Just to clarify- xDrive is a full time awd system - Page 2 - Bimmerfest - BMW Forums

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X3 E83 (2004 - 2010)
Talk about the E83 BMW X3 in this forum!

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Old 01-28-2010, 01:35 AM
thayerV thayerV is offline
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Originally Posted by vrooom3440 View Post
Yes I have watched the video and yes they can and very likely do use the brakes to do that. The last bit with the Quattro and Xdrive on the rollers is very telling. The Quattro does what I would expect of an open differential and just spins the rear wheels. The Xdrive gives the rear wheels a little bit of spin at which point the computer notes a mismatch between front and rear rotational speeds and applies the rear brakes to slow that rotation down to match the front. The affect is that the rear wheels become harder to turn, the front wheels easier relative to rears, and power gets transferred to front.
Wheelspin side to side is controlled by the brakes. Torque split front to rear is controlled by the clutch pack in the transfer case.
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Old 01-28-2010, 02:14 AM
thayerV thayerV is offline
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Originally Posted by foxwalk View Post
I shared that video on Facebook, and a friend of mine said "My 1947 Jeep does that." and no I don't think it's true. but I don't know anything about 1947 jeeps.
All conventional 4WD's are locked front to rear so they will get on and off the rollers with no wheelspin at all. But they can't be driven on hard pavement while in 4WD as the system will not allow for rotational differences between the front and rear. They also cannot be used to keep you out of a jam on ice and snow as a wheel constantly has to break loose to even out the rotational differences. They will go everywhere but straight if one tries this with them:

Borg Warner came up with something called TOD to allow 4x4's to be more AWD like:

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Old 01-28-2010, 10:22 AM
vrooom3440 vrooom3440 is offline
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Originally Posted by X3emist View Post
watch the video and LISTEN to it. There is, as many cars now have, a viscous (spelling) clutch that "slips" for a better word power to the front or to the rear.
That is not what the following description you quoted says. It slips only to the front and the back is always locked. Therefore that clutch can only get you up to 50% to the front wheels.

Originally Posted by X3emist View Post
The DSC uses the brakes to control under/over steer and keep the rear end from swinging out such as if you enter an off ramp to fast.
And how is controlling under/over steer different than redirecting engine torque to front or rear?

Originally Posted by X3emist View Post
Here is a better explanation of it-

Both the new X3 and X5 use an innovative all-wheel drive system called xDrive.

Rich Brekus, manager of product planning and strategy, says, "Most companies show you how their four-wheel-drive systems go through the mud. We show you how well ours goes around corners."

With xDrive, driving torque is always transmitted to the rear wheels, while the portion sent to the fronts is controlled by a multi-disc clutch that can be fully open, fully engaged or at any level in between. Engagement pressure is applied by a servomotor through a linkage of levers, a ball ramp and a disc cam, directed by an electronic control system receiving inputs from the DSC via sensors for the rotational speed of each wheel, steering angle, vehicle yaw, lateral acceleration and the brakelight switch.

In normal driving, the split ranges from a nominal 40/60 to a maximum of 50/50 front-to-rear. In tight curves (including parking maneuvers) with low to medium torque, during heavy understeer and when antilock braking is active, the system is 100 percent rear-drive. Conversely, the rear proportion approaches zero when both rear wheels have near-zero traction. The DSC's traction control can reduce engine torque and apply individual wheel brakes to achieve maximum possible force to move the vehicle.

Transparently to the driver, xDrive also optimizes handling agility and stability on any surface by adjusting the torque split to correct for understeer or oversteer by directing more torque to the non-slipping wheels. It also increases torque to the rears under heavy acceleration and decreases it for light acceleration. All this happens so quickly (reaction time from sensing to control actions) that the system almost operates pro-actively, BMW says.

...While xDrive can handle torque split front to rear, side to side duties are handled by the DSC which is electronically linked to xDrive.
So back to my original question... front brakes are not necessary to transfer torque to get to 40/60 f/r split. It would be interesting how they gauge the amount of clutch slip in the system though? I might guess relative tire slip angles so a slight scrub is expected.

I still think there is a lot more magic with brakes with Xdrive than anybody wants to admit. As described the brakes deal with all the lateral torque transfer, which will be a MAJOR factor in cornering. Also as described for anything more forward biased than 50/50 the brakes WILL be required. This is all evident from the hardware available to apply to the problem.

