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  #11  
Old 02-20-2011, 06:07 PM
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Originally Posted by Fraser View Post
A know it's an extra expensive but if I was you I buy two you tyres so that all four are the same. This is a full-time 4WD vehicle and it will always be happier with four tyres in as close to identical condition. The trouble is that once you get into the cycle of two older tyres and two newer tyres you'll always be repeating that cycle as you replace two tyres at a time.
Good point!

I should have mentioned the back two were already new.

Given I use to work in a driveline reconditioning shop this was my first concern...I remember JEEP's use to fail catastrophically when owners replaced only pairs of tyres.


Are they any links where I could read up on my AWD system? I am keen to know some more about it.
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  #12  
Old 02-20-2011, 06:24 PM
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This is BMW explanation of the E53's xDrive system:

xDrive: Intelligent grip to match even more power
BMW’s revised X5 has the grip to match the power of its up-rated engines thanks to a new intelligently controlled infinitely variable torque splitting drive train called xDrive.
This system raises the benchmark for on and off-road capability in the luxury market and will also be shared with the 2004 X3 all-wheel drive Sports Activity Vehicle.
The xDrive system delivers improvements in stability, driving pleasure and safety, both on and off-road.
Even though critics around the world hailed the original X5 for its secure and confident handling, its muscular and agile performance on and off road, BMW engineers have devised a new system that is even more refined, more responsive and more controlled, all with the aim of enhancing the driving experience under all road conditions.
The key xDrive benefit is that it ensures drive forces are always delivered to the axle that needs it most – in an instant.
BMW’s xDrive is not simply a reactive system. Using a multitude of inputs from the Dynamic Stability Control system, xDrive is almost clairvoyant in its ability to predict vehicle behaviour and act early to enhance traction at the wheels with most grip, to maintain the vehicle’s balance and control.
The xDrive concept has two key ingredients – a centrally mounted, electronically activated, multi-plate clutch to distribute power between axles, combined with the familiar DSC system to regulate power to individual wheels.
The electronically controlled clutch is able to respond more quickly than conventional four-wheel drive systems that require the build-up of hydraulic pressure to change drive distribution.
It is also fully variable, constantly monitoring and channelling optimum drive forces from axle-to-axle.
DSC sensors constantly monitor individual wheel speed, steering angle, lateral acceleration and yaw rate angles – giving xDrive the predictive information it needs.
In extreme conditions where wheel spin is inevitable, DSC builds on xDrive, acting on individual wheels, cutting power and applying brakes if necessary. Whether the car is used on or off road, new xDrive breeds driver confidence by reducing the risk of understeer or oversteer.
Off-road, on rough tracks or slippery surfaces, xDrive responds in milliseconds, redistributing power from the slipping wheels to those with most grip, just as a rock climber, who senses his feet are about to slip, immediately puts all his energy into bracing himself with his hands.
In normal driving, the multi-plate clutch is able to distribute power from an extreme of 100 percent rear drive (with the clutch fully open) through to 50:50 front-to-rear drive with the clutch completely closed.
In theory however, if the rear wheels were sitting on ice, DSC removes power to the slipping wheels giving virtually 100 percent drive to the front axle.
The new xDrive system reacts in just 100 milliseconds. Put in context, this is just half the time it takes for the pedals to react to driver inputs.
Whenever the car threatens to oversteer, xDrive closes the multi-plate clutch, increasing power to the front wheels and ‘pulling’ the car around the corner.
Equally, where understeer threatens, xDrive reduces the power to the front wheels to a maximum of 100 per cent to the rear if necessary.
BMW did not hesitate to adopt an electronically controlled clutch rather than an electro hydraulic one (as used by some competitors).
The electronically controlled clutch provides instant power transfer in all situations, rather than an electro hydraulic system that requires movement, generating hydraulic pressure before power transfer occurs.
Hence BMW’s xDrive system is far quicker and less ‘reactive’ than competitors.
Simple four-wheel-drive systems use a viscous coupling or a Torsen differential that respond mechanically to a difference in speed and torque between the front and rear axles.
Conventional, all-electronic set-ups require at least one wheel to be spinning for power reduction. Systems using a Haldex coupling use engine control data alongside wheel speed signals.
However, BMW’s xDrive benefits from the full range of DSC information including yaw rate and lateral acceleration, allowing the car to predict the road conditions and react far sooner.
In a first for an all-wheel-drive vehicle, xDrive replicates the function and locking action of a differential with a multi-plate clutch (without resorting to a weighty central differential).
By simply using the clutch, the front and rear wheels can be powered or completely separated if circumstances require, such as in fast, dynamic situations.
On hard throttle acceleration and without any wheel slip being detected, the clutch fully engages, providing a 50:50 power distribution and maximum traction.
Under normal driving conditions, the clutch provides fully variable distribution to front or rear axles.
Transferring power to the front wheels is the responsibility of the two front drive shafts that are of equal length, assisting power distribution and helping eliminate drive train feedback through the steering.
The right hand shaft is mounted in a bearing case, passing through the sump to the opposite hub. This assists the car at parking speeds, where drive to front wheels can compromise maneuverability. In such cases, full power is transferred to the rear wheels
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  #13  
Old 02-20-2011, 06:36 PM
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Awesome read! Thanks mate.

