IHateMyJob2004
Lifer
- Sep 29, 2004
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Couldn't the difference between FWD and RWD on the highway simply be because RWD vehicles are typically sports cars. Thus they have way more power?
Zenmervolt
Elite member
- Oct 22, 2000
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FWD is less than 10% for a manual? I'd be really impressed with that. (951 is RWD and lists 217 hp, stock versions dyno ~198 hp at the wheels for an 8.7% drivetrain loss.)Originally posted by: OS
a bit tangential but FWD is also a little more efficient in terms of drivetrain losses assuming same transmission type. Thus better fuel economy, another reason econoboxes are all fwd.
ZV
Zenmervolt
Elite member
- Oct 22, 2000
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OS
Lifer
- Oct 11, 1999
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Originally posted by: Zenmervolt
FWD is less than 10% for a manual? I'd be really impressed with that. (951 is RWD and lists 217 hp, stock versions dyno ~198 hp at the wheels for an 8.7% drivetrain loss.)Originally posted by: OS
a bit tangential but FWD is also a little more efficient in terms of drivetrain losses assuming same transmission type. Thus better fuel economy, another reason econoboxes are all fwd.
ZV
I don't think so, they say rule of thumb is FWD is about 2-3% more efficient than RWD, example ~15% or so for manual fwd, vs ~17% manual rwd. The theory is less rotational mass/assemblies and such.
I wouldn't trust dynos for determining actual power, even more so for working backwards to determine crank hp/drivetrain loss. Some import rag ran an article a while ago where they took the same 350Z to a bunch of different dynos and got a large variance in readings, something as large as ~25HP difference. And then you can have the underrated/overrated issue where the manufacturer fibs the actual output of the car and such.
Of course dynos are still useful in tuning to determine changes in power as long as the proper SAE correction factor is used and it is on the same dyno, but comparing HP numbers measured with different methods/different dynos mostly doesn't yield anything meaningful.
I drive a Prelude SH most of the time which is one of the best handling FWD cars out there and my dads old Volvo 740 still corners better and feels completely different when you push it in the turns.
all you have to do is drive a high powered FWD car to discover their short comings.
For day to day transportation, FWD is a good way to go. For a hobby/fun car, RWD all the way
For day to day transportation, FWD is a good way to go. For a hobby/fun car, RWD all the way
I owned a Prelude SH and could vouch for the handling. I bought a GS300 right after and it couldn't hold a candle to the SH in terms of handling. I'd try taking the same turns in the GS that I easily did in the SH and my whole dashboard would light up with warning lights. The GS was a pig though.
Oh, I don't know, there are so many under $500 RWD cars on craigslist that I can't name just one...
FWD is cheaper at least partly because it has become standard to make econoboxes FWD, and to reserve RWD for performance vehicles or trucks. Not because the transmission is that much cheaper.
Hardly....driving my Celica (FWD "sporty" car) and my MR2 (MR "sporty" car) is a WORLD of difference...it has nothing to do with power. They both have about the same. It has to do with how weight transfers between the driving and steering tires, and in what direction force is being applied around a corner.
Makes a difference in acceleration and braking, too...the car transfers weight (and therefore traction) to the powered tires when acceleration, and the braking tires while braking (but there's still some weight in the back to let the rear tires brake).
Err, I don't know what to tell you. You obviously put a lot of effort into that post but you're wrong. The biggest problem with your explanation is that it requires one wheel to turn faster than the other before the torque steer effect. Anyone who has driven a FWD car will till you that torque steer occurs from a stopped position when you apply a lot of throttle, but without losing traction. Your explanation also doesn't explain why torque steer is extremely noticeable from a stopped position but is rarely experienced when applying throttle while already moving (unless you have a heap of HP).
Torque steer is really caused by having two unequal length half shafts having power applied at the same time. The half shafts twist slightly when the power is applied because of the traction between the tyres and the road. The longer shaft will twist more, meaning there is a slight delay between the power being applied to one wheel and the other. When one wheel has power applied before the other the car will obviously veer to one side. I know my explanation doesn't sound as fancy as yours but that's the real cause of torque steer.
And to those who claim torque steer is only an issue with high HP cars, that's incorrect. As an example, my brother owned a Toyota Carina with a wussy little 4 cyl (don't know the power output, but it was slow as hell) and it suffered badly from torque steer. It comes down to the gemoetry of the drive train and suspension system.
3chordcharlie
Diamond Member
- Mar 30, 2004
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ElMonoDelMar
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3chordcharlie
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Wait, someone thinks FWD is more efficient?
Think about it, there's no way to mak a FWD more efficient in terms of driving wheels directly...
RWD is more efficient, but only by a hair, and FWD is safer for general use, that's why FWD took over - safer, and especially better traction in bad conditions.
If you want to DRIVE though, RWD is still the way to g (AWD is more capable, but RWD provides the most immediate and best feedback).If you want to drive by the seat of your pants, RWD is unbeatable.
