The Difference between all Wheel Drive and four Wheel Drive
What is the difference between all wheel drive and four wheel drive? In essence, in terms of the engineering aspect of the automobile there is very little. In reality a four wheel drive vehicle, when this option is engaged, will perform in the same way as an all wheel drive vehicle.
In a normal automobile the power is driven to two of the four wheels. This means that the other two wheels have less traction and are lighter in terms of road-holding. The four wheel drive option allows the driver to engage a system which changes the power to a position where all four wheels are being driven instead of the two. Because this increase traction, four wheel drive is particularly useful in times of seriously inclement weather and is ideally suited for off road driving, for example, in situations where the terrain is difficult to traverse and rough. However, for normal road driving the driver can disengage the four wheel drive system, thus making a saving on such items as fuel consumption.
In essence, the all wheel drive performs in the same way as the engaged four wheel drive system. The only difference between an all wheel drive and four-wheel drive vehicle is that an all wheel drive vehicle has all four wheels permanently engaged in the driving process and the driver does not have the option or indeed the facility, to be able to disengage this system.
In reality, one can draw a similarity between "all wheel v four wheel drive" with the difference between an automatic and geared car. In both of these cases with the former option the driver has little option with regard to selection as these systems are, by definition. However, with the latter option in both cases the selection process is very much within the control of the driver. For instance, in the same way as it is a positive driver command to select gears in a car that has a manual gearbox so the driver makes the decision as to whether the system should be engaged in the case of a four by four vehicle.
A number of manufacturers, including Toyota with the RAV4, have produced all wheel drive vehicles, as they are easier to use and do not need any input from the driver. However, one has to consider the running cost differences. The consumption of a four-wheel drive vehicle is greater when it is locked into the four-wheel drive option than when this is disengaged. Therefore, it follows that an all wheel drive vehicle, whilst having the benefit of ease of use, may cost more to run.
All wheel drive and four-wheel drive are the same system with simply a different style of operation, namely that with the former the selection is automatic and with the latter it is a manual decision that relies upon driver choice.
