bdronsick

Yes but under normal driving conditions the car would be strictly 2WD (unless the rear end loses traction). Interesting

VintageCollector

My 2001 996 TT seems to have a bit of a drivability problem between 1500-2000 RPM. There's a bit of a stutter there, and sometimes I even stall the car car in 1st or reverse.

Has anyone else experienced this?

Porschetech3

In theory only, in reality there is only one other tire that is the same diameter as the 295/30/18 and that's the 255/35/18 which won't fit on the front, and even if it did, in just a few thousand miles you would once again start getting torque to the front drive due to rear tires wear twice as fast as fronts.

If you want 2wd, just remove the front drive like everyone does, easy peasy. Thinking about any other way is an excercize in futility.

theprf

People have reported strange and unpredictable driving dynamics with the front/rear tire size ratio switched. The fronts backdrive the gearbox because the viscous coupler works in both directions. Just remove the cardan shaft, it's a 20 minute job.

Porschetech3

Very true, I have no idea why anyone would put a smaller tire on the front, than the rear, on a 996 AWD, but that is a big no no....

911Syncro

If i may add a little bit to the VC discussion, my other car is a Vanagon Syncro which is AWD with the same drivetrain architecture as the 996 including the VC in the front diff case. Those were produced starting in 1986, and given that the Vanagon community is quite DIY and we love dissecting the car; there is much research study and on the silicon fluid in the VC and how the VC works.

Perhaps some more explanation about the VC. The silicone fluid in the VC has a characteristic that causes it's viscosity to change dramatically when it is agitated, or more accurately when it undergoes shear forces. The VC has a set of closely placed rotating plates with notches in them, every other plate is attached to either the front shaft or the rear shaft. When those shafts (and the plates) are turning at about the same speed the fluid stays at low viscosity. But when they are turning at different speeds (i.e. wheel spin), the fluid become quite solid because of the shear forces applied by the plates. The fluid is designed so that up to about 5% of a difference in the plates speeds causes it to stay low viscosity -- otherwise the wheels would lock up in a parking lot or bind in tight turns. But of course the end result which is the whole purpose is that when any one wheel spins a bit, the VC fluid locks up and transfers power from that axle to the other one.

The Syncro VC has a history of failing if not treated well -- driving too long on hot freeways in the desert is suspect. And of course mismatched tire circumference which causes the plates to constantly be rotating at different speeds which will wear out the fluid and then need to replace the VC. Syncro VCs can fail both in an open condition (no AWD) and an aggressive condition, AWD drive always on. For the Vanagon there is also an aftermarket option to replace the VC with a straight shaft, and then add a manually controlled drive shaft decoupler. This gives the Syncro true 4WD on demand and no potential of VC failure which is very useful for off-road activity as Syncros are often used; but you loose the benefits of the AWD system. The straight shaft / decoupler makes no sense for a 996.

And the 996 VC seems to be really reliable, we rarely hear of failures. But yes, as Porschetech3 says, if the tires are mismatched enough the VC will be in a constant state of "tension" and the fluid will wear out. I've accepted I will have to stay with the stock (specified) tires sizes on the C4S, no problem for me. But the VC can fail, and failure is difficult to diagnose. For the Syncro the test is to jack up the rear wheels using a floor jack with wheels, then place a 2x4 in front of the front wheels. Apply gas and if it drives over the 2x4 then the VC is good.

Last comment, I really like the AWD on the 996, I think it makes the car so much more stable, and going on power out of a turn, this car really pulls out. It's is kinda odd, my 2 cars are both rear engine, same AWD drive-train architecture, both silver, both grey interior. I pretty much alternate between as daily drivers every other day. And I like the safety provided by the 996 AWD, and the safety of the PSM, and the safety provided by the 996 body structure and it's available power to quickly get away from idiots on the road and into a safe spot.

pulpo

https://www.goodingco.com/lot/2002-p...996-carrera-4s

What a spec! We will see what an 85 thousand mile C4S can really do..

jta98z

It will do well. Guards red is not even a fair assessment of the market as they seem to go for 15-20% more based on that alone.

FirstFlatSix

This is accurate.

According to the "996 Essential Companion"

"Under all conditions the rear drive 996 carrera models have 100% drive delivered to the rear wheels. AWD 996 Carrera 4 versions have a minimum 5% drive permanently available on the front wheels and 95% on the rear wheels. Max forward drive available through viscous coupling front drive unit is approx 40% and this will generally only occur when the rear wheels are spinning. Under autobahn or track driving conditions, 155 mph the VC will have transferred approx 30% drive to the front wheels".

FirstFlatSix

I tried buying this car from Porsche Conshohocken in (December 2020?). I called the min it was listed. Got vids and pics. They didnt have a price yet, and were waiting on "appraisal from the GSM". I was hoping to steal the car. Unfortunately they came back to me with an ask of $31K i think, which at the time with 85K plus miles I thought was too much. I passed. A gentlemen in kentucky bought it and exchanged some texts with me. There were a few issues, i cant recall them all (the aftermarket litronics wiring was a disaster) and I cant find the texts as I get so many. He didnt own it long and then Rudy scooped it up. Not sure what Rudy did to it given the time he owned it. Cool spec nevertheless.

bdronsick

Yes, 5% minimum as designed, but that is due to the radius difference between front and rear tires (rear smaller and turning faster)

Since the rear tires wear much faster on the 911, increasing this differential quickly over time, the effective drive transfer increases linearly to about 15% max with no rear wheel slip

Until you replace the tires, and this linear progression resets

So everyone is right here. It's somewhere between 5% and 15% depending when you ask

(AND even my facetious suggestion of using equal-diameter tires to convert the car to semi-permanent 2WD would only work for a few seconds; until the rear tires start wearing faster again; thusly transferring in this case from 0% to 15%)

bdronsick

Good grief that car has at least doubled in value in less than two years

FirstFlatSix

No one is paying $60K for that car. Cars with half the mileage in a cool color are 55Kish, PTS example, maybe 60. I see it as a low 40's car if you have to have a Zanzibar 4S.

joetaf27

Must be COVID related...

joetaf27

Will be interesting to see considering the platform it is being sold on.. rather than an online only auction...