Car Talk 101 Driving Systems

Difference between driving wheel systems

There are a number of different ways an engine can move s car forward.  What do they all mean and what system is good for where?

Front Wheel Drive (FWD)

This is the most common setup for almost all cars. It simply means that the engine is powering the front wheels and the front wheels only. FWD cars have an advantage with space saving and good performance (i.e. grip) in wet or snowy conditions. Due to the engine, the transmission and the driving mechanics all being up front, more space can be saved under the car and in the rear for passenger and cargo room. With a thick solid engine and transmission in front of the driver, it also means in a head-on crash there is something quite sturdy between the driver and the impact to take some of the blow. Also, with all the weight from the major parts being over the wheels to drive and steer the car, it just means that FWD cars have better traction.

Examples: Honda Fit, Civic, Accord; Toyota Yaris, Corolla, Prius; Ford Fiesta, Focus, Fusion; VW Golf, Jetta...

However, due to the placement of the engine and the driving wheels, and therefore the weight distribution, these cars will almost never be able to compete performance-wise against a comparable car with All Wheel Drive or Rear Wheel Drive.

Rear Wheel Drive (RWD)

RWD can be set up in a few different ways. It can have: an engine up front, a mid-mounted engine, or a rear-mounted engine. For most large cars, trucks, and buses, the engine will be up front and the rear wheels will be connected by a drive shaft. RWD systems tend to be more robust and sturdy as the system does not have to deal with both delivering power and steering the wheels at the same time. RWD vehicles usually have a better weight distribution which means brakes and rotors will wear out more equally. RWD systems can handle and deal with higher power outputs better than FWD cars as when a car accelerates the weight is shifted to the rear of the car. This means that the driving tires will have more pressure on them and therefore will have more grip. 

Examples: Ford F-150; Lexus IS; Hyundai Genesis Coup; F-1 cars; Dodge Challenger...

However, due to the driving wheels being different than the steering wheels, under heavy acceleration and around corners the car may not have the best steering as the front wheels will have less grip.

4 Wheel Drive (4WD)

Many people get this and All Wheel Drive mixed up, but they are quite different. 4WD is simple: the vehicle usually drives in RWD but when needed, the driver can select the 4WD option which then "locks" all four wheels together so they are turning at the same speed. This has some advantages but many disadvantages. The main advantage is that in very slippery conditions such as deep snow, mud, sand, or loose rocks, all four wheels will be trying to move the car forward, and there is a good chance that at least 1 wheel will have traction. The disadvantages are: it can and should only be used during low speed driving, it can and should only be used when the conditions are very slippery (wet pavement does not count) and when you do not need to be turning excessively. This is because all 4 wheels are turning at the same rate. However, when a car turns, the wheels do not all go the same distance, which means they need to turn at different speeds. If 4WD is kept on during not slippery conditions, with a lot of turning, either the wheels will start to tear themselves apart, or something in the driving system will. 

Usually only large vehicles will have the 4WD option like: army vehicles, trucks, and large SUVs.

Examples: Honda Pilot; Ford Explorer; Almost every Jeep...

Unfortunately many companies are mixing the term 4WD and AWD which is a bad thing as they are very different and people may be thinking they are getting one type of system when in fact they have the other and they inadvertently wreck their new vehicle.

All Wheel Drive (AWD)

AWD really is like a mix of all of the systems. The AWD system is similar to 4WD system in that all the wheels have power going to them, but the main differences are that with AWD, there are certain parts to the system that allow for each wheel to spin at a different speed, and AWD can be used at any speed. Most AWD vehicles have the system working all the time however, to save on fuel, during most diving conditions most power is being sent to the front wheels instead of being split up fully. Once the system detects wheel slip it will automatically send power to the appropriate wheel, sometimes up to 80% of the power. In some modern vehicles with AWD, there is also a setting to lock the system into a 4WD set-up that may or may not unlock itsself once higher speeds are reached. AWD systems are usually seen as the safest system as they work well in all conditions except the very worst snow or mud/ sand. 

Subaru has been a pioneer in offering high quality AWD systems in their entire lineup for decades. 

Some examples of AWD vehicles are: Every Subaru; Honda CRV; Toyota Rav 4; Ford Edge; any Audi with their "Quattro" system....

The only downside the vehicles with AWD systems have is that they tend to be quite heavy and due to the power being split to all 4 wheels, use more fuel than their FWD or RWD brothers.

Individual Wheel Drive (IWD)

This is a relatively new term that is mostly used for electric vehicles. These cars can actually use a small electric motor for each wheel instead of one large one. In this case they each power their own wheel differently and can work like any of the other systems. They also have the advantage of an electric motor's superior torque abilities. Most vehicles with IWD have what is called a "hub motor" which means the motor is actually inside the wheel and can be protected from the elements.

Current examples: the Mars rovers.



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I hope you have enjoyed reading this and have learnt something if you didn't already know it.

J,K.