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Old 12-19-2012, 07:23 PM
henrycyao henrycyao is offline
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Location: Bay Area, California
Join Date: Oct 2012
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Mein Auto: BMW X5 35d
Originally Posted by solstice View Post
Porsche's description of the two systems on page 49 and page 50. It's not very detailed on the diesel / hybrid but as far as I know that system uses a Torsen diff. I think the 60% rear wheel bias it offers is far to little for the 911 where the electronically controlled Porsche system used in the other Cayennes is a must since it gives ~90% rear wheel bias at good grip. This more advanced system is supposed to offer a purer sports feel, be lighter and be better off-road. The old Cayenne / T-egg system with a low range transfer case is history.

To me, it seems like you are giving up quite a lot of important Porsche AWD advancements with the diesel in good and poor grip.
The PDF helps quite a bit. It looks like Porsche uses brake as in the case of BMW X5 for side to side adjustment.

If one of the wheels is about to lose traction, PTM uses the ABD function to apply the corresponding brake. As a result, more drive is automatically transferred to the opposite wheel.
Speaking of rear wheel bias, why does BMW X3 offers an option to go 80% rear and 20% front where as the BMW X5 is 60% rear and 40% front? I thought it is just a software thing to keep the ratio different. BMW X5 supposed to be able to move 100% torque in either axel or did I remembered this wrong.

As for my reference for electronic locking differential, I thought that was the term for using brake to emulate limited slip differential. It slows down the faster wheel hence more torque applies to the wheel with the grip.

Besides off road, is there any reason why you really need a locking differential on center and all wheel locking differential? Does snow change that characteristic that much?
2012 BMW X5 Vermilion Red Xdrive35d with Premium Package, 3rd Row Seats, and Adaptive Drive

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