Car Question: AWD vs. RWD

[WinkOsmosis]

That 95% to the front wheels is crap. I don't know how they can even call it a sports sedan. It's the same as FWD until you hit a puddle or something.

 

[incallisto]

Originally posted by: ElFenix
i love how the forums dies every night at ~ 4am eastern

Hahahah! So true.

 

[dirtboy]

RWD.

 

[BigSmooth]

Originally posted by: DivideBYZero
BUT, the Haldex coupling failed 4 days ago. In the shop for repair, Warranty job thank FSCK.

A VW in the shop? That's unpossible!!

Sorry, I just couldn't resist.

 

[BigSmooth]

What the hell? Did the server eat my last post?

Edit: that was really weird, the entire second page of this thread was not showing up despite refreshing. The threads view only shows 50 posts despite the fact that there's at least 55 posts right now. Must be the server hiccups that happened last night.

 

[Zenmervolt]

Originally posted by: Dari
But which is better for a sports sedan? AN AWD with the Front wheels (initially) getting 95% of the power or RWD?

If you have to have AWD, the LAST thing you want is for it to be biased towards the front wheels. In a truly sporting AWD system, the front wheels should ONLY get power when the rear wheels are slipping. If you bias an AWD system towards the front, it mimics the behavious of a FWD car, and FWD has no place in any sort of sporting automobile.

ZV

 

[LAUST]

Originally posted by: Syringer

Originally posted by: Dari
But which is better for a sports sedan? AN AWD with the Front wheels (initially) getting 95% of the power or RWD?

AWD pros:

*better traction in bad weather
*harder to go crazy and create hazards
*off the line, all else equal will beat RWD

AWD cons:

*adds a lot of weight
*more power lost to the wheels
*arguably not as "fun"
*repairs most costly
*acceleration on a roll not as good compared to RWD

This was ALMOST correct minus the *off the line, all else equal will beat RWD

Reciprocating mass, a AWD vehicle will have a better launch, but do to all the extra mass in the drivetrain it will have a slower high end.... take my truck, in order for me to get my 32 X 11 tires to hook up I run in 4x4... I destroy people in the 300', then I begin to fall over myself and get a 14.9 @ only 89mph, a RWD vehicle would normally run a 14.9 at about 93mph

 

[Zenmervolt]

Originally posted by: Shockwave
Why is an AWD slower on a rolling start then a RWD.
Why is a RWD preferable to a FWD from a start? I thought the FWD would launch better and run a better trap time overall then a RWD, all other things being equal.

AWD is slower from a rolling start because an AWD system has several times the rotational inertia when compared to a RWD system, plus all the extra friction that comes from having an extra driveshaft and set of halfshafts. Also, AWD adds typically at leat 150 pounds of weight. The real thing that slows AWD down though is the rotational inertia. All those extra rotating parts in an AWD system must be accelerater TWICE. They must be accelerated linearly (in the direction of the car's travel) AND they must be accelerated rotationally (in the direction of their spin). This effect is common to any rotating mass added to a car (which is why people want light wheels) and the typical conversion rate is that one pound of rotating mass is equal to three pounds of stationary mass.

RWD is much better than FWD from a start beause of weight transfer. For the instant before, weight transfer occurs, it's possible that FWD would be better, but that time period is instantaneous and hence it's not worth considering. Once the car begins to accelerate, the weight is transferred to the REAR wheels. The same force that throws you back into your seat is the force that takes weight off the front wheels and puts it on the rear wheels during acceleration. So during accleeration, the front end of a car gets light, and there is less traction available to the front wheels, conversely, the back end gets heavy and there is more traction available to the rear wheels. The weight transfer is much greater than the front weight bias of an FWD car, so even if a RWD car had the same static weight distribution as a FWD car, the RWD would be better for acceleration runs since it would have more traction available to its tires.

ZV

 

[Dari]

damn, with all these responses, my head is in a tizzy. But I think I get the message.

 

[Triumph]

Originally posted by: Shockwave
BTW, these quesitons arent to be a asshat. I really dont know the answers. i would say from a roll RWD/FWD would eat AWD, all other things being equal due to the extra power lost on the wheels. And I would say an AWD would launch much better then either. But I have heard that a FWD launches better then a RWD.
And to set up a theoretical question, if you have a RWD and a AWD car, both dyno...say....250 HP to the ground, which would luanch better in a rolling start? Provided no wheel spin occurs (Say a 30 MPH roll)

The RWD car would most likely win, because it would be lighter and it would lose less power through the drivetrain.

