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#254 of 828 AWD's Mysterious capability. . .saving fuel?!? by markcincinnati Feb 25, 2006 (6:06 pm)
The following "discussion point" has been moved from the 2/25/2006 LPS sedans discussion of AWD and its "certain" widespread adoption (IMHO.)   Regarding the quattro AWD drive line:   The total weight penalty is ~ 165 lb more than a contemporary rear-wheel drive. And, in the spirit of full-disclosure, there is extra friction from the extra drive-line components and the required “supporting cast” of technology, e.g., the oil seals.   The burning question becomes, how does this additional weight and friction manage to produce an apparent “synergy” that actually saves fuel?   Well, for a long time it was a mystery to Audi’s engineers, too. Dr. Piech has been quoted saying, “Our tests repeatedly showed that the car with four-wheel drive had a higher top speed and used less fuel than the same car with two-wheel drive. [And] it took us a year to find out why.”   Here is a brief history of what was done to unravel this mystery. First Audi spent the equivalent of about $750,000 (USD) on a test rig to measure the power consumed at each stage from the engine to the wheels. Initially there were no surprises. As expected, they were losing up to 3% of total power in driving all four wheels (about the same as they lost with an automatic transmission – 1.5% - 3%.) Dr. Piech came to the conclusion that “the secret must lie in the tires.” The reason? There was nowhere else to look. But the tire manufacturers couldn't explain or support “why” either. Their dynamometer tests couldn't provide the information Piech and his engineers needed.   They ultimately unraveled the mystery via a test program run on a so-called “rolling road” – and, not in Germany but in a US lab which was able to plot the power consumed by a tire throughout its entire operating range.   Piech knew that a tire driving a car consumes power. Likewise, a tire under braking, or [negative] torque consumes power. Furthermore, even a tire that is rolling freely also consumes [some] power.   Here, however, is a not expected finding: The lowest power consumption recorded was with the torque input experienced in a four wheel drive car. Put another way, a tire taking the torque required for two-wheel drive absorbs significantly more power and the total of two driven tires which were being pulled (RWD) or pushed (FWD) along, was measurably greater than that of four driven tires. This means that given an “efficient” transmission, it is revealed that an AWD drive-line, in addition to all its other [performance] advantages, can save fuel.   Moreover, this fuel saving advantage actually increases with the power transmitted.   Some would argue that as power increases the need for AWD also increases (hmm perhaps Subaru has known this all along?) ___________________   The preceding is from several sources, however, the key "bibliography" is cited below.   ____________________ Bibliography:   R.M. Clark ISBN 1 85520 3030 Brookland Books Ltd Replies to this message: dhanley (Mar 08, 2006 5:14 pm) markcincinnati (Mar 15, 2006 2:06 pm) dhanley (Apr 04, 2006 11:35 am) and 1 more...