Think about it, there's no way to mak a FWD more efficient in terms of driving wheels directly...
RWD is more efficient, but only by a hair, and FWD is safer for general use, that's why FWD took over - safer, and especially better traction in bad conditions.
If you want to DRIVE though, RWD is still the way to g (AWD is more capable, but RWD provides the most immediate and best feedback).If you want to drive by the seat of your pants, RWD is unbeatable.
Originally posted by: OS
except for alltrac turbo celicas
Yeah...those are beasts!
The MR2 needs more horsepower, though...once I get a real job, I'll have to find a mk2 turbo for a good price (ha, ha).
You two are saying the same fvcking thing for the most part.....and you're both right and wrong.
Torque steer is caused by one wheel spinning faster than the other. Yes.....even without loss of traction. Unequal shaft lengths causes/intensifies the effect.............
Best explanation in the first few google results:
http://www.mph-online.com/mag/streetknowledge/003
"How does torque steer happen?
In a front-wheel-drive car, engine power is applied to wheels that also want to turn, unlike in a rear-wheeldrive car in which these two tasks are separate. When you turn the steering wheel, the wheels pivot about the appropriately named steering axis. Power is applied pretty much equally over the tire's contact patch (the part that's touching the road), which we'll approximate to a single force at the center of the patch. Now, if you extend the steering axis to the ground, it will be offset from the center of the contact patch. In case you were wondering, yes, this is called the steering offset.
The fundamental reason for torque steer is that the power applied at the contact patch wants to turn the wheel around the steering axis, which, you'll remember from the last sentence, is offset. If you compare it to a door, the steering axis is the hinge, and the center of the contact patch is where you push to swing the door open, hence the offset.
Most cars, of course, have two front wheels, so the forces on each wheel should counteract each other. But if the forces on each wheel are different, or if a tire's contact patch changes, that imbalance will cause one tire to twist more than the other, and that's when you get torque steer.
What variables contribute to torque steer?
One of the main causes of torque steer is the fault of packaging. Frontwheel- drive cars have to fit the transmission under the hood with the engine and the steering rack. In these cramped conditions, the transmission doesn't end up in the center of the car. That means the two driveshafts connected to the front wheels are of unequal length. Because the shorter shaft is stiffer, it transfers power more quickly. So when you hit the gas, the shorter shaft sends the power to the wheels immediately, while the longer shaft twists itself a little and takes time to catch up. Once the longer shaft catches up, it unloads the stored energy from the twisting. This is why, in cars with unequal-length driveshafts, there is a big pull in one direction and a smaller pull in the opposite direction when you feel torque steer?the first lurch is from the initial transfer to the short shaft, and the secondary lurch is from the longer shaft unwinding.
This is also why high-horsepower cars are more prone to torque steer. The more energy that goes through the drivetrain, the more severe the effect. Turbocharged and supercharged engines also tend to cause more torque steer because of the abrupt increase in power when the boost increases.
A simple fix to this is to make both driveshafts the same length. This is done with an intermediate shaft (also called a half shaft) on one side of the transmission. Since the intermediate shaft comes straight out of the transmission, it doesn't affect torque steer. Most modern front-wheel-drive cars have equal-length driveshafts.
So why is there still torque steer? Even equal-length driveshafts aren't perfect. The linkages and bearings in the intermediate shaft, and the shaft itself, still have torque-output delays.
Other causes of torque steer can't be helped, which is why torque steer can never be totally cured. It goes back to the problem of having the front wheels do all the work. Any time the tire contact patches are unequal, you'll get torque steer. Under cornering, for instance, one wheel has more weight transferred to it and?depending on suspension and steering geometry?might have a differently shaped contact patch. Another time this happens is when each tire has varying grip, as in wet or wintry conditions."
OS
Lifer
- Oct 11, 1999
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Originally posted by: jagec
Originally posted by: OS
except for alltrac turbo celicas
Yeah...those are beasts!
The MR2 needs more horsepower, though...once I get a real job, I'll have to find a mk2 turbo for a good price (ha, ha).
good luck homie, you and everyone else with a taste for imports wants a cheap mk2 mr2.
Vic
Elite Member
- Jun 12, 2001
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Let me clean up this thread.
Most AWD cars are primarily FWD (with AWD coming on only when needed), so that is why most people can't tell the difference between FWD and AWD cars. The main exceptions to this are newer Subarus with manual transmissions and Mitsubishi Evo/Eclipse(AWD). I can easily tell the difference in my Subaru WRX, primarily due to the increased weight of the drivetrain, plus the extreme level of confidence that comes from feeling that losing traction is almost (but not entirely) impossible (this is coupled, however, with the knowledge that traction, once lost, is a bit harder to regain with control in AWD than in RWD/FWD, for obvious reasons that when AWD loses traction, it loses traction completely to all 4 tires, and then when it regains traction, it regains it completely, often with very abrupt transitions that can be very hazardous, i.e. snap oversteer, etc).
