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X Drive System

Discussion in 'Roundel Magazine' started by Rick Vanasse, Oct 23, 2014.

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    Rick Vanasse

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    I am curious as to what Scott Blazey found impressive about the BMW all wheel drive system in this weeks Roundel Weekly. When I tried out the BMW X5 3 or 4 years ago at the BMW center in South Carolina I chose not to purchase the vehicle. The X5 was having a terribly hard time getting up and over a rock. The instructor gave lots of direction on how to go slow and let the vehicle climb up over the rock, but it just didn't want to do it. It would get almost to the top, then slide back down. The problem seemed to be in the way BMW (and perhaps other manufacturers) have designed these all wheel drive systems.

    I asked the instructor why I was smelling brake burn. He then explained that the way the system works is that it applies the brake onto the wheel that was slipping pushing power to the other wheel.

    What happened to the good 'ol locking and/or limited slip differential? My old Land Cruiser had three differentials (front, center, rear) and I could set it to lock any one of them ... that vehicle would have climbed over that rock without a thought. I understand other vehicles have either a locking or limited slip in the front, back and middle (Range Rover?). Why does BMW not use this kind of system? It would certainly save the brakes!

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    Interesting experience you had at the Performance Center. I'm surprised they offered up such a challenge for their SUV/SAVs. You clearly have experience with proper off-road vehicles. But, that puts you (and me) in a distinct minority when it comes to BMWs.
    The short answer ... Target Audience.

    The long answer ... With the exception of adventurous people like yourself, taking part in that kind of company demo (and maybe a very few other people), the typical American buyer of a new BMW X5 / X3 will never consider taking on an obstacle like that in the real world.
    BMW sells them to soccer moms and retired couples, orthodontists and insurance agents, etc, etc, etc. Typical Americans. And they sell a Lot of them.
    BMW (and every other manufacturer) sells legions of them to Americans who simply want to enjoy comfort, style, convenience, versatility and maybe a little assurance that weather will not deter them from their daily pursuits. Most never see a dirt road.
    We lease one for my wife so that I have that assurance for her. Our typical 4-8" snows are no problem for her in the X3 or her previous 330xi and 335xi.
    For us, when the weather gets more serious, the X3 stays in the garage and the Grand Cherokee takes over. For others, it's their 4x4 F-150 or Wrangler, etc.
    If one's current resources discourage having multiple vehicles and one feels compelled to tackle boulders ... a BMW might not be the best bet. Just sayin'

    Rover, Jeep, Merc and others still offer serious off-road capabilities in some SUV models but, not really all that many are actually put to the test. I don't envision BMW joining that group (for the American market).
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    Actually, I never said I found xDrive impressive. The airport perimeter road we used for the test drives was dry and smooth and could never pose a challenge for an all-wheel drive vehicle—except maybe that time in 1993 when the Missouri River flooded the area.

    What I said was that I had 57,000+ miles of experience with xDrive and that I know how well it works. Which is pretty well. xDrive, in my opinion, is made for the hundreds of thousands of BMW customers who need a car that can recognize and react faster than they can to situations in which one or more of the tires is losing grip. Also for drivers who, when they step on the gas and don't move, step on the gas harder. It is also made for drivers who are great in minimal traction or (mildly) off road who no longer live for the throw-and-catch thrill of driving where their skill is the only thing between them and disaster. xDrive is not foolproof. For example, it can be defeated in deep snow when wide snow tires with less-than-optimal tread spread out the load and the vehicle can't get to the pavement or compress the snow enough to get bite. On the other hand, I've drive 3 Series with xDrive and good tires that were some of the best snow cars I've ever driven—and I've driven in a lot of snow. I know I can get around well in an X5 without xDrive, because I did it for over 100,000 miles in an E53. But if you ask which one I would rather let my wife drive, I'd pick the one with xDrive.

    Being computer controlled, there is always the danger of xDrive malfunctioning. I drove an X3 on some twisty roads—a rally, actually—during which, if I tried to take the corner fast and the inside rear wheel got light, the computer would take away my throttle. Hard cornering is not, as you know, the best time to have the computer "lift" for you. It was some sort of sensor or computer problem. If something in the AWD electronics malfunction, you might be screwed; with a mechanical system, not so much.

    BMW has built X5s that crawl over rocks, but unless you enter the Dakar Rally, you'll never drive one. There are off-road situations the X5 can handle, but 95 percent of X5s will never see them.

    While the U.S. is an important and influential market for X vehicles, the majority of X5s are shipped overseas, where many X5 buyers are even more affluent that U.S. X5 owners. I'm guessing most of them don't want to think about adjusting their driving style for low-traction situations; so for them xDrive is fine. BMW has to take the rest of the world into consideration and that may also help drive BMW's one-size-fits-all approach to the X5's all-wheel drive. Plus, you have to remember that BMW loves computers and sensors and driver assistance system and is always looking for more ways to use them.

    Personally, my favorite four-wheel drive vehicle was my M151A1, if I could jump in the driver's seat before my driver could and none of the higher brass were around. Now that was fun.
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    Rick Vanasse

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    Thank you both for responding. This confirms that a BMW X vehicle is not right for us. Granted it is less than 1% of the time, but when in soft sand crawling around beaches looking for that favorite blue fish spot you really need a mechanical system. All four wheels are constantly spinning in the sand, even with low tire pressure. Having the brakes constantly trying to correct for this spin just wouldn't work. That is where I have found locking differentials best ... unless your in Scott's M1!
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    Doesn't the X6M come with Dynamic Performance Control, which is a torque-vectoring rear differential? Or is that feature no longer available. Of course you have to want an X6...
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    I own two xDrive cars (2008 328xi and a 2014 328 xDrive Wagon) and I have found them to be most impressive driving in snow and ice conditions. The combination of the xDrive with the stability control is excellent and makes the car basically unstoppable unless the snow is so deep it lifts the wheels off the road (unlikely).

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