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    Aug 6, 2008 6:00:07 AM

    Minok
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    Limited Slip Rear Differential Lock

    Ok, on the 4wd variants, we have the option of a Limited Slip Rear Differential Lock.

    Anyone that has a 4wd variant with Limited Slip Rear Differential Lock, could you tell me how you have used this option / when has it come in handy?

    I can certainly see snowy/icy driveways with somewhat steep incline, as well as roads up hills here in the Puget Sound area... so its appealing to me...

    Aug 6, 2008 7:02:29 AM

    ADias
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    Reply to: Minok

    Re: Limited Slip Rear Differential Lock

    LSDs can be useful on fast tight hairpins.

    Aug 6, 2008 7:11:19 AM

    reginos
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    Reply to: Minok

    Re: Limited Slip Rear Differential Lock

    The LSD is standard on 4wd 997.2 and optional on 2wd.

    You don't engage and disengage this differential yourself. It is there and works according to the set parameters and you might not understand that it works.

    Generally speaking a limited slip differential automatically reduces the loss of drive which can result from spinning wheels on one side of an axle. Spinning wheels can occur in a variety of situations like tight cornering, pulling away from a standstill or accelerating abrupty.

    With an LSD the electronics like PSM intervene at a higher threshold.

    Aug 6, 2008 8:57:13 AM

    rantanplan
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    Reply to: reginos

    Re: Limited Slip Rear Differential Lock

    a LSD basically shifts the drive to the outside wheel in a corner so that the wheel with more weight on it will get more power.
    normally in a tight corner the wheel with less weight on (inside wheel) will spin and the outside wheel will get less power, hence less traction and drive...LSD corrects that.

    Aug 6, 2008 12:59:44 PM

    Grant
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    Reply to: rantanplan

    Re: Limited Slip Rear Differential Lock

    A clutch-type LSD (like those used by Porsche) also provides much more stability under hard braking and corner entry. It should be a standard item on all 911's. At least it's an option now in the US (not available on a Carrera in the US for the last 10 years).

    Aug 6, 2008 2:21:12 PM

    cibergypsy
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    Reply to: Grant

    Re: Limited Slip Rear Differential Lock

    Correct me if I am wrong but, wasn't LSD available in the US as an option until 2000? I thought that Porsche stopped offering it as an option on the 2001 cars onwards with the advent of PSM... Is this accurate?

    Aug 6, 2008 2:38:21 PM

    Grant
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    Reply to: cibergypsy

    Re: Limited Slip Rear Differential Lock

    Quote:
    cibergypsy said:
    Correct me if I am wrong but, wasn't LSD available in the US as an option until 2000? I thought that Porsche stopped offering it as an option on the 2001 cars onwards with the advent of PSM... Is this accurate?


    Last year to offer it was 1999 (first year of 996). It was also included as part of the 2004 Anniversary edition (first comingling of PSM and LSD).

    Aug 6, 2008 3:24:19 PM

    buzzinfrog
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    Reply to: Grant

    Re: Limited Slip Rear Differential Lock

    Do you really need LSD once you have PSM in hand?

    talking in the matter of safety issues not ride joy of course.

    Aug 6, 2008 3:29:37 PM

    reginos
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    Reply to: buzzinfrog

    Re: Limited Slip Rear Differential Lock

    Quote:
    buzzinfrog said:
    Do you really need LSD once you have PSM in hand?

    talking in the matter of safety issues not ride joy of course.



    PSM is for safety, LSD for better handling/cornering.

    Aug 6, 2008 3:43:27 PM

    Grant
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    Reply to: buzzinfrog

    Re: Limited Slip Rear Differential Lock

    Quote:
    buzzinfrog said:
    Do you really need LSD once you have PSM in hand?

    talking in the matter of safety issues not ride joy of course.


    You don't "Need" it, but it makes driving the car much more enjoyable on the street and faster at the racetrack.

    Aug 6, 2008 4:59:46 PM

    Carlos from SpainM
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    Carlos from Spain
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    Reply to: Grant

    Re: Limited Slip Rear Differential Lock

    Quote:
    Grant said:
    Quote:
    buzzinfrog said:
    Do you really need LSD once you have PSM in hand?

    talking in the matter of safety issues not ride joy of course.


