FishBike

I haven't been able to find anything either, and I've been looking a lot (what else is there to do while waiting for delivery? )

There is yet more snow in the forecast here for the next couple of days. Can anyone think of a way to test what the snow mode is doing? I mean short of a fancy ramp with rollers on it, which I don't have. When I asked the dealer about this, they said it just makes it start out in 2nd gear. It feels like it is doing that, certainly.

In the last round of snow, my street remained unplowed, so I did a few laps around the neighborhood to try it out with snow mode on or off. It definitely felt different around the slowest corners with it on vs. off. The rest of the time it seemed about the same, which is not surprising given it was in 3rd gear most of the time anyway.

The other thing I am suspicious about is the "50/50" torque split. Looking at how the center diff works, there is a clutch that connects the front and back driveshafts together. That clutch is variable (not just on or off) but if it locks up firmly enough this should work like a locked center diff, which is anywhere from a 100/0 to 0/100 torque split depending on where the traction is. I think they call it 50/50 just because it's easier to explain that way.

NobodyHere

Just found a Lexus brochure which can be found here:

http://www.lexus.com/lexus-share/v2/...S-Brochure.pdf

Following clip is of interest:

ALL WEATHER DRIVE
By monitoring current driving conditions, available all-wheel drive automatically allocates engine power between the front and rear wheels from a rear-biased 30/70 (front/rear) torque split to 50/50, depending on conditions. This can provide improved traction and control on a wide range of road surfaces and in inclement weather.

So there it is!

DonOH

Good to know. Thanks for posting.

IS340

Finally actually used the AWD system in the snow! I agree, the car handles excellent, great acceleration, very efficient use of Trac, vsc, abs, snow mode. Mine is all stock with bridgestones, clearly effective AWD. I am happy! Who needs chains

GM11

Yes, this is what I had read that made me believe snow mode was 50/50 (and that the car handling does feel different to me, felt through the steering wheel) BUT reading it again now, it does not actually say snow mode is 50/50 by default - I inferred it. By "monitoring current driving conditions" I'd thought that would have meant pushing the snow button is saying to the car, I'm in the snow so 50/50 please. But maybe be this is all academic, the point is the car handles great in the snow.

SW17LS

No, I don't believe snow mode locks the differential 50/50.

You may not want 50/50 all the time in the snow...I like being able to steer it a little with the throttle in the snow.

FishBike

I'm also pretty sure the center differential clutch isn't intended to be continuously engaged. It's a friction clutch, so it would wear our pretty fast if it was having to slip all the time (say, if you engaged snow mode and then left it on when you got to dry roads). That clutch is the only way the torque split can be changed, it's 30/70 normally due to the design of the gearing in the center differential.

My main question about the system is how much the clutch is allowed to engage when wheel slip occurs. I suspect it's actually a lot better than just a 50/50 split under some conditions. I may have to find an ice patch to put the back wheels on, and see how much acceleration I get with the front wheels on pavement. 50/50 torque split would be pretty useless in that condition, so if it grips well, it'll be clear it can go farther than 50/50.

SW17LS

50/50 torque split wouldn't be useless in that condition. You would have enough torque in the front wheels to pull you out of that situation with just 50% of the available torque. Bear in mind that even with sophisticated SUV 4x4 systems a low range or locked differential for the most extreme situations splits torque 50/50.

FishBike

Here is where I think the mixed up terminology comes from: To me, 50/50 torque split means the torque applied to the front and rear driveshafts is always equal. This is what you get in a 4x4 with an open center differential. If you have no traction at one end, you cannot apply any torque to it, and the differential action prevents you from applying any torque at the other end either.

It's like what happens with 2WD cars with no traction control. They have a 50/50 torque split from side to side, and if one wheel is on ice and the other is on pavement, you go nowhere as the open differential can't send any more torque to the wheel with traction than can be applied to the one without. Torque to both wheels is always equal.

Our 4GS AWD is normally like that, just with a mechanically clever center differential that makes the ratio 30/70 instead of 50/50.

A fully locked differential doesn't have a defined torque split. It can be anywhere from 100/0 to 0/100 depending on how much traction is available at each end. I think that is closer to what is going on with our 4GS, where it normally has an open center differential, but with a clutch that can progressively lock it up. I kind of think "50/50" in the marketing literature means "capable of locking the center differential completely", which is much better than 50/50 in my book.

Anyway, not trying to argue, just trying to explain what the terminology means to me.

SW17LS

Correct...we're talking about the same thing...

