Whats the difference? I hear it occasionally mentioned, and it leads me to believe that there are certain pros/cons to either. Can anybody shed some light on this?
From here
That being said, I think there’s more to it than that. Front wheel drive became popular in the 1970s, when car makers were trying to make cars more fuel-efficient. That goal necessitated smaller cars with smaller engines (I’m over-simplifying, I’m sure). Changing things so that the engine was over the drive wheels, I imagine, helped offset some of the handling and traction problems associated with smaller, lighter cars.
WAG quotient of the portion of this reply I dreamed up: 30%
Real wheel drive cars have more of a chance of fishtailling on slippery roads. But one (of the many I’m sure) pros of real wheel drive as that your not trying to apply foward motion to the wheels that are turning, it makes for a lot more moving parts in a small area.
As someone who’s driven front and real wheeled cars in slippery conditions, FWD is much better on snowy/slippery roads. I can’t believe I ever drove a RWD vehicle in the winter; they are like sleds.
I’m not aware of any specific downsides of FWD, other than you can’t do donuts in the parking lot after school unless you’re in reverse.
While front wheel drive cars usually do better in low-traction conditions, there are some situations where they fare worse than rear wheel drive vehicles. They can be treacherous on steep curvy descents.
Rear wheel drive cars are favored for racing. Having the steering/power/handling forces more evenly distributed among all four wheels makes them more controllable.
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- Slippery inclines: front-wheel-drive cars may not be able to get up going forwards, rear-wheel-drive vehicles may not be able to get up backwards (or for example, back out of a muddy ditch they slid into).
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- Under “normal” conditions, rear-wheel drive cars accellerate better because as they accellerate, their weight shifts to the rear end, helping prevent the rear wheels from slipping.
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The other thing that allows fwd’s to be more compact than rwd’s is that you can turn the engine in a fwd sideways, so that the long axis runs across the car, allowing a much shorter nose. In a rwd, the engine’s long axis runs the length of the car, so that the drive train runs back towards the rear wheels.
The other reason that racing people prefer rwd is that you can more easily control both ends of the car: the front through steering and the rear through wheelslip.
Well, the literal difference is that one sends power to the front wheels and the other to the rear, but I presume you’re curious about the merits of each. There are several pros and cons to either system. Here are a few I can think of.
Advantages of front wheel drive:
- Simpler packaging - you have all the drivetrain at one end rather than spread throughout the car.
- Lower drivetrain losses, simply because there aren’t as many parts.
- Better traction on slippery surfaces.
- No driveshaft or other parts running under the car.
- Allows for a more space efficient rear suspension - many RWD suspension layouts eat up what could be space for the trunk or gas tank.
Advantages of rear wheel drive:
- Often, these get better traction on dry surfaces because acceleration will transfer the weight onto the rear wheels. You should see some of the complicated stuff FWD drag cars do in an attempt to get traction.
- By moving the transmission and differential back, these cars often have better weight ballance.
- This layout is often easier to work on than FWD cars - unless you’re dealing with something like the newer Camaros, which tuck the engine under the windshield.
- With front wheel drive cars, the forces that accelerate the car can also interfere with the steering linkage, causing the car to pull to one side or even yank the steering wheel violently, even if the car has a good alignment. This is not a problem with RWD cars.
Ok, you tell me which is worse:
- On a front wheel drive car, apply too much power on a corner and you’ll pretty much lose your steering and go straight ahead. Do the same thing in a rear wheel drive car, and you’ll spin the tail end around.
Rear wheel drive cars are often favored for high performance machines, but there are some front wheel drive cars that have excellent handling too. While front-drivers are at a distinct disadvantage in drag racing, they can often hold their own against rear wheel drive cars in the entry level road racing and autocross classes.
Well, the literal difference is that one sends power to the front wheels and the other to the rear, but I presume you’re curious about the merits of each. There are several pros and cons to either system. Here are a few I can think of.
Advantages of front wheel drive:
- Simpler packaging - you have all the drivetrain at one end rather than spread throughout the car.
- Lower drivetrain losses, simply because there aren’t as many parts.
- Better traction on slippery surfaces.
- No driveshaft or other parts running under the car.
- Allows for a more space efficient rear suspension - many RWD suspension layouts eat up what could be space for the trunk or gas tank.
Advantages of rear wheel drive:
- Often, these get better traction on dry surfaces because acceleration will transfer the weight onto the rear wheels. You should see some of the complicated stuff FWD drag cars do in an attempt to get traction.
- By moving the transmission and differential back, these cars often have better weight ballance.
- This layout is often easier to work on than FWD cars - unless you’re dealing with something like the newer Camaros, which tuck the engine under the windshield.
- With front wheel drive cars, the forces that accelerate the car can also interfere with the steering linkage, causing the car to pull to one side or even yank the steering wheel violently, even if the car has a good alignment. This is not a problem with RWD cars.
Ok, you tell me which is worse:
- On a front wheel drive car, apply too much power on a corner and you’ll pretty much lose your steering and go straight ahead. Do the same thing in a rear wheel drive car, and you’ll spin the tail end around.
