A common way to describe aerodynamic drag is "CdA"; in one comparison of racing cycles, there were several two-wheel streamliners with less than half the CdA drag of the best three-wheeler. Air drag is most significant for high-speed events; as of 2016, the world record for a 200-metre sprint on near-level ground is about 145 km/h for a two-wheel streamliner and about 120 km/h for any vehicle with more than two wheels, meaning the two-wheel vehicle was about 20% faster. Aerodynamic power is roughly cubic in speed, so at lower speeds the difference is much less pronounced. At the same time, two-wheel streamliners require a way to stay upright when stopped and at very low speed, and are more sensitive to blowing over in cross-winds. These factors limit the use of streamliners, despite their aerodynamic advantage. The fairing on a velomobile sometimes makes it more subject to cross-winds than a similar unfaired cycle. The effect of cross-winds is complicated because the force of the wind can act as a steering force, as-if the rider had tried to steer the cycle. "Wind steer" can be a safety issue and may also hurt performance, as a serpentine path is longer and thus slower than a straight line. Thus, a design with inferior aerodynamics may be better overall. For example, it is common for time-trial bicycles to use a solid disk rear wheel for best aerodynamics, and a spoked front wheel that has worse aerodynamics than a disk, but is less likely to steer the bicycle in a cross-wind. Velomobile fairings have analogous concerns, leading to trade-offs in fairing design. For example, a longer "tail" on the fairing will increase the total side-wind profile and total side forces, but can reduce the percentage force acting on the steered wheels and so an improve stability in side winds. A larger fairing also hurts weight and has more skin drag), but as with time-trial bicycles, worse aerodynamics but better handling is sometimes a good trade-off. Velomobiles with fairings that are mainly for weather protection can use a more upright seating position. This tends to improve both the ability to see and be seen. However, to retain stability against tipping (both cornering and cross-winds), the wheel track needs to be wider than a comparable velomobile with a low seating position.