Well... it was bound to be done eventually http://www.i-club.com/ubb-files/smilies/smile.gif

Actually these are the two cars that I'm basically looking at... Not sure what I should get, wait for the RX-8 or get a WRX now? The new Renesis engine does kick ass... N/A 1.3 2 rotor side-port wankle (drool)250hp @ 9000 RPMs....

However all the other specs I've heard are basically rumor (curb weight, torque curve... but I do know that they plan to have both high and low end torque on the car, the high end is there but they are working on the low end for the Americans cause we wuv our low end pull) The fact that it's a true 2+2 is very appealing in a sports car. The suicide doors are also a nice addition for the obvious reasons of it remaining a coupe but allows easier access to the back seats hey as long as they found a way to make sure the B pillars are still rigid more power to them...

It's a 6 speed, only problem is thus far it's not a manual... it's actually an automatic that you can change gears (in other words it's a pedal shifter like an F1 car or some Ferrari's) Some may not like this I happen to find it kinda cool http://www.i-club.com/ubb-files/smilies/smile.gif

It has 14-in. venter discs (not cross-drilled or slotted mind you, these are some whacky new design) but you can't go wrong with brakes that size... (I'd assume 4 pot)

Only problem I'm worried about is weight (14 inch brakes = heavy car...) It could be a real porker at 3500lbs but that is all opinion right now...

The styling is truly subjective... Both the Rex and this have grown on me alot... The exterior is very nice, except the little smile they got going on but unlike the WRX's headlights this can be fixed easily http://www.i-club.com/ubb-files/smilies/smile.gif

The interior, I think, won't be like that in the production model to much chrome on the center console.... But either or it's ok..

To me, it boils down to can I wait to see if the RX-8 will be any good? Or will I just go for the WRX..... Also I've heard about that Lancer 7 coming here this year.... Mmmmmmm more fuel to the fire http://www.i-club.com/ubb-files/smilies/biggrin.gif

Any thoughts?

The RX8 won't have all those fancy things once it hits production. The 6 speed would be a true manual, and the wheels and brakes will be smaller. They allways put all sorts of fancy stuff on the prototype models. Look at the RSX prototype with brembo brakes, 18" wheels, and recaro's. The original MR-S prototype had no manual, just the tiptronic. Basically all manufacturers put glitsy parts on the prototypes.

As for the RX8 itself. I'd take the it without a second thought. I've always loved the concept behind rotary's. With the new engine it should be much more efficient and reliable than the old. The car shouldn't weigh that much. Those little rotarys aren't that heavy and I think I remember hearing estimates around 2800 lbs. The interior looks awsome. I hope all the aluminum stuff actually makes production and is not just a glitsy prototype thing. My only problem would be the price. I heard rumors it would be around $30k though, comparable to the S2000. Thats a little out of my range right now.

[This message has been edited by Eby (edited February 21, 2001).]

One more consideration is, how long are you willing to wait? I haven't heard a definite date as to when the Mazda will be produced. I read one article that said it is 2 years away from hitting the showrooms.

Check out the new issue of "Road & Track". Normally I don't buy this mag, but anytime they have a article on a Rotary, I just have to look. The production version shouldn't change too much from what they show. Remember the RX8 has evolved from a show car Mazda did a few years ago called the Revolve or something like that.
I for one hope the six speed stays a automatic. Normally I would want a manual, but if I buy a RX8 it would have to become a bracket racer. Manuals just won't cut it in this case.
One last thing, look at the Tachometer picture in R&T......12,000 rpm!!!!! Even if it is limited to 8500 rpm the tach is way cool.

I don't know what your budgets at but the price i've seen they've been shooting for in the rx-8 is mid to high thirties, past my limit right now. That would be the main diciding factor, because think of how much aftermarket stuff you could buy with the difference in the price of the WRX.
p.s. you got to have the awd...

why have a 12,000 rpm tach when its cutoff is 8,500 rpms? http://www.i-club.com/ubb-files/smilies/rolleyes.gif

all in all, the rx looks like its going to be a hot car, but i wouldnt expect it to be less than 30k ...

Basically, if you can afford it, get it. If I had $46,000 to blow on a ride, I'd buy the new M3 instead of the WRX. Uh oh, now I've done it--flame on.

You can always keep waiting for the next new thing. Just buy the WRX and then if you want trade it in in a few years for the RX-8.

Let me tell you, though, after seeing the RX-8 at Detroit, it is very, very much just a concept car at this point. Long way to go before production.

yeah, but the 12000 RPM redline... That is so amazing. The writer who drove a modified miata with that engine in it said that it is amazing. I want one of those. I guess ill have to start saving pennies. Maybe in 2 years, ill be making 200,000 a year. Then i can afford all the stuff i want.
--Adam

Well from rotarynews.com (http://rotarynews.com) Shigeo Hirata (the lead Designer of the RX-8) said the car is 90% done and mostly everything you see now will go in the final version... While Philip Martens (Mazda Marketing Director) said the body weight will be 1260kg which is roughly 2635lbs (I can live with that compared to what Road and Track said 3500lbs Oi!) He also said it'll be in production Spring of 2002.... (So that is why I say why buy a WRX for less than a year? Kind of a waste if I get the RX-8) But I still like the WRX so..... it's hard to say... It's only a year's wait so unless I buy both (hmmmm there's an option lol) there's no point in getting a Rex if I'm stuck on this RX-8, on the other than WRX is race proven, it has a turbo (however AWD Is good... but if you're going to get a sports car you need RWD... AWD sucks at turning compared to RWD, AWD is just great for stability... to bad the RX-8 isn't an MR rotary! drooooool)

Also R&T said the car is slated to be high 20's... 27-29k I can live with that... Bah this sucks http://www.i-club.com/ubb-files/smilies/smile.gif

oooooh, MR Rotary, that is toooo sweet...
--Adam

I saw that Road&Track issue.....I had planned on getting that if it came out. I have ben dying for it since the RX-01 was in the mag. BUt I am getting the WRX and I dout I will want to trade it in. Only time will tell. What I really need to do is find a way to make enough money to buy them both!! http://www.i-club.com/ubb-files/smilies/smile.gif I owned a 79 RX-7 years ago with like 200,000 miles on it....and it was still a fun car to go fishtailing in http://www.i-club.com/ubb-files/smilies/smile.gif The rotary is a cool engine. I can see the high horsepower RX-08's now!!!

