Distance from front axle to center of down force is the shortest distance from the centerline between both front wheels to the point on the same horizontal level where the sum of all aerodynamic down forces is projected.

If there are no wings on the car and you have no data resulting from wind tunnel tests, disregard the down force by entering a zero ("0") in the "Aerodynamic down force at top speed" field. As a result, the value of the "Distance from front axle to center of downforce" field has then become irrelevant.

Without wings, there probably will be some negative down force (lift) at higher speeds, most likely on the rear end of the car, but there is no way of guessing in the right direction without any further tests.