fabchef

Lexs... so on my 2009, all 4 wheels are turning all the time, correct? When they slip, they redirect power to wheel that's not spinning?
fab

Toys4RJill

If your Lexus is all wheel drive, then your all-wheel-drive system is always working. The system doesn’t split power to each individual wheel just front to back which is in permanent mode always. If you have a RX hybrid that would be different as it’s on demand.

fabchef

Lexs, okay, thanks. I guess it's not that bad of a system? I do have an awd (non-hybrid) model.
would you say it's a bit better than having fwd-based awd, that shoots power to the back when needed?
fab

lesz

I find myself being confused by terminology, specifically the difference between 4-wheel drive and all-wheel drive.

The 4-wheel drive systems that were used, say, in the 1980s, with vehicles like the 4Runner, were ones in which the vehicle normally operated in 2-wheel drive mode. But, the driver could manually change to 4-wheel drive mode.

As the technology evolved, vehicles, like the 2005 Lexus GX that I owned for 15+ years, moved to what they called full-time 4-wheel drive. The vehicle operated constantly in 4-wheel drive mode and shifted power, I think, to the wheels that needed it. I have never driven any vehicle that felt more secure on other than dry pavement than did that GX, but the downside of operating continuously in 4-wheel drive mode was/is a significant decrease in fuel efficiency.

More recently, I thought that the term all-wheel drive has come to refer to vehicles that normally operate in 2-wheel drive mode but that automatically shift power to all 4 wheels when slippage is detected and having power available to all 4 wheels is desirable.

Toys4RJill

I think full time is superior. I am sure others will disagree.

‘Where Toyota does this really well is with 4R. They give you a choice, you can buy 4wd where you shift, or you can buy full time 4wd.

Motorola

Completely false. The GA-K platform AWD vehicles have always used Haldex AWD, which is by definition on-demand. Toyota didn't transform the RX into a Subaru as you claim.

mmarshall

Although the details (and different/successive developments) of the two systems are of course more complex, the simplest and most basic way of differentiating between the two is that 4WD (particularly the traditional part-time 4WD on trucks and older SUVs) lacks a center differential, is driver-controlled by a transfer case, and cannot be used on dry pavement, because it drives all four wheels at exactly the same rotation-speed and does not allow for tire/wheel-slip on dry corners. AWD, on the other hand (or what is known as car-based 4WD) uses a mechanical or electronic center-differential/final-drive unit that allows all four wheels to rotate at different speeds. The driver does not have to concern himself of herself with what kind of surface is under the wheels.....drive and forget.

Obviously, all else equal, it costs more to produce and assemble an AWD vehicle over traditional 4WD...which is why auto manufacturers resisted it for so long on pickup trucks and traditional SUVs. Traditional 4WD also tends to be more durable off-road.

JDR76

The e-AWD system in the hybrids often gets trampled on a bit here but from personal experience, I have found it to be really solid. We have it in our Highlander and the online reputation of the system had me a bit hesitant to put it through its paces, but once I finally did, I was quite impressed. The rear axle motor always provides power when accelerating from a stop up to 25 mph, then is "on demand" after that, but it's getting started that's most crucial, and as it is always on in that condition, you don't have to wait for it to pick up some slip and then engage.

I've taken it over mountain passes layered with compact snow and ice without any issue while many 2wd cars were struggling. I took it through 9 inches of fresh snow without a blip, even from a full stop on a hill where the cars around me couldn't get moving, and I just pulled away easily. And this was on factory all season tires.

My favorite AWD system is the one in my GS, but the GS usually gets left at home in the snow. We just use the truck or the Highlander in those cases. Plus, they have more ground clearance.

SW17LS

I also find it funny that people want their AWD/4WD system to always be delivering power to all 4 wheels. Why?! If I don't need AWD at a certain time, I'm happy to let the system leave it in 2WD and adjust itself on the fly.

LeX2K

Don't think people want that, they want power to go to the wheel(s) when it's actually needed. Must be really hard to do because almost all cars fail the 1-wheel traction slip test, many the 2-wheel as well. I've seen Toyota hybrids get 100% stuck because the computer refused to give any power where it was needed. The car would not move at all.

Toys4RJill

Do you find it funny too that some people do not want their engines to shut-off at every intersection or every time someone stops their car?

Up until a certain time, Toyota and Lexus were using permanent all wheel drive systems in their RX and Highlander and it is a very nice choice.

SW17LS

Not at all, I don’t want that. But there’s a physical annoyance involved there. When driving you have no idea whether the car is driving all 4 wheels or 2, AWD is not providing you a benefit driving straight down a dry road, so why do you want it active? It’s just causing wear and fuel for no benefit.

Give me an adaptive system that gives me AWD when it decides i need it and 2WD when I don’t anyday.

Toys4RJill

All of these Mercedes models are permanent all wheel drive. I think your Mercedes is permanent too. You’d really rather have a on demand system?

mmarshall

That was one of many things that sold me on the Encore GX....the console-mounted button that chooses between FWD an AWD whenever you want it....or don't want it.

I run it in FWD most of the time, and switch on the AWD for a few minutes each week or so to keep the extra mechanical parts moving, lubed, and free from corrosion.

Toys4RJill

You cannot keep your Encore GX in “permanent” awd can you?