Dari, it's very confusing because there are many different types of all wheel drive systems. The answer isn't very simple. I suggest you start reading at howstuffworks.com if you're really interested. there are lots of good animations and clear descriptions there.

 

[isekii]

Drive an RWD vehicle

it handles like a dream

well.. i guess that depends on the car..

 

[WinkOsmosis]

RWD is fun, especially when you have two computers in the trunk and only 155hp/160tq and can floor it turning left onto a main road with no wheelspin. Not to mention the fun without the two computers in the trunk.

 

[WinkOsmosis]

Originally posted by: Zenmervolt

Originally posted by: Dari
But which is better for a sports sedan? AN AWD with the Front wheels (initially) getting 95% of the power or RWD?

If you have to have AWD, the LAST thing you want is for it to be biased towards the front wheels. In a truly sporting AWD system, the front wheels should ONLY get power when the rear wheels are slipping. If you bias an AWD system towards the front, it mimics the behavious of a FWD car, and FWD has no place in any sort of sporting automobile.

ZV

The thing is, with every AWD car with a traverse mounted engine, the front wheels are connected directly to the transmission. The rear wheels get the viscous coupling or whatever. I think Audi is the exception since they use a Torsen center differential.

 

[Dari]

another question: Is it harder to steer with a FWD car than a RWD car?

 

[Howard]

Originally posted by: Shockwave

Originally posted by: Syringer

Originally posted by: Shockwave
Why is an AWD slower on a rolling start then a RWD.

More weight, more power loss to the wheels..and when you push on the gas weight is shifted to the back of the car, giving RWd an advantage.

Why is a RWD preferable to a FWD from a start? I thought the FWD would launch better and run a better trap time overall then a RWD, all other things being equal.

Again, off the line, you push on the gas, weight transfers to the back, giving RWD more traction.

Traction is rather relative isnt it? As long as wheel spin doesnt occer (Loss of traction) then weight transfer shouldnt really play a part should it? If we're talking about less then ideal conditions, then I would tend to agree.
However, i have heard from some that FWD launches better then RWD hence my questions.

Well, you DO see more FWD dragsters with wheelie bars.

 

[Howard]

Originally posted by: WinkOsmosis

Originally posted by: Zenmervolt

Originally posted by: Dari
But which is better for a sports sedan? AN AWD with the Front wheels (initially) getting 95% of the power or RWD?

If you have to have AWD, the LAST thing you want is for it to be biased towards the front wheels. In a truly sporting AWD system, the front wheels should ONLY get power when the rear wheels are slipping. If you bias an AWD system towards the front, it mimics the behavious of a FWD car, and FWD has no place in any sort of sporting automobile.

ZV

The thing is, with every AWD car with a traverse mounted engine, the front wheels are connected directly to the transmission. The rear wheels get the viscous coupling or whatever. I think Audi is the exception since they use a Torsen center differential.

Audi's Quattro system does use a Torsen center, but I don't see how the mounting position of the engine affects the choice of center differential?

 

[WinkOsmosis]

Originally posted by: Dari
another question: Is it harder to steer with a FWD car than a RWD car?

It doesn't make a difference. Steering difficulty depends on the caster. The steering axis is angled, so the center point of the wheel trails the point of the axis that intersects the ground. Same reason you can ride a bike without holding the handlebars.

If you're talking about cornering, it depends on the situation. Understeer of oversteer.. pick one.

 

[Dari]

Originally posted by: WinkOsmosis

Originally posted by: Dari
another question: Is it harder to steer with a FWD car than a RWD car?

It doesn't make a difference. Steering difficulty depends on the caster. The steering axis is angled, so the center point of the wheel trails the point of the axis that intersects the ground. Same reason you can ride a bike without holding the handlebars.

If you're talking about cornering, it depends on the situation. Understeer of oversteer.. pick one.

For the last question, I'm not sure what each mean.

 

[WinkOsmosis]

Originally posted by: Howard

Originally posted by: WinkOsmosis

Originally posted by: Zenmervolt

Originally posted by: Dari
But which is better for a sports sedan? AN AWD with the Front wheels (initially) getting 95% of the power or RWD?

If you have to have AWD, the LAST thing you want is for it to be biased towards the front wheels. In a truly sporting AWD system, the front wheels should ONLY get power when the rear wheels are slipping. If you bias an AWD system towards the front, it mimics the behavious of a FWD car, and FWD has no place in any sort of sporting automobile.

ZV

The thing is, with every AWD car with a traverse mounted engine, the front wheels are connected directly to the transmission. The rear wheels get the viscous coupling or whatever. I think Audi is the exception since they use a Torsen center differential.

