NateJG

Amplifying Vlad's post, see: http://www.caranddriver.com/features...e-test-feature

vlad_a

And if your vehicle came equipped up to door sills with LSDs, here's how you would take a turn properly :

vlad_a

Since we are a hybrid forum and talking differentials, none of the above complexities are needed if individual electric motors are driving each wheel.
No limited slips, no locking differentials, no mechanical torque-vectoring , no brake torque-vectoring. Even brakes are not a necessity in an all-electric implementation. Maybe even steering.

Toyota/Lexus hybrid AWD still has ways to go to be fully-developed. That's why GS450h is RWD only.
Acura is the one company that has taken a first stab at getting rid of the rear and center differential and replacing it with 2 rear motors:

Droid13

It's a neat idea and in an ideal situation 4 electric motors would be awesome, but I think cost will always limit this option, especially in all-electric cars that rely 100% on the motors (like Tesla offering their single or dual motor options).The RLX's rear motors are only 36hp each, just a tad more combined that the single rear motor in the RXh. It would be interesting to have something like that in the RXh to see how it does...

MellonC00

I was curious and began to look for popular cars with good handling and whether these guys had LSD. As it turns out they do, M3 has had it for for a long time. Ferrari 458 had it. Nissan Z had it. Volkswagen Corrado had it too. I understand some Corvettes had them too.

Here is an interesting question. From what I've been reading it's actually not that big of a deal in terms of cost and weight to incorporate an LSD into a front drive transaxle, which houses both the tranny and differential. Yet, I don't see too many cars that have it.

Another observation. All these cars you see on youtube with systems similar to VDIM, or electronic traction control with 4 wheel drive really don't do a good job in poor traction. They are all "jerky." the ABS grabs the brakes and let's go depending on the traction for that particular wheel but it's so slow..... it feels like I can do it with my own right foot.

and check out this testing. I guess there is a reason why subaru's are so well liked by the granola crowd up in the pacific northwest.

vlad_a

Of course all of sports cars will have some form of LSD. They simply wouldn't be able to apply all that power to the ground if they didn't. Even with LSD, most are still traction-limited.
Don't get me started on the Ferrari 458 e-Diff - it is pure magic, nonstop bliss, amplified by the sweet sound of high-revving V8.
Most AWD systems are not suitable for serious road conditions. I helped pull out plenty of stuck AWD crossovers.
While I had my STi, when we were done pushing cars out of a snowed-in parking lot, I was asked if I also needed help.
My reply was, no - I drive a Subaru. Subarus and Audis (A4+) were built ground-up for AWD architecture, Subaru even choosing to go with a boxer layout, as the engine sits longitudinally in front of the front axle to minimize its length.

Now, the electronics can be a very good supplement for an already capable 4x4 system, as the driver cannot control all 4 wheels individually:

Crawl control is available for Lexus GX as well, with some top (pricey) options.

NamesEd

I just got a 2011 RX450h AWD (with 18k miles, believe it or not). Two of the existing original tires have severe checks (did she run em flat?) so all four are going to tire heaven.
I live in Colorado, and ski a lot, so I want to get snow tires now, then next spring get new road tires. Then swap twice a year.

1. What are the best-ever snow tires for this vehicle? No studs, please, I don't like their noise
2. What are the best-value snow tires for it?
3. Any other advice is welcome

Current tires say P235/55R19 101V, for what it's worth. Yes, the 2011 has a snow mode.
Ski Country driving sometimes involves deep snow and steep driveways, and a bit more often, there's packed snow (sanded or not). Mostly it's freeway speed through slush created by a zillion gallons of magnesium chloride, sprayed from the backs of huge plows and even 18-wheel tankers. Black ice on a bridge is an occasional entertainment. About 10% of our traffic is morons who think having a "4X4" decal changes the laws of physics, plus another 5% who can't afford tires with any tread. I've driven snow for 60 years. This is my first hybrid.
Thanks! ...Ed

Htony

Snow mode is just different from AWD systems like Subaru symmetrical AWD, Acura SH-AWD, Audi Quattro, BMW X-drive. etc. I have to pay more attention driving out to my cabin in the mountain. I always use winter tires in winter. I am thinking about going back to Audi or BMW when my RXh becomes 4 years old. Honestly it is hard to trust snow mode 100% in the snow. Out of ~60 years driving, 50 years are in the
snow country.

NateJG

Please consider writing a more in-depth comparison of the systems that you’ve driven, as I suspect that I’m not the only one here interested in understanding Snow Mode's attributes better.

