SPUDMTN

I know that the SH-AWD works great and that on paper it is the most technologically advanced all-wheel-drive system out there. But how does it compare to the other AWD systems out there? Can anyone compare the various systems, and can anyone compare the systems by means of experience with the various systems?

SPUDMTN, who is patiently awaiting an auto mag comparo between midsize-lux AWD sedans (or special feature on the various AWD systems)

CGTSX2004

iTrader: (1)

Let's compare...

SH-AWD : FWD bias during regular driving. 70/30 front rear power split. Capable of 30/70 split under certain conditions and capable of actively sending all of the power in the rear to either wheel during hard cornering.

Quattro: FWD bias during regular driving, rear differential is not always engaged. When the front wheels begin to lose traction, powerful is diverted from the the front to the rear via a Haldex differential. 4MOTION on the VWs is the same thing. Maximum of 50% power transfer to the rear.

4Matic: All-time AWD system with 50/50 (I think this is right?) split. Capable of transferring power forward or backward depending on traction with up to a maximum of between 60-70% at either axle at any time.

X-Drive: RWD biased with 35/65 power distribution. Capable of transferring power forward when rear loses traction. Maximum of 50/50 split.

ATTESSA-ETS: RWD bias (or fwd depending on application, but let's assume the G35x for now). 100% power to rear except when traction lost. Maximum of 50/50 split. Capable of actively transferring power between front and rear axles.

So essentially, the SH-AWD takes the ATTESSA-ETS system one step farther by using an active rear differential. Many of the AWD systems simply split power between front and rear with an open differential between the left and right wheels. SH-AWD uses an open differential up front, but an active differential in the rear with an active differential connected to the transmission to allow the power to be routed depending on the computer's sensor inputs.

rets

CGTSX2004, you have said everything I could know and even put more stuff into this excellent comparison post. Points for you.

CGTSX2004

iTrader: (1)

Thanks, man!

BarryH

The Volvo R's have a very similar system to to SH-AWD. Using a special Haldex setup, 90% of the power can be directed toward the rear wheels. It reacts to wheel spin in 1/7 of a tires rotation. In addition, the 4C system has accelerometers positioned througout the car to determine pitch, yaw, and lateral forces and proactively transfers power front to rear to prevent over/under steer. Steering wheel angle, speed, and the position of the accelerator are also monitored. SH-AWD can shift power left to right (rear wheels only) while the R's accomplish the same thing through the use of ABS. The R's 4C system is adjustable which changes the suspension/performance behavior pretty dramatically in each of three modes (comfort, sport, advanced sport).

http://new.volvocars.com/r/us_index.asp

phile

The SH-AWD system is pretty much almost the same as every other advanced AWD system out there. Its main difference is that it can transfer power from one wheel to another wheel...on the same axle. The only other system that comes close is Nissan's ATTESSA, which cuts off power to the inside wheel so that the outside wheel can accelerate - but unlike SH-AWD, it does not transfer power. Everything else just sends power from front to back and vice versa, but not side to side.

CGTSX2004

iTrader: (1)

What separates SH-AWD from the other AWD systems is that AWD doesn't require wheel slippage to transfer power. It actively monitors vehicle motion to determine where power can best be used and then routes power to those wheels. Other AWD systems react to slippage and wheel spin, but aside from the ATTESSA-ETS, no other system actively shifts power quite like the SH-AWD.

SPUDMTN

Very cool...however, how does the system do in real life? Let's say snow. Do we have any real life experiences where we can compare the various systems? We know which should theoretically work the best, but which really does? Does any of this new technology really make that big of a difference?

phile

I know that when I was at the NY auto show, the video highlighting the SH-AWD on the RL concept had it going through snow as well as tarmac. My guess is that Honda has optimised SH-AWD for performance as well as bad weather.

BarryH

Not true. The Volvo R's proportion power based on vehicle dynamics, same as the RL. The only difference is SH-AWD transfers power across the rear wheels which the Volvo accomplishes with ABS. And all AWD cars react to slippage, even the RL.

phile

How? I would assume the ABS just cuts off power, like the Nissan system, whereas SH-AWD actually transfers power from wheel to wheel.

CGTSX2004

iTrader: (1)

That's exactly the difference. By actuating the brakes, the Volvo system forces the differential to route power to the other side. SH-AWD allows the computer to tell the rear differential to force power to the outside rear wheel in a turn.

first99TL

Great description, but you have missed one of the most important parts of the system which is why it is called SH. In addition to transfering up to 100% of the power to either rear wheel, the system will also accelerate the outside rear wheel during cornering producing yaw that improves it's handling ability. The difference is quite remarkable and reminds me of the difference between skiing on shaped skis vs. the old straight ones. The car corners amazingly well!

biker

Then why does a simple RWD M35 with 20HP less beat the RL at the track? As has been said many times before, AWD only helps to start in slippery conditions with the right tires. In most other cases it does nothing for you (and the extra weight works against you). The only thing the SH-AWD adds to the current RL is slightly better track times than could have been achieved had they had left it FWD like the last generation - and without saying lots of fodder for the marketing guys.

