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4WD & AWD systems explained

1377 messages,  Last post on Dec 05, 2009 at 1:47 PM

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#31 of 1377 William by drew_ Feb 11, 2001 (6:18 pm)
The Quattro system (but only with the Torsen - Torque Sensing - diffs) is superior...kind of, sort of, to the BMW/MB systems. The reason for this is that it is almost purely mechanical, and can react almost instantaneously to even a small amount of tire slip.   As you know, I think, Audi's Quattro is split 50/50. Audi has also started using using traction control, but only to distribute the torque side to side. They used to have 3 Torsen diffies before (front/centre/rear) and that was complex and pricey...which brings us to the next point. The problem with the Torsen based Quattro system is its high cost, as well as fairly high weight. As such, Audi has started using a Haldex clutch based AWD system for their TT and the A3 (not sold in N.America) partly because of this. This system is actually more reactive than proactive, but it's very quick and hence that makes up for some of the differences between it and the Torsen system.   The Passat's 4-motion system uses the A4's Torsen based Quattro system since it is basically a lengthened, but de-contented version of the A4. It shares all of the benefits, but also the disadvantages (the acceleration times are not very quick).   Subaru's manual transmission AWD vehicles and the new H6 VDC Outback wagon have permanent AWD (50/50 split and 45/55 split for the VDC OB). Subaru's auto tranny vehicles (excluding the VDC OB) have full-time AWD systems which are partly proactive like the MDX's system. Power is transfered to the rear upon acceleration, as well as in 1st, 2nd, and reverse gears. The Toyota Highlander and the RAV4 both also have a 50/50 split in no-slip conditions. I suspect that the new Toyota Matrix hybrid small SUV will have the same system.   FWIW, a torque split ratio of about 50/50 produces very neutral handling, but some consider it boring. This is why BMW and MB (for the cars) have reverted to a RWD biased AWD torque split ratio. To emulate some of the RWD feel of their RWD vehicles. Frankly though, I really don't think that MB 4-matic owners care too much about that 2WD feel. I certainly don't.   As for the suspension system, no, not that I can think of in N.America anyway. The Lexus LX470 and Range Rover both have pneumatic air suspension systems (R.R has had it for decades), as does the '00+ MB S-class.   Drew Host Vans, SUVs, and Aftermarket and Accessories message boards
#32 of 1377 re:drew #24 by rrmcdonald Feb 11, 2001 (6:23 pm)
Drew/William: thanks for the clarification (I went and re-read post #2 - duh!). I was looking at MDX vs. Highlander FWD with traction control or Highlander with AWD (I understand the Highlander AWD is permanent unlike MDX). No one has the Highlander AWD with traction. This is one of the factors I am considering between these two. I likely won't be driving in snow (unless I take it north for the holidays) but we have lots of hard rain with slick roads in FL.
#33 of 1377 rrmcdonald by drew_ Feb 11, 2001 (7:06 pm)
We get a lot of rain in Vancouver as well and if you choose the Highlander, I would recommend that you get the AWD/VSC (which is stability & traction control) version of the HL. With the wet roads, the FWD with TRACS may cut (especially when you're starting out and in intersections) and that can be annoying. I know because just a couple of years ago I was also occasionally driving a '99 Toyota Camry XLE V6 with TRACS. Being a long time RWD/AWD/4WD driver, I was constantly frustrated by the lack of traction in many rainy/snowy situations. It was enough for us to get rid of the car after 1 year of ownership and 6600kms.   Drew Host Vans, SUVs, and Aftermarket and Accessories message boards Replies to this message: tearlach (Nov 21, 2009 7:29 am) ateixeira (Nov 21, 2009 3:01 pm) tearlach (Nov 22, 2009 4:16 pm) and 1 more...
#34 of 1377 Drew by wmquan Feb 11, 2001 (7:16 pm)
Thanks for the great explanation about Quattro. I do remember a long time ago you mentioning that it was excellent but expensive. Wow, three Torsen differentials in past vehicles. I'm also more impressed with the 4-motion now too, I had always (and wrongly) assumed it was a cheaper implementation.   As far as mechanical reliability, which is sometimes a function of complexity, is today's Quattro any more difficult / expensive / problem-prone than other systems?   And is it issues (cost?) in integrating automatic transmissions that causes Subaru to not have permanent AWD in their automatic tranny vehicles, except for the H6 VDC?
#35 of 1377 Drew by rrmcdonald Feb 11, 2001 (7:31 pm)
Thanks for your response. Unfortunately, we haven't been able to find an AWD with the VSC option. Have found FWD with VSC or AWD without it.
#36 of 1377 rrmcdonald by drew_ Feb 11, 2001 (8:00 pm)
Your dealer should be able to order the vehicle to your specifications. They don't like to do this, but it is definitely possible. Have you considered purchasing out of state? Read through the Toyota Highlander topic, and you will find customer recommedations for dealerships.   To see a major reason why VSC is beneficial, watch this video clip. FYI, skids usually occur before rollovers, so if you can prevent a skid from occuring and going out of control, the probability of rolling over will be significantly reduced as well.   Drew Host Vans, SUVs, and Aftermarket and Accessories message boards
#37 of 1377 Drew by rrmcdonald Feb 11, 2001 (8:15 pm)
Nice video. Thanks. I am surprised MDX doesn't offer VSC.
#38 of 1377 William by drew_ Feb 11, 2001 (8:19 pm)
Yup, 3 torsens. Overkill for a street vehicle, don't you think? Audi prides itself on having state-of-the-art AWD technology though, so in the past, just about anything went. Did I mention that you could even lock the front, middle and rear differentials via dashboard switches in some of the older Audis (1980's era)? Wow!   MB's and BMW's AWD systems are actually relatively simple compared to Audi's system (hence the significant cost and weight savings). As you know, much of the work is electronically controlled. I would think that they would be cheaper to maintain in the long run. Then again, Audi has been in the AWD business for many years as well.   VW did initially want a different (called Syncro) AWD system for the Passat. However, it wouldn't be very cost effective to design a whole new system when the sister company has a (proven) system right there and then. FYI, Skoda and Seat (also VW owned, I think) use the Torsen & Haldex Quattro systems as well.   I'm currently watching a segment on the restyled VW Passat and I have to admit that it looks pretty good. Those new HID Xenon headlamps are impressive, and no doubt borrowed from the Audi division. Like just about all factory Xenon headlamps, lighting performance is improved by 250%. Now, if only the standard warranty was longer than 2 years...the price is also pretty close to a basic ML320. Wow...the new C230K coupe is also being covered in this MotorVision segment.   Drew Host Vans, SUVs, and Aftermarket and Accessories message boards
#39 of 1377 rrmcdonald by drew_ Feb 11, 2001 (8:27 pm)
Acura may choose to add their version of ESP/VSC, called VSA - Vehicle Stability Assist, in future MDX's. The MDX's wider track (vs other mid-size SUVs) and VTM-4 AWD does somewhat make up for the lack of a stability control system. The AWD cannot assist in a skid the same way that stability control can though, simply because it does not have any sensors/computer controls that tell it that the vehicle is not going the direction that the driver is pointing the steering wheel.   As I mentioned, perhaps Acura will decide to add VSA in future versions of the MDX.
#40 of 1377 Drew - Minivan AWD / 4WD by wmquan Feb 11, 2001 (8:33 pm)
What type of AWD/4WD system do the Chrysler minivans have?   By the way, you said with authority that the next-gen M-class won't arrive until 2004 (2005 model year). Any news on when the MB 4Matic minivans will be on the scene?

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