Well, I hope it comes to production soon, but that Detroit show car was really just a one off concept. Everything about it was mocked up. I'd be surprised if it even had an engine in it.

Regardless, the RX-7 was quite possibly the best sports car ever to come out of Japan. I should have bought one when I had the chance. I can only hope the new one will be as awesome.

I did some searching around for information on this car. It's supposed to have a peak 153 ft-lbs of torque at 7500rpms. So it won't be a torque monster like some of you were thiking. It will probably drive somewhat like the S2000, except a little faster because of possible lighter weight and higher HP. It should be really lightweight, the new Renisis engine is lighter than the previous RX7's rotatary. A spokesman at the Detroit Auto Show said Mazda is really concerned about the power to weight ratio, so it will be lightweight. All in all it sounds like a really cool car if you don't mind revving the engine like an S2000. Estimated price is $30-35k. Oh, and I'll bet any of you 50 bucks they offer a true manual 6 spd, and loose the huge wheels and brakes.

Jspec: Please explain "AWD sucks at turning compared to RWD"

Maybe you meant 4WD sucks at turning compared to RWD

No, I meant if you had an AWD car with exactly the same specs as a RWD car and had them go through some cornering tests the RWD would win... AWD is meant for stability that's why ALL wheels are turning all the time... that's why the ONLY sports car you see that doesn't rally is a GT-R, but even they are thinking of making their car RWD for the R35 model... RWD is built for pushing a car through a turn... geeze 98% of the sport car models can't be wrong http://www.i-club.com/ubb-files/smilies/smile.gif AWD is meant for stability through turns... you won't spin out as much, etc.

Not exactly. Read this test: http://www.subaru.co.nz/autocar_feature/autocar_content.html

The STI out handled some of the best hanlding RWD cars in the world.

I'm sorry, I dig the WRX a lot, but I think that test is a load of crap. There is only so much you can get out of the traction envelope of a 225 series tire.

Ignoring incliment weather or poor road surfaces, and assuming a smooth surface, AWD still has advantages beyond just the launch:

AWD lets you get on the throttle more quickly out of the apex than a RWD car. However, the RWD can rotate alot more easily. However, one can help the AWD rotate more easily (plow less) with suspension adjustments... but a RWD will always punish you if you get on the throttle too early past the apex.

I'd say the easy rotation, lighter weight, lesser complexity, and and greater drivetrain efficiency is the reason for most sports cars being RWD. However, well tuned AWD cars can still rotate, drivetrains are getting more efficient, and their launches and power out of apexes can make up for the extra weight. Example: 911 Turbo, WRX, etc.

I'd say the AWD sports cars are easier to drive at the limit, which means better driver performance relative to the car's capability. However, on a perfect surface with a perfect driver, I'll conceed the advantage to the RWD. Since I'm not a perfect driver, I'll stick with my AWD preference (and spoolin' at the apexes).

-- ConeMasher

[This message has been edited by ConeMasher (edited February 22, 2001).]

No, you shouldn't concede. You brought up a good point with the 911 turbo. I don't think porsche would have made it AWD unless it helped.

Also, Audi has been banned from several races for their advantage with AWD.

[This message has been edited by Eby (edited February 22, 2001).]

Yeah, but the races they were banned from were against almost exclusively front drive cars.

Here's a different example: Porsche GT3 vs. Turbo. Turbo has 60hp on the GT3, weighs about 350lb more, and has AWD. That said, it just barely beats the GT3 around the Nurburgring by only 3-4 seconds.

Have you guys heard of the tarmac gear? the thing that splits the torque ratio from the front and rear. The whole point of that is to have the advantage of both AWD and RWD. Kinda like the GT-R where it gives power to the front wheels when it needs it. If tuned right the AWD will out perform the RWD anytime anywhere.

I don't know a whole hell of alot about this so please correct me,
4 wheel drive has a locked differential which mean when its turning the outside tire will spin at the same rate the inside does which causes it to skip around the corner, which is why your not supposed to run 4wd on dry pavement

RWD obviosle won't have this problem the differential allows the outside wheel to spin at its on rate.

AWD subarus are FWD by nature until the tires start to spin then it begins to shift power to the rear wheel for Traction and to maintain stability.

The point should be a muscle car has an advantage over a FWD car which is what a subaru is until the wheels start to spin, once in all wheel drive and an experienced AWD driver (which I am not, though I would love to be)behind the wheel I would say an equally powered AWD car against a RWD car the AWD car would blow it away on any course.

JMO

AWD subarus are FWD by nature until the tires start to spin then it begins to shift power to the rear wheel for Traction and to maintain stability.

