Gravity is a weighty subject. Gravity is a force of nature, and also, a force in dynamics and simulation within Cinema 4D. The effects of gravity will be the main contributor to any dynamics and physics sims that you perform in Cinema 4D. Earth normal gravity is not 1.0 in the dynamics engine, as all of the information is expressed in actual values, and as such, needs to be properly input in order to get the correct results. -9.81 on the Y axis is the correct value to use for Earth-normal gravity in the dynamics engine (representing the free fall force of 9.81 m/sec). In addition, you will need to factor for the proper air resistance value (which varies with altitude), and the mass of the involved objects, as a start.
That said, you are free to use any number necessary in order to acheive the desired result, but any other number will not be accurate with regard to Earth-normal results.