    You don't "Need" it, but it makes driving the car much more enjoyable on the street and faster at the racetrack.



    Agree 100%, I didn't have in my ex-996C4-10mm and now have it on my 997C2S-20mm and I think it should be standard on these cars.
    Gives more stability on braking into the turn and a more fluid as well as more effective exit of the slowers corners, in essense its makes the car handle sportier and also handle better without any drawbacks.

    Aug 6, 2008 5:14:56 PM

    mnalla
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    Reply to: Minok

    w/LSD -20mm how dies it affect...........

    how does it afect ride height and curb rash especially when entering and exiting driveways, over speed bumps, etc? Does it sit too low that you have to be extra careful?

    Aug 6, 2008 5:25:35 PM

    ADias
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    Reply to: mnalla

    Re: w/LSD -20mm how dies it affect...........

    Quote:
    mnalla said:
    how does it afect ride height and curb rash especially when entering and exiting driveways, over speed bumps, etc? Does it sit too low that you have to be extra careful?



    LSD does not relate to ride height, suspension type does.

    Curb rash? what do you mean?

    Aug 6, 2008 7:13:37 PM

    Minok
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    Minok
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    Reply to: ADias

    Re: w/LSD -20mm how dies it affect...........

    Let me clarify my original request.

    Yes, on the 4wd cars, LSD is standard.

    What is NOT standard is the LSD LOCK, which is an option one can spec. This LSD LOCK, of course, limits what LSD is allowed to do; as the LSD is electronically controlled, its likely another button on the dash.

    The option (220 for $US 950) as described is:

    Friction disc lock on rear axle. Pull - 22% and Push - 27%.

    So the question is: when have people with P-4s used the LSD LOCK to benefit?

    Aug 6, 2008 7:21:07 PM

    ADias
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    Reply to: Minok

    Re: w/LSD -20mm how dies it affect...........

    That's news to me. I still think that the 911.2 LSD is a mechanical LSD not an e-diff.

    Aug 6, 2008 7:35:24 PM

    reginos
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    Reply to: Minok

    Re: w/LSD -20mm how dies it affect...........

    Quote:
    Minok said:
    Let me clarify my original request.

    Yes, on the 4wd cars, LSD is standard.

    What is NOT standard is the LSD LOCK, which is an option one can spec. This LSD LOCK, of course, limits what LSD is allowed to do; as the LSD is electronically controlled, its likely another button on the dash.

    The option (220 for $US 950) as described is:

    Friction disc lock on rear axle. Pull - 22% and Push - 27%.

    So the question is: when have people with P-4s used the LSD LOCK to benefit?


    Option 220 is the mechanical LSD which is standard on 4wd and optional on 2wd.

    There is nothing else.

    Aug 6, 2008 7:37:58 PM

    mnalla
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    Reply to: ADias

    Re: w/LSD -20mm how dies it affect...........

    ADias

    I am referring to -20mm which I assume is that the car is lowered 20mm? If that is the case do the front fenders rub the driveways or speedbumps causing rash/scrapes etc?

    Thanks.

    Aug 6, 2008 7:51:24 PM

    ADias
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    Reply to: mnalla

    Re: w/LSD -20mm how dies it affect...........

    Quote:
    mnalla said:
    ADias

    I am referring to -20mm which I assume is that the car is lowered 20mm? If that is the case do the front fenders rub the driveways or speedbumps causing rash/scrapes etc?

    Thanks.



    OK. I imagine you need to be more careful and exit/enter driveways on a diagonal. My current Vette has an air dam up front and is lower than an 11 and I have to drive it like I described above. My former 996 C4 did not have an air dam but given the long front overhang I had to be very careful exiting steep driveways.

    I would not buy the -20mm suspension in the US - too many miles of less than billiard perfect freeways (bigger country, many more road miles to maintain pristine). And even in Europe I wonder how that is in cites with poor street surfaces (very common) and cobblestones.

    Aug 6, 2008 8:24:56 PM

    Minok
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    Minok
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    Reply to: ADias

    LSD LOCK Option...