On manual 2.5RSs (the only ones i have [limited]knowledge about) the car isnt FWD by nature, as under normal driving the power is distribuited 50% to the front and 50% to the rear, and under hard acceleration (not necesarily wheelspin) power can shift to the back wheels up to 100%! I hardly think that that qualifies as being FWD By nature...

now on automatic 2.5RSs (up to 01 models) the power is split 90/10 with the 90 going to the front under normal driving conditions... (that is a big AFAIK there)

Everyone! Run, don't walk to go and buy Sport Compact Car this month. There is a whole article by Shiv on how the Subaru drivetrain works. It is a really awesome piece of machinery. The vehicle is NOT fwd biased at all. Rather it is a 50/50 split. The shaft that goes to the front differential actually passes through the transmission output shaft. Very ingenious.

Hashiriya,

That is totally false. If AWD can be made to outperform RWD in all conditions, then why are most road race cars RWD? Why are F1 cars RWD? Clearly, if AWD was such an advantage, they would be using it.

They don't use AWD because when Audi was in Lamans they were blowing the crap out of everyone with the AWD. They have outlawed AWD in most racing circuits as an unfair advatage for close to 15 years.

The Lamborghini Diablo VT has all wheel drive and I bet that would blow away most other cars in handling of the same power.

Copyright © 1997,1999 by Eliot Lim. This article may be distributed freely, provided it is distributed in its entirety.

Introduction to All Wheel Drive systems
By Eliot Lim
Third major revision: March 2 1997
Last update: February 26 1999 (all other versions obsolete)
The latest revision of this article is always available at: http://www.eskimo.com/~eliot/awd.html
This page has been visited times