I feel a lot better reading my car doesn't have a 'viscous coupling' in the transfer case.

I wondered how they got away with staggered rim widths/tyres because surely there is a slight discrepancy in rolling diameter.. not an issue with the xDrive as I read it.

Sounds very much like the Active YAW in my mates EVO only more complex!

Any idea on fluid change intervals?

Also

I let my older brother have a steer of my X5 he drove it about 1.5 hours back to Sydney.. he was a little reluctant to hand me back my keys... lol and this is a guy who hates SUV's ... he had to swallow his own words yesterday! he loves it
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  #14  
Old 02-20-2011, 06:54 PM
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Originally Posted by JDM-20L View Post
Any idea on fluid change intervals?

Also

I let my older brother have a steer of my X5 he drove it about 1.5 hours back to Sydney.. he was a little reluctant to hand me back my keys... lol and this is a guy who hates SUV's ... he had to swallow his own words yesterday! he loves it
BMW says the fluid is for life of the vehicle but there's lots of debate on this. Use the search function here and you should find lots of info.

As for the brother's reaction, he's not alone there!
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  #15  
Old 02-20-2011, 07:10 PM
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Will do mate.. I will not agree with that whole fluid for life B.S.

I'll be doing some research on that for sure.


He he I though it was funny! Well seeing how he's normally not one for euro cars and SUV's and an avid Holden lover!
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  #16  
Old 02-20-2011, 07:26 PM
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He he I though it was funny! Well seeing how he's normally not one for euro cars and SUV's and an avid Holden lover!
And I bet he thinks differently about diesels as well now.
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  #17  
Old 02-20-2011, 07:34 PM
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Actually he's an existing diesel enthusiast funny enough, He drives freight locomotives for Pacific National and also a train buff (that is an understatement)

In saying that.. I think it has more or less steered him towards a diesel BMW next time round! I keep questioning his desire to waste his hard earned on a V8 Statesman or Calais that he keeps talking about! God knows why he wants to put himself down that path again?
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  #18  
Old 02-21-2011, 10:28 PM
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In saying that.. I think it has more or less steered him towards a diesel BMW next time round! I keep questioning his desire to waste his hard earned on a V8 Statesman or Calais that he keeps talking about! God knows why he wants to put himself down that path again?
Can't see the value in a new Calais or Caprice myself (I think the Statesman is gone now) but these things are pretty good shopping second hand. Just wait until the price of petrol spikes up and watch the huge number of them that come on to the second-hand market at bargain-basement prices.
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  #19  
Old 02-21-2011, 10:39 PM
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He has a V8 in the garage too... lol

I don't understand his desire to be double dipping on V8 fuel bills.

I love those Cayenne's and it was on the option list before I decided on the X5 3.0D but it's senseless for me to be driving one around town and towing my other cars about would incur a hefty fuel bill and only reasonable performance gains in comparison, put simply the X5 was pretty hard to pass up when compared with anything else on the market!

Must get pics up too I guess?
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  #20  
Old 02-21-2011, 10:48 PM
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Originally Posted by JDM-20L View Post
He has a V8 in the garage too... lol

I don't understand his desire to be double dipping on V8 fuel bills.

I love those Cayenne's and it was on the option list before I decided on the X5 3.0D but it's senseless for me to be driving one around town and towing my other cars about would incur a hefty fuel bill and only reasonable performance gains in comparison, put simply the X5 was pretty hard to pass up when compared with anything else on the market!

Must get pics up too I guess?
Pretty hard to go past the 3.0d I reckon. V8 torque with 4-cylinder fuel-economy. It's a win-win situation. I also have a old (1990) 3.9-litre V8 Range Rover that uses nearly twice as much fuel as the 3.0d, even though I nurse it along and fang the X5.
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