    Ok, well I have a new theory then. Given that the porsche.com/usa configurator for the Targa 4, lists, as the standard info, that the Targa 4 is RWD , it could be that this screw-up in the spec data has the configurator showing the optional in RWD car LSD as an option for the Targa 4 (which, as a 4wd, comes standard with LSD).

    That would also indicate why my dealer is saying that option 220 (LSD LOCK) is being kicked back as "conflict with model".

    This is what happens when someone doesn't properly test websites before releasing, nor provides enough data for the user to understand. After all, how hard would it be to say "For RWD cars, the LSD provides friction disc lock on rear axle. Pull - 22% and Push - 27%." At least then it would be clear to us that the option is erroneously being offered.

    Good times... good times....




    Aug 6, 2008 8:49:03 PM

    Carlos from SpainM
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    Reply to: mnalla

    Re: w/LSD -20mm how dies it affect...........

    Quote:
    mnalla said:
    ADias

    I am referring to -20mm which I assume is that the car is lowered 20mm? If that is the case do the front fenders rub the driveways or speedbumps causing rash/scrapes etc?

    Thanks.



    The 997 with -20mm is not too bad in terms of ground clearance due to its fornt bumper underneath design. I had previously a 996 with -10mm and the GT3 aerokit and it was much worse (part also due to the nose being lower due to the GT3 front bumper), would rub the bottom lip everywere, wereas in the 997S-20mm I rarely ever scrape it. Its fine for everyday use.

    Aug 6, 2008 11:12:36 PM

    devo
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    Reply to: mnalla

    Re: w/LSD -20mm how dies it affect...........

    Quote:
    mnalla said:
    ADias

    I am referring to -20mm which I assume is that the car is lowered 20mm? If that is the case do the front fenders rub the driveways or speedbumps causing rash/scrapes etc?

    Thanks.



    The base Carrera is lowered 20mm with the addition of SPASM, however, the Carrera S is only lowered 10mm with this option. Sorry if this was already addressed.

    Aug 6, 2008 11:54:54 PM

    mstams
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    Reply to: devo

    Re: w/LSD -20mm how dies it affect...........

    So if SPASM (-20mm lower in total) is not too bad as far as scraping, how is it in terms of additional firmness?

    I have selected it on my current order, but I must confess that I am a bit unsure. Will my wife complain about the ride comfort too much?

    Aug 7, 2008 2:04:59 AM

    devo
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    Reply to: mstams

    Re: w/LSD -20mm how dies it affect...........

    Quote:
    mstams said:
    So if SPASM (-20mm lower in total) is not too bad as far as scraping, how is it in terms of additional firmness?

    I have selected it on my current order, but I must confess that I am a bit unsure. Will my wife complain about the ride comfort too much?



    You will have a normal and a sport mode. I would imagine sport mode would be very stiff, almost GT3 like. I don't know how stiff normal will be. I would think that it would be okay, but that's a subjective thing. I am certain that each mode will be more harsh than standard PASM, respectively. I know that I will get it, unless I go turbo. You should have your dealer check with the Porsche rep.

    Aug 7, 2008 4:28:45 AM

    Minok
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    Minok
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    Reply to: ADias

    Re: w/LSD -20mm how dies it affect...........

    Quote:
    ADias said:
    That's news to me. I still think that the 911.2 LSD is a mechanical LSD not an e-diff.



    According to the Porsche press release:


    The electronically controlled PTM system replaces the viscous multiple-plate clutch all-wheel drive system of the previous Targa models, which results in a more pronounced, Porsche typical driving characteristic. To ensure maximum traction and agile handling at all times, PTM feeds exactly the right share of engine power to the front wheels, as needed, in every driving situation through an electronically controlled multiple-plate clutch. As on all new Carrera 4 models, a standard rear-locking differential gives the car even greater driving dynamics.

    Aug 7, 2008 4:38:14 AM

    reginos
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    reginos
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    Reply to: Minok

    Re: w/LSD -20mm how dies it affect...........

    Quote:
    Minok said:
    Quote:
    ADias said:
    That's news to me. I still think that the 911.2 LSD is a mechanical LSD not an e-diff.



