Almost all the drag racers I know use low pressures for increased traction. The low pressures also allow for elongation of the tire at higher wheel RPMs also allows for gearing increase. It's visually apparent on NHRA funny cars, but the same applies on any car/tire in general. In enduro/ road race karting we use this to our advantage too- since we run anything from 8psi (CIK sprinters using 7" wide tires) to 14 psi (laydowns using 5" or 6" widths) on 5" or 6" wheels we tune gear ratios based on not only static diameter but also tire expansion. This is something I have a lot of experience with, over a decade racing cars and karts...

 

^Nick
looks like we are saying the same thing.
tire pressure is what has the biggest impact on contact patch.

 

Steve = 1 and Nick = 1
You guys are both right.

Question: Why don't the Tip transmission TT's have LSD? (and don't insult my manhood...)

 

^i have absolutely no idea. i've always wanted to know that myself. and also, how does "porsche torque vectoring work" (is it all software) ?

those are the two things i cant get an answer to.

 

What is "lower gears"? Is that the 1st gear and the test you mentioned? 997T has 40:60 torque split from the start and flooring it in 1st from 3500rpm will just transfer the torque to the front. When I do accelerate pedal-to-the-metal in 3rd gear from 40mph getting out on the highway I do not feel any wiggle in the rear, in a couple of seconds I already travel at speed when I would lose the license, go to jail, and pay very high fine.

In any case, I spoke with a long-term Porsche tuner Sportec and they told me this test is no good. The way to see if LSD is shot is to measure the breakaway torque on the lift, if it is below specified than LSD is dead (basically that is the indicative test described in the LSD Buster thread).

I do not do accelerations in 1st from 3500 rpm, as I see no point of this exercise in a car like Turbo. It seems to me, then, the advantage of LSD in a Turbo is limited to braking from very high speeds and to be able to do powerslides. I do not do powerslides. And what is the difference if a car wiggles a bit on deceleration from very high speed? I do not track at all.
Basically, LSD is only useful in extreme situations induced by the driver, or on track, or in RWD car. Am I right or wrong?

Maybe it all sounds stupid, but I am just trying to see if the 3500 cost of LSD rebuild is worth it (the way, say, 3500 cost of brake upgrade is worth it).

 

Practical, everyday reason to rebuild your diff if it's not functioning correctly- PSM will interfere earlier with the car if it senses excessive wheel spin. That will trigger one or both rear brakes being applied, meaning the very act of trying to move forward makes the computer try to arrest that progress much earlier. So the net result is (and you really won't feel it) your rear pads will wear excessively relative to the fronts because the traction control is fighting you every step of the way. I have this problem with my GT2- so I shut off SC immediately after cranking the engine- but my GT2 has over 620whp on the lowest setting. In my case, since I drive my car on the track too, it has put premature wear on my rear PCCB rotors- a $7500 replacement cost (wear circles have appeared on the rears but not the fronts).

 

Thanks, Nick, very helpful. The whole discussion in this thread is very interesting, in fact!

As soon as I start the engine I turn Sport Mode on (cannot drive without it) and most of the time turn PSM off (unless it is wet outside). My car is rated at 575hp.