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  Spartan Rides - Transmission and Drivetrain 

Category: Tech Talk, Transmission, Drivetrain, 4WD, AWD, FF, FR, MR, RR

Short description How the different drivetrain setups perform and transfer their power.
Subjects 4WD, AWD, FF, FR, MR, RR, Transmission, Drivetrain
Last Update 2007

A transmission or gearbox provides speed and torque conversions from a rotating power source to another device using gear ratios. How do the different drivetrain setups perform?

Techtalk - Transmission and Drivetrain

Transmission - Manual VS. Automatic

In manual transmissions, the driver must switch from gear to gear him/herself. A lot of experienced drivers and racers use this type of tranny because of the added control it gives. Manuals also give faster acceleration than automatic transmissions. In day to day driving, more people use automatics for the ease of use in traffic and there is less maintenance/skill required.

Drivetrain - Summary

FF - This is Front Engine/Front Wheel Drive. These type of cars aren't very stable under hard acceleration. Trouble occurs in bends since the wheels that put the power down now are also asked to steer the car: understeer. For these reasons, most FF sports cars are not considered serious racing machines. The weight of the engine is positioned over the wheels that drive the car, so there isn't often a loss of traction. Moreover, in cars with relative little power, FF can be usefull since this drivetrain layout offers weight reduction by it's simplicity in power delivery.

Understeer - When turning, the force that pushes you toward the outside of a turn. Cars with understeer are less likely to spin, therefore FF cars are considered a beginner's drivetrain.

FR - This is Front Engine/Rear Wheel Drive. This is the drivetrain that a lot of high end sports cars and racing bred cars use. The front engine provides the power, which is transferred to the rear axle for power delivery to the road. It provides a lot a traction in straight line acceleration since the weight of the car shifts over the rear wheels under full throttle. While cornering, the car will invoke oversteer.

Oversteer - A characteristic of rear wheel drive cars. When cornering the car's tail tends to slide due to the rear wheels providing the acceleration. This drivetrain makes it easier for experienced drivers to whip/slide through turns, but in the hands of novice drivers will have a tendency to lose control or spin out, especially in conditions with less grip (rain, snow, mud, ice, etc.)

MR - This is Mid Engine/Rear Wheel Drive. Some supercars/exotics use this drivetrain. It benefits by having equal weight distribution to all wheels (because of the engine mounted just behind/in the area of the cockpit). The rear wheels (which drive the car) in an MR car always have some traction on them, making them a little more stable in cornering and especially in the department of correcting in the corner than FR cars. They will still invoke understeer, but not as hard to control/correct as in a FR car.

AWD - This is All Wheel Drive (the engine is usually in front). AWD cars are the most stable. They are great for unexperienced drivers. There is always traction at one wheel or another, making them ideal for dirt/off-road racing. Due to this traction and the added weight with this drivetrain, they can be slightly hard to turn at times.

RR - This is Rear Engine/Rear Wheel Drive. This is the rarest type of drivetrain. Since the weight of the engine is over the rear wheels, traction when accelerating is optimal. This drivetrain can have the most detrimental effects with oversteer if you don't take care with the throttle when cornering. They will also wear out the rear tires amazingly quick.

Drivetrain - in more detail

Front Engine, Rear Wheel Drive (FR)

The classic drivetrain setup, it's not really that "efficient" or "economical" due to drivetrain losses and interior space (main reason why most manufacturers use FWD in street cars now), but it delivers the best acceleration and often top speed, so the majority of performance cars still use this type. As stated, the advantage to these cars is raw power, acceleration and speed. However the downside to these cars is that they tend to get "loose" in the turns; the back-end of the car wants to slide outward in the corner. This is due to a combination of power delivered to the rear wheels, as weight transfer wants to pull the ass of the car outward. This is known as oversteering.

Quick reflexes and experience are required to drive these cars, with great skill in "countersteering". However when it comes to accelerating out of the corner, and blowing them away down the straightaway, these cars are really fun to drive and the true cars of the masters. Many racecar drivers often comment that they prefer classic RWD to All-wheel drive and especially Front-wheel drive, as it offers the most overall control for the driver.

Beginner versions of Rear Wheel Drive cars include the Madza MX-5/Miata. Advanced cars in this class include the TVR Cerbera, Corvette and the ever-popular Dodge Viper.

Front Engine, Front Wheel Drive (FF)

These are cars that have the engine located at their front, under the hood as you may normally see. However the thing to note is that the power is delivered to the FRONT WHEELS, not the rear wheels. Most conventional cars these days run FWD. On the one hand, Front Wheel Drive cars are much more efficient because they eliminate most of the drive train (eg. drive shaft, rear differential), thus reducing frictional horsepower. They are also economical in the minds of manufacturers because the localization of the drivetrain totally to the front allows them to maximize cabin space.

