AWD comparisons

[Choleric]

They were arguing about it in the other thread so I just made a new one focusing on AWD cars.

Feel free to post any other comparisons I just started it with these.

Snow, Allroad, X5/3?, lexus, volvo, 5series, nissan

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Dry land, Allroad, volvo, suburu

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[Just_me]

Do you have videos of the latest system of Xdrive?

[EnI]

For any up-hill driving (also in perfect road conditions) also other factors are important: engine power & torque output, transmission, cars weight, tyres etc.

And looking at those cars I'm not sure all the other factors (except AWD system) were equal. If not, that is not a seriuos & credible AWD test.

Looks more like Audi commercial.

[klier]

Originally Posted by Choleric

They were arguing about it in the other thread so I just made a new one focusing on AWD cars.

Feel free to post any other comparisons I just started it with these.

Snow, Allroad, X5/3?, lexus, volvo, 5series, nissan

- ONLY REGISTERED AND ACTIVATED USERS CAN SEE ALL LINKS - CLICK HERE TO REGISTER

Dry land, Allroad, volvo, suburu

- ONLY REGISTERED AND ACTIVATED USERS CAN SEE ALL LINKS - CLICK HERE TO REGISTER

WOW!!! THANK YOU SO MUCH for showing me this video of a 10 year old BMW and making a whole new thread with the exact same info as in the other existing thread !!!!

What I have to say is this:

[Choleric]

Originally Posted by klier

WOW!!! THANK YOU SO MUCH for showing me this video of a 10 year old BMW and making a whole new thread with the exact same info as in the other existing thread !!!!

What I have to say is this:

No need to be an ass.
The other thread was suppose to be about AWD vs FWD vs RWD, so I started a new one.
I wasn't intending it to be showboating for audi or any other brand I was simply posting some video reviews that were available. I said if you guys know of any other ones post them.

[warot]

Enough of this BMW vs Audi thing. What I'm curious to know is what is MB doing about all this.

[martinbo]

Oh dear... here I go again. Sorry if I bore the pants off you but here it is:

Well then, it seems that there is a fair deal of consternation, misperception and conjecture being bandied about in this debate on which AWD system is superior. The sad fact is however, in plain and simple terms: there is no such thing as the perfect all-wheel drive in existence today. Some are better than others in certain aspects but no outright superior AWD system exists because of one simple concept. All wheel drive systems cannot be judged as merely drivetrains in isolation but need to be assessed together with the engine (including its placement and integration with the drivetrain) as a cohesive mechanical solution.

All wheel drive systems are in each example an object lesson in engineering compromise. Take Audi’s Quattro system for longitudinally mounted engines for example. It’s a magnificently elegant, symmetrical (more on the importance of that later) and compact design. However, it necessitates the placement of the engine ahead of the front drive shafts that emerge from the transmission casing, causing the wheels to be mounted further back relative to the engine thus giving the car an undesirable nose heavy front-to-rear weight bias. So, by hanging a big V8 or V10 ahead of the gearbox, Audi engineers then have to grapple with the extremely difficult task of tuning the front suspension to cope with all of that mass out front whilst still ensuring that the ride, handling and turn-in characteristics remain competitive. Ever noticed the A6 quattro’s jarring ride quality over sharp extrusions? Compromise. And certainly not a sensation that you’d experience in a 5 series.

Subaru’s symmetrical all-wheel drive suffers the same limitation, hence their adoption early on of the lightweight alloy boxer engine in an attempt to alleviate the situation somewhat. As a cohesive, integrated mechanical layout, Subaru’s is one of the more elegant and well-rounded ones out there. But it’s far from perfect. The benefit of Audi and Subaru employing this centre-aligned layout is symmetry, particularly important at the front axle where (because the front wheels are now given the duty of both propulsion and steering) equal length driveshafts negate the torque steer that results from uneven torque distribution caused by unequal length driveshafts. So, as far as all-wheel drive systems go, this layout interferes less with the steering loading and provides the best steering “feel”. Note that these types of AWD systems where designed from the outset to be all-wheel drive and never started out life as front-wheel or rear-wheel drive systems. Another important benefit is the balanced left to right weight distribution that such a layout provides.

A typical example of Audi’s longitudinally configured AWD system:


And here’s Subaru’s elegant and compact layout:


So, what of xDrive? As you’re all aware, BMW choose to mount their engines further back to achieve that hallowed 50:50 front to rear weight distribution. Hence, xDrive was engineered as a mechanical add-on or enhancement to this pre-existing layout. In that it necessitates rather more complex, bulky and heavy re-engineering in order to arrive at an all-wheel drive solution, BMW’s xDrive too is compromised in a number of respects. This is with particular regard to weight and maintaining a left to right balanced symmetrical drivetrain layout. The added complexity further compounds the inherent inefficiencies that characterise all-wheel drive systems: the loss of engine power reaching the wheels through driveline drag or frictional losses. The heavier and more complex your AWD system, the less efficient it is. This affects performance and fuel economy markedly. Note the large and heavy componentry and multi-clutch pack of the xDrive transfer case in the image below. Also note the external propshaft leading to the front axle and how this results in an off-centre front differential which isn’t desirable as this then necessitates the fitment of additional components to achieve equal length driveshafts. Quite a long way off the traditional BMW ethos wouldn’t you agree?




