"Here at Popular Science, we wanted to know just how well Santa's sleigh could travel at high altitudes. So we partnered with ANSYS, a company that specializes in virtual simulation software, and asked them to model how air would flow around the sleigh as it soars through the air on Christmas Eve ..."
Source:
http://www.popsci.com/why-santas-sleigh-poorly-designed-aerodynamic-efficiency