FishBike

I re-read one of the documents I downloaded a while back from techinfo that goes into some detail about how the center differential is controlled. The translations into english are sometimes... not the best.

Anyway, there are a bunch of different control strategies described:

"Start up and low speed turn control". If I'm reading it right, when starting from a stop, the center diff will normally be locked (the document says "directly coupled before starting the vehicle"). So it doesn't wait for wheelslip to occur, it always starts up that way. The "low speed turn control" part of this is that based on steering angle, it will reduce hydraulic pressure to the center diff clutch when turning at low speeds to allow it to slip. Otherwise the car will handle really strangely when turning (as you might have experienced in a traditional 4WD vehicle when you lock the center diff).

"Slip control at vehicle start up" seems to follow on from the one above, when you start moving with the steering wheel turned. This watches for excessive difference in front vs. rear wheel speeds and will re-lock the center diff if this happens ("directly couple the center differential immediately" is what it says).

Once you get up to speed, it moves into "slip control" mode, which again watches for speed differences between front and rear. This time though, it says it only applies enough pressure to the center diff clutch to limit that speed difference. This mode only kicks in at medium or high speed driving when not accelerating.

"Acceleration control" is the final one, that also only happens at medium or high speed, but when accelerating. This one again watches for front vs. rear speed difference and locks up the center diff ("directly couple" is the phrase used again) if that happens.

The traction control system is actually independent of all this and is handled by a different ECU and described in a different document. That's the one that uses the ABS to stop individual wheels from spinning and reduces throttle to control wheel spin. RWD cars have this as well, AWD cars just do it for the front wheels as well as the rear. And all of these ECUs talk to each other (e.g. the 4WD ECU gets wheel speed inputs from the ABS ECU, steering angle info from the steering ECU, etc. etc. etc.) Then there's the stability control that tries to keep the car pointed in the right direction by braking individual wheels... there's a lot to this!

SW17LS

Just wanted to update on this. My wife had our twins on the 16th, so I've been leaving the Jeep for her and driving the GS through snow that I normally would just take the Jeep for over the past 1.5 weeks, most significantly last Saturday. It really is excellent in the snow, so impressed. White knuckle drive up 270, totally unplowed roads with about 6-7 inches on them and it never felt overwhelmed, always solid and in control. Towards the very end as I approached my home I started to feel like it was getting so deep that it was dragging the underside of the car. Went back out later that day and took the Jeep as snow totals got closer to a foot.

Very happy with the GS in the snow, wouldn't even worry about taking the Jeep until it gets to 6 inches or so...

yardie876

Congrats! Hope you're getting enough sleep.

sick21

Lol my thoughts exactly. Odds are, he's not. He might start lashing out on us!!

Fwiw, my RWD w/summer tires is still stuck in the driveway

SW17LS

Yeah, if I come across particularly nasty in some threads you'll know why haha

99alta

Congrats on the new additions to your family! Kids are awesome!

Thought I would chime in here as I had a bad experience with my brand new GS AWD with the Michealin MX4's. About 5" of new snow and first time on snow with this car, used to driving a FWD TL which is great in the snow.
Turn a corner, touch the gas and the *** end slams into a curb Not good for the wheel or bearing lol
The dealer put new 18" wheels on and Michelin IceX3's. Since then we've had a ton of snow and guess which car I drive in nasty winter conditions now?

The difference is night and day!! The cars fun to drive now and feels like it's on rails compared to the all seasons! If the *** end does move out a bit, give her a little gas and pull youself around the corner!
Deep snow, no problem! Just the other day I was driving and the snow was deep enough the undercarriage was dragging. But I could still stop and go with no problem!
Amazed!
But you do need winter tires so the AWD and Trac. Control will work as designed, which is very good

SW17LS

Thank you!

I think this has more to do with you being used to the FWD TL and how it behaved vs the the RWD biased GS. The rear will kick it on you if you apply throttle in a turn, and VSC or not if you aren't used to correcting for oversteer (which you wouldn't be in a FWD car) you can get into trouble. I've driven RWD cars so much in the snow that correcting for the oversteer just happens naturally for me.

Even with all seasons (they are new, but still all seasons) I'm very impressed with the car.

Need is a relative term. You definitely need them up where you are, but here where we don't get a ton of snow, and typically winter temps are in the high 30s on a cold day (this winter notwithstanding lol) we don't really need winter tires.

