Center Locking Diff.. when to engage and for how long?
 

To make a long story short.. We went on sojourn through forest service roads in rogue national forest. It was extremely beautiful and the cayenne did amazing. The road surface was dirt and gravel and mostly graded but there were some rutted, eroded or less traveled sections. There were also portions we traveled in the rain.. so the surface was unstable and slippery at times.

I decided to go into low range for a portion because it was steep. Upon engaging "reduction" I noticed an additional option. Apparently its for locking/unlocking the center diff - even though the menu text is cryptic. I learned you can really "wind up" the transmission if you leave it locked for too long. In the case of our cayennes.. when do we actually NEED or really want to lock the center diff? What are the scenarios? And for how long can it be engaged?

I think you'd only want to engage that lock if you were stuck in deep mud, sand or snow. I'd then disengage it when the vehicle was free. Maybe I'm wrong, but that's what it seems like to me...

The only times I locked the center diff was when there was a chance that the truck would not "make it" unlocked. For me this was steep ascents on dirt/gravel/grass, mud, and creek crossings. As I'm sure you know, failing in these scenarios is not ideal, and I have had enough instances where I "barely made it locked" to know that not locked would have most likely been messy. I also think the traction control works less when the center diff is locked, which is easier on the brakes.

Good to know fellas. So basically only engage it when you are about to really have some fun.

Absolutely

Center diff lock engaged http://www.flickr.com/photos/2058658...7624134675338/

great pic.. i wish i had gotten a picture of going around this spot in the forest service road that had washed away dropping off into a chasm... Had to pull some trickery to get through... and then the road dead ended and we had to cross it again.

I think it would helpful to understand how a center differential works. In a nutshell, as I understand it, it locks in a 50/50 power distribution to the front and rear axle, regardless if all traction is lost on the front or rear axle. The Cayenne normally has a Front 38% Rear 62% power distribution.

Without locking the center differential, it is possible to spin both front tires or both rear tires, while sending ZERO power to the other axle on the ground when very little traction is available. This means that unless PSM can save you, you are stuck. The front and rear differential locks work in the same manner and prevent just one tire on each axle from spinning and sending no power to the other wheel on the same axle. When a differential is locked (center, front, rear), it will send power to ALL wheels linked to that differential REGARDLESS of any traction situation. This means that you will have the best chances to get through anything, including slick muck.

Using this understand, it would be beneficial to lock the center and front/rear differential BEFORE you get stuck in very low traction situations. Slippery snow, slick mud, and ice (speed will be limited with gear reduction) and aggressive offroading where one axle might leave the ground entirely. So for the most part, you will hardly ever need it. This is something that the Land Rover guys have for extreme offroading that is a not necessary (but nice) for a Porsche.

This is one of the reasons I bought my CTT. Tough NE winters.

One of the reasons that I sold my GTS is that I actually did need more offroad traction. Even with AT tires, there were places I needed my truck to go where the Cayenne had difficulty (very steep ascents on grass/dirt and mud); whereas, my present and past Land Rovers did not.

I absolutely loved my GTS, with the exception of driving it in stop and go traffic (manual). When I do not need the absolute offroad capability again, I will be back in a Cayenne - why I'm still around, other than being able to be the first to jump on Mike's truck when he (eventually) puts it up for sale.

I only engage it if:
- crossing water (flowing or deep)
- befor entering mud
- wet grass

otherwise, low range w/ PSM on is way more than enough. a lot of people are VERY surprised to see a porsche go places a lot LR discos can't go.