<P> Torque converters respond quickly to loss of traction (torque) by an increased speed of the driving wheels for the same engine speed . Thus, under most conditions, where the static friction is higher than the kinetic friction, the engine speed must be brought down to counteract wheelspin when it has occurred, requiring a stronger or quicker throttle reduction by the driver than with a manual transmission, making wheelspin harder to control . This is most apparent in driving conditions with much higher static friction than kinetic, such as packed hard snow (that turns to ice by friction work), or snow on top of ice . </P> <P> In situations where a driver with a manual transmission can't afford a gearshift, in fear of losing too much speed to reach a hilltop, automatic transmissions are at a great advantage--whereas driving a manual car depends on finding a gear that is not too low to enter the bottom of the hill at the necessary speed, but not too high to stall the engine at the top of the hill, sometimes an impossible task, this is not an issue with automatic transmissions, not just because gearshifts are quick, but they typically maintain some power on the driving wheels during the gear change . </P> <P> Earlier hydraulic automatic transmissions were almost always less energy efficient than manual transmissions due mainly to viscous and pumping losses, both in the torque converter and the hydraulic actuators. 21% is the loss on a 3 speed Chrysler Torqueflite compared to a modern GM 6L80 automatic . A relatively small amount of energy is required to pressurise the hydraulic control system, which uses fluid pressure to determine the correct shifting patterns and operate the various automatic clutch mechanisms . However, with technological developments some modern Continuously variable transmission are more fuel efficient than their manual counterparts and modern 8 - speed automatics are within 5% as efficient as a manual gearbox . </P> <P> Manual transmissions use a mechanical clutch to transmit torque, rather than a torque converter, thus avoiding the primary source of loss in an automatic transmission . Manual transmissions also avoid the power requirement of the hydraulic control system, by relying on the human muscle power of the vehicle operator to disengage the clutch and actuate the gear levers, and the mental power of the operator to make appropriate gear ratio selections . Thus the manual transmission requires very little engine power to function, with the main power consumption due to drag from the gear train being immersed in the lubricating oil of the gearbox . </P>

What is p r n d s in automatic transmission