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      01-07-2013, 04:48 PM   #78
Cyberdemon
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Drives: 2013 335i M Sport
Join Date: Jun 2012
Location: Long Island NY

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Quote:
Originally Posted by JohnVidale View Post
From the BMW site:
Time to 60 - 335i 5.1s, 335ix - 4.7s - the advantage of the xDrive is much larger for the 335, so I am not sure why you're bringing up the 335.

The lesson I'm getting from this is that four-wheel drive is faster until one is going pretty darn fast, and should have better traction and handling in a range of conditions.

The slightly less optimal weight distribution may be a downside, the car is 5mm higher, and the extra gears cost ever so slightly in gas mileage.

While I have little enthusiast driving knowledge, I do have a doctorate from Caltech, so I know some physics.
Then let me explain this way:

Forget what BMW says - I've already shown why BMW's 0-60 can be wildly inaccurate, and are primarily for marketing purposes (so that the dealer can claim the car is .1 second faster than the Audi, as well as helping to justify the extra performance and security that the $1800 X drive premium gets you).

Now that we've left the world of marketing spin all we're left with is the physics.

Acceleration comes down to the mass of the car, the power of the engine, and the ability to deliver that power to the ground through the tires.

We already know that the mass of a RWD car is lower. The power of the engine (regardless of what model) is equal, so the only difference left is the traction.

Traction comes from the tires ability to create friction (which is a function of many variables including tire compound, tire/surface temperature, tire pressure) and the drive wheels.

We know the RWD car will deliver more power to the wheels due to the lower parasitic loss of the drivetrain. And we know that the AWD vehicle will be able to better distribute the power to the ground via all 4 wheels.

At the end of the day that means the only time the X drive vehicle is faster is when the RWD driver is turning the tires to smoke.

In the real world that generally means:
-From any type of a roll, the RWD car is faster
-If the RWD car is on summer tires and the AWD car is still on all seasons, the RWD car is faster.
-From a standstill, the AWD car will launch faster until the RWD car hooks up (which is also a function of driver skill, traction control - which is exactly why BMW's posted #'s are virtually meaningless other than for marketing)
-In general driving (merging into traffic,passing on the highway) the RWD car will be faster and more responsive.
-In dry weather the RWD car will always handle better. Less weight, better weight distribution, more power. Same reason virtually every race car on earth is RWD until you get to rally racing, and even many rally cars which are purely driven on dirt are still RWD.

AWD is great when it's snowing and you're travelling up-hill from a standstill. But even in the rain I've pushed this car to the limits wanting to break traction on the snow tires and the RWD still has more grip than I want. That included driving home in the Noreaster we had right after Hurricane Sandy, and the car was still extremely well planted even in 3" of snow and with my summer tires still on the car.

I also won't get into the fuel economy issue because that's too variable - but if you have a car that weighs more, you're going to spend more fuel lugging it around. The EPA numbers are useless - the 328i and 335i both have the same exact EPA numbers with the automatic, which I'm sure any of the fuel economy conversations on here will disprove pretty quickly.

RWD is subject to a lot of myths and marketing hype to push more expensive AWD vehicles. In reality, the vast majority of people "need" AWD almost as often as an SUV owners "Need" to drive off road.

//Lowly bachelors from Virginia Tech.
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