#255 of 828 AWD and snow by dfrancia Mar 06, 2006 (2:28 pm)
I am looking into a awd sedan ie. S40 G35 Has anyone driven any of these awd sedans in snow. Replies to this message: car_geek (Mar 06, 2006 3:13 pm) esf (Mar 07, 2006 8:25 pm) markcincinnati (Mar 08, 2006 5:47 am)
#256 of 828 Re: AWD and snow [dfrancia] by car_geek Mar 06, 2006 (3:13 pm)
Replying to: dfrancia (Mar 06, 2006 2:28 pm) While I haven't driven them all in snow I think that I have driven or ridden in enough of them to say that pretty much any AWD vehicle will get around pretty good in snow. Proper tires and ground clearance are things to consider. With sport sedans you are trading off ground clearance for handling. Most of the AWD versions of these cars will have slightly higher ground clearance but not as much as your average SUV. Getting around unplowed city streets and unpaved roads with a foot or less of snow should be no problem but venturing into really deep snow is best left for a proper 4WD vehicle/truck.   The other thing to note is what type of tires you will be using. All seasons are adequate for driving year round but if you are looking at several months of heavy winter driving switching to a dedicated set of winter wheels will provide the best traction. Some manufactures such as Audi provide performance versions of their AWD sedans that come equipped from the factory with summer performance tires. These will NOT work in snow and a second set of wheels/tires would be mandatory with such a vehicle. So pay attention to the type of tires that come on the vehicle.   So other than that, it would make sense to concentrate on the other features of the cars to help make your decision, as the AWD systems will perform pretty much on par with one another in the snow. One other thing to keep in mind is that AWD only helps get your moving (which can be a really good thing in slippery conditions), it will have no positive effect on how quickly you can stop This is where having the dedicated winter tires will help..... Replies to this message: esf (Mar 07, 2006 8:25 pm)
#257 of 828 Re: AWD and snow [car_geek] by esf Mar 07, 2006 (8:25 pm)
Replying to: car_geek (Mar 06, 2006 3:13 pm) Something odd that I've noticed is that my A3 2.0T DSG FronTrak, which I got as a winter car beside my S4, is significantly better than the S4 in the snow (and the '98 A4 quattro that we sold when we bought it).   Maybe it's the winter tires
#258 of 828 Re: AWD and snow by _matty Mar 07, 2006 (11:24 pm)
Some manufactures such as Audi provide performance versions of their AWD sedans that come equipped from the factory with summer performance tires. These will NOT work in snow and a second set of wheels/tires would be mandatory with such a vehicle.   I've driven my S4 on snowy roads a few times this year. Even with performance tires I had no drama at all. Hills were not a problem either. I was amazed. I don't recommend doing this though unless you're very comfortable driving in the snow.   I've had my '06 S4 for 3 months now and 7K miles later I couldn't be happier. I admit though, I'm kicking around the idea of maybe trading it in on a new RS4 in a few months, but I may hold out for a couple of years and see if the 2008 RS6 gets approved for production. If not, I may have to at least check out the S6. Audi's decision to buy Lamborghini was pure genious. Audi is tapping the Lambo V10's as we speak and I can't wait to get behind the wheel of one. The engine specs on the '08 RS6 are already known- 550bhp V10 according to Motor Trend, but Audi is being real quiet about it and will continue to do so until after the R8 comes out in late 2007.
#259 of 828 Re: AWD and snow [dfrancia] by markcincinnati Mar 08, 2006 (5:47 am)
Replying to: dfrancia (Mar 06, 2006 2:28 pm) You have picked, deliberately?, two cars that approach AWD very differently.   Volvo's version is 95% FWD "at rest" and can move power in reaction to wheel slippage.   Infiniti's version is biased "at rest" to be an RWD car, and the faster it goes, the more RWD-like it becomes. It, too, reacts to wheel slippage and shifts power where it is needed.   Most of the primary and secondary roads eventually are plowed to a reasonable (whatever that means) depth after a snow event. Having said that, during the snow event or during the plowing, the depth of the snow may be greater than a normal ground clearance sedan can straddle, so to speak. Even with pure winter tires, even with studded tires if the depth exceeds the ground clearance, no AWD system is of much use.   I, too, have done things I do not suggest others do -- I kept 4 UHP Z rated summer only tires on a 2003 Audi allroad through the winter here in SW Ohio (which normally is very "moderate" insofar as snow accumulation is concerned.) In one year, however, we did have a bad winter season (for a couple of days) and although I was never stranded, the tires were less than desirable.   The main advantage of UHP all season tires is their resistance to cold temps, not their superior snow traction.   With the AWD systems, however, UHP All Seasons, even here would rarely be inadequate.   With either of the cars you have chosen you will find, broadly speaking, superior winter capabilities.   I would choose the car, however, on the other characteristics, capabilities and content given your two choices. If your only concern is snow traction, to underscore the point, flip a coin; and, based on your location, consider all season or two sets of wheels and tires.   The Volvo has ONE key advantage over the Infiniti -- and that is the Volvo S40 w/AWD (and a nifty turbo 5) can be had with a sport suspension AND AND AND a manual transmission. For me, the Volvo should only be acquired with the stick shift. Given your two choices if you must have the auto trans, go with the Infiniti for many reasons you will be able to glean here with some research on edmunds.   Drive it like you live.