Introduction
This article was originally written in the fall of 1992. Back then as is now, there was a general lack of good information regarding all wheel drive vehicles and how they differ from traditional four wheel drive vehicles. I have updated the original article to mention current vehicles. This article has been very well received by the internet community.
Definitions
It is important to get the definitions down first, since for any four wheeled vehicle, all wheel drive and four wheel drive literally mean the same thing. Generally speaking "all wheel drive" implies permanently engaged or automatically engaging four wheel drive and "four wheel drive" implies manually engaging, part time four wheel drive. The auto industry usually abide by these definitions but not in all cases. The now departed "all wheel drive" Ford Tempo and Subaru Justy were really part time manually engaging systems, like the older Subaru GLs. The term on demand four wheel drive is quite ambiguous. It can either mean that it is a part time manually engaging system or a part time automatically engaging system!
The automotive media shares a lot of the responsibility for the confusion. Factual errors are common, so is the careless use of the various terms interchangebly.
For this article I shall be using the terms loosely and will be more specific where necessary.
Differentials
A differential is a mechanical set of gears which takes input torque from a driveshaft and splits it evenly to two output axles, allowing them to rotate at different speeds. A differential in a front wheel drive or rear wheel drive car allows both wheels to apply power to the road and yet be able to rotate at different speeds so that the car can turn without resistance.
A permanently engaged four wheel drive system needs to have three differentials to enable it to apply power to four wheels and be able to turn without resistance: The front, rear and center diffs. (diff = short for differential) This is because the distance traveled by the turning front wheels is not the same as the distance traveled by the non articulating rear wheels.
Power leaving the gearbox first goes to the center diff, which then splits it via the driveshafts to the front and rear diffs. Manually engaging part time four wheel drive systems in most cases do not have a center diff, so they cannot be used in the dry. When four wheel drive is engaged in such a system, the front and rear axles are locked together and will rotate at exactly the same speeds. The difference in front and rear wheel speeds have to be scrubbed off by the tires.
Differential locking
This is a core design issue in all wheel drive technology because these have a profound effect on the cars' road behavior. Consider the case of the simplest all wheel drive car with 3 "free" diffs. The car can be rendered immobile if any one of the four wheels lose traction because basic differentials equalize the torque output. A simplistic way to look at this is to think that the basic "free" differential sends power to the axle with the least grip, so if one wheel loses grip, all the power is sent there, leaving nothing for the remaining three. In reality, the differentials are equalizing the power distribution, so everything is equalized to zero in this case. Remember that a four wheel drive vehicle has twice as many wheels as a two wheel drive to lose grip and mobility on. And since four wheel drive vehicles would tend to be used more in bad conditions, it is quite important to have some form of differential locking. Every full-time four wheel drive car on the market today has some form of diff locking. A good way to understand this concept is to trace the evolution of the very early systems to the state of the art.
Audi was the first manufacturer to successfully sell high-performance, permanent four wheel drive with the quattro, released in Europe in 1981 and in the US in 1983. (The car goes by the more popular name turbo quattro coupe in the US and more recently, the Ur Quattro around the world). The cars were very successful in rallying , winning several world titles and it set the automotive world ablaze because four wheel drive was never previously associated with ultra high performance. Even though the 1966 Jensen FF was the first vehicle to have full time four wheel drive (and also anti lock brakes) the car was a commercial failure and it was left to Audi to break through the public consciousness and go into the history books for launching the full time four wheel drive revolution.
During the 1980s Audi decided to spin off four wheel drive and the quattro name to its entire range of cars. The first generation quattros had simple locks for the center and rear diffs, which locked one or both of them solid (no speed difference) to dig one out of deep trouble. When the center diff was locked, it meant that one had to lose grip on one rear and one front wheel to become immobile. When both the center and rear diffs were locked, one had to lose both rear wheels and one front wheel to get stuck. The locks on these Audis were manually engaged and were quite cumbersome since the driver already had to worry about shifting and steering in addition to this. Audi found that many drivers forgot to disengage the locks once they got going again.
Thus development went in the direction of automatically locking differentials. First on the scene was the viscous coupling (VC for short) which used a silicone liquid in a casing designed so that minor speed differences were allowed between the two axles but increased slip would lead to a rapid increase in the viscosity of the fluid which would then lock up the coupling. The viscous coupling was used in two radically different ways:
Some manufacturers used regular differentials in conjunction with the VC where the VC functioned as a diff lock that acted automatically when conditions needed it. The current Mitsubishi Eclipse GSX and current manual transmission all wheel drive Subarus use this scheme. The departed BMW 325ix and Toyota Celica turbo all-trac also used it.
Audi, during the development of the original quattro, also played with VCs and came up with a completely different way of using a VC. In this implementation, the VC is used as the center diff, resulting in a part-time, automatically engaging four wheel drive system. In this implementation, the car is basically front wheel drive, with the rear wheels coasting along and minor speed differences absorbed by the VC when the vehicle was turning. When front wheelspin occurred, the speed difference would increase to the point where the VC with its viscous liquid churning would start transferring some of the torque from the front to the rear wheels and thus the vehicle would become four wheel drive. Note the difference between this system and the former. The latter is auto-engaging part time four wheel drive, while the former is full-time auto-diff-locking four wheel drive.
The part time automatically engaging system was never put into production by Audi but was instead spun off to VW, which did put it to market as the syncro system. The simplicity of this implementation has drawn a very wide range of manufacturers to use it as well, from all the minivan implementations, many of the newer SUVs to exotics like the current Porsche 911 turbo and Carrera 4 and the Lamborghini Diablo VT (these have permanent drive on the rear wheels, of course). Volvo is a new player in this field and its latest all wheel drive offerings also use this scheme, with an unusual cocktail of limited slip devices thrown in, namely a traction control system at the front and a regular mechanical limited diff in the rear. Several magazines have found this system to be in need of further refinement.
Next came the torsen (stands for TORque SENsing) differential, which was embraced by Audi in its second generation quattro system. Audi was approached by FF development (owners of the VC patent) during development of the original quattro back in the late 1970's but the VC was rejected for reasons that will become clear shortly. The torsen diff was invented by an American company (Gleason corp.) and had all the advantages of the VC and none of its disadvantages. It is a fully mechanical device of worm gears and a worm wheel whose workings are quite difficult to describe with words and probably beyond the scope of this article. However, the torsen's characteristics is the issue that is of interest here. The torsen differential will split torque 50:50 in a no-slip condition. However, when one axle slips, the torsen diff will send more torque to the axle with more grip, in other words, it works in an exactly opposite way to a conventional diff. Torque splits of up to 80:20 are available, depending on the pitch of the worm gears. And since it is a completely mechanical device, the locking action is instantaneous and progressive as opposed to the VC, which has a very slight lag for the viscous fluid to heat up and suddenly lock. The torque sensing characteristics of the torsen also allows it to be proactive in preventing wheel spin rather than reactive, in correcting a wheel spin situation. The torsen diff is thus "more sensitive" to slip than the VC. Its locking action is also more progressive. (Porsche also rejected the VC in the 964 Carrera 4 because they felt that the VC was too difficult to control and that it had exponential rather than linear locking characteristics.)
More importantly, the torsen does not lock or inhibit speed differences under braking, thus allowing all 4 wheels to rotate independently at their own speeds when no power is applied. The torsen diff only locks in a power application situation while the VC locks both during acceleration and braking. The torsen has a torque sensing characteristic while the VC has a rotational sensing characteristic.
The VC's rotational sensing characteristic initially caused lots of problems for the engineers. Anti lock braking systems rely almost entirely on speed differences between the 4 wheels to detect a locking wheel. Thus, when the transmission tries to force 4 wheels to rotate at the same speed, it creates serious difficulties for the ABS system.
The engineers had to use a variety of hacks to get around this problem. Mitsubishi delayed ABS for a while for its first generation GSX, then finally decided to make ABS and rear VC limited slip mutually exclusive options. The VW syncro system simply disconnected four wheel drive the moment the brake pedal was stepped on via a secondary clutch. Most other vehicles using this implementation of VC have a very similar disengage feature. The very successful World Rally Championship Lancia Delta Integrale even went as far as to apply a little bit of power (via the engine computer) to reduce the drag of the VC when the brakes were applied! Some very crude systems used a overrun device that is conceptually similar to the bicycle crank. This meant that while four wheel drive was disengaged during braking it was also inoperative when reverse was engaged!