Rexus300

iTrader: (1)

After a few weeks with winter wheels and Bridgestone LM32 245/40R19 tires, My car is phenomenal in the snow! I am not joking nor making the comment for the sake of it. Its truly leaps and bound better then the all seasons. The car slows to a stop well and I can turn hard with minimal slip from the rear. I can do a fast u-trun without losing much control. Sometimes I am too confident that I am driving 10mph faster the others on average. Sounds bad I know I know. BUT I highly recommend people to pay for winter tires and transform their cars during the winter time for safety reasons.

vinodc

Thanks for the update Rexus300. I've decided to hold off on getting the winter tires for now, since my car is a lease. But I will decide before the lease is up, if I'm going to keep it. If I do, I will most certainly buy those winter tires, I really think they can make a big difference!

Trek

I love my AWD GS 350 Premium. It came stock with the Michelins. I don't understand why some got a car with Bridgestones, although my 2002 Nissan Altima V6 came with Bridgetsone Turanzas and even with FWD, I had no trouble with the car even in Minnesota winters except getting up my slosh and sleet-covered driveway which had an incline.

The best AWD system I've driven is my on my 2008 Acura RDX. It's called "Super-handling" AWD, and it is phenomenal. Power shifts to any and as many wheels as needed. Two wheels, three wheels, one wheel....none of that front and back only stuff which is basic AWD. I'm glad I kept my RDX instead of trading it in toward the GS. I decided to bite the bullet and keep both.

On another topic, Acura has made many design mistakes and appears to be fading as a result. They've abandoned the SH-AWD in the RDX and the turbo (it was Acura's only vehicle with a turbo charger) to make the RDX a mommy mobile. It now has regular front and back AWD (the larger MDX still has SH-AWD) and two additional cylinders instead of a turbo charger. Boring. I also test drove the new RLX sedan before going for my first Lexus in the GS. My sense was the RLX has the usual phenomenal Acura quality build and reliability but it was boring to drive compared to the 2008 RDX and the Lexus 4GS. It was at least as roomy as the Lexus LS but in the same price range as the GS. The problem: FWD only (with rear steering) unless you go for the Hybrid model which costs (similarly equipped) in the range of a loaded MB E350 w/4-matic or loaded BMW 535Xi. Actually closer to the 550.

I'm a Lexus guy now, although the GS Premium/Luxury is the only Lexus vehicle that is acceptable. Lexus SUVs are elephants. A bunch of high-center of gravity, bloated whales, and the RX interior is hideously unattractive. The competition does SUVs much better, and the useless ES is an Avalon with different sheet metal. As long as they keep improving the GS, I'll stick with Lexus for now.

SW17LS

I'm not a huge Lexus SUV fan either, but the RX is the best selling luxury SUV by a WIDE margin. That "useless ES" also outsells the GS by about 4 times.

The RX and ES ARE Lexus...those two models make up more than half of Lexus total sales. The only reason they can make a car like the GS is because of the RX and ES. So for that...I'm a big RX and ES fan lol.

To add to the traction discussion, I just got back from a 700 mile road trip in the GS to WV to visit family. Our family home down there has a fairly long gravel driveway that has needed gravel for some time. Well...they had a LOT of snow, and then it got warm very quickly and the snow all melted very fast. The driveway had about two feet of standing water at the bottom, and was mud all the way up. I instantly wished I had brought the Jeep when I came down the hill and saw that as you can imagine.

Well...the GS rolled right through that water (up to the middle of the license plate in the front) and went right up that muddy driveway to the top, with the wheels spinning and the trac light blinking the whole way. My cousin's FWD Mazda 3 wouldn't do it.

As you can imagine my poor GS was FILTHY...finally washed it today...

zicogold

Read with interest the discussion between FishBike, GM11 and SW13GS about the the snow mode and the AWD system. This is what the service dept told me. The centre differential uses a planetary gear multi-plate wet clutch system to manage the slip and works with the ABS to control braking and throttle response. I got a chance to try out this system recently. I applied a heavy throttle with one or more tires slipping. The car's ABS applied brakes to the slipping tires and then throttled down the engine, despite I still applying pressure to the accelerator. The car then applies the required torque split through the front and back diffs and electronically managing the throttle. The car will return braking and throttle response to the driver when there is no slip at any tire.

I am told the torque split, ABS management is available full-time, so snow mode is for 2nd gear starts. So AWD does manage each wheel independently through the ABS. Would be interested what others have found out from their dealer or Lexus itself.