Transmission is a word thrown around in forums every now and then, but very few of us know how they work and how efficient they are. This is beginners description for people to understand the fundamentals about the types of transmission and their efficiency. Transmission losses in a modern synchromesh transmission are pegged at 21 percent(these include losses when transferring the torque from the gearbox to the road via the axles), i.e when a manufacturer like Suzuki claim that the Suzuki Swift is producing peak power of 87bhp, what you actually get on the road is close to 68bhp, for automatic transmissions, these losses are decidedly higher. Automotive transmission in layman terms, is a Mechanism used to increase the flexibility of an engine for use in varying condition of load and speed requirements. It maximises the torque of an engine as and when needed(gears selected by the driver). They can be broadly classified into the following categories: 1.Manual Sub-Types 1.a Non-synchronous: In this type of a gearbox the input shaft(coming from the engine) and the output shaft(connected to eh axles) are directly coupled, and a selector is used to engage gears on a splined shaft, though these gearboxes are simple to manufacture, it requires utmost care to match the engine speed to the road speed while changing gear, not doing so results in gear 'chatter' which is detrimental to the gearbox as well as the engine, which has rendered these types of gearboxes obsolete in passenger cars, however, they still have applications where high loads are concerned and so find their use in heavy/farm machinery and trucks(18 wheelers)1.b Synchromesh Gearboxes: Courtesy:gadgetgq.com These types of gearboxes are the mostly widely used type of manual transmission, the above animation shows that the input gear and the output gear never lose contact, a dog clutch is used to couple the shaft via a selector and the dog clutch is coupled with the gear using 'Synchro rings' , which altogether eliminates gear teeth clashing, the animation shows only one pair of gears but in a typical gear box, there are rows of these to facilitate greater range of speeds. 1.c Sequential: This is a type of gearbox only allows the operator to select the one lower or higher gear, and allow the transgression from one gear to another without the need for synchro less dog clutch engagement, except when engaging first. However synchro less and Sequential engagement are mutually exclulsive to each other. These are most often used in bikes/scooter also for some cars which are designed for race use. The main advantages of this design is non complexity of its design, lightness and/or the use of clutch less gearshifts in competitive environments. 2.Automatic: Are transmission which change gears on their own without the operator having to affect one 2.a Torque Convertor: Though previously very expensive as it used a torque convertor to exert hydraulic fluid pressure to affect the change of gears, now with the advent of use of computers to control the gear change, these types of transmission have become much more cost effective. Also instead of using torque convertors, sets of Epicylic gear terrains are used(also referred to as Planetary gear terrain). 2.b Continously Variable Transmission: This type of a gearbox offers torque multiplication, is not complex, and has few transmission losses. In this type of a gearbox, the output and input shaft can be thought to be as cones, as the speed of the input shaft increases the momentum of the belt forces it to the end where the diameter is the smallest, and diameter of the output shaft is the largest to offer maximum torque, as the torque demand subsides, the belt is moved where speed multipilcation is possible(i.e when the input shaft has its largest diameter and the output shaft has the lowest).