CGTSX2004

iTrader: (1)

That's all fine and good, but I would like to see the AWD M35x in a head-to-head comparison against the RL. The M35 has a significant advantage in weight (I think it was over 200+ lbs) which made a huge difference. Cut down that weight advantage with the auto tranny and AWD system and then let's see how the two cars compare. That 2 sec. advantage the M35 had, I think, would disappear.

first99TL

From your original post: "Road Course - Believe it or not the M35 ran 1'10 in Tsukuba circuit, the RL was in the 1'12 range. The staff praised the RE050A tires on 19" rims and the torquy engine with the M. The only complain was that it's hard to hook up the car on corner exits where the M35 left long trails of black rubber mark from the inside tire. (Eh? No LSD!?) The RL was very composed and handled corners very well, the SH-AWD allows the RL to carve through corners with ease and hook up immediately at corner exits. Still...... losing by 2 seconds is a pretty big deal.

And the M35 is no lightweight at over 3800lbs."

Doesn't sound like the M handles all that well. Leaving rubber and can't "hook up" up on corner exits. This is the classic problem of AWD and probably shows that the car exhibits understeer. Also with 19" rims and higher performance tires, I am not surprised that there was a difference. I think we need a rematch using similar wheels and tires.

By the way, have you driven the RL?

Bitium

Yes 4-matic if better in that sense, but it does need something more than momentum like wheel slippage or lost traction.

Well SH-AWD has the best of both worlds, safety and performance. While I personally think 4-maitc is better for safety (theorectically) because, 4-matic can shift power from all 4 wheels to all 4 wheels (front, back, left, right). In other words, it could take power from any of the 4 wheels and transfer that power to the other 3 wheels. In that aspect is smarter than SH-AWD, because SH-AWD can't shift power in the front axle. 4-matic works with ESP estability control, and something needs to happen for the system to activate, not including just cornering. Cornering is where SH-AWD outperforms any other AWD system out there, because it predicts the car's tragetory, it reads the car's motion, yaw angle, speed, throttle position and G-force. The system sends up to 100% to the outer wheel of the power allocated to the rear axle which is a minimum of 30% and a maximun of 70%. This in fact creates a inward momentum to help the car achive the corner easier. It also has an acceleration device, that allows the rear wheels spin at the same speed the front does. This helps reduce draging, making the car feel like like it was riding on rails. In making a big different, just it does. I know the comparisson with the m35, but if you have the same car, same power, same everything, except one has SH-AWD and the other FWD, RWD, AWD. SH-AWD will outperform on the track everytime.

Is not an acomplisment, is call stability control or traction control, all companies will have a different name for it. Any car with stability control will react to slippage as well as traction control. The only difference between staliblity control and traction control, is that stability control goes one step further by trying to control under and over steering somthing SH-AWD does without braking. The RL SH-AWD works with VSA when slippage is detected to control the affected wheel. What he was trying to say is that the RL does not need something to happen except for cornering for SH-AWD to be activated. In other words no traction needs to be lost for the RL SH-AWD do its job, this is something the 4-matic and other AWD system need.

read above. It does not accelerate the outside rear wheel, just sends the power to that wheel, which will accelerate the car. It does not produce YAW, it knows the YAW angle of the car, it produces inward momentum or defects the outward momentum.

first99TL

Not true. The following is from Acura's own description of the system.

"SH-AWD ingeniously varies the amount of torque to the left and right rear wheels. When cornering, a planetary gear set overdrives (or accelerates) the outer rear wheel faster than the average of the front wheels to dramatically enhance the cornering, steering feel, overall handling and stability of the RL. The result is class leading cornering precision as well as enhanced traction.

Direct Yaw Control System Theory

SH-AWD counters understeer under power with the Direct Yaw Control System. Spinning the outside rear wheel faster than the average speed of the two front wheels allows the system to use engine power to yaw the vehicle while turning. By relieving the front tires of some of the work of turning the car, the system reduces understeer and the vehicle stays balanced and controllable. In addition, with the cornering load more evenly distributed between the front and rear tires, the total cornering grip is increased. In conventional cars, cornering is created almost entirely by the steering angle of the front tires; In the RL, cornering is created by steering angle of front tires combined with the extra drive torque supplied by the outside rear tire.