End of post 1 – continues…

[martinbo]

Whereas BMW’s xDrive systems relies almost entirely on electronic processing to work effectively as a true all-wheel drive solution, Audi’s Torsen equipped Quattro system does not. It is a purely mechanical system designed, not for off-road use – though it copes admirably with all types of road and track surfaces – but for a dynamic and infinitely variable on road driving experience through the use of the widely lauded torque sensing centre differential. BMW does not make use of a traditional, open centre differential to distribute power and torque front to rear in the same way that, say, Audi or Subaru do by virtue of a regular differential coupled with a limited slip device. So, BMW’s system relies wholly on electronics to even out the differences in axle wheel speed front to rear when cornering. It’s a drivetrain that doesn’t lend itself to abuse either in the way that Quattro or Symmetrical All-wheel Drive do. Standard launch procedures in an A4 quattro? Get the revs up to 5000 rpm and sidestep the clutch. Somehow that drivetrain manages to take all of that punishment without disintegrating into a thousand pieces. It’s a seldom published fact that BMW’s system doesn’t cope as well with such brutal treatment.

So, BMW have gone the route of an electronics-centric all-wheel drive solution and Audi have gone the mechanical route. Note, the AWD system in the Audi is in no way connected with the ESP system. ESP operates over and above the Quattro drivetrain as it would in any two-wheel drive Audi. It does not interfere with the operation of the Torsen differential directly. Now which one is better? It would be remiss of me to disregard the capability of xDrive based solely on its reliance on electronics. Let’s face it: modern electronics make cars work far far better than they ever did. In the engine, at the brakes, in gearboxes, in drivetrains and so on, electronics have enabled astounding progress in the capability of modern automotive engineering. Look at today’s modern engine? Where the hell would we be without knock sensors and lambda sensors and electronic fuel injection and variable valve timing and electronic throttles and (phew!) and…? Nowhere. So, step in electronically enhanced all-wheel drive. Electronics allow for precise, micro time-frame calculations that measure a loss of traction long before the driver is remotely aware of the problem. In doing so, a driver input that may cause traction to be lost is softly and imperceptibly adjusted by xDrive and the DSC (or DTC or whatever they want to call it) in conjunction to produce a fully integrated system that is able to dynamically react to any loss of traction, make the required decision and affect the necessary action (at engine, differential and brake systems) in a fraction of a second. This is why the xDrive systems perform so well in truly icy conditions. It’s all down to complete electronic intervention.

That’s not to say that xDrive is superior. The mechanical systems of the Audi provide for some of the most seamless, intuitive and enjoyable AWD experiences, around free from the constant intervention of the nannying electronics. Let’s face it, electronic systems save the day but a purely mechanical interface between the driver and the road is still deemed as being the most rewarding because it’s the most communicative and involving no? This is where Quattro in cars like RS4 shines. It’s an all-wheel drive system that was designed from the get go to enhance the motoring experience behind the wheel; it’s mechanically pure and hence unencumbered in delivering that “connected” feeling. This argument, admittedly, can be considered as being circular because no one can deny that cars that employ extensive electronic aids in their all-wheel drive systems such as the EVOs and GT-Rs of this world are equally enthralling from a driver involvement perspective. There just isn’t a right or wrong answer here…

Ultimately it boils down to consumer preference, because no post, no matter how long will solve the debate around which system is superior for on-road use in both good and inclement conditions. And that leads me on to the next discussion…

End of post 2 – continues…

[YoungWarrior]

Very good write up cant wait for post 3

[martinbo]

Originally Posted by YoungWarrior

Very good write up cant wait for post 3

When it comes to serious off-roading, xDrive and Torsen address only a fraction of the requirement for a truly capable off-road machine. This is not a discussion on driving on a dirt road; we’re talking about serious bundu-bashing on hardcore trails. This is where Gene is quite correct in his assertion that off-roaders are beasts of a wholly different nature. Remember, the golden rule of off-road driving: as slow as possible and as fast as is necessary.

In order for a vehicle to perform accordingly, it needs more than just a clever limited slip centre differential (Quattro) or hyper intelligent, hyper active electronics (xDrive). Believe me, an Audi Q7 will be just about useless off-road compared with a two-wheel drive, hi-rise suspension Mazda pick-up with rear diff lock. A real off-road vehicle needs good ground clearance first and foremost and anything under 220 mm is considered soft-roader territory. Furthermore, the approach, departure and (particularly) break-over angles are critical too. In order for a vehicle to go as slow as possible it needs a true 45 to 50 percent low range reduction ‘box. A locking locking differential is essential for serious off-road vehicles. This type of differential has the same parts as an open differential, but adds an electric, pneumatic or hydraulic mechanism to lock the two output pinions together. This not simply a limited slip differential. This device ensures that even if traction is completely lost at one end of the diff, the other wheel can still exert maximum torque on the surface with adequate purchase. In addition, the vehicle needs outstanding suspension travel and super strong suspension and chassis components.

Rocks and sand and ditches and river beds and logs break cars. That’s why, when doing serious off-roading, I trust only a handful of vehicles - most notably the Toyota Land Cruiser pick-ups and wagons and the Land Rover Defenders. I have extensive off-road experience in both and I know exactly why they exist. X5’s, Q7’s and ML’s are on-road vehicles with a measure of off-roading ability (the ML does come with an off-road package option which does enhance it’s capability significantly) and shouldn’t be used without due consideration when discussing off road ability.

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