Note that anywhere you read "DSC" you can think "brakes" as that will be the most likely initial control system response.
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Old 01-28-2010, 01:36 PM
noego noego is offline
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lets say an X3 is really stuck. trying to get the X3 unstuck with DSC enabled would mean that DSC is applying the brake to the wheel(s) that is (are) spinning - correct? therefore, in order to keep from over heating the brakes DSC should be off and the X3 will be in 4-wheel drive. at least this is how my aforementioned sales person described the procedure to us.

even though the X3 has been driven in some pretty deep snow it has never been close to getting stuck and the DSC has never been off. there have only been a few times that the DSC light has come on, and whatever it is that gets the X3 around corners in all conditions is amazing to me.
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Old 07-21-2012, 10:03 AM
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DBU DBU is offline
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Originally Posted by iamthewalrus View Post
Then why on earth do we have to deal with them? Why can't I go to www.bmwusa.com, configure what I want and submit a deposit? I do this with a Dell or Apple computer, so why not a car?

The manufacturers should do build to order with no inventory, or hold very limited inventory in1 or 2 locations nationwide. Scattering thousands of cars across hundreds of dealerships is wildly expensive. Personally, I have no problem waiting 4 months to have the car built to my specifications. I have to do that anyway since I drive manual and most dealerships stock very few manuals.

Think how much money we'd all save!
1) Holding all that inventory is expensive. The dealership is paying the bank ~5% for the loan to hold onto all of that inventory. A $50K car sitting on the lot for 4 months adds $50K*5%/3 = $833 to the cost.
2) Dealers need to inflate prices to keep a cushion so that they can make a deal with the guy who wanted silver but settles for white, because white's on the lot. You're also paying more because at the end of the model year the dealer has to drop prices to move the old inventory. If they pooled their inventory in 1-2 centralized locations nationwide or had perfect forecasting, you wouldn't have this over/under inventory situation.
3) You're paying for multi-tiered advertising: ever see those really cheesy, low quality BMW ads on TV? That's because you local dealer is also advertising in addition to BMW's national campaigns. But, the dealer's ads aren't relevant nationwide, so they get limited local runs which are less efficient than leveraging the manufacturer's ads nationwide. But, you're paying for that.
4) You're paying for the dealership itself, the lease, insurance, employees, benefits. Working directly with a website is much, much cheaper.

Lastly, service and sales do not need to be bundled. The fact that they've been bundled historically is not a reason to keep it that way going forward. When my Audi was out of warranty, I took it to a great, high-quality, local (walking distance) independent German car garage. It was great. As soon as my BMW goes off warranty in 2012, I will go back to FatCity here in Seattle.

People say, "The majority of people aren't yet willing to buy online." Well, I bet if word got out, that you got a great price, a really hassle-free experience, and avoided clueless salespeople by shopping on www.bmwusa.com, I bet that would change. Who had heard of Amazon.com ten years ago and look at them now!

So, imagine an experience like Apple's stores: you go in, there's a showroom for you to play with select models. But most purchases, particularly those that require configuration are ordered online and shipped to you. www.DWR.com works the same way. You go to the showroom to buy a $5K couch; you sit on similar couches and then custom order the combination of fabric and options you want. But there's no bargaining. There is only one price. You don't come onto boards like this and ask, "Did I get a good price?"

Why isn't this happening? Politics. The North American Dealers Association (NADA) has strong political clout and is lobbying against online car sales to "protect the consumer." They also have language in their contracts with the manufacturers to prevent the manufacturer from going direct and leaving the dealership with "stranded costs".

The first manufacturer to go out and acquire all of its dealerships and go direct could do incredibly well. Note that Tesla, which is starting a car dealership from scratch, is NOT building a dealership network. They're doing manufacturer-owned stores/showrooms (like Starbucks and Apple) and a built-to-order model (like Dell). Once they get big, they're going to have a $2K/car price advantage on every other manufacturer. There's a lot of cost built into the current supply chain. And as all of you know from WalMart, Amazon, Dell, etc. tightening up your supply chain is a huge opportunity.

This might seem revolutionary today, but think about when my 5-year-old niece goes to buy her first car 15 years from now. "What do you mean I can't just buy it online? I buy everything else online!"

Seattle, WA
Realise this is an old post, but I just had to respond (new on the E83 sub-forum).

Here is how I puchased my E60:
- did on-line research of options and prices
- located about 20 local dealers (from BMWNA web page. I live in the greater Los Angeles area)
- sent each dealer an email with the exact specs I wanted and asked for ONE piece of info from them: "How little profit would you make this deal for?"
Important foot note: I was interested in ED (European Delivery) only. You cannot do this with local delivery for all the reasons you mention in your post.
About 1/3 of the dealers replied to my email. Their quoted profits ranged from $1000 - $3000.
I made the deal with the cheapest dealer and only met him when I picked up the car.
Please go to the ED section of this forum and check out the ED Wiki.
His: 2017 X4 M40i with all the options (except cold weather stuff - not needed in SoCal

Hers: 2007 X3 3.0Si
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