This is a significant advance over conventional drive systems. To deal with high power output, front- or rear-drive systems generally use some type of limited-slip device to maintain traction under power. The linking effect of the inside and outside drive wheels in these systems resists turning, however. This is a factor that works against the front tires as they attempt to turn the car. Conventional AWD systems have a similar linking effect between the inboard and outboard tires and front and rear axles, causing a similar resistance to turning. This is part of the reason why traditional AWD systems typically lack the more nimble feel of the best two-wheel drive systems. By using drive torque to actually help turn the car, the RL can be more responsive, neutral and predictable, while simultaneously offering all of the usual benefits of all-wheel drive. "

8-)

Next time I see that RWD get defeated by the snowy hill, I'll be giving lots of thought to my AWD RL's poor track time as I casually blow by it.

BarryH

What you're saying is true, but 4C isn't a stability control system. It actually stands for Continuously Controlled Chassis Concept. It's a totally seperate sub-system available only on the R's that monitors the car's dynamics and makes changes to the suspension and power transfer 500 times a second to improve handling and braking. There are about 14 different sensors and gyroscopes positioned throughout the car to sense what the car's doing and compares it to the driver's intentions based on steering wheel angle, increasing vs. decreasing speed, acclerator position, and gear selection. It's actually a lot more comprehensive than SH-AWD and also controls the suspension setting at each wheel dynamically. The only thing it doesn't do that SH-AWD does is transfer power left to right which it accomplishes through the ABS system. Even then, SH-AWD's power transfer only effects the rear wheels. Follow the link in my original post if you want to understand what 4C is.

rets

Thanks.

biker

Like I said other than slippery starts.

If the conditions are such that a RWD car with snows can't make it up a snowy hill, either the RL won't make it either or one should not be out driving.

biker

I don't have to drive it - the track times speak for themselves. Besides, other than discussions on forums like this virtually no one cares about track performance (for this kind of car). Everyday driving is what counts - and for that you don't need any kind of AWD unless you live in the snow belt. Like I said SH-AWD is a great thing for the salesmen and marketing guys but average Joe Public could care less (again with the caveat of living in the snow belt).

I live in Switzerland where lots of cars have an AWD option (there's a Corolla down the street with AWD) - very few folks who live below 1000m (3000ft) in altitude opt to get AWD - just not needed.

8-)

Wrong.

8-)

Biker: Do you see many studded snow tires where you are at?

I never see them around here, not for lots of years.

first99TL

I would really recommend that you actually drive the car. It would give you a new perspective on what an AWD car can be. I own an AWD Volvo that has been very good in inclement weather. I bought the RL because of it's handling capabilities. I don't have any interest in taking it to the snow.

Living in Switzerland, you might find that the car puts a smile on your face as you drive some of those beautiful backroads in both Winter and Summer. Beleive me, the SH is more than salesman and marketing hype.

Joe Public

BarryH

I have an AWD and a RWD car, both with snows. The problem with RWD is that only two wheels have a chance at gaining traction. In a AWD car, you have two more opportunities. Where I live it's hilly and icy. The AWD car can get up the hills because power's transferred between all of the wheels and at times, only one wheel can bite. The RWD car loses traction than the DSC kicks in and throttles the engine back so you're more or less stuck. Turn the DSC off and the car fishtails while trying to get traction. FWD performs no better than RWD with snows with the exception that the added weight over the drive wheels can increase your chances of gaining traction. Once moving, they're all pretty much the same unless the AWD system is smart enough to compensate for an individual wheel losing traction while driving at speed. Stopping, where most accidents occur, they're all the same.

biker

Sorry to say - you're no Joe Public. Joe Public does not hang out at car forums (especially the typical RL owner).

I might have let the un-needed (to me) AWD system in the RL pass while considering the car if only it came with an MT.

BTW, the new Legend has yet to be made available in these parts.

machination

Could it be the sport-suspension tuning, larger, more aggressive tires, and lower weight perhaps?

Like CGT said, just wait until there's a head-to-head rematch with US spec AWD models. I'd bet money that 2 second advantage will disappear.

dseag2

Sorry, but I can't agree with you there. You've obviously never lived in So. Florida where we get several inches of standing water within a few minutes during our summer downpours. When you take that into consideration, AWD definitely DOES serve a purpose outside of the snow belt. When I had my A6 Quattro I used to pass other cars like they were standing still during rainstorms. I'm sure my FX w/ AWD and RL w/ AWD will perform the same.

Ken1997TL

I would say the biggest difference is that the RL's SH-AWD system is pro-active rather than reactive to loss of traction. It anticipates such events, enhances safety AND performance.

To me, complexity and cost are the only real downsides.

wavshrdr

Something else that Audi does on most systems is they use the EDL system or electronic differential lock. Depending on the car this could be on the both the front and the rear. Also many Audis use Torsen or multi-plate hydraulic clutches and not only Haldex for the center diffs. With this system an Audi can normally take off even if only 1 wheel has traction so in effect it could transfer 100% of its power to any individual wheel.