On the other hand the engines in FWD cars tend to make a lot less power because they are situated over the front wheels, which puts a strain on suspension and drivetrain components, as well as the issue of weight.

The disadvantage of the front wheel drives cars is caused by the delivery of power to the wheels that are steering, as well as the weight of the engine on them. FWD cars tend to have excellent turn-in characteristics because the rear-front weight transfer caused by braking increases traction. However from that point on, a FWD car tends to understeer in the corners because of the inertia of the weight on the front wheels combined with the torque delivery, meaning the front end wants to drift to the outside of the corner.

The worst knock against FWD cars however is in the acceleration department. No matter how much horsepower they have, they are not as good as acceleration off the line or out of corners as RWD/AWD cars. This is because weight transfers from the front of the car to the back during acceleration (by Newton's Law, an equal and opposite reaction to the force of acceleration). Thus, the front wheels lose traction. While it's not true that EVERY RWD/AWD car will out-accelerate EVERY FWD car, the fact remains that given similar conditions (like weight and horsepower), the RWD/AWD car will win the battle.

A FWD car's rear-end tends to stick like glue around the corner, since there is no power spinning the back wheels. A loose condition can only be induced in a FWD car by a) locking up the wheels which, while inducing a slide, can slow the car too much and b) by seriously upsetting the chassis, usually by a very fast, sudden jerk of the steering.

Remember these techniques well, in case you find your FWD car in a position that requires a quick snap into a line. For this reason, proper apexing of the corner is required, especially when driving this kind of car. Also note that, due to this huge weight transfer onto the drive wheels, they will tend to wear quite fast and lose traction.

Beginner versions of Front Wheel Drive cars include the Honda Civic and Mazda Demio A-Spec. Advanced cars in this class include the Honda Integra type-R and Mitsubishi Eclipse GT.

Front Engine, All Wheel Drive (AWD)

These are the best of both worlds above, really. All Wheel Drive vehicles are special because power from the engine is delivered to all FOUR wheels. Therefore, these cars have good acceleration, and more importantly they handle GREAT in the corner. They can hold a turn quite well for the same reason the FWD can, because weight transferred during braking applies traction to the front wheels. At the same time, they can accelerate well when weight is transferred to the rear wheels. Thus, the AWD cars tend to be the quickest THROUGH the corner. An AWD car with a lot of inertia heading into a corner will be more likely to understeer, however similar techniques used with the FWD car can be used here to break it into an oversteer, because traction control prevents you from snapping the wheels loose with torque in most cases. The one possible disadvantage to AWD is that, in most cases, the car weighs more than otherwise equal FWD or RWD cars. This is due to the additional drivetrain components.

Beginner versions of All Wheel Drive cars include the Nissan Sunny/Pulsar GTi-R. Advanced cars in this class include the Mitsubishi 3000GT Twin Turbo and the Nissan Skyline GT-R.

Mid Engine, Rear Wheel Drive (MR)

These special cases are different from other RWD cars because the engine is mounted midway through the car, instead of at the front. These cars tend to handle the weight transfer into the corner much better, since they do not have the tremendous weight of the engine sitting at the front. This helps to create a weight distribution of 50/50 (although some front engine/rwd cars can achieve this), minimizing weight transfer during oversteering OR understeering, creating a very neutral feeling. However the engine's weight is still situated closer to the REAR wheels, so it can sometimes cause excessive weight transfer and oversteer under throttle.

Rear Engine, Rear Wheel Drive (RR)

This is also a somewhat special case that exists with cars like Porsches. The weight of the engine is situated almost entirely over the rear wheels, creating a rear-biased weight distribution. On the plus side, this makes for absolutely optimal acceleration, because front-rear weight transfer PLUS the engine itself places almost all the car's weight entirely over the drive wheels. This also ensures a very neutral feeling to start into the corner, if not a little bit of understeer due to lack of weight on the front wheels. However, rear Engine cars experience what is sometimes referred to as "snap oversteer". The car will go through the corner very neutral, but if pushed hard enough the centrifugal force of cornering will eventually unload the weight of the engine to the outside of the corner. The problem here is that you've gone from a perfectly neutral cornering condition to a wild oversteer caused by most of the car's weight swinging outward. While this does sound serious, a good driver that has gotten used to this condition can not only correct early enough to maintain good speed, but can also create dangerous 4-wheel drifts.

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