porsche's on the fly sway bar adjustment.

Discussion in 'OT Driven' started by mastershake, Apr 29, 2007.

  1. mastershake

    mastershake so then i punched her in the mouth

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    Ive heard something about this but nothing detailed, anyone want to shed light on this for me?
     
  2. danewreed

    danewreed OT Supporter

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    surprising from a factory that doesn't offer an LSD on most of its models

    (subscribed)
     
  3. I wouldn't trust most porsche owners to adjust their seat position, much less sway bar settings.
     
  4. MrBonus

    MrBonus Et Tu, Brute?

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    You're thinking of Corvette owners.
     
  5. Good comeback.:greddy:
     
  6. Cachee0

    Cachee0 OT's Technical Recruiter, Send me your resume

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    it was ok I chuckled:mamoru:
     
  7. deusexaethera

    deusexaethera OT Supporter

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    Limited-slip differentials aren't the be-all and end-all of traction control. They decrease gas mileage and they only serve to compensate for inadequate traction to begin with. If you've got wheelspin, you should upgrade your wheels and tires first, then your suspension, then if you still have problems you should get an LSD. Or better yet, learn how to control the power yourself so you don't get wheelspin.
     
  8. They also allow you to put down MORE power. If you can put enough power to the inside tire in a turn to make it spin, you may well be far short of your traction limit on the outer tire. With the LSD you can apply more power to the outer tire (which has a much larger contact area.)

    It's not a matter of "inadequate traction to begin with" It's just another way to gain more traction. Nobody ever complained that their car had too much traction. I can just see M Schumacher finishing a race and saying to the media "Well, the car was good, but it was too easy to apply power coming out of the turns, next race we'll see if we can get more wheelspin on the inside wheel."
     
  9. deusexaethera

    deusexaethera OT Supporter

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    Anybody who stomps the gas (or the brake) in the middle of a turn is an idiot asking to spin out, crash, explode, and die.** The last thing you want is to shift the weight balance of the car fore/aft while it's already leaning to one side and rotating. No LSD is going to keep your car from spinning out if you apply a hair too much power coming out of a turn (or a hair too much brakeforce going in), because no LSD can increase the car's overall traction -- really good tires, on the other hand, most certainly can. Furthermore, you want the extra contact patch on the outside wheels to be used for keeping your car under control, not for changing its speed, so in that respect an LSD is actually detrimental.

    Michael Schumacher has more experience driving than anyone here ever will, so his commentary, whether real or imagined, is totally irrelevant.

    As previously stated, don't buy an LSD unless you've already got the best rubber you can put on your car and you're still getting wheelspin GOING IN A STRAIGHT LINE. If you're getting wheelspin in a corner, you need to take your foot off the gas.

    **Dramatization. Results not typical. Do not attempt.
     
    Last edited: May 2, 2007
  10. deusexaethera

    deusexaethera OT Supporter

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    Aside from that, the on-the-fly swaybar janx sounds dangerous. The car's handling needs to be progressive and predictable. Cranking a knob to make it lean less or have a smoother ride at a moment's notice (or worse, having the engine computer adjust it for you) could be disastrous.
     
  11. Ok, you're obviously correct. All of these world-class cars have been engineered by fools. If only they had consulted you first, they would have not added that awful LSD. Maybe they should keep you on retainer, as your knowledge of powertrain design is vast. I've already explained precisely what it's for, but you either don't get it, or can't admit that I (and the engineers of some of the worlds fastest cars) am right. I didn't say it's to apply full power coming out of a turn, and yes coming OUT of a turn; you accelerate through the apex. It allows you to apply MORE power than you would be able to without the LSD.
     
  12. P07r0457

    P07r0457 New Member

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    deuse aint the brightest at this stuff.
     
  13. deusexaethera

    deusexaethera OT Supporter

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    Nah, I'm just strongly-opinionated. I do a better job of keeping it under control in real life. I'm sure you're familiar with that behavior pattern.

    - - -

    But yes, Market Garden, the world would be a better place if people consulted me before they did anything, if for no other reason than because that way they would make decisions based on a wider perspective than just what they themselves see and think. And no, I don't exempt myself from that philosophy.

    Anyway, if prior posts are to be believed, Porsche DOESN'T include LSDs on most of their cars -- in fact, the realtime-adjustable swaybar (though I question its effectiveness) is proof that Porsche engineers know that it's more important to keep the side-to-side weight balance (and thus the available traction on each wheel) as neutral as possible in a corner, than it is to compensate for poor weight balance by transferring power to the already-overburdened outer wheels. So...which world-class carmakers were you referring to that prefer to spend money on an LSD instead of an improved suspension?
     
    Last edited: May 2, 2007
  14. Just off the top of my head, the Enzo, M3, Lambos, Corvette, F430, I could keep going...

    The 997 GT3 has a LSD. I guess Porsche puts them on the cars that are actually intended to be raced.

    Formula 1 cars use LSDs too. I guess the F1 engineers could benefit from your insights too.
     
  15. deusexaethera

    deusexaethera OT Supporter

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    Note the highlighted words; I suspect you don't actually know what you're talking about anymore, or else you just didn't read what I asked you, because I think Ferrari, Lamborghini, and BMW might have a differing opinion on their design priorities. Chevy...well, you're probably spot-on about them.

    Okay, so they put LSDs on cars that already have the best tires and suspension setups they possibly can have. That kinda supports a previous statement of mine, which I will once again reiterate since its meaning has apparently gone unappreciated:

    Do I need to point out that all the cars you listed have capabilities so far above the average driver that only people with the skill and experience necessary to actually push them to their limits (without spinning out, crashing, exploding, and dying, as also mentioned previously) will ever get a single iota of benefit from the LSD? Hmm...maaaybe, that's why they don't put them on Camrys.

    Are you done assailing my perspective yet? You must be getting tired by now.
     
    Last edited: May 2, 2007
  16. You don't seem to understand that all the suspension and driveline components are part of a system. You say that tires must be perfectly optimized, and sway bars too, and springs, THEN you can add a LSD. Road cars are compromises. You might be able to make a 2% improvement in lap times by spending $5 million to tune a sway bar, but you can make a 5% improvement by adding a LSD, for less money. A LSD is a component no different from any other part. You seem to have some