Top speeds in the National Class are easily as high as in the other junior formulae of BMW and Renault, but cornering speeds tend to be lower as Formula Ford cars lack the downforce-producing aerodynamic aids on the other cars; handling is therefore entirely down to mechanical grip, and the lack of wings ensures that cars following another are not aerodynamically disadvantaged, allowing some of the closest racing with plenty of overtaking. Series' rules may permit slick or treaded tires, generally supplied either by Dunlop or Avon. As the rules limit engine modifications, all cars are relatively equal and racing results tend to be close. Formula Fords allow suspension, damping, gearing and braking bias changes, but not aerodynamic options such as winged cars.