Thete kai epixeirhmata:
Ta piswkinhta exoun mikroterh prosfysh se odwstrwma kakhs poiothtas logw mikroterou askoumenou barous stous kinhthrious troxous.
Rear-Wheel Drive Benefits:
-Predictable steering and handling
-Interfaces well with specialty driving controls
-Capable of high speeds
-Retains maximum forward stability
Rear-Wheel Drive Disadvantages:
-Climbing obstacles may be difficult
-Small front casters may sink into soft surfaces
-May exhibit rearward pitching if not properly configured
More difficult to master - While the handling characteristics of rear-wheel drive may be useful or fun in the hands of someone who knows how to use them, in the hands of most drivers, having the rear wheels move about is unintuitive and dangerous. Rear wheel drive rewards skill, and punishes the lack of it. Other layouts are much more forgiving, but don't offer the same rewards in handling.
Decreased interior space - This isn't an issue in a vehicle with a ladder frame like a pickup truck, where the space used by the drive line is unusable for passengers or cargo. But in a passenger car, rear wheel drive means: Less front leg room (the transmission tunnel takes up a lot of space between the driver and front passenger, less leg room for center passengers (there is also a smaller tunnel for the drive shaft), and sometimes less trunk space (since there is also more hardware that must be placed underneath the trunk).
Increased weight - The components of your typical rear wheel drive vehicle's power train may be less complex, but there are more of them. The driveshaft adds weight. The transmission is probably heavier. There is extra sheet metal to form the transmission tunnel. There is a rear axle or rear half-shafts. A rear wheel drive car WILL weigh slightly more than a comparable front wheel drive car (but less than four wheel drive).
Front-wheel Drive Benefits:
-Retains maximum rearward stability
-Offers obstacle-climbing capabilities
-Performs well on soft surfaces
Front-Wheel Drive Disadvantages:
-Low maximum speeds
-May be difficult to steer on outdoor terrain
-May exhibit catastrophic forward pitching during aggressive descends
Kai an thelete ki alla.bebaia opoios xerei 2-3 pramata gnwrizei pws kammia lysh den einai idanikh.
The controversy has gone on for decades: which is better - front wheel drive or rear wheel drive? We used to have predominately rear wheel drive (RWD) automobiles on the road, but by the late 1970's, front wheel drive (FWD) vehicles were beginning to dominate. While the majority of current passenger cars are still front wheel drive, rear wheel drive vehicles are becoming more common. For example, Infiniti has gone back to RWD on their G35 model, and Cadillac has RWD on their new CTS model. So what are the advantages and disadvantages of each drive system?
Let's look at front wheel drive first, as it is most common. Reduced cost: that is often the reason manufacturers design and build the way they do. FWD systems are cheaper to manufacture and install than RWD systems. There is no driveshaft or rear axle housing to build. The transmission and differential are located in one housing and less parts are needed. It also makes it easier for the designers to locate other parts beneath the vehicle, such as brake lines, fuel lines, and exhaust system.
Reduced weight is another advantage. Lowering a vehicle's weight improves acceleration, braking, and fuel economy. Traction is improved by having the weight of the engine and transaxle over the drive wheels. This is a big advantage on slippery roads.
A big advantage of FWD is interior space. No large bumps in the floorpan are required to accommodate mechanical parts. Look at current Honda Civics, and you will find great rear seat room in a small vehicle because of a flat floor pan. With no rear differential, trunk space can also be increased.
The disadvantages of FWD are mainly the decrease in vehicle handling ability. With more weight over the front of the automobile, the back end tends to become very light. Rear tire traction is decreased and the car may swap ends on icy roads easier. This has been overcome by designers somewhat by placing as much weight as possible further back in the vehicle. Ideal weight distribution is often described as 50/50 front to rear, but FWD cars seldom get near this.
Another disadvantage is the load placed on the front tires. They must transfer all acceleration, steering, cornering, and braking forces to the road. The tires have only a finite amount of grip, so using some of it for acceleration must decrease it in other areas. The rear tires have very little load on them and are basically only along for the ride. This is why accomplished FWD racers say "put the gas to the floor and steer - the rear will follow".