#260 of 828 Re: AWD's Mysterious capability. . .saving fuel?!? [markcincinnati] by dhanley Mar 08, 2006 (5:14 pm)
Replying to: markcincinnati (Feb 25, 2006 6:06 pm) Well, that's a very interesting theory( AWD saving fuel ) but it seems highly specious. Every car i know of that's offered in FWD/RWD and also in AWD gets worse fuel economy in AWD. This includes audi torsen systems. The a4 front trac gets 23/34 and quattro gets 22/31, both 2.0T and 6-speed manual.   This is also borne out anecdotealy by acquaintances who have a particular car in both 2 and 4 wheel drive. The 4 wheel drive car always gets a few mpg less with the same driver/driving patterns.   I'm not saying it doesn't exist, but i can't think of one car that gets better MPG with an AWD drivetrain when it's also available with the same engine/tranny in 2wd. Replies to this message: markcincinnati (Mar 15, 2006 2:06 pm) dhanley (Apr 04, 2006 11:35 am) tradscott (Apr 18, 2006 12:04 pm)
#261 of 828 S4 as winter car by ateixeira Mar 10, 2006 (9:44 am)
You might say it has too much power. I'd get a winter beater too, if I had one.   -juice
#262 of 828 Re: AWD's Mysterious capability. . .saving fuel?!? [dhanley] by markcincinnati Mar 15, 2006 (2:06 pm)
Replying to: dhanley (Mar 08, 2006 5:14 pm) It has been so long since I had a 2WD car I can't recall if I, personally, would ever claim that an AWD car that one can actually purchase when compared with it's fraternal twin 2WD version saves fuel.   The point of my summary of someone else's findings was to present some findings that while perhaps specious may actually be factually based rather than "made up."   "This means that given an “efficient” transmission, it is revealed that an AWD drive-line, in addition to all its other [performance] advantages, can save fuel.    Moreover, this fuel saving advantage actually increases with the power transmitted."     There are data that support the preceding. The info to most of us would be darn near arcane. And, despite its apparent veracity, I am not in a position to even be interested in fully attempting a full-blown "Myth-busters" on it.   A college professor I had, as if that makes much difference these days, said "you need to make certain what you are reading (and writing) has the requisite verisimilitude" for you and from you.   I was probably 19 and had little idea what verisimilitude meant -- so, being the dutiful and well-trained son of a librarian, I looked the word up and I can conclude that the stuff written (and summarized by yours truly) seems to represent and contain the "requisite verisimilitude."   I can imagine many reasons why my production Audi A6 quattro gets a mile or two lower mileage than an otherwise identical 2WD version would get. This does not mean, however, that I think Piech's (or whoever's) "discovery" of the potential for improved economy is bogus.   You, after all, may be right -- but just because something seems to be counter-intuitive, doesn't mean that it is inaccurate.   I am not suggesting a lengthy Thesis Defense is needed. If you find it is bogus, and want to dispute it, that is OK with me.   At this point, even if the study were false, I find many more compelling reasons for the widespread adoption of AWD than reasons to the contrary.     Replies to this message: dhanley (Apr 04, 2006 11:35 am) tradscott (Apr 18, 2006 12:04 pm)
#263 of 828 Am I Alone? by esf Mar 30, 2006 (9:29 pm)
Seriously! Not one person has posted here in fifteen days!   IT'S BEEN TWO WEEKS, AND I CAN'T THINK OF SOMETHING TO SAY!     Replies to this message: markcincinnati (Mar 31, 2006 12:12 pm)

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