PURPOSE, AIM, DEVELOPMENT PROCESS AND RESULTS
PROJECT BACKGROUND
The Limitless project began in 2017 and was first launched to riders in 2019 with the 48 Limitless Aero Disc, the most aerodynamic wheelset in the world up to and including 50mm depth wheels. The aerodynamic performance was made possible by the extra wide external shape measuring 34.5mm at its widest point, making it the first road racing focused wheel with an external width over 30mm. HUNT achieved this extra width while minimizing the rim mass with patented Limitless Width Aero Technology which utilizes a strip of low-density structural polymer inserted in a molded channel within the rim sidewall with carbon molded over it, allowing for extra width while minimizing material mass. The award-winning wheelset was widely used by HUNT-supported teams and athletes such as world tour Team Qhubeka-ASSOS, British Continental team Canyon dhb Pro Cycling, and US Criterium squad LA Sweat, racking up wins at every level of the sport including a Grand Tour stage win under Victor Campenaerts at the 2021 Giro d’Italia. Through in-depth conversations with these riders, the feedback was consistent; the aero performance and stability of the 48 Limitless was unmatched but the riders wanted less weight.
Over the course of a long and winding dynamic road stage riders were accelerating dozens if not hundreds of times: out of corners, closing gaps, and returning from the cars. Our riders asked if the HUNT engineering team could find a way to maintain the aero performance and stability while significantly reducing system weight. In the meantime, key wheel competitors introduced new, wider profiles, including some unique front and rear-specific rim designs offering impressive aero-to-weight advantages for riders. These innovations from select competitors and the seemingly impossible request from supported riders initiated the SUB50 Limitless Speed Project, proving that the collective innovation cycle throughout the industry leads to better product solutions for all riders.
DEVELOPMENT PROCESS: CFD, 3D PROTOTYPING, WIND TUNNEL TESTING
The engineering team at HUNT relied on three key technologies to rapidly develop, test, validate and re-test numerous rim profiles: CFD, 3D prototyping, and wind-tunnel testing. Over approximately 2500 hours of CFD (computational Fluid Dynamics) analysis, the engineering team evaluated 38 front rim profiles and 18 rear rim profiles to narrow down potential shapes.
Once narrowed down to 3 front and 4 rear rim profiles the team then 3D printed rims in sections, then assembled into fully built wheels to create representative prototypes for wind tunnel testing in a controlled and repeatable environment, representative of real-world wind conditions and yaw angles. Carbon fiber prototypes were then produced and re-tested in the wind tunnel against relevant competitors to validate the new designs and provide transparent data for riders to review and consider. Throughout the SUB50 Limitless Speed Project, the HUNT engineers performed a combined total of 90 wind tunnel runs over two multi-day sessions to test, compare and validate the new profiles.
AERODYNAMIC EFFICIENCY: UNIQUE FRONT AND REAR HOOKLESS PROFILES
To maximize the aerodynamic efficiency of the wheelset as a system while reducing weight, the team chose to focus on creating the most efficient rim profile for managing clean airflow at the front of the bike. After evaluating potential profiles using CFD, then testing the most promising shapes in the wind tunnel, an engineered rim shape 49.5mm deep and 34.2mm at its widest point was chosen for the front rim profile. Since the rear wheel encounters heavily disturbed airflow affected by the front of the bike and rider, the engineering team saw an opportunity to minimize material in the rear wheel without negatively affecting system aerodynamics.
The team evaluated 18 rear profiles, also utilizing CFD analysis followed by wind tunnel testing, to choose a slightly narrower and lighter rear rim profile with dimensions of 49.5mm deep and 30mm wide. Some competitors pair a shallower front rim with a deeper rear rim to increase aerodynamic benefit while maintaining ride characteristics.
HUNT patented Limitless Width Aero Technology offers ample stability and predictability, allowing our engineers to maximize aero benefits at the front of the bike by optimising the shape and depth where it has the greatest impact on overall bike-and-rider system aerodynamics. The result, as evidenced by the wind tunnel data, is a faster wheel system that doesn’t compromise on handling characteristics.
WIND TUNNEL PERFORMANCE SUMMARY:
SUB50 Limitless offers best overall performance of all wheels 50mm and under when tested, the closest competitor (DT Swiss ARC 1400 DICUT 50 DB, 1456g) tested aerodynamically faster with a 28 mm tire (Run A: 0.6 W faster, Run B: 0.14 W slower) predominately due to the DT Swiss’ 3mm narrower internal rim width producing a narrower tire profile. The SUB50 produced a 1.85 watt gain compared to the DT Swiss 50 with a 30mm tire, while also providing all the benefits of a wider internal rim with reduced rolling resistance and increased grip and comfort.
The SUB50 Limitless aerodynamically outperformed the deeper Zipp 454 NSW (55/58mm undulating depth, 1428g) wheelset by 3.07 watts when both wheelsets were tested with 30mm tires, and by 0.99 watts when both wheels were tested with 28mm tires.
While weighing just 1428 grams with traditional steel spokes and 1380 grams with available UD Carbon Spoke Technology, the new SUB50 Limitless with a 30mm tire offers a 1.40 watt savings compared the preceding 48 Limitless with a 28mm tire, meaning the HUNT engineering team has reduced overall aero drag while increasing tire width by a full size. Compared to relevant wheels in the mid-depth category, the SUB50 Limitless aerodynamically outperforms the relevant competitor wheels up to and including 50mm in depth, when mounted with modern 30mm tires, and performs similarly to significantly deeper wheels tested. When aerodynamic drag-to-weight and aerodynamic drag-to-depth ratios are considered, the SUB50 significantly outperforms the competitive set.