The easiest hack was to reduce the effective viscosity of the fluid in the coupling, so that the drag was reduced. This also meant that the VC's locking effectiveness was reduced, which is probably quite acceptable for a vehicle intended primarily for paved roads. The VC's attraction is its simplicity and cheapness, not its sophistication.
In the late 1980s Porsche and Mercedes were treading slowly and came out with all wheel drive vehicles of unparalleled complexity. Mercedes' 4Matic system used the ABS sensors to determine wheelspin. In the dry, the Benz was a rear wheel drive car. When the wheel sensors determined that the rear wheels were spinning, a signal was sent to the computer to start engaging a hydraulically actuated multi plate clutch to send power to the front wheels. Clutch engagement was progressively altered by the computer. When the computer determined that even more traction was needed, a second clutch would start locking the rear diff. When the brake pedal was pushed, both clutches disengaged instantly to allow ABS to work without interference.
The Mercedes 4Matic was a part time, automatically engaging four wheel drive system. The reason given by Mercedes why they went to great pains to design a part-time four wheel drive was that they did not want to upset their loyal clientele with a full-time four wheel drive, which because of the driven front wheels, would "change the traditional feel of a Mercedes". One could also speculate that they were too proud to use anything less complicated than Audi, which in the marketplace is considered "lower". In practice, the 4Matic system worked no better and no worse than the other crop of full-time four wheel drives, but its cost and complexity made it look bad. This original 4Matic system has been ditched and the latest 4WD Mercedes is now a full time system, including the system to be used in the "M" class SUV. The Nissan Skyline GTR uses a system that is conceptually similar to the original 4Matic.
Porsche used a similar system of locking clutches (though they are implemented quite differently) as the Mercedes in the limited production, state of the art 959, but the center diff (which is actually just a hydraulic clutch) was engaged at all times except when parking so that the steering would be easier to turn. Torque split in the 959 varied with load and conditions. (via the progressive locking of the clutch). Unlike all other implementations of all wheel drive, the 959's torque split varied under no slip conditions. i.e. In every other all wheel drive system, the split is fixed until slip occurred, after which the various limited slip devices would begin to alter the split. In the 959, the all wheel drive computer is fed information from many sources, including the throttle position, steering angle, g force accelerometers and even the turbo boost gauge. In a straight line, under maximum acceleration, the system will send up to 80% of the power (from a normal 40 front/60 rear split) to the rear wheels, even if all 4 wheels are turning at exactly the same speed. This was by far the most complex and sophisticated all wheel drive system ever built.
The 959 was followed by the 964 which was first introduced in 1989 as the 911 Carerra 4. Porsche claimed that this was an evolution of the system used in the 959 and is even more advanced. However, this was a fixed split system like all the others, with computer controlled clutches acting as limited slip devices. The 964's trump card, however was that the speed sensors and accelerometers were used with the computer controlled locking rear differential to cure the 911's natural tendency to oversteer if the throttle was suddenly lifted off in a turn. The rear diff would start locking when the computer detected that oversteer was imminent. A locked rear diff would induce understeer, which in turn countered the oversteer. Through the use of all wheel drive and smart differentials, Porsche was able to tame a formerly unruly beast into a much more docile animal. This, according to their chief engineer was their main reason for implementing all wheel drive in the 911, as the 911 with its rear biased weight distribution is not in a real need of extra traction.
In 1993 Porsche updated the 911 with a brand new rear suspension. Even the rear wheel drive version was tamed and thus the justification of using a highly complex computer controlled all wheel drive system disappeared. The four wheel drive version of this 911 (alias the 993), has a much simpler, lighter and cheaper part time automatically engaging VC system such as those found in the Golf syncro and most minivans. However, the smart rear differential that fought the deadly oversteer was retained to quell any remaining tendency to oversteer. The new watercooled 911 (aka 996) C4 uses essentially the same system as the 993 C4, but with additional computer controlled stability assistance tweaks. It is somewhat disappointing to see that Porsche, once the clear technological leader in this field retaining the viscous coupling in its latest AWD offering while many other new AWD offerings such as the new VW Golf 4Motion and 1999 Jeep Grand Cherokee resort to more sophisticated designs.
Subaru deserves mention here because in the automatic version of the Legacy and Impreza (including the Outback variants), it uses a computer controlled system much like those found in the Mercedes 4Matic, automatic Audi A8/V8 and the earlier Porsches. Subaru has been offering this sophisticated system for a long time in a relatively inexpensive car. Much more recently other makers have started offering conceptually similar systems. The Honda CR-V, the 1999 VW Golf 4Motion and its derivatives such as the Audi TT now use a system that is conceptually similar.
The Audi A8 (as well as the automatic version of the Audi V8) also used a computer controlled clutch to lock the center differential, in a manner similar to the systems just described. The automatic transmission supplied a ready source of hydraulic pressure to lock a pack of clutches, so it was tapped. This system represented Audi's first successful mating of automatic transmission with quattro all wheel drive. Current quattro models with automatic transmission use a center torsen differential with the exception of the A8.
Traction control
For all its technological glitz in the 1980s, all wheel drive cars eventually turned out to be a commercial failure with the exception of the niche brands like Audi and Subaru. In the late 1980s there were all wheel drive offerings from every major manufacturer as it was the latest fad. Many of these manufacturers have since dropped their all wheel drive models in favor of highly profitable truck based sport utility vehicles or SUVs in short. For the cars a more simple and inexpensive alternative was there waiting to be exploited.
Anti-lock braking systems have speed sensors on two to four wheels to detect differences in speed between wheels so that the computer could intervene and "pump" the brake on the locking wheel. By a few simple extensions to the system, it could be made to brake a spinning wheel, thus effectively transferring power to the one with grip. More sophisticated systems would reduce engine power to further slow the wheelspin, but generally speaking, traction control is merely an optimization of two wheel drive using ABS technology.
Current versions of Audi quattros (dubbed quattro IV) use all wheel drive in conjunction with 4 wheel traction control. Under no slip conditions, power is delivered 50-50 to the front and rear via a center torsen differential, which would take care of limiting slip between the axles. The traction control system would take care of limiting slip between each wheel of a given axle. Thus for the first time, the quattros have to lose traction on all 4 wheels before they become immobile.
The prior generation of quattros had center torsen differentials (except A8/V8) and manually lockable rear diffs which locked it solid. This featured automatic unlock at speeds exceeding 15 mph to aid the forgetful driver. The V8 quattro had a torsen diff in the rear and either a computer controlled clutch in the center (for automatic transmission) or a torsen (manual transmission).
The new Mercedes ML320 (and ML430) SUV uses a relatively simple implementation of open differentials and four wheel traction control. This implementation has been criticised from several sources as being inadequate. The main disadvantage of the M class AWD implementation is that excessive demands are placed on the brakes under extreme conditions and the system can also be prone to hunting. Zexel engineers found that if a torsen center differential is added to this system which would act before the onset of wheelspin, TCS brake activation would be reduced by over 50%. The presence of this data suggests that Mercedes might have gone a little too far in cutting costs by eliminating limited slip or torque sensing capability in its center differential.
Torque splits
The subject of torque splits has been quite misunderstood. Basically, every four wheel drive vehicle with the exception of the Porsche 959 has a fixed split when there is no slip. For the full time systems, 50-50 is common, but also not unusual is 60+% rear 30+% front. The latter is usually found on cars that started life as rear wheel drive vehicles, while the former on cars that were originally front wheel drive.
For the part time VC systems this ratio is usually quoted as 95% front, 5% rear. Some have argued that the 5% constant rear drive would qualify it to be considered a full time system. Regardless of the merits of this argument, the fact remains that the main reason why there is a dribble of power going to the rear wheels is because a little "slip" is deliberately engineered into the driveline to keep the VC tight, so that when the front wheels spin there is little or no lag before the rear wheels start driving. The VC in this implementation always thinks that the front is slipping slightly relative to the rear even if all four wheels are running at exactly the same speed. Slightly different final drive ratios are used to achieve this.
