Yes it is a problem. That's why I make sure to drive in reverse for every time I spin those rear tires!

 

^i dont think it would add up to more than a mile or two over the life time of our cars.
most of us are spinning out in 1st for a couple of seconds at what ,15-25 mph....

 

If you watch some of the vids on utube, guys in winter driving are adding 5-10 miles in a matter of 5 mins

 

To the OP. I have been asserting the same thing for years even thought I live in dry weather and never see snow.

I think a good test would be to get the rears spinning faster than just above idle. Try spinning at higher revs, maybe in 2nd to see if the diff will apply some power.

 

I'm also left wondering how well the system is engineered to work in reverse? I do realize it's a purely mechanical system and would think it should work normally, but that video is indeed quite odd if the example is actually having a functional AWD drivetrain still installed.

The more I read about the 996TT/C4 version of the AWD system, the less impressed I am by it's actual capabilities. I plan to convert mine to RWD eventually, and these kinds of cases only help me to realize how little I might actually be giving up by making the switch to RWD.

 

Like I said, the AWD system works great. I have driven many miles in the snow with mine and never got stuck. At times I was driving with snow coming up and over the front hood. It works like any other AWD system with open diffs. It is just a little more rear wheel biased than most, which actually helps this car in the snow due to weight distribution. Trust me, I live in mountain snow country with an annual snow fall that is crazy.

 

5-10 miles in a matter of 5 minutes = tires slipping @ 60-120mph! Ha!

 

I woudl love to have smeone test my theory. Really spin teh rear tires. The vidoes we see seem to be mostly all near idle. I can't see hhow viscous diff coudl transfer much power when teh front/rear wheel speed ratio is low.

That said, I have driven my car with the front drive-shaft removed, there is no question AWD helps in the dry on a higher HP car. My car tends to spin, grab and go in the dry.

In RWD only mode it just spun...

 

Ari - I tested your theory the other day. I revved it past 4k with the rear tires flying and the front tires didn't even TRY to spin on pure ice.

That said, when I launch the car now with all 4 snow tires on there, it does seem to bite at some point...very odd. Especially on hills.

 

Here is what the Porsche Service Information Tecknic has to say about the 996 Z96/00 system

 

I will say, I am still perplexed. The behavior you are describing is how a *torque sensing* center diff (ex Torsen center in Quattro) would behave, not a *speed sensing* viscous coupling.

A torque sensing diff only transfers torque when there is a *difference* in torque... On pure ice, with rear tires spinning at a constant speed, there is no torque going to the rear diff, hence no torque sent to the front diff. Bottom line, I could see Quattro behaving this way. In this scenario, simply get on and off the throttle in gear, (put a small amount of torque on the rear diff by *accelerating* the rear drivetrain) and the front diff will begin to see torque and off you go...

Based on the described behavior, there has to be more to the 996 awd system than just a viscous coupling connecting the front and rear diffs IMO.