Deemed as the hardest physical and mental feat in gravel cycling, Unbound is a place where the best of each cycling discipline meet. Located in Emporia, Kansas, this annual gravel event recently took place in the Flint Hills region of the Great Plains in the United States. Established in 2006, the event initially started as a 200 mile (320 km) race, but as years passed, additional distances were introduced to attract a wider range of participants. This year, four thousand riders ventured to the Flint Hills to take on a range of course lengths, including 25, 50, 100, 200 miles, and the challenging 350 mile XL distance.
Unbound has attracted both professional and amateur riders from across the globe, who embark on a journey to conquer this challenge. This gravel race has certainly become one that every gravel enthusiast has on their cycling bucket list. Its allure has contributed to the growth of the global gravel community and has inspired many to start gravel cycling. A depiction of grit, strength, and equipment, riders are up against various terrain, weather conditions, and remote landscapes; the ultimate combination for an epic gravel pursuit.
Unbound has been known to have unpredictable weather conditions, with some years having temperatures exceeding 100 degrees Fahrenheit while others have seen rain or hail, turning classic dirt roads into clay like terrain. Although the race provides multiple checkpoints with support for the participating riders, each cyclist is responsible for carrying their own water and food, with expected bike ‘know-how' in order to fix their own bikes and change tires in case of mechanical issues. Riders are only allowed to seek support within the official checkpoints of the race, otherwise immediate disqualification will transpire if not done so. Unbound is an unpredictable endeavour, known for its demanding nature, with a course best described this year as one which was “unforgiving, an emotional rollercoaster, and an epic adventure.”
Unbound has created an event that is truly special. One that welcomes everyone and caters to professional riders, to amateurs, and weekend riders. This encapsulation is a reason for which gravel cycling and its community has grown so rapidly over the years. Known for its epic conditions, Unbound leaves riders each year with an element of unknown for what is to come on race day.
Certainly with Unbound, it is an event that tests a rider and their tire choice to the limit. Everyone has their own opinion about tires and tire choice for an event such as this one. You may think you are on the best tire but if you are not riding with control, caution, and a sense of finesse, you may not be able to get through the ultimate test. No tire is going to outride the rider so the importance of focusing on control for each rider is essential. The aspect of safety is especially vital. Cycling tires play a crucial role in the overall performance, safety, and comfort of a bicycle. Tires are one of the most talked about topics when it comes to preparing for any race, especially on gravel.
Factors that affected most riders this year were the mud and the heat. Although most riders rode the infamous mile 10 sector of road a few days prior, on race day the conditions changed drastically. Quite often riders were required to dismount and play ‘hike a bike' as several bikes tended to plug up requiring each rider to clear the mud off the bike to prevent it from clogging. In this case for Unbound, mud had much more of an effect on the bike than it had on the choice of tire; however, there still lies many essential aspects of tire choice which should be taken into consideration.
Below are the fundamental aspects of tires along with notes taken by several athletes who participated in Unbound 2023:
Tire Width
Tire width is one of the most talked about topics before any gravel race. Many Unbound racers typically went for the standard width of 40c tires, with the ability to have more give and volume with rocky terrain without the tire weighing too much. Much of the gravel at Unbound was relatively smooth with occasional rocky sections, so the choice of 40-622 tires striked the middle ground of choice which was the best choice for many riders. The choice of a narrower tire in a race such as this would provide less stability. In races that are more purely gravel, allowing for a tire to have more give will allow for ultimate comfort and a greater puncture resistance.
Pressure + Tire Inserts
The relationship between pressure and tire inserts is incredibly important. A foam insert is a 1 centimeter thick piece of foam that stretches the rim of the tire. When a foam insert is installed, the volume of air that is filling naturally increases. When an athlete is running a tire at a lower pressure, you do not have the same tire bend where the tire wants to fold to the side when running lower pressure.
By adding an insert, a rider can run low pressure, having more grip with a lower rolling resistance. This is the best of both worlds. Inserts which help support the side walls, keep structure of the tire and allow for better stability and protection of the rim. This makes a huge difference when you are in such a long race.
Tread
The tread pattern of your gravel bike tire is likely the most crucial factor in your choice, ranging from a subtle low-profile tread or smooth tire, to a robust design with aggressive, mud-dispersing tread and shoulder knobs. Ultimately, a cyclist's selection should depend on riding location and prevailing trail conditions. Typically, the tread extends all the way to the shoulders of the tire and comes into contact with the ground when riding straight or leaning the bike during cornering.
In general, you will find a smoother central line on the tread for better speed and efficiency, accompanied by raised ribs. These ribs may have a ramped design on directional treads, and the shoulder tread is often more prominent to enhance grip while cornering. Tires designed for wetter conditions are equipped with deeper grooves, more aggressive tread, and wider spacing between treads. This configuration aids in shedding mud and provides better traction.
Our Tire Suggestions
Despite there being a myriad of tire brands used, several athletes chose Pirelli Cinturato Gravel RC tires for this feat. Specifically designed for gravel racing, the Cinturato Gravel RCs are meticulously crafted to excel on a wide array of surfaces. These tires position themselves in between Pirelli's Gravel H tire, optimized for hard surfaces and Gravel M tire, designed for soft terrain.
Inspired by Pirelli's renowned Scorpion XC RC pattern highly regarded in the mountain bike tire domain, the Cinturato Gravel RCs have performed exceptionally well across diverse landscapes including muddy roads or single track seen at Unbound Gravel. These tires have low staining knobs in the center of the tire for fast rolling sections and higher ones on the side of the tire for maximum grip when cornering. Pirelli has used its rubber specific gravel formulation called SpeedGRIP which helps increase speed and lower rolling resistance, providing versatility for a variety of terrain conditions. An additional feature that Pirelli has employed is the TechWALL Gravel fabric, used to enhance puncture resistance. While road punctures typically occur within the tread and off-road flats are caused by cuts on the sidewall, Pirelli has combated both of these potential threats by enveloping the entire tire in this fabric.
Most recently released by Pirelli is the Cinturato Gravel RC-X tire. With the RC characteristic tread design intact, the RC-X was designed for gravel racing on rough surfaces. This tire has greater puncture protection and was made to meet the demands of gravel cycling in North America. This tire, like the Cinturato RC is available in 700x40mm and 300x35mm being tubeless-ready with a folding bead that is best used for wider rims and lower pressures. Released at a pivotal time, the Cinturato Gravel RC and RC-X are the perfect tires that you can rely on for your next gravel feat.
Final Thoughts
Regardless of what distance one participates in, Unbound has shown what the true spirit of gravel cycling is. Combined with a thrilling energy of cyclists from all over the world, anxiously ready to conquer one of gravel cycling's most difficult feats, Unbound is an experience that tests a riders ability, fortitude, and tenacity. Gravel cycling is a humbling experience and Unbound certainly provided that for many riders.