The conventional idea of slip suggests a scenario where one or more wheels are spinning when the vehicle is operated under slippery conditions. There is however an additional concept of slip to consider. Recall that the front wheels travel a greater distance compared to the rears in a turn. Thus to a limited slip device sitting on the center differential, the front axle is "slipping" relative to the rear. The limited slip action thus directs more power to the rear in a turn. For nose heavy vehicles such as Audis, this effect reduces the amount of driving the front tires need to do, thus allowing them to be used for increased turning power. This small dynamic optimization in torque distribution allowed Audi to greatly reduce the terminal understeer experienced in the first generation cars.
Consider the case of the Mercedes ML 320 SUV where with four wheel traction control and an open center diff. When one end loses grip completely, the system would transfer some power to the other end. Theoretically speaking, if one were to jack up the rear end of the vehicle off the ground, the system could potentially transfer 100% of the power to the front, making it a front wheel drive vehicle, and vice versa. In reality since traction control merely pumps the brakes rather than lock the spinning wheels completely, less than 100% of power can be transferred to the front.
The point to note is that quoted torque splits like 37/63 only apply when there is no slip. Given the extreme example above of one axle being jacked up off the ground, a AWD system with any type of limited slip devices can theoretically go from its nominal split of say 50/50 (or whatever it may be) to 0/100 or 100/0 depending on how solidly the center limited slip device or 4 wheel traction control system locks. Mercedes does not quote the percentage locking factor on its traction control system, so one cannot really tell what its true variations of torque splits are under extreme conditions. Part time manually engaging systems with no center differential as well as early full time systems such as the first generation quattros with manual locks can have the variation of going between 100/0 front/rear and 0/100. These extreme variations also mean that no speed differences will be allowed between axles, which is why most modern systems never achieve 100% transfer of power. A 80% locking ratio would allow the speed differences of turning wheels to occur without interference.
A system that can lock the center diff solid would also mean that each axle will have to be engineered to be able to handle 100% of the engine's output, when in reality it would be loaded no more than 50% most of the time. This would lead to a virtually indestructible system with a life that would far exceed the rest of the car. The downside is that the doubling of rotational masses would make the car sluggish when moving off the line, affecting automatic transmissions variants the worst because these tend to have a higher (numerically lower) 1st gear.
Stability management systems
An emerging trend in vehicle dynamics development is the use of "stability management systems", which use much of the ABS and computer controlled AWD hardware to further optimize all available grip. The more sophisticated AWD systems will reproportion the power distribution according to available traction at each wheel, leading to a very safe and neutral feel when powering out of a turn. However these systems do not work if the driver lifts off the accelerator pedal completely in a turn.
Recall that Porsche progressively locked the rear differential to handle such a situation. The latest 996 Carerra 4 will in addition to this, selectively brake individual wheels as needed to stabilize the car when it is driven in a clumsy manner to its limits. Specifically it will brake the inner rear wheel to correct an understeering situation and the outer front wheel for an oversteer. This is done independent of driver input. Stability management systems have started to appear in other more expensive car models and will undoubtedly trickle down and be as common as ABS one day.
Consumer considerations
Many potential buyers of all wheel drive cars wonder if the extra "stuff" would mean more problems or if the system would lead to heavy penalties in fuel consumption. Real world experience has shown that all wheel drive systems are not known for any kind of teething problems. The probability of an extra set of driveshafts failing has turned out to be as probable as a V8 engine failing because it has double the number of cylinders over an inline 4. This is a good analogy because with the power split over more wheels, the drivetrain is less stressed.
Those implementations that rely on ABS wheel sensors to lock differentials would be as likely to suffer from problems as any car with anti lock brakes. i.e. no greater than average.
In fact, many of the suspicions of all wheel drive come from the world of manually engaging part time systems where attempts were made to make four wheel drive engagement less cumbersome, with features such as automatically locking hubs and/or "shift on the fly four wheel drive". An all wheel drive system is always engaged and is actually simpler because it eliminates the need of these convenience "features" and their associated parts, which are the usual source of problems.
Accusations that four wheel drive wastes a lot of gas is only applicable to part time manually engaging systems. A full time system with a center diff has none of the tire scrubbing waste of the former. Furthermore, research by Audi showed that as tractive loads built up, the tire losses of two wheel drive exceeded the losses caused by the extra weight and inertia of a full time four wheel drive system. Tire losses were found to rise disproportionately with load. Consider the extreme case of the "burnout" or wheelspin scenario, where 100% of the tractive energy is converted to burning rubber rather than propelling the vehicle.
Part time, manually engaging versus full time/part time auto engaging
Part time, manually engaging four wheel drive systems also make it extremely difficult to have a decent suspension set up. For cars with front-wheel steering the front wheels have to travel a greater distance than the rears in a turn. Because there is no center differential, the rears would therefore have to scrub its excess speed and in doing so, lose some adhesion for cornering. With less grip in the rear, the vehicle becomes oversteery which to an average driver does not constitute safe behavior. The result is that a lot of positive camber is applied to the front, making the front wheels resemble an upright "V". The effect is that the front wheels now have a smaller contact patch and thus less grip in a turn. Remember that all this tweaking is to make sure that the vehicle is semi neutral in four wheel drive mode. When four wheel drive is not engaged, which is typically the majority of the time, one is left with a hopelessly understeery vehicle, because the front still assumes a rear end that has to scrub off excess speed. Anti lock braking, if offered will also be inoperative in four wheel drive mode, just when it is needed the most.
It does not take much to see that this is a very suboptimal implementation compared to all wheel drive systems, which are on the other extreme of being able to dynamically alter the division of power to each axle depending on which end is sliding. The behavior of a full time or part time auto engaging system is completely predictable and is therefore optimizable to dramatic effect.
Average consumers also tend to dismiss the need for good handling. The line "I am not going to race this vehicle" is repeated often enough. However, even if we were to judge vehicles solely as appliances, good handling does enter the equation. A good handling vehicle, such as the many excellent all wheel drive examples mentioned, will hide the difficulty of negotiating a turn, making it seem more effortless. The average driver would then feel more comfortable and confident and will therefore shed less speed entering a curve, leading to less momentum being lost, which in turn means that the vehicle does not have to consume energy reaccelerating back to its original speed. In other words, it would be a more energy efficient appliance. This point is hardly ever raised when discussing the appliance value of vehicles.
It is unfortunate that old fashioned part time, manually engaging systems are still being sold on many SUVs today with high prices that are a match for their mediocrity. There is no reason, from a conceptual point of view that these vehicles should not have an all wheel drive system. It is this author's opinion that consumer ignorance and a uncritical media are the main reasons for the slow progress in the truck/SUV market.
It is false that a permanently engaged system is incapable of handling the rigors of off roading as well as the antiquated part time system. The Range Rover has been on the market since 1976 and it has had a full time system with a center differential since the very first one rolled off the production line. Likewise, the ultimate off roader, the Hummer uses a permanently engaged system with torsen differentials rather than solidly locked axles and part time manual engagement. Both of these vehicles are held in the highest regard with respect to their off roading capabilities.
The 1999 Jeep Grand Cherokee is significant for being the first mainstream mass market SUV to feature an AWD system that is more advanced than most of its peers. The Grand Cherokee uses hydraulically controlled progressive locking differentials on both front, rear and center resulting in a system that can deliver all available torque to any one wheel if it is the only one with grip. Unfortunately this highly advanced AWD system is merely an option and consumers who are suspicious and distrustful of technology would end up buying the much cruder 4WD/AWD system which is not necessarily more reliable because of its multitude of selectable drive options.
4WD/AWD vehicles today
Audi and Subaru continue to successfully market all wheel drive vehicles and both marques actively compete in motorsports to show the worth of their technology. The Audi A4 quattro has been particularly successful in demolishing its two wheel drive competition in seven major touring car series last year despite severe weight handicaps. The Subaru Impreza turbo has been extremely successful in World Championship Rallying. The Mitsubishi Eclipse GSX has been less successful in the marketplace, with the vast majority of buyers opting for the front wheel drive version. Die hard Porsche enthusiasts prefer the rear wheel drive version of the 911 to the all wheel drive version. Four wheel drive is increasingly outlawed in competition because they tend to do too well.
With the success of sport utilit