Rear wheel drive cars are often favored for high performance machines, but there are some front wheel drive cars that have excellent handling too. While front-drivers are at a distinct disadvantage in drag racing, they can often hold their own against rear wheel drive cars in the entry level road racing and autocross classes. You’ll notice, however, that at the higher levels, road racing tends to be dominated by Porsches, Corvettes, Vipers, and various rear wheel drive creations that bear no resemblance to any production car.
the engine in a front wheel drive car is sitting crossways, it is more difficult to work on when repairs are needed.
I think they call this “torque steer,” and I know the feeling exactly. My previous, powerful, FWD GM (220hp) experienced it severely. From a dead stop, I would floor it and take off like a bat out of hell, but had to fight the steering wheel in order not to go off the right side of the road. It can be controlled with proper engineering, however. My current, even more powerful FDW Ford (275hp) will stay dead on straight with barely a touch to the wheel (and a lot less noise).
I can’t add much to whets been said, but I can reiterate some points.
FWD cars are harder to work on. A lot of stuff under the hood. Clutches require many hours more work. FWD cars “push” or “understeer” in corners. RWD cars are “loose” or “oversteer”. To an experienced RWD driver this is a GOOD thing (unless its severe as with mid and rear engined cars) compared to understeer.
Balthisar, what GM FWD car has 220hp and what Ford has 275hp?
I believe Torque Steer is a result of the transverse mounted engines in most FWD cars. This results in drive shafts of unequal length, since the transaxel (equivilent of the transmission in RWD cars) is closer to one drive wheel. So you have two hunks of spinning metal of different sizes, causing different torques.
Are counter-rotating drive shafts the solution to this? Or do they move the transaxel to a more central locations somehow?
BTW, the Pontiac Bonneville produces 240 HP, 280 ft lbs of torque. Most of the Cadillacs with the Northstar engine produce around 300 HP.
dead0man:
I can’t really answer for Balthisar, but in fact GM’s Buick Park Avenue Ultra (and its former Oldsmobile equivalent) with a supercharger makes 240 HP and is FWD.
Oh, and the 2001 Lincoln Continental made 275 HP and had FWD.
go AWD!
MadScientistMatt’s post is almost dead on except for a few glaring errors:
The opposite is in fact true: RWD cars have lower drive train power losses because the layout is much simpler. in a RWD car, the power only has to “turn” 90 degrees to reach the wheels, whereas in a FWD car, the power has to turn 180 degrees.
And:
Again, the total opposite is true as far as RWD cars go.
First: nearly every production car today is designed to head towards understeer (front plows straight) as it loses traction under ALL conditions (power on, power off)
Second, even in a “twitchy” car such as a race car or a 1970s Porsche, applying throttle in a RWD car will make the car UNDERSTEER, while removing throttle or applying the brake is what causes oversteer (a spin out). Racers call this TTO for “trailing throttle oversteer” (trailing in racer parlance means “letting off of”).
If you think about it for a minute you will see why this is true. Oversteer happens when the rear tires have less traction than the fonts, and understeer happens when the opposite is true.
So if you apply throtle, you shift weight to the rear tires, giving them more traction than the fronts and causing understeer. Whereas if you apply brakes, you cause a weight shift to the front and cause oversteer.
NB: As I mentioned earlier, this doesn’t really apply to street cars, which will nearly always understeer, regardless of what the driver does.
Matt may have been thinking of a car with enough power to break the rear wheels loose under acceleration, but that is a different situation, and has little to do with the layout of the drivetrain.
RWD cars have lower drive train power losses because the layout is much simpler. in a RWD car, the power only has to “turn” 90 degrees to reach the wheels, whereas in a FWD car, the power has to turn 180 degrees.
I think Matt was referring to driveshaft flex and differential housing torque. Simplicity isn’t the issue, and neither is the power “turning.” Said turning is done through gears, which have neglible power loss.
So if you apply throtle, you shift weight to the rear tires, giving them more traction than the fronts and causing understeer. Whereas if you apply brakes, you cause a weight shift to the front and cause oversteer.
Might be true with some rear-drive cars, but there are plenty where applying throttle reduces rear wheel traction. It’s not all about weight transfer. When the driving wheels are applying power, there is less lateral grip available to prevent their sliding sideways. Letting up on the throttle is the way to stop fishtailing. Braking is the way to lose control.
Telemark, dead0man…
Telemark was close on dead0man’s question – I screwed up the HP. My 2000 Bonny only has 205HP; for some reason I thought it was 220 and the supercharger was 20 more (a lot of money for a supercharger that only adds 35 HP).
The 2001 Contentintal is dead on. It’s perfect. Except it doesn’t automatically lock the doors, tell me when the tires are low, or when to change the oil. But, not having torque steer is worth it.
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- The cause of torque-steer is that the front wheels do not pivot on their centers of traction. In an ordinary car, they can’t possibly all the time: if they did at rest (which most cars don’t) then they wouoldn’t under hard cornering.
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- There was a car built a while back that had a front supension just to eliminate this effect (a Saab or something Euro), but on most vehicles they usually just put a big power steering unit on the thing and forget about it.
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