Why do car manufacturers make automatic transmissions with less gears than standard?

Question

Yea today I was thinking about transmissions for cars. I was wondering why auto manufacturers always make their automatic transmissions 1 gear less than the same car with a standard transmission. Anyone with insight on this would be appreciated, so I could sleep now without wondering :P

Answer 1

The automatic has lower gears for driving up hill and snow. they aren't meant to be shifted like a manual. But I do think that they correlate to first and second gear. As far as I know the automatic transmission has the same amount of gears a manual.  

Answer 2

Actually none of the above answers hit upon the correct answer. You ever notice the auto trans cars motor idles and can be reved as high as 2,100 rpms in gear with your foot on the brakes. That slippage of the torque converter makes what we call torque multiplication. Think of that as more piston power strokes per revolution of the rear wheels.  So actually the auto trans with torque-converter 4 speed has a much higher gear ratio in first. So it can go 30 to 40 miles an hour before it shifts to second at full throttle vs the 5 speed or 6 speed manual in the same car. However that is now becoming not as true Lexus has a 8 speed automatic. Several engineering considerations how many gears can we pack into the trans before it gets to heavy and cost gas milage.Continuously Variable ratio transmissions or CVT transmissions have an infinite amount of ratios. Gas milage is gained by keeping the motor at slower turning speeds. But fast enough to produce torque to give the power feel people want.

Answer 3

Cost is likely the primary reason, and torque converter in an automatic giving somewhat more range of speed in each gear due to slippage under power and less slippage (or lock up torque converter) when cruising.  The less gears and torque converter slippage is why a manual can usually out perform an automatic.  For example when I bought my 95 Maxima many years ago, car mags showed my 5 spd manual 0-60 mph at 6.6 sec vs. 7.6 sec for 4 spd auto.

But some newer vehicles are getting more automatic gears and electronic clutch to eliminate slippage and shift quickly for improved performance and economy.

Answer 4

Not all of them do this, my car is an auto with seven gears and the manual version only has five.

Answer 5

Less to brake. some sticks have the first gear really low torc and autos don't have as much so I would say for towing and stuff.

Answer 6

valve body

also engine size is greater then smallest stick engine