Um, that is quite possibly the LONGEST post I've ever NOT read.

Holly SHi+, that is probably the longest post I have ever seen next to Joel Gat's stuff!! BAHAHHAH
Sorry, I have nothing to add, but this. I was playing with a friend of mine last nite. He has an older rx7 (I dont know nething about them, so dont ask) NEways, its snowing out and he does a cool little 360 in front of my house, and then I was gonna follow him out to do some donuts. Neways, when we get ready to leave, he cant move. I am on a <u>SMALL</u> hill and his car was unable to move 4 feet!!!!! HE actually had to roll backwards and turn the wheel to straighten out. I couldnt stop laffin!! BAHAHAHAHAH I just pulled right out with no problem.
My point:
RWD kicks ass.
In bad weather RWD goes no where!
AWD kicks ass
In bad weather AWD GOES!
Main point.
get awd and stop arguing about which one makes a differnce.
thank you and have a nice day
Keith
bored at work http://www.i-club.com/ubb-files/smilies/biggrin.gif

Sorry guys I didn't realize it was so long. It didn't seem that long when I read it. Next time I'll just post a link.

Point is AWD is better than RWD, and I learned something about the 50/50 split under now slippage.

Anyway if you ever want to know about AWD there you go, and try not to fall asleep.

Kinda odd I missed this thread till now. I actually own 2 RX-7's, wanting to get an RX-8, but instead of waiting, have been looking at Impreza's.... http://www.i-club.com/ubb-files/smilies/smile.gif Kinda want AWD for my practical car though, my '93 is less than decent in anything but dry, smooth pavement.

