Editor’s Note: Our last article addressed the high-impact and high-strength plastics for high-level bike races. Today we focus on bicycle tires.
The Tour de France is one of the most competitive bicycle races in the world. There are, of course, a number of rules for all aspects of the race, but I was surprised to find out that when it came to tires, there are no real regulations. There are certain wheel regulations, (Union Cycliste Internationale Regulations 1.3.018 as seen on page 65) but it seems that the choice of tire, including its pressure, size, and materials is up to the individual (or the team’s sponsor).
The riders must consider all the environmental factors in the race when they are choosing a tire. The Tour de France incorporates difficult climbs up the mountains, and long sprints over flat breakaway areas, and even a bumpy traverse over cobblestone streets. In addition, the course can be punishing to the bicycles, which usually weigh less than 15 pounds (approx. 7 Kg). To produce a bike that light, attention must be paid to the materials used. The tires have to support the bike itself and the rider. In an article about a similar bicycle race held a few years ago, Velonews wrote that ”rider size, tire size, tire casing rigidity, weather, rider skill and elapsed tire pressure drop for a given tire all play into what is best described as an artistic science experiment.”
A mechanic who was interviewed by Bicycling magazine, explained that “In general, with all of those variables [like weather and riders’ personal preference], tire pressure is 8 to 8.5 bar for the road stages, and then 9.5 to 10 bar for the time-trial stages. Around 115 psi in the front and 125 psi in the back for the road stages and 130-135 psi for time-trial stages. And we drop that by 10 or 15 for rainy days. They run about 10 psi lower in the front for more control as well, and with tubular tires, they tend to run slightly lower pressures. Clinchers need to be kept around 110 to 120 psi in order to avoid pinch-flatting.”
There are 22 teams and 198 riders this year, and a variety of bicycles and tires. Many riders have custom, handmade tires for the event.
One tire manufacturer explained that the rubber on the treads of their products is made from locally-sourced natural rubber in their own factory in Thailand. They believe that natural rubber is more supple than synthetic rubber — which accounts for the majority of the world’s tire production — and the grip is far superior. In addition, the manufacturer noted that one of the benefits of handmade tires is that the handmade one can avoid the heat and pressure process (called vulcanization), which most tires undergo in production. Vulcanization binds the materials, but the company claims it compromises the ride quality when the rubber gets stiffer. When treads are handmade, they say, the latex and rubber maintain their ideal quality. (You can learn about vulcanization and its behavior and characteristics in this Polymer Processing Mixer Test article and webinar.)
Another tire manufacturer claims it invented a revolutionary puncture resistant tire made from special India rubber and a more flexible mixture that has unique characteristics. Still, a competing tire, handmade in Germany, is touted for its unique tread rubber mixture which has “revolutionised bicycle tyres” and improved rolling resistance grip compared to activated silica compounds.
As you can see, the ‘recipe’ involved in tire manufacturing is a varied, yet precise business. In the research and development laboratories of the German bicycle manufacturer, three considerations went into the development of a well-established tire they developed a decade ago: static friction (grip), rolling resistance and mileage. However, they found that if they improved one of these factors, they could worsen at least one other factor. For example,
“a tyre with maximum grip wears out faster and rolls slower. If one makes the tyre faster or more durable, then this in turn reduces grip. With the then current highest standard of compound technology, the activated silica compound having already reached a very high standard of compromise, our developers wanted to take compounding to an even higher level. This led them to venture into new territory, exploring new ways so that in 2005 they made a breakthrough in mixing technology…a revolutionary compound based on the latest findings on polymer and other raw material research…. we refine newly developed synthetic rubbers with natural rubber with the proven high-performance tread compound. We use these rubbers with special nanometric carbon soot particles, which are optimized in shape and surface properties for best uses for the intended tyre.”
Carbon black rubbers (CBRs) are heavily used in tires. The material adds reliancy and conducts heat effectively away from the tread, extending tire life. Carbon black is added to rubber as both a filler and as a strengthening or reinforcing agent. For various types of tires, it is used in inner liners, carcasses, sidewalls and treads utilizing different types based on specific performance requirements. As we just noted, the ‘recipe’ for each tire is different, and sometimes even patented, so analyzing the material is an important step in the development process.
As we wrote in a previous article, CBRs can be challenging to analyze because they are opaque to infrared light except when cut by cryo-microtomes which are not commonly available in analytical laboratories. At even a few microns of thickness, CBRs become opaque in transmission mode infrared spectroscopy. However, attenuated total reflection (ATR) is a powerful sampling technique ideal for samples which absorb or scatter strongly in transmission. ATR works well for these samples because the evanescent wave (the part of the IR beam that interacts with the sample) probes only a thin section near the surface, usually 1-3 microns deep, making the technique generally insensitive to overall sample thickness. Homogeneous solid samples, the surface layer of a multi-layered solid or the coating on a solid are good candidates for ATR analysis.
CBRs have a high index of refraction – close to that of the preferred ATR crystal, diamond. When using a diamond ATR, this causes the spectra from CBRs to be badly distorted. In contrast, spectra from germanium (Ge) ATR crystals show clean and well-defined peaks. This is the result of the much higher index of refraction for Ge, and the resulting shallower depth of penetration.
We conducted an experiment using an FTIR spectrometer with diamond and germanium ATR crystals in order to identify and verify the materials used in carbon black rubber. The diamond ATR spectral data were heavily distorted, appearing almost like first derivative spectra. In contrast, spectra collected with the Ge ATR showed sharp peaks. In both cases, the carbon-black material also causes scattering (due to microparticulates, almost like soot, in the CBR). This leads to a sloping background, clearly seen with the Ge ATR. Read Carbon Black Analysis Using FT-IR with Germanium and Diamond ATR to learn about the study, instruments used, and results. Spectra are shown from both the diamond and Ge ATR crystals, which clearly demonstrate the benefit of Ge ATR in the analysis of CBRs. This enables infrared spectroscopy to be one of the most important analytical tools for the analysis of tires, for automobiles as well as bicycles.
UCI rules state that “The finish occurs at the instant that the tyre of the front wheel meets the vertical plane rising from the starting edge of the finishing line.” We’ll find out the Tour de France winning tire on July 24th.