No, fender flares do not improve performance. They are purely aesthetic additions to a vehicle and serve no functional purpose. Some people believe that the added width of fender flares can help to stabilize a car on the road, but there is no evidence to support this claim. In fact, many experts believe that wider tires are actually more prone to hydroplaning and provide less grip on wet or icy roads. So, if you're looking to improve your car's performance, you're better off investing in other upgrades like a new engine or suspension system.