any appropriately sized rim with a tube.
Benefits include improved ride quality similar to tubulars, increased ride efficiency because energy is not lost to tube creep (aka hysteresis), and because there is no tube, pinch flats are not an issue. Tubeless tires can also be run at lower pressures for better traction and comfort. The downside is that they can be more difficult and messy to install, are more expensive for the same tire, and are more difficult to repair on the road or trail.
Tubulars: This type of tire is primarily used for road racing, cyclocross and triathlons. They are unique in that the tube is integrated into the tire. The tire casing wraps around the tube and is stitched to form a closed tube. The tire is then glued to a tubular specific rim. Because of the glued attachment and because tubular tires don’t have beaded open casings, tubular rims don’t have upright ridges needed to hold a tire on. Consequently tubular rims can be lighter than clinchers with the same or higher strength. Other advantages include the fact that they are lighter than similar clincher and tubeless rim/tire combinations, and provide excellent ride quality with fewer pinch flats. The downside is that they are more expensive, more difficult to install, and the most difficult to repair.
Just like with car tires, bike tire sizing is a combination of diameter and width. Modern road tires are sized in millimeters. An inflated 700x23 road tire is about 700 millimeters in outside diameter and 23 millimeters wide.
The most common road tire diameters are 700c. However tires that are 650c are used on some small-sized bikes, and some time trial and triathlon bikes. There are also 27-inch road tires, but this is an uncommon, older American size.
ISO Tire measurement: The International Standards Organization (ISO) has adopted more precise metric standards for tires and rims. Unlike traditional sizing, e.g. 26x1.95 or 700c, the ISO tire standard is based on accurate measurements of a tire’s Bead Seat Diameter and its inflated width. For instance, the ISO equivalent of a 700x25 tire is 25-622, where 25 is the width of the inflated tire in millimeters and 622 is the diameter of the tire’s bead in millimeters.
The 622 is called the Bead Seat Diameter (BSD) because it is also the diameter of the inside of the rim where the inflated tire beads will seat. Here is a chart of common tire sizing equivalents:
Tubes are the butyl or latex rubber bladders that hold the air in standard hook-bead clincher tire and inside tubular tires. Latex tubes are considered a higher performance tube because they are more supple and lighter. Their downside is that they leak air more quickly so they need to be re-inflated more often, maybe after every ride. Butyl tubes lose air slower, so re-inflation may be necessary only once a week. Butyl tubes can be made lighter by reducing wall thickness. This makes them accelerate better but makes them more susceptible to punctures.
Unlike tires, tubes fit a range of tire sizes. For instance a 700 x 28-32 tube is compatible with any tire between 700x28 and 700x32. Tubes are commonly available with one of two valve stem types: Presta (skinny European-style stems) and Schrader (common U.S. car valve stem).
All Schrader valves have screw-in removal cores that allow tightening or replacement if they leak or to add tire sealant. Most Presta tubes do not have removable cores, and those that do are easily clogged by sealant. Presta tubes are available with different length stems to accommodate the depth of the rim used. The most common is 35mm, but you can also find 48mm and 60mm. These longer stems are handy for exceptionally deep rims.