Audi's Quattro system does use a Torsen center, but I don't see how the mounting position of the engine affects the choice of center differential?

AWD cars with the traverse engine are FWD vehicles adapted to RWD, for example Mitsubishi 3000gt. AWD cars with longitudonal mounted engines are RWD cars adapted to AWD, for example Nissan Skyline. With a FWD car, the front wheels get direct power. When converted to AWD, the rear wheels get power through a viscous coupling that doesn't transfer power unless slippage causes the viscous stuff to expand and lock. I guess that 5% power to the rear comes from the slight friction in the viscous coupling.

 

[WinkOsmosis]

Originally posted by: Dari

Originally posted by: WinkOsmosis

Originally posted by: Dari
another question: Is it harder to steer with a FWD car than a RWD car?

It doesn't make a difference. Steering difficulty depends on the caster. The steering axis is angled, so the center point of the wheel trails the point of the axis that intersects the ground. Same reason you can ride a bike without holding the handlebars.

If you're talking about cornering, it depends on the situation. Understeer of oversteer.. pick one.

For the last question, I'm not sure what each mean.

Understeer is when front wheels lose traction and spin. Oversteer is when rear wheels lose traction. Either can put you in a ditch .

 

Understeer is when front wheels lose traction and spin. Oversteer is when rear wheels lose traction. Either can put you in a ditch

Oversteer is not losing traction, it's when the vehicles steers more than the steering wheel input, understeer is exactly the opposite.

 

[tm37]

Originally posted by: Roger

Where have I heard what? FWD launches better then RWD? Couple places. Hence me asking.

RWD will always be better than FWD when it comes drag racing, why ?

Weight transfer as was stated before, upon launch of any motor vehicle, weight is transfered to the rear wheels, the front wheels lose this downforce, on top of this the front wheels have an additional duty, steering, this causes the engineers to compromise on the design of the front suspension, the lateral stability of the knuckle assembly cannot be made as stiff as compared to a non-steering suspension, this has the effect of lateral deflection of the knuckle/tire assembly causing the alignment to deviate, which in turn causes additional loss of traction.

OK so it is pretty obvious at this point that roger is too smart for 90% of us here

 

[Zenmervolt]

Originally posted by: WinkOsmosis

Originally posted by: Howard

Originally posted by: WinkOsmosis

Originally posted by: Zenmervolt

Originally posted by: Dari
But which is better for a sports sedan? AN AWD with the Front wheels (initially) getting 95% of the power or RWD?

If you have to have AWD, the LAST thing you want is for it to be biased towards the front wheels. In a truly sporting AWD system, the front wheels should ONLY get power when the rear wheels are slipping. If you bias an AWD system towards the front, it mimics the behavious of a FWD car, and FWD has no place in any sort of sporting automobile.

ZV

The thing is, with every AWD car with a traverse mounted engine, the front wheels are connected directly to the transmission. The rear wheels get the viscous coupling or whatever. I think Audi is the exception since they use a Torsen center differential.

Audi's Quattro system does use a Torsen center, but I don't see how the mounting position of the engine affects the choice of center differential?

AWD cars with the traverse engine are FWD vehicles adapted to RWD, for example Mitsubishi 3000gt. AWD cars with longitudonal mounted engines are RWD cars adapted to AWD, for example Nissan Skyline. With a FWD car, the front wheels get direct power. When converted to AWD, the rear wheels get power through a viscous coupling that doesn't transfer power unless slippage causes the viscous stuff to expand and lock. I guess that 5% power to the rear comes from the slight friction in the viscous coupling.

It's perfectly possible to put the "center" differential in the front of a car with a transverse engine. You just have to have the take-off for the rear wheels before the front differential. It's also perfectly possible to set up an AWD system with a transverse engine that will have a "base" setting of 50/50 split between front and rear, or any other ratio that you would want.

ZV

 

[jlee]

Originally posted by: Roger

Understeer is when front wheels lose traction and spin. Oversteer is when rear wheels lose traction. Either can put you in a ditch

Oversteer is not losing traction, it's when the vehicles steers more than the steering wheel input, understeer is exactly the opposite.

Losing traction can cause understeer..at least in a FWD car (front wheels are spinning...as such, they aren't too great in the steering department).

Roger: The above is not directed at you..just thought I'd clarify.

 

[RossMAN]

What's so special about RWD vs FWD in a luxury car?

Let's assume in dry pavement and rain conditions.

Thanks.