Htony

Simply real AWD has all 4 wheels independently vectored. Rear axle should have two motors for that. Acura MDX hybrid interestingly has two motors. Toyota/Lexus is very conservative implementing evolving technology. Nowadays most everything is done by software(firmware) control using fuzzy logic, AI logic rather than hardware. We have to keep up with technology. One reason why Toyota/Lexus is reliable(?)
I did not have looked at Audi, Porsche, BMW hybrid AWD. Few miles from highway to my cabin has rough road. One thing I feel is RXh rear end is too light. Feels like rear wheels are trying to float in deep snow.

Really it comes down to driver should understand fully what kind of vehicle (s)he drives tackling all terrains. Many are vehicle operators vs. drivers. Everything in life has a limit.

Droid13

I can't tell you which tires are best, as I'd like to know myself, but I can say I haven't been impressed with the Goodyear UltraGrip WRT I have. While I have to say they stop quite well in snow, which is guess is important, their forward traction is not good. Frankly, I find no difference in forward traction in snow between my Michelin all-season tires and the Goodyear snow tires, maybe the Goodyear snows are actually worse.

Regarding snow mode, this is just a little bit of electronic hocus-pocus for the most part. It does two things: a) puts the gas pedal in super-eco mode to make it harder to drive aggressively which might cause excessive wheel spin by an over zealous driver b) it adds more emphasis for the rear electric motor to stay active during acceleration.

In light to medium snow, you'll find the hybrid is a much gentler beast in snow. It's very tame to accelerate and control with the electric motors providing more precise traction control and if you are looking for this kind of experience in light to moderate conditions the hybrid is very, very good, perfect for the somewhat nervous driver. However, if you are looking to rock n roll your winter driving experience, well, maybe disappointment looms. I learned winter driving in the early 80s so I know how to rock n roll winter driving without traction control, VSC, and ABS. Nothing like driving an old Firebird with summer tires through deep snow but I made it work pretty well! Nothing like going up hills with the rear end at 45d angle rooster tailing snow off the rear wheels onto the sidewalk.

I digress...

You'll find for optimum acceleration in the RXh you'll want to shut off traction control if you don't mind and can handle dealing with the front meandering about with high torque steer combined with very slippery roads.

salimshah

"Snow M<ode" on Lexus vehicle is a poorly named mode .. but then again what else could they call it.

When you engage the tranobmsissiion in drive, the auto trans engages 1st gear when you are starting from a stopped vehicle. [There are exceptions like the earlier GS4s]. First gear provides the most torque at low [read not moving or barely moving] forward speed. If your tires have poor grip/traction with the ground below, due to snow/mud and the inertia of the vehicle is more than the force of traction to be overcome, the wheel will start spinning without the vehicle moving. IN case of snow, the heat will melt the snow/ice and further reduce the traction.

Technology comes to aid and the "Snow mode" switch is used to override the normal selection of of first gear and the 2nd gear is selected.. This reduces the spinning speed and torque.

Analogy, is when you are wearing leather soled shoes and you want to run fast in snow, you will start out gingerly and if you bust out like Bolt, you will need balancing skills or you will fall flat.

In summary the ''Snow mode' does not make a vehicle capable of driving in snow. It just improves your odds of getting moving in a sticky situation mud or snow.

Salim

vlad_a

Salim,

Toyota Hybrids have no gears.
You are correct in terms of torque reduction. With electric motors in play, there's so much more control electronics have over wheel spin than a traditional automatic would.
It also keeps the rear motor active longer in AWD models than it would otherwise. There's also a good chance VDIM (450h feature) will have its thresholds adjusted to intervene sooner and react differently compared to normal mode.

Best snow tires for the money? I swear by Michelin Lattitude XIce Xi2. I can't say enough things about these snow tires.
I've used them now on 5 different vehicles I owned, including the RX. My Audi S4 is already on winter tires as we are starting to see some light snow and freezing temps.
They surprise me every time in how little compromise there is when I switch sets. And the best thing - they last!
I used to run all-season tires on my IS300 because I got tired of Blizzaks lasting me only 2 seasons. RX is going into its 6th winter season on the XIce2s and there's plenty of thread left.

salimshah

My bad ,,, forgot thet the post is in 450H ... apart from gear1 the theory still should hold .. reduced torque from motor.
Salim

vlad_a

Personally, I never got the whole starting in 2nd gear thing. All the years I've been driving stick-shift cars, I never started in 2nd gear in snow or ice.
Even 4x4s go into a low range when presented with difficult off-road situations.