In any racing competitions, the aerodynamic performances of the equipment are determinant. This is true, for example, for cars, where the geometry of the bodywork and of the wings can ensure a lower Cx coefficient and/or a higher down-force and a higher handling. In other competitions, like rowing, the aerodynamics of the hull can reduce the effort done by the athletes. In the cycle and motorcycle racing competitions, other aspects related to aerodynamics become important, such as the manoeuvrability and stability. In the present research, a numerical approach was used in order to compare different front-wheel geometries (of a racing motor-bike) in terms of drag, lift and axial forces. Three different wheel designs have been compared. The first one consists in a traditional seven spokes aluminium design, the second wheel is a 6 spokes magnesium solution and the third a solid-disk wheel. Steady state as well as transient simulations was performed with OpenfOaM®, a free open-source software. This was selected because it allows a higher flexibility with respect to any close-source commercial software. The possibility to customize the solver as well as the boundary conditions allows the analysis of the physical problem of interest. The free license allows a high parallelization of the computations. The steady-state simulations were performed by freezing the wheel position and introducing a rotating reference frame. In this way, the computational time was significantly reduced. For the transient simulations, the computational domain was split into two subdomains. The internal one is cylindrical and contains the wheel. The rotational velocity of the wheel was imposed by applying a rigid rotation to the mesh of the internal subdomain. Mesh interfaces ensures the continuity of the solution across the domains.
CFD, Motorcycle, MRF, performance, OpenFOAM®, wheel
 Kyle, C.R., Selecting cycling equipment. In High Tech Cycling, ed. E.R. Burke, 2nd edn., Human Kinetics, pp. 1–48, 2003.
 Lukes, R.A., Chin, S.B. & Haake, S.J., The understanding and development of cycling aerodynamics. Sports Engineering, 8(2), pp. 59–74, 2005. https://doi.org/10.1007/bf02844004
 Greenwell, D.I., Wood, N.J., Bridge, E.K.L. & Add, R.J., Aerodynamic characteristics of low-drag bicycle wheels. Journal of the Aeronautical Sciences, 99(983), pp. 109–120, 1995.
 Zdravkovich, M.M., Aerodynamics of bicycle wheel and frame. Journal of Wind Engineering and Industrial Aerodynamics, 40(1), pp. 55–70, 1992. https://doi.org/10.1016/0167-6105(92)90520-k
 Tew, G.S. & Sayers, A.T., Aerodynamics of yawed racing cycle wheels. Journal of Wind Engineering and Industrial Aerodynamics, 82(1–3), pp. 209–222, 1999. https:// doi.org/10.1016/s0167-6105(99)00034-3
 Kyle, C.R. & Burke, E., Improving the racing bicycle. Mechanical Engineering, 106(9), pp. 34–35, 1984.
 Kyle, C.R., Aerodynamic wheels. Bicycling, pp. 121–124, 1985.
 Kyle, C.R., New aero wheel tests. Cycling Science, 3(1), pp. 27–32, 1991.
 Fackrell, J.E. & Harvey, J.K., The flowfield and pressure distribution of an isolated road wheel, advances on road vehicle aerodynamics. Fluid Engineering, ed. H.S. Stephens, BHRA, pp. 155–165, 1973.
 Fackrell, J.E., The Aerodynamics of an Isolated Wheel Rotating in Contact with the Ground, Ph.D. Thesis, University of London, London, U.K., 1974.
 Fackrell, J.E. & Harvey, J.K., The aerodynamics of an isolated road wheel. In Proc. of 2nd AIAA Symposium of Aerodynamics of Sports and Competition Automobiles, ed. B. Pershing, LA, Calif., USA, pp. 119–125, 1975.
 Wray, J., A CFD Analysis into the Effect of Yaw Angle on the Flow Around an Isolated Rotating Wheel. Ph.D. Thesis, Cranfield University, U.K., 2003.