[] Mike McLeish Jr.
[] 1993 Black Mazda RX-7 (FOR SALE)
[] 1988 Red Mazda RX-7 Turbo
[] RX-7 Club of Indiana / TeamFC3S

Any more current news on the RX-8?!
When, how much $$ & what kind of transmission?

Just caught the post. I'll run it back.

ProgWRX - to answer your question about the 12K tach, it's probably not just for looks. Rotaries aren't RPM limited by mechanical stress like many piston engines. The redline is really more of an indication of powerband than it is a necessity. The IMSA GTP drivers would often throw an early downshift on the 4-rotors to setup more power on the exit. Testing of last RX-7 did not reveal mechanical failures until ridiculous RPMs.

I love rotaries. If the last RX-7 was not so unreliable, I would not be on this board today. I truely belive that if the development that has gone into the convention IC engine went into the rotary, we would be making much more power with less fuel consumption than the current standard. Since this is not the case, I hesitate to spend my money on a peripheral port rotary design. I have not seen anything to convince me that the apex seals will hold up any better than the first gen. Thoughts?

Joel

I would say if you can wait and you don't need a car right now, wait for the new Z!!!! It looks bad ass, and should be fast than the RX8 or WRX!

RX-8 = Torqueless
WRX = torquey

RX-8 = Expensive
WRX = Cheap

RX-8 = NSX
WRX = GTR

:D

Originally posted by Eby
Not exactly. Read this test: http://www.subaru.co.nz/autocar_feature/autocar_content.html

The STI out handled some of the best hanlding RWD cars in the world.

That is a pretty cool article... I would have loved to be in on the testing for that. An M3, 911, Elise, and a WRX. (I don't care much for Puegot's, you can have 'em. :) )

/bill

Originally posted by WRXRob
Hashiriya,

That is totally false. If AWD can be made to outperform RWD in all conditions, then why are most road race cars RWD? Why are F1 cars RWD? Clearly, if AWD was such an advantage, they would be using it.

That's like saying turbos suck, b/c if they were any good, every race car would have them.

Got me thinking if there are any photoshoppers out there that would put a Intercooler on a Nascar!;)

I was interested in the RX-8 as well. The reason I went with the WRX is because RWD is not practical here in Madison. AWD is gonna be much more user friendly. I do love the RX-8 though.

rx-8 is going to be pretty expensive, so I don't really see how you can compare the two. They are totally different from each other. This is like comparing the wrx to m3 or corvette.

Man. When I first saw the new RX-8 I could not contain my drool...err I mean excitement =). But then I started thinking about some things. I live in Colorado and so I wouldn't beable to drive it for about 5 months out of the year. I would lose 20% of those lovely 250 horsies up here.

That's why the WRX was so perfect for me personally. I mean with all the new cars coming out my decision was fairly easy when I figured in the fact that I could NEVER buy another NA car again since I live at altitude.

The only thing I would consider in your case is this. Do you have another vehicle to drive in the winter. Becuase I grew up in Nebraska/Iowa and the winters there are very cold and usually very snowy/icy for the majority of the winter. So it seems to me that if you can get past that then go for it. Although they have rumored a slightly more expensive turbo RX-8 variant coming out pretty soon too =). NOW THAT would KICK ARSE!!

yesterday i went to a mazda dealer.
he had recently been in a sales rep meeting that said it would be 16-19 months before the car is released. he also said that was a change from the 12-14 weeks mazda was saying before. the botom line is there is gonna be a long wait for the car...maybe as long as the wait for a sti.

Originally posted by WRXRob
Yeah, but the races they were banned from were against almost exclusively front drive cars.

Here's a different example: Porsche GT3 vs. Turbo. Turbo has 60hp on the GT3, weighs about 350lb more, and has AWD. That said, it just barely beats the GT3 around the Nurburgring by only 3-4 seconds.
Actually when the quattro system was banned from most all of the Touring Car Series, BMW was one of the teams screaming for the ban.
Another good example of RWD vs AWD was in the IMSA Trans-Am series back in 1988 when Audi Quattros entered the series for the first time and simply destroyed all of the RWD cars (and the Audis had less hp, also)
My thoughts on the subject are that, everything else being fairly equal, driven properly, an AWD car will always be faster through a road course than a RWD car.
A RWD car might be considered by many to be more fun to drive though.
As to someone's comment that if AWD was better then Formula 1 would be using it...I believe that it is not allowed by the F1 rules. The rules are extremely specific, for example they even specify how many millimeters a wing must be from the road surface.

Well, I have test driven a A4 and a subie... and the nose of the car just don't wanna turn!! maybe I'm not used to driving 4WD cars, but the Audi rep was raving about his 1.8 TT and how he thinks it can outhandle my RX-7. Is it me or the 4wd cars do tend to understeer a weeee bit?

Bigred4:

You probably got this by now, but the question itself, "AWD vs RWD" is very ambiguous since there are several diff types of AWD systems(due to diff types of diffs).

Subaru's VC uses 50:50 split on front/rear wheels until slippage occurs(manual transmission). For automatics, they use something else more sophisticated (VTD? or something else.. forgot) and will split the power to 45(front):55(rear).
They did this to give automatics a bit sportier feeling, but not sure if it really works that way.

I think the only reason most sport cars use RWD is that AWD has more power loss than RWD wheels especially at the higher speed. Unless the racing was done on the gravels, water, or the snow just like world rally, AWD will probably bring higher powerloss for needless stability on the dry pavement. I know you still need stability under very high speed racing, but they will probably go after the extra power than increased in stability(as the driver could be taught to handle such case).

I am not an expert on all this, but Subaru's AWD DOES increase the stability no matter what, from what I experienced.