In this case, 'overdriven' means that in this ratio, the engine will not reach its power peak and thus the vehicle's potential top speed. If it is the latter scenario, some other gearing combination would allow the car to reach 8000rpm and thus a higher potential top speed. an impossibiity given adequate traction), or it may be that there is more power at 8000rpm but at 7000rpm there is not enough power to push the car past 190. At 190, it may be that the engine is at its power peak (the car's highest potential speed) and so the car can go no faster (if the engine were to rev higher, its power would drop off and the car would slow down while needing its wheels to turn faster.

And it continues to increase in power as the revs rise, meaning the car can continue to accelerate till it reaches 190mph. If you down shift then to 5th, putting the engine at 4500rpm, you can accelerate because at 4500rpm the engine makes enough power to overcome the drag at 155. At 3000rpm, the engine is not putting out enough power to overcome the aerodynamic drag at 155mph. Let us assume a car has a top speed of 190 mph in 5th at 7000rpm but only 155mph at 3000rpm in 6th. You will find that many very high performance cars (such as the dodge viper) reach their top speed in 5th rather than in 6th. It is a meaningless simplification of a very complex technical concept.

and anyway, this definition has no relevance to most people. The wikipedia definition as quoted above needs clarification before it makes sense. In the context of automobiles, it refers to gear ratios that result in the output shaft turning faster than the input shaft. (wikipedia is a good source but not a definitive one.)įirstly, The word 'overdrive' itself gives us the real fundamental meaning: Any gear in any machine is said to be overdriven if it turns faster than the gear that is driving it. THis wikipedia definition is not completely straightforward. The most fundamental meaning is that of an overall gear ratio between engine and wheels, such that the car is now over-geared and can no longer reach its potential top speed,

A vehicle in perfect balance