    According to the Porsche press release:


    The electronically controlled PTM system replaces the viscous multiple-plate clutch all-wheel drive system of the previous Targa models, which results in a more pronounced, Porsche typical driving characteristic. To ensure maximum traction and agile handling at all times, PTM feeds exactly the right share of engine power to the front wheels, as needed, in every driving situation through an electronically controlled multiple-plate clutch. As on all new Carrera 4 models, a standard rear-locking differential gives the car even greater driving dynamics.



    PTM is the Porsche 4wd system that is electronic now borrowed from the Turbo.
    This is supplemented by a standard mechanical LSD that has nothing to do with the 4wd system. It can also be optioned for the 2wd models.

    Aug 7, 2008 6:19:52 AM

    ADias
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    Reply to: Minok

    Re: w/LSD -20mm how dies it affect...........

    Quote:
    Minok said:
    Quote:
    ADias said:
    That's news to me. I still think that the 911.2 LSD is a mechanical LSD not an e-diff.



    According to the Porsche press release:


    The electronically controlled PTM system replaces the viscous multiple-plate clutch all-wheel drive system of the previous Targa models, which results in a more pronounced, Porsche typical driving characteristic. To ensure maximum traction and agile handling at all times, PTM feeds exactly the right share of engine power to the front wheels, as needed, in every driving situation through an electronically controlled multiple-plate clutch. As on all new Carrera 4 models, a standard rear-locking differential gives the car even greater driving dynamics.




    The electronic control is for torque distribution between rear and front through PTM. The LSD in the rear is purely mechanical.

    Aug 7, 2008 7:45:07 PM

    Carlos from SpainM
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    Reply to: ADias

    Re: w/LSD -20mm how dies it affect...........

    Right, centre differentail is being confused with rear differentials. They are two different thing with different functions.

    Simple:

    - The PTM is a CENTRE differential -> modulates torque between front and rear axl (i.e AWD). Happens to be electronic type diff vs the viscous type of the Mk-I carerra and all 996.

    - the LSD option is a REAR differential -> modulates torque between left and right rear wheels (i.e grip between rear wheels when one spins). Happens to be mechanical limited slip type.

    Aug 9, 2008 9:49:43 PM

    C2Nerves Offline
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    Reply to: Carlos from SpainM

    Re: w/LSD -20mm how dies it affect...........

    Has anyone actually tested the LSD on the 997.2? How does it affect PSM control? is it in anyway linked to it? Somone mentioned in a post that the PSM threshold becomes raised due to this option. If so, is there a disabling switch for Difflock, or is it permanently active?

    Also, LSD option 220 has nothing to do with -20mm lowering option. Right?

    Please can anyone assist in technical details on how LSD works exactly. Can you still throw the rear of your porsche into corners, without being interrupted by a PSM like cutouts or artificial interventions?


    I believe many of us get too busy adding fun optoins while missing out on such an important handling feature.

    help pls while my order is still open...

    Aug 9, 2008 11:34:22 PM

    Misha011
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    Reply to: C2Nerves

    Re: w/LSD -20mm how dies it affect...........

    Quote:
    C2Nerves said:
    Has anyone actually tested the LSD on the 997.2? How does it affect PSM control? is it in anyway linked to it? Somone mentioned in a post that the PSM threshold becomes raised due to this option. If so, is there a disabling switch for Difflock, or is it permanently active?

    Also, LSD option 220 has nothing to do with -20mm lowering option. Right?

    Please can anyone assist in technical details on how LSD works exactly. Can you still throw the rear of your porsche into corners, without being interrupted by a PSM like cutouts or artificial interventions?


    I believe many of us get too busy adding fun optoins while missing out on such an important handling feature.

    help pls while my order is still open...



    Difflock and LSD are two different things . This site is very good and engineeringly acurate !! http://www.carbibles.com/transmission_bible_pg2.html

    Aug 10, 2008 5:17:58 AM

    Grant
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    Reply to: C2Nerves

    Re: w/LSD -20mm how dies it affect...........

    Quote:
    C2Nerves said:If so, is there a disabling switch for Difflock, or is it permanently active?


    It's a totally mechanical device that is alway active. There are friction clutch discs that keep the two rear wheels connected (like a solid axle), unless there is sufficient differential torque between the two wheels to make the discs slip. This is a very important feature and should be standard on all sportscars...
     
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