All the disadvantages of FWD systems are advantages of RWD vehicles. With some of the mechanical parts removed from the front and installed at the rear, vehicle balance and handling are much improved. Using the rear tires for acceleration traction takes the load off the front, so drivers accelerating out of a corner have much more lateral grip. RWD is used on all the world's fastest road course race cars and many performance production vehicles for this reason.
Repair costs are another advantage of RWD systems. Although costs vary greatly by make and model, if you have transmission problems with a RWD vehicle, the cost of differential repair is not required, as it might be on a FWD system. The reliability of FWD cars has increased so much over the decades, that this might not be a big concern.
Disadvantages of RWD are higher assembly and production costs, more parts to have problems with, and less interior room in the vehicle. Independent rear suspension, used on many current RWD cars allows the engineers to position the body closer to the differential and driveshaft, so interior room has improved.
Traction has always been a problem with RWD vehicles, because of the lower rear vehicle weight over the drive wheels, but modern electronics has changed that. Traction control and vehicle stability systems enable RWD cars to rival FWD vehicles on slippery surfaces. Improved tire designs have also helped.
Even with the decrease in passenger compartment room and increased mechanical complexity, I am still a rear wheel drive fan. I guess I just like the feel of the handling when pushed into corners. Other very good drivers I know would disagree with me.
So what is the answer? How about all wheel drive! Porsche uses AWD on a Carrera model to enhance performance and traction. Subaru has won several world rally championships with all wheel drive. The debate on what drive system is best still continues, and probably will for as long as we drive.
kai
How many driven wheels does a vehicle really need? The proliferation of SUVs on America's highways and byways over the last ten years would suggest that two simply isn't enough. But what exactly are the advantages of four-wheel drive (or all-wheel drive) versus front-wheel drive and rear-wheel drive?
First of all, before we're "driven" to confusion by all of this terminology, let's lay a few ground rules. In most automotive circles (and for the purposes of this discussion) the following acronyms will hold true:
AWD = all-wheel drive
4WD = four-wheel drive
RWD = rear-wheel drive
FWD = front-wheel drive
Each of these drive systems has its own advantages and disadvantages which I'll cover in greater detail.
Since the majority of vehicles sold today are front-wheel drive, we'll start here. As the name suggests, FWD vehicles use only the front wheels to deliver power from the engine to the pavement. While relatively rare on the streets of America during the first half of the 20th century, FWD cars now account for approximately 70 percent of new car offerings. Why the recent switch from RWD to FWD in new cars? Well, since most vehicles carry their engines up front, it is a simpler task to get that engine power to the driven wheels when they are both on the same end of the car. Essentially, you turn the engine sideways and connect a short driveshaft between either side of the engine and the two front wheels. Less distance and fewer parts between the engine and the driven wheels means less horsepower loss through mechanical inefficiency. Additionally, fewer parts means reduced production costs and, ultimately, a lower sticker price. One final advantage of FWD is that it puts the engine weight directly over the driven wheels which can improve traction on slippery or snow-packed roads.
Despite its practical advantages, FWD has several disadvantages when related to vehicle performance. First of all, since vehicle weight shifts to the rear of a car during hard acceleration, FWD cars will always be fighting a losing battle when it comes to straight-line acceleration. Handling performance also suffers on FWD platforms since the option of using "throttle-induced oversteer" or sliding the rear end doesn't exist (unless you get really creative with the emergency brake).
In the end FWD is a very practical way to power a vehicle but its inherent design is contradictory to performance. Look at it this way: Your car came with four wheels, why put the stress of steering, braking, and acceleration on only two of them?
Take everything I just said about FWD cars and reverse it for RWD cars. Performance goes up because now the two rear wheels handle the duties of acceleration, leaving the front wheels to focus solely on directing the vehicle (plus the majority of braking). This means that when you punch it, vehicle weight transfers to the rear end, just where you want it during acceleration. You can also "steer" a RWD car with the gas pedal by applying power and sliding the rear end while in a corner. If you don't think this is an advantage, try driving a Mazda Miata and a Chevy Cavalier convertible through the same set of backroad twisties. Even though they're both top-down, four-cylinder compact cars, the experience will be very different with a clear victory in "fun factor" going to the Miata.