 McManus, J. & Zhang, X., A computational study of the flow around an isolated wheel in contact with the ground. Journal of Fluids Engineering, 128(3), pp. 520–530, 2006. https://doi.org/10.1115/1.2175158
 Godo, M.N., Corson, D. & Legensky, S.M., An aerodynamic study of bicycle wheel performance using CFD. 47th AIAA Aerospace Sciences Annual Meeting, Orlando, FL, USA, 5–8 January, 2009, AIAA Paper No. 2009-0322.
 Godo, M.N., Corson, D. & Legensky, S.M., A comparative aerodynamic study of commercial bicycle wheels using CFD. 48th AIAA Aerospace Sciences Annual Meeting, Orlando, FL, USA, 4–7 January, 2010, AIAA Paper No. 2010-1431.
 Concli, F., Gobbi, M. & Gorla, C., Comparative study of the aerodynamic performances of motorcycle racing wheels using numerical cfd simulations. WIT Transactions on Engineering Sciences, 120, pp. 185–191, 2018. https://doi.org/10.2495/afm180181
 OpenFOAM®, www.openfoam.com
 Concli, F. & Gorla, C., Windage, churning and pocketing power losses of gears: different modeling approaches for different goals. Forschung im Ingenieurwesen/Engineering
Research, 80(3–4), pp. 85–99, 2016. https://doi.org/10.1007/s10010-016-0206-9
 Concli, F. & Gorla, C., Numerical modeling of the churning power losses in planetary gearboxes: An innovative partitioning-based meshing methodology for the application of a computational effort reduction strategy to complex gearbox configurations. Lubrication Science, 29(7), pp. 455–474, 2017. https://doi.org/10.1002/ls.1380
 Concli, F., Gorla, C., Della Torre, A. & Montenegro, G., Churning power losses of ordinary gears: A new approach based on the internal fluid dynamics simulations. Lubrication Science, 27(5), pp. 313–326, 2015. https://doi.org/10.1002/ls.1280
 Concli, F. & Gorla, C., Analysis of the oil squeezing power losses of a spur gear pair by mean of CFD simulations. ASME 2012 11th Biennial Conference on Engineering Systems Design and Analysis, ESDA 2012(2), pp. 177–184, 2012.
 Concli, F., Gorla, C., Stahl, K., Höhn, B.R., Michaelis, K., Schultheiß, H. & Stemplinger, J.P., Load independent power losses of ordinary gears: Numerical and experimental analysis. 5th World Tribology Congress, WTC 2013, pp. 1243–1246, 2013.
 Concli, F., Della Torre, A., Gorla, C. & Montenegro, G., A new integrated approach for the prediction of the load independent power losses of gears: Development of a meshhandling algorithm to reduce the cfd simulation time. Advances in Tribology, 2016, art. no. 2957151.
 Concli, F. & Gorla, C., Numerical modeling of the power losses in geared transmissions: Windage, churning and cavitation simulations with a new integrated approach that drastically reduces the computational effort. Tribology International, 103, pp. 58–68, 2016. https://doi.org/10.1016/j.triboint.2016.06.046
 Concli, F. & Gorla, C., Influence of lubricant temperature, lubricant level and rotational speed on the churning power loss in an industrial planetary speed reducer: computational and experimental study. International Journal of Computational Methods and Experimental Measurements, 1(4), pp. 353–366, 2013. https://doi.org/10.2495/cmemv1-n4-353-366
 Concli, F., Thermal and efficiency characterization of a low-backlash planetary gearbox: An integrated numerical-analytical prediction model and its experimental validation. Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, 230(8), pp. 996–1005, 2016. https://doi.org/10.1177/1350650115622363
 Rasedul Islam, Md., et al, Drag reduction of a car by using vortex generator. International Journal of Scientific & Engineering Research, 4(7), pp. 1298–1302, 2013.
 Leśniewicz, P., Kulak, M. & Karczewski, M., Vehicle wheel drag coefficient in relation to travelling velocity—CFD analysis. Journal of Physics: Conference Series, 760(1), p. 012014, 2016. https://doi.org/10.1088/1742-6596/760/1/012014