Drive = Saves Fuel, Shift Points For Fuel Conservation, 1-4th Gears and uses overdrive
S3 = Performance Gear When Accelerated, Will Shift quickly through 1st and 2nd for faster launch, will hold in 3rd, allowing car to rev longer in this gear = more power. Wastes a lot more fuel, no overdrive
S4 = Performance Gear When Accelerated, Will Shift quickly through 1st and second for faster launch, will go into 4th. Wastes more gas, no overdrive
Trust me when you smack the accelerator you DO feel the difference between S3 and regular Drive mode. "S" stands for Sport.
-overdrive=>taking about gear ratio
-gear ratio = primary ring gear diameter/ secondary ring gear diameter.
-If gear ratio>1 = underdrive. The driven gear turns slower than drive gear but has greater torque.
-If gear ratio<1 = overdrive. The driven gear turn faster than drive gear but has lest torque.
Overdrive gear ratio allowed car cruise at high speed at lower motor' RPM thus save fuel.
On car with a switch to turn on/off overdrive ( Toyota...?) overdrive should be turnned off in the city and on on the freeway.