This doesn't necessarily make rear-wheel drive the "better" configuration since it has disadvantages too. As mentioned earlier, RWD cars require a driveshaft (and dreaded interior "hump") and a differential to get power from the engine to the rear wheels. These components add extra cost and weight to a vehicle while robbing horsepower and making RWD cars generally less efficient than FWD vehicles. This layout is also more challenging to drive in inclement weather where, without the aid of traction control, a RWD car can more easily end up on somebody's front lawn or stuck in a ditch.
I personally have an affinity for RWD because its biggest disadvantage is also its biggest advantage; it's less practical and, consequently, more fun.
Both of the previous drivetrain layouts are based on using only half of a vehicle's wheels to deliver power to the ground. But those other wheels are just sitting there, why not use them too? Actually, the concept of using all-wheel drive is not new. A Dutch manufacturer named Spyker had one of the first full-time 4WD vehicles on display at the Paris Motor Show in 1903.
While we're here let's go over what the supposed differences are between four-wheel drive and all-wheel drive. 4WD was basically the original term used to describe all four wheels being driven on early Jeeps and trucks. These systems were not very advanced in that they simply put power to all four wheels, usually after an interior shift lever was moved and/or the vehicle's hubs were manually "locked" by the operator. During this period 4WD was thought of as a purely off-road utility. Today 4WD still refers to vehicles that can opt for two- or four-wheel drive. These vehicles often have a 4WD "low" and "high" setting that can be switched using an interior lever. The "low" setting provides even greater torque for pulling or climbing in an off-road environment. The "high" is useful for slippery on-road situations like packed snow or ice. 4WD also uses a locking center differential to avoid unnecessary slippage between the right and left wheels while off-road.
AWD generally operates all the time with no "low" or "high" gearing options. While 4WD is basically an SUV term, associated with off-road use, AWD is a car/wagon/minivan term that means traction improvement for performance or bad weather reasons. Some vehicles, like the Mercury Mountaineer or the Lexus RX 300, are tougher to classify because they are SUVs in appearance but use AWD instead of 4WD. Many of these types of vehicles are being called "crossovers."
The "all" part of all-wheel drive is a bit misleading since the majority of AWD vehicles use the front wheels primarily and only direct power to the rear wheels when a sensor detects front-wheel slip. Other cars, like the Porsche 911 Turbo, use AWD for performance purposes like getting from zero-to-sixty in 3.7 seconds. Even with sufficient horsepower, a Porsche with only two-wheel drive would be traction-limited to high 4- or low 5-second zero-to-sixty times. AWD also helps keep Subaru wagons and Chrysler minivans from sliding on wet or snowy roads by redirecting power from "the wheels that slip to the wheels that grip."
So, it seems like 4WD/AWD is the best way to go, right? Well, not exactly. Both of these systems add substantial weight, complexity and cost to a vehicle. They also reduce gas mileage because of increased drag on the drivetrain. When you consider that traction control is becoming more and more common on front- and rear-wheel drive cars, the supposed advantages of 4WD/AWD start to wane.
By now it should be obvious that there is no "best" drivetrain layout; just different designs with different characteristics. Hopefully, after reading this column, you'll have a better idea which one is right for your circumstances and not get suckered into buying an all-wheel drive Subaru for your daily commuter in Phoenix or a BMW M3 for exploring the Yukon.
Akomh
http://www.autoforumz.com/Ford-Mecury-Winter-safe-driving-FWD-RWD-Police-car-ftopict72385.html
http://www.totallychrysler.com/chrysler/chrysler-archive/chrysler/chrysler-p-730.html
http://www.automotiveforums.com/t165104.html
http://autozine.kyul.net/technical_school/handling/tech_handling_5.htm
Mporei h pisw kinhsh na einai pio diasdkedastikh alla thelei kai xerades.Fysika h exelixh ths pisw kinhshs eunoei th pisw kinhsh(ta hlektronika pou elega)Kai gia thn istoria opados ths Williams eimai.Alla den mporw na mhn paradextw pws h Alfa den exei mia dynamikh auth thn periodo.Autes oi syzhthseis exoun ginei kai exantlhthei.Sthn ellada aplws exoume syndesei BMW me mourh kai pisw kinhsh.
