What are they and why have mullet wheels caused such a stir on the road?

The mullet concept is used in mountain biking to refer to the mix of wheel sizes used in the most aggressive disciplines, where a 29-inch front wheel is usually combined with a 27.5-inch rear wheel. Now, the concept is starting to be applied in road cycling as well, as we could see with the Red Bull-BORA-hansgrohe cyclists in the early classics.

Different wheel profiles on the Red Bull-BORA-hansgrohe in the early cobbled classics

No, we are not talking about going back to the 90s when time trial bikes used a 650b front wheel or even smaller to achieve the most aerodynamic position for the rider, although wind resistance is also a factor.

During the races last weekend, Omloop Het Niewsblad and Kuurne-Brussels-Kuurne, we saw the Red Bull-BORA-hansgrohe cyclists using their particular interpretation of the mullet concept applied to the road, consisting of using wheels with different profiles.

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Actually, using different profiles on the front and rear wheels is not something new. What is innovative is how the German team has employed it. While it was common to place the wheel with the higher profile at the back and choose a shallower rim for the front to reduce the impact of crosswinds, Red Bull-BORA-hansgrohe has started to do exactly the opposite.

They used the Roval Rapide CLX II wheels they usually use on the rear, with a 60mm profile. However, the front wheels were visibly of a higher profile compared to the usual combination of Specialized wheelsets, where the front wheel has a 51mm profile in what seems to be the new step for the Morgan Hill brand to improve the aerodynamics of their bikes.

Obviously, the front wheel used in this particular road mullet is a completely new version since the Californian brand does not have a model with a higher profile than the 60mm of the rear wheel, and what better terrain to test this concept than the Belgian classics where the wind always plays a role and changes direction constantly due to the routes of the classics.

The idea of mounting a front wheel with a higher profile delves into the same concept that has been applied in recent years to aerolight bikes, enhancing aerodynamics at the front, the first part that faces the airflow impacting the bike, and using the rear half to contain the weight.

In principle, with the studied aerodynamics of current wheels, this should not be a problem since the designs of aerodynamic profiles make the wheels increasingly stable, even in very strong crosswinds. However, no one seems to consider that this philosophy is increasing the weight in the front, which could eventually affect the bike's reactions or even the rider's position on it to compensate.

In any case, if Specialized has proposed this to Red Bull-BORA-hansgrohe to test in competition, it is because the numbers from this mullet configuration in their wind tunnel in Morgan Hill have shown that the invention works, and only the approval of the cyclists is needed to extend it to their commercial offering. Who knows if we will see a paradigm shift regarding wheel profiles.