The widespread adoption of disc brakes in all formats of modern racing has offered the opportunity to transform rim profile development without the dimensional constraints of rim brake calipers, allowing for wider, aerodynamically optimized rims shapes. On top of the aerodynamic possibilities, riders also benefit from wider tires and lower pressures, known to reduce rolling resistance and road vibration while improving grip. Time trials, triathlons, and criteriums are specific disciplines in which the high average speeds and typically flat courses offer the opportunity to generate significant aerodynamic benefits for the rider through deep rim profiles. However, the high speeds and common crosswinds require those deep wheels to be stable and predictable, so that the rider can maintain a low, aerodynamic position on the bike regardless of conditions. These demands (fast and stable) are both met through wider profiles.

CFD PROCESS

In recent years, HUNT has invested in developing its Research and Development capabilities to deliver science and engineering-led, high-performance wheels to their riders. One key focus has been to build in-house expertise in using Computational Fluid Dynamics (CFD) modelling techniques in the aerodynamic design of performance bicycle wheels.

CFD is the analysis of fluid flow around an object using numerical methods and a computational model to replicate the desired conditions, such as a bicycle wheel in a wind tunnel, and assess the aerodynamic performance. It is a development tool that accelerates the engineering process and allows us to explore new ideas and iterations at a rapid pace, but it is not a replacement for wind tunnel testing, which combined with real-world rider testing, provides the final validation of product performance. Traditionally, aerodynamic profile development has been conducted in the Wind Tunnel, which involves manufacturing several prototypes to test theories and profiles. This often means executing a wind tunnel test session without clear prediction of the outcomes, which can then necessitate the time and investment-intensive process of repeated prototyping and testing to identify the optimal solution.

PROFILE DEVELOPMENTS

The HUNT engineering team selected a depth of 73mm for shallowest front rim profile, chosen to minimize the effects of side forces from crosswinds whilst maximizing aerodynamic efficiency in a straight line. The validated wind tunnel performance of the 60 Limitless Aero Disc served as the benchmark and starting point for the 73mm profile. Feedback from HUNT-supported WorldTour riders (2021 Team Qhubeka Assos) suggested that the extra wide rim profile of the 60 Limitless Aero Disc resulted in an ultra-fast wheelset that handled cross winds and side forces like a much shallower wheel, an attribute that would be extremely valuable in an even deeper format.

The initial design concept for the deeper 83mm front rim profile began more traditionally in terms of width and shape. However, the CFD and wind tunnel-led development process quickly identified the potential for a wider shape to improve performance, even at the 83mm depth. A wider profile was modelled using CFD, then prototyped for further testing.

WHY WE CREATED FRONT AND REAR SPECIFIC RIM SHAPES:

Due to the generally laminar (constantly attached) nature of airflow, an object immediately behind another object will be subjected to disordered airflow of different speeds and directions, and therefore must be designed to reduce drag in those disordered airflow conditions. Applying this to cycling, and in particular, wheels, front and rear wheels encounter different airflow conditions and therefore have unique aerodynamic roles to play in the system. The HUNT engineering team has purposefully designed the front and rear rims in this system for their specific role, creating an optimal combination of drag reduction, crosswind stability, and low weight.

THE RESULTS

As shown in the graphs, the HUNT 7387 Aerodynamicist and HUNT 8387 Aerodynamicist Carbon Disc wheelsets produce exceptionally low drag values when compared to numerous leading relevant competitors with both 25mm and 28mm tires (see white paper for full tested competitive set). The DT Swiss Dicut 80F / 80R produced the lowest aerodynamic drag from the competitor tested and became the benchmark competitor for further testing.

The 8387 Aerodynamicist Carbon Disc provides an advantage over most competitors when it comes to all out speed. When combined with a 25mm tire, the HUNT 8387 Aerodynamicist Carbon Disc wheelset follows the leading DT Swiss Dicut 80mm Wheelset (1777g) by 0.17W according to the Mavic Std WAD (Wind Averaged Drag), while offering a stable steering moment profile resulting in predictable handling. However, when simulating the performance considering the asymmetric wind conditions at KONA (World triathlon Championships), the HUNT 8387 Aerodynamicist is the leading performer in the wheelset class tested. After extensive testing, a 25mm tire proved to be the aerodynamically superior setup. The 8387 Aerodynamicist is still a very competitive wheelset when combined with the 28mm tire, with maximum differences of 0.34 Watts from the 25mm tire option.

The HUNT 7387 Aerodynamicist Carbon Disc wheelset, our shallower front wheel offering, was designed to maximize aerodynamic benefit with minimal steering moment magnitude. The final tests concluded that the HUNT 7387 Aerodynamicist Carbon Disc wheelset provides very low steering moment given its depth, easily outperforming most industry leading competitors in both stability and minimising aerodynamic drag, performing only 0.35W slower than the deeper 8387 offering in the same conditions whilst minimising steering forces. The HUNT 7387 Aerodynamicist delivered results within 0.52W of highest performing DT Swiss Dicut 80mm, when paired with both 25 and 28mm tires.