Mud flaps are designed to protect a vehicle from dirt, mud, and debris that can be thrown up from the road. While they are effective at protecting your vehicle, they can also negatively impact your gas mileage.
The added weight of the mud flaps can increase your fuel consumption as your engine has to work harder to move the extra weight. Additionally, the mud flaps can create drag on your vehicle which also reduces your gas mileage.
If you are looking to maximize your gas mileage, you may want to consider removing your mud flaps. However, if you live in an area with a lot of dirt and mud on the roads, you may want to keep them on to protect your vehicle.