2. The speed of driving gear,
3. Speed of driven gear or velocity ratio
4. The centre distance.
Following necessities have to be met in design of a gear drive :
(a) Gear teeth must have enough strength so that they will not fail under fixed loading or dynamic loading during usual operation conditions.
(b) Gear teeth must have wear characteristics so that their life is suitable.
(c) Use of space and material should be inexpensive.
(d) The position of gears and deflections of shafts have to be considering as they effect on the performance of gears.
(e) The lubrication of gears must be suitable.