RWD is not more dangerous than FWD in slick conditions. The issue there is that, in any type of skid, driver inputs in FWD are intuitive whereas, in RWD, they are counter-intuitive. Skilled drivers have little difficulty understanding this, whereas panicky drivers don't. A great example I can think of this at the moment (beyond the obvious of counter-steering) is the "look where you want to go" rule. Panicky drivers tend to give into the intuitive tendency to look right at what they don't want to hit, usually with disastrous results.
Torque steer is caused by the unequal distribution of torque to the 2 front drive wheels (whereas torque is the moment of force while power is those moments of force measured over time). The wheel that receives more torque (or which has more traction and thus is able to transmit more torque to the ground) will "want" to go ahead of the other, but that not being possible, and the drive wheels also be responsible for turning the car, it will have the effect of causing the car to turn in the opposite direction (i.e. right wheel = turn left, left wheel = turn right). The RWD equivalent of torque steer is the effect of driveline twisting which causes an RWD to kick its rear end out to the right under sudden heavy throttle even while driving perfectly straight. Similarly, it is the right wheel in FWD that most often tends to torque steer, with the tendency to try to steer the car left into oncoming traffic (which has caused tragic results). The primary factors that cause torque steer are, in order: (1) open differentials, (2) unequal-length halfshafts, (3) uneven pavement. A good limited-slip differential can solve or greatly reduce most torque steer.
Most AWD cars are primarily FWD (with AWD coming on only when needed), so that is why most people can't tell the difference between FWD and AWD cars. The main exceptions to this are newer Subarus with manual transmissions and Mitsubishi Evo/Eclipse(AWD). I can easily tell the difference in my Subaru WRX, primarily due to the increased weight of the drivetrain, plus the extreme level of confidence that comes from feeling that losing traction is almost (but not entirely) impossible (this is coupled, however, with the knowledge that traction, once lost, is a bit harder to regain with control in AWD than in RWD/FWD, for obvious reasons that when AWD loses traction, it loses traction completely to all 4 tires, and then when it regains traction, it regains it completely, often with very abrupt transitions that can be very hazardous, i.e. snap oversteer, etc).
RWD is not more dangerous than FWD in slick conditions. The issue there is that, in any type of skid, driver inputs in FWD are intuitive whereas, in RWD, they are counter-intuitive. Skilled drivers have little difficulty understanding this, whereas panicky drivers don't. A great example I can think of this at the moment (beyond the obvious of counter-steering) is the "look where you want to go" rule. Panicky drivers tend to give into the intuitive tendency to look right at what they don't want to hit, usually with disastrous results.
Torque steer is caused by the unequal distribution of torque to the 2 front drive wheels (whereas torque is the moment of force while power is those moments of force measured over time). The wheel that receives more torque (or which has more traction and thus is able to transmit more torque to the ground) will "want" to go ahead of the other, but that not being possible, and the drive wheels also be responsible for turning the car, it will have the effect of causing the car to turn in the opposite direction (i.e. right wheel = turn left, left wheel = turn right). The RWD equivalent of torque steer is the effect of driveline twisting which causes an RWD to kick its rear end out to the right under sudden heavy throttle even while driving perfectly straight. Similarly, it is the right wheel in FWD that most often tends to torque steer, with the tendency to try to steer the car left into oncoming traffic (which has caused tragic results). The primary factors that cause torque steer are, in order: (1) open differentials, (2) unequal-length halfshafts, (3) uneven pavement. A good limited-slip differential can solve or greatly reduce most torque steer.
soydios
Platinum Member
- Mar 12, 2006
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AWD minivans are usually FWD-biased.
To compare Front Wheed Drive and Rear Wheel Drive, think of what it would be like to have the front wheel on a bicycle pulling you. Then imagine that front wheel pulling you through a turn.
The front wheels pull the car through the turn. When you lean on the accelerator in a turn in a FWD car, you'll notice.
Rear Wheel Drive is preferred for racing, because each pair of wheels only has to exert force in one direction at a time, unless the car is braking (sideways for front, front/back for rear).
To compare Front Wheed Drive and Rear Wheel Drive, think of what it would be like to have the front wheel on a bicycle pulling you. Then imagine that front wheel pulling you through a turn.
The front wheels pull the car through the turn. When you lean on the accelerator in a turn in a FWD car, you'll notice.
Rear Wheel Drive is preferred for racing, because each pair of wheels only has to exert force in one direction at a time, unless the car is braking (sideways for front, front/back for rear).
Originally posted by: Linux23
This is the dumbest post in this thread.
What other AWD car besides the Acura RL is primarily FWD based?
The Volvo's (all of them), the Ford Escape (and it's clones, and every other Ford based AWD), every Honda AWD, Every Mazda (except the Mazdaspeed6), the Toy RAV4 and Matrix (Pontiac's clone also), the automatic Subaru's, and probably some more that I can't remember.
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