The RL system seems somewhat similar to the system that Honda had on the old Preludes to improve the handling of the FWD cars but adapted to an AWD platform.

biker

I'm sorry to say that's one of the stupidest reasons I have yet heard to get AWD. Those other people were going slow through standing water or a down pour because that's the smart thing to do not becasue they lacked AWD.

Rob L

biker,

why argue about something you have NO EXPERIENCE with?

Also, it is not stupid to bring up AWD use in the rain.

As for the track comparo, as others have said, first just look at the tires involved with both cars. If you dont think tires play a huge role in handling/track times then you have some serious learning to do. Go slap the same rubber on the RL and see how it does...

I just have to chuckle when I read people who have not even driven the RL go on about its AWD system and criticize it. Having come from a very good handling RWD car (Lexus IS300) I can tell you the system in the RL does wonders in the handling department. Hell, even that track test article said the system in the RL made it cut through corners in a great way. Why then act like the system is useless with respect to dry pavement handling?

I would like to see the RL with some good high performance summer rubber on it since the all seasons on it now are known to be conservative in handling.

Why do people feel the need to argue against fact? The fact is the SH-AWD system in the RL is great and gives the car impressive handling.

tompd

As for driving in the rain... California is getting some pretty good rain showers right now. I was passing cars left and right heading over Highway 17 to Santa Cruz. Not even needing to slow down because of the "slippery" conditions.
Mind you, I didn't drive unsafely, just the speed limit or a little bit over. All other cars were doing 10-15 mph under.
SH-AWD Is great! (just my $.02)

lindros2

Sorry this is an old subject but I want to correct something.

"quattro" is NOT the same as "4Motion" except in the B5 (last-gen) Passat (which used Audi engines). quattro (currently on generation 5) utilizes a TORSEN (torque-sensing) differential, and requires longitudinally-mounted engines. Although it's expensive my A4 quattro actually retained $2000 more Blue Book value than a non-quattro car (and the new-car option was only $1650 at the time).

"4Motion" (which uses the Haldex clutch system - same as on Volvos) is called "quattro" on the Audi A3 and TT. It can use transverse-mounted engines, and is the method going forward for all VW cars (see: new Passat uses it with transverse VR6 engine).

hondamore

The most amazing thing about the SH-AWD system in the RL is how EASY it is to drive. Yes, a professional driver on a closed race track loves to step the back end out around a corner in a RWD car and the weight advantage of the RWD gives faster track times, but the whole point of the RL is that ANYBODY can drive the RL quickly and have wonderful control at all times, including snowy conditions. If you put two 55 year old accountants at the wheel of an RL and an M35 out on a race track, I'd be quite confident that the RL would run circles around the M35. Add snow or rain to the mix and I believe the M35 would be lapped regularly.
I'd also like to add my 100% agreement with first99TL regarding tires making a huge difference in race track lap times. Remember, however, that whatever benefits 19 inch wheels and summer tires gain on the race track (a place that the vast majority of M35 or RL drivers will never find themselves) they lose on bumpy roads and wet or snowy roads (where we all find ourselves on a daily basis). That said, the OEM tires on the RL are marginal and upgrading to proper rubber makes a huge difference, both on the freeway and on the racetrack.
To Biker, SH-AWD makes a huge difference to the RL's handling on dry pavement, not just in the snow. You really should go drive one and then you will understand.

kgd

I doubt I will ever drive the RL in the snow, but I love the AWD in the mountains. I drive on a winding mountain road each day on my way to work and I can assure you the AWD makes a huge difference. Even freeway driving you can notice the lack of FWD while accelerating. So I would disagree that what they have done makes no difference in real world driving vs. the track.

With respect to the track times for the M vs the RL, the rims and tires on the M (19" performance tires vs. 17" stock tire that was basically designed just to hold air) will account for much much more than the 2 second differential on the track times. I drove the demo RL with the 17" rims and stock tires and the car I purchased upgraded to the 18" rims with the Pilot Sport tires. The handling was much improved with the 18" tires. I also drove the M and can't imagine that the RL would not outperform it with similar tires. Its just my opinion, but I would not buy the M based on the fact that it will out perform the RL.

Kris

chickenprotein

however, Subaru WRX does the same thing except SH-AWD is electronical and WRX is mechanical..

AcuraRLBlue

It was snowing hard in Boston yesterday, and I was sailing safely alone while all others stopped or were slower. The only thing I was really worried was another car skidding into my.

I really think that the SH-AWD allowed my car to take curves alot more secure than most other cars on the road. It is not just simply another AWD. "Torque-vectoring" was the term used for the performance aspect of the SH-AWD. I think with the buggs I have had with this car, the only thing that puts a smile on my face while driving it is the AWD.