That day last Saturday when I was out in the Lexus and it was really bad, temps were 16-18 degrees, and even with the all seasons I was doing great. It'd be even better with winter tires.

Nobeanspls

I got the awd F sport yesterday and today it's sleet all over the place. On 19inch wheels with all seasons the GS was very stable. I am very impressed as I just traded in a Awd Rav4 with snow tires and this car did not do any worse. Not all awd are created equal. The system on this car is good.

dinachroek

hey guy, this is from my experience.
My sister have an IS, and her tires are michellin, and I have the GS my tires are Bridgestone.
i can't stress out how much I like the michelin tires better in the snow. when i drive my GS it get slippery when i turn or stop. but when drove my sister IS, it handle much much better. hope that help..

zicogold

Thanks to all, for the Blizzak LM32 tire recommendation. A couple of weekends ago we got a fair bit of snow together with wetter conditions. This made for very greasy roads and the GS would struggle to grip on stops and fishtail on starts. The car gripped after about 10 min of driving (warmer tire compound perhaps) and engaging the snow mode mitigated the fishtail starts.

FishBike

This being my first full winter with the GS and those same tires, they're definitely much better in snow than the Michelin all-seasons. And really good in dry (but cold) conditions, unlike some of the even more aggressive winter tires. Because of the how the AWD system works, when moving off from a stop in a straight line, there is enough traction to climb a wet mirror (center diff locked).

When moving off around a turn, a little bit of caution is still needed. Snow mode definitely helps. The main technique I found to work the best is, give it enough gas to get it rolling, but then DON'T give it any more as the initial acceleration fades - just hold that throttle position until you're around the turn and pointed straight again. This is needed because with the steering wheel turned, the center diff doesn't lock until wheelspin occurs, so if you just give it a bunch of gas, the tail will briefly kick out.

Whenever I feel like the GS+LM-32s is not doing so well in snowy conditions, I notice other cars actually having an even worse time, and also I can barely walk on the snow when I get out. Some of those snow falls we've had in the past few weeks have been really very slippery!

JTMav

I've been running Blizzaks on my cars for years and have been very happy with them. With the year we have had here in Boston I can't tell you how happy I am to be running winter tires right now. It's all about the tire and the rubber compound especially when it get as cold as we have had it this year not just the snow.
YMMV
JTMav

GregCanada

I'm running Blizzak WS80's on my AWD GS - it does great. However, when it's more than 6" i prefer to drive my tacoma with winters - mostly because if someone rear ends me it's alot less hassle to fix. I also cant tow people out of ditches with the GS

Honestly i wont drive in a car in the snow that does not have snow tires. It's way too dangerous - like driving slicks in the rain.

Mcb345

Just acquired a 2015 GS AWD F-Sport on Saturday and Sunday morning had to drive 350 miles from OH to IL. With 3 inches of new snow on the ground the car pulled out in to an unplowed street like a champ with no slipping at all and even with highway speeds of 70-75mph rolling through slushy/wet conditions it always felt planted with plenty of grip.

These Michelin all-seaons are 10x better in slippery conditions so far compared to my previous tire on my Acura TL, the Bridgestone Turanza EL400. The Bridgestones had terrible grip whether it was dry, wet or snowy and these Michelins seem to have very very good ratings on tirerack.com which gives me some reassurance.

Since I'm leasing I didn't want to have to fork over extra $$ for a 2nd set of tires for the winter and I was praying I wouldn't see any Bridgeston tire on the GS. I'm VERY thankful to have these Michelins. I'll be taking is slow and steady the rest of the winter with my all-seasons and will just have to make up for it in the summer when I can really open it up and push these tires to the limit

FYI - In my opinion, if you are looking at a GS and see the Bridgestone tires on a particular car, look elsewhere for a car with the Michelins instead (or Dunlop maybe?), you'll be very grateful you did in the long run, especially after that first rain or snow storm!

jhyphen

Yea, I'm pretty happy with my GS in the snow as long as you get rid of those bridgestones(AWD) It is quite capable. I'm running Pirelli Cinturato P7 All Season Plus 235/40/19 and I haven't been stuck once during our 104+ inches of snow we had this winter. Going up unplowed hills I even stopped on hills just to see if I could continue up and I did, with no problem. I'm a believer in the AWD system of the GS 350. I think Lexus did a great job with this car.