mikeg123

So I got a call from some friends and last Sun they were heading back from a wknd of Snowmobiling near Steamboat. My buddy, his wife and their 13 month daughter were traveling on I-80 in WY, abt 45 mph, when my buddy hit a patch of ice and lost control, fish-tailed into the median and rolled his 2001 Expedition. Fortunately, he, his wife (asleep), and his daughter were surprisingly unharmed in the rollover. Their DOG, (COSMO) a Chow/Shepard mix, was thrown from the vehicle 60-80 feet, but escaped with no major injuries. I told my buddy that the big one upstairs was watching over them that day!

Here's the question: my buddy says in his AWD Exp. that when the rear wheels began to slip the traction control, sent power from the rear wheels to the front and that this caused the front to wheels to spin faster, thus causing him to further lose traction and thus lose control of the vehicle. He states that had he had the vehicle in high 4 the power transfer would've stayed constant to all wheels and thus better control of the vehicle. Could this be right? With Quattro, doesn't the differential automatically send the power to the wheels with the most traction, or least amt of slippage? I'm wondering how Quattro would perform under similar circumstance? What happens, when all wheels have no traction? I thought I had read somewhere that ABS is engaged -not sure?

Just one last thought-Quattro is amazing, but don't be baited by false confidence that just because this and other AWD vehicles have better traction -this should mean that we can go faster -you hit ice/ black ice, and 4 wheels slipping is the same as two slipping. My friends were very fortunate -be safe out there!

ex-quattro PETE

otherwise, I don't see how going straight through an icy patch at 45 mph would cause a spin-out. Unless the AWD on the Expedition is that bad.

In your A4, if you started spinning-out like this, ESP would engage and try to straighten you out and help you regain control going forward. Not sure if Expedition has any kind of stability control program like ESP, probably not.

mikeg123

I was thinking that the quattro with ESP is pretty advanced, and I would agree that the Audi engineering of the quatro system is far superior to anything that Detroit puts out.

atel

My brother has one, and when the system is in the "Auto" mode, it functions as a rear drive until the rear slips, then power is directed to the front. There is a noticable lag time, and you can hear it engaging (really annoying and not fun) When in 4-high it send power to all 4 wheels at all times, like a traditional 4WD Jeep. But this is not suitable for highway driving as it causes extensive wear to the drivetrain and x-fer case.

Jimax

not when you're off the gas. As Quattro Pete said before, either he was still accelerating or he turned and set the Expy out of balance slightly which caused a chain reaction of correct, over correct, correct again, etc. Just because you lose traction, doens't mean you're going to have an accident. If you lose traction and try to make a turn, accelerate, or brake, then that's a different story. ESP or not, you can't overcome the laws of physics. ESP does definitely help, but only up to a certain point.

Ford AWD is fine, there's nothing wrong with it.

ex-quattro PETE

if it's one of those reactive types, which normally gives the power to the rear wheels and only starts transferring it to the front when the rears begin to lose grip, then I prefer quattro (Torsen) with 50/50 split to begin with.

This sudden power shift from rear wheels to front wheels could temporarily upset the vehicle's balance I suppose.

ToastR

end first it could have been due to injudicious use of the accelerator or something as simple as a gust of wind. If the coefficient of friction was essentially zero there was no traction to be had to regain control with, regardless of the AWD brand's abilities. Chances of a rollover in a car would likely have been less, those Expeditions sit pretty high.
This is all supposition of course.
It's wonderful that he and his family are safe.

jprice@CPS

That, and if the front wheels were spinning, that means he was accelerating. Maybe it was the cruise control doing it.... if so.. bad design by Ford.

Just another reason to have winter tires.

Glad that they are ok.. they are VERY lucky. Time for them to upgrade to an A6 Avant :-)

RKA

The transfer of power from back to front should not have de-stabilized the vehicle enough to *cause* the accident. The fact that the rear wheels were initially powering the vehicle when he hit the ice was certainly a big factor, and that will send the back of the car around (into a spin). What he did as a driver might have been able to save him from the end result, but with the typical all season tires equipped on these big SUV's, it's likely that he had little traction to work with, so even the best of drivers might not have been about to recover once the truck began the spin.

The Audi system has all four wheels pulling the car all the time. Torque is adjusted front to rear to accomodate slippery conditions, but it can never send 100% of the power to the front or rear wheels (the limit is up to ~65% torque to front or back). Anyway, quattro might have prevented the back end of the car swinging around so quickly, but it's still possible that a less competent driver could still have spun the car on that ice (easing off the throttle will cause a temporary weight transfer to the front...the rear end gets light, and it will start to swing around).

sandwood

not bc of the quattro but bc audis obviously have a lower center of gravity. suvs may or may not have better traction under some circumstances or provide better crash protection to occupants, but they roll!
I'm glad they are all ok.