AERODYNAMIC STABILITY: PREDICTABILITY EMPOWERS SPEED
Pro rider feedback on the 48 Limitless reiterated that the extra-wide profile not only held speed and cheated wind like a much deeper wheel, but offered stability and predictability in changing wind conditions like a much shallower wheel, which is exceedingly important in chaotic feed zones, and dynamic sprint situations.
It was imperative that our engineering team achieve these characteristics in the SUB50 Limitless Speed Project, as this predictability through variable wind conditions allows riders to comfortably stay in a low, aero position on the bike for longer, which can have a considerable impact on efficiency and expended energy throughout a long road stage or classics race. This stability is attributed to the wide radius at the rims’ spoke bed, which achieves more consistent and controlled stall conditions, shown on the steering moment co-efficient graph as lower fluctuations around the stall points. Steering moment co-efficient is proportional to side force on the rim.
LOW SYSTEM WEIGHT: A SUM OF COMPONENTS
While designing a best-in-class set of hookless front and rear carbon rim profiles to maximize aerodynamic efficiency while reducing weight, the engineering and product development team was simultaneously seeking out other ways to reduce mass and increase performance across the wheel system. HUNT’s world tour-proven TaperLock UD carbon fiber spoke technology was chosen as an upgrade option for this wheelset, along with the industry-leading Pillar Wing 20 Elliptical Aero spokes for the steel spoke offering. Recent advancements in composite lay-up capabilities also allowed our team to achieve previously unreachable strength-to-weight ratios in the construction of these new, wide rim shapes, resulting in lighter rim weights.
To further reduce wheel system weight the HUNT engineering and development team worked with our trusted industry-leading suppliers to develop and test a double ratchet hub system with a 40-tooth drive ring that achieves the same level of reliability HUNT hubs are known for, offering increased engagement surface area while using less shell materials relative to our race-proven pawl-based systems. The floating ratchet rings are contained as a cassette, meaning they won’t pop out in pieces during routine service. The HUNT H_Ratchet DBL hubset weighs just 305 grams per set for the steel spoke version with an in-house FEA developed spoke interface and hub shell. Reliably offering 9-degree engagement, the system is designed for high torque load and easy servicing, with tool-free end cap removal and double sealed main hub bearings. The hub shell is made using 6066 aluminum alloy, offering high strength-to-weight, with an extra strong 7075-T6 alloy axle and freehub body with H_Ceramik reinforced coating to protect against gouging. To put the system through the paces, HUNT-supported adventure cyclist Boru McCullagh embarked on a fully-loaded, around-the-world journey on one of the early test sample sets, featured in the 48 Limitless Gravel Adventure wheelset, clocking 25,000 kilometers (and counting) on the system.
TIRE PROFILE: HOOKLESS PERFORMANCE, ETRTO COMPLIANCE AND AERO OPTIMISATION FOR 28-30MM TIRES
Both front and rear rim profiles feature hookless/TSS (Tubeless Straight Side) beads with an internal rim width of 23mm, adhering to 2023 ETRTO standards for use with 28mm and wider tires, while being optimised for both 28 and 30mm tires. Hookless rim technology allows HUNT to slightly reduce rim weight, improve manufacturing consistency, and improve aerodynamics at the tire-to-rim interface by reducing the “lightbulb” effect that inwardly protruded hooks have on the tire profile. A wider hookless bead profile also helps reduce the chance of pinch flats, due to the blunt, flattened profile.
HUNT was forward looking in 2018 when optimising around 28mm tires for the 48 Limitless project. In 2024, based on emerging trends, data points from specialist pro riders across the sport, and tire sales data, we found it essential to optimise around tires ranging from 28 to 30mm for the next generation of race wheels. A growing number of professional climbers, rouleurs, classics specialists, super domestiques, time trialists, and sprinters have adopted 30mm tires and wider in search of incremental gains in aero efficiency, vibration reduction, cornering traction, and lower rolling resistance.
SUMMARY AND RESULTS: REAL WORLD RELEVANCE AND UNMATCHED PERFORMANCE METRICS
While the SUB50 Limitless Aero Disc was designed to meet the needs of riders at the top of the sport, pushing the performance of the wheel at all yaw angles can create even greater benefits for those of us riding at lower average speeds. At higher average speeds, the rider experiences narrower, more ‘head on’ wind yaw angles, whereas lower average speeds generate wider average wind yaw angles. Riders are encouraged to review the data for themselves in our publicly available research white paper and see how the SUB50 Limitless Aero Disc stacks up against the competitive set.
Leveraging rapid development techniques such as CFD analysis and 3D prototyping along with the proven validation method of wind tunnel testing, the HUNT engineering team has raised the expectation level for aerodynamic efficiency while simultaneously reducing the wheel system weight and increasing responsiveness, creating a world-beating combination of performance attributes. The result is the ultimate all-around mid-depth wheel system for riders unwilling to compromise. The SUB50 Limitless Aero Disc = completely unreasonable.
If you’d like more information, please read our research white paper for full engineering and development process details and wind tunnel testing data for the SUB50 Limitless and competitor wheels.
