4wd, awd, rwd, fwd, what's up?
Dec 27, 2001 Write an essay on this topic.
The Bottom Line Read the conclusion
What's with all the acronyms? I'll explain each one and its individual benefits. They each have their own place, and some vehicles have more than one choice of the above.
I live in Minneapolis, MN and consequently have the opportunity to drive in snow and ice for about 6 months of the year. So most of the points here will be geared to driving in snow.
Front Wheel Drive. Many people are familiar with this setup. Most modern cars are front wheel drive. This means that the engine is turning the front wheels propel the vehicle.
* This happens to be more efficient in terms of gas mileage. Shorter half-shafts coming out from the transaxle means less moving parts and less inertia and less weight, which means better mileage.
* In terms of driving in snow or ice, the FWD vehicle can easily pull itself away from a stop sign or stop light. It will tend to pull itself straight and forward, even if you are turning the steering wheel.
* In terms of stopping on snow or ice, this type of vehicle can be potentially dangerous. If you quickly let up on the gas pedal, the balance of the car shifts toward the front. The engine slows down, consequently engine braking slows the front wheels. Now, physics says that the faster turning wheels tend to move foward. Those would be the rear wheels at this point in time. This means that the vehicle will tend to fishtail. Trust me, I've done it. Not fun.
* Not good for towing heavy trailers, especially in snow and ice. There is a high potential for jackknifing the vehicle with an attached trailer that does not have a seperate trailer brake system.
* Most modern cars are FWD, and some of the small SUV's are FWD
Almost all of the older American cars were built with Rear Wheel Drive. It was in the early eighties that american builders were starting to produce some cars with front wheel drive. Most of the performance cars are rear wheel drive. The reason for this is that the front to back weight balance of the vehicle is more equal.
* Gas mileage is lower due to more weight and more rotating mass (long driveshaft, seperate rear axle)
* Better for towing heavy trailers
* For pulling away from a stop sign on snow, this type of vehicle will tend to fishtail and spin wheels. You may need to correct steering angle and throttle to get moving straight.
* For stopping on snow or ice, this vehicle will perform better than a FWD vehicle. If you let up on the gas pedal quickly, the engine braking will slow the rear wheels. This will tend to keep the vehicle in a straight line. (Note that if you brake, all bets are off.)
* Most pickup trucks are RWD, along with some full size cars (ford crown vic), performance cars (bmw, some porche), larger trucks, busses.
This type of vehicle usually is equipped with a switch or lever that will change it from rear-wheel drive to 4 wheel drive. What this switch does is engage the transfer case, which sends engine power to the front axle and the rear axle at the same time, and usually with the same power (50/50).
* Worst gas milage if all other factors are the same. There is a weight penalty to having another axle, along with front/back friction losses when 4wd is engaged.
* In terms of starting from a standstill, 4wd will perform very well. You generally can steer the vehicle while accelerating and go in the intended direcction.
* In terms of stopping, enging braking will affect all 4 wheels. If some of the wheels are slipping, but some are not (say left wheels grip, right wheels slip), 4wd will have an advantage. The gripping wheels will keep the axles turning thus giving you some control of the vehicle.
* Many pickup trucks are 4wd (chevy, ford, dodge, toyota), along with many SUV's (jeep, large and midsize suv's)
If a vehicle has All Wheel Drive, it means that the engine will be turning usually the back wheels, but when slippage is detected, it will automatically power all the wheels. Usually these vehicles don't have a switch or lever to engage them, with the exception of the large Chevy SUV's (Tahoe, Suburban).
* Same weight penalty as 4wd, but slightly better gas milage, as the transfer case usually only sends the power to the rear (you don't have the frictional losses).
* Very similar start performance of the 4wd vehicles, but it may take a second or two to transfer power to the front wheels.
* Not quite as good for stopping as the front and rear axles are not locked together.
* Generally more expensive than the other systems.
* Vehicles with this include: some pickups (chevy), some small suv's (Honda CRV, Toyota RAV4), some large suv's (chevy tahoe, suburban), several european suv's (mercedes, bmw), a number of subaru's.
As you can see, each one of the technologies has its benefits and disadvantages. Which one is the best?
If you don't mind having to think about which mode to be in, 4wd controlled by a switch or lever is probably the best way to go. You have true front/back locking as well as just rwd.
If you don't want to mess with anything and just want to drive, AWD is the way to go. It has most of the benefits of 4wd.
If you don't live in a snowy/icy climate, FWD is just fine.
If you want better performance from better front/back weight balance (among other benefits), RWD is the way.
Sorry that this doesn't contain SUV exclusive information, but there was no category specifically for this type of info. I felt that it can help people choose between the different types of drive systems available.
Remember to always drive within the limits of the vehicle and the conditions. 4wd / awd won't allow you to go 50mph on pure ice, and retain control. Be smart about how you drive any vehicle. I see a lot of SUV's in the ditches here in Minneapolis, probably because people have too much confidence in their 4wd systems. They think just because they have 4wd, they can drive the maximum speed anywhere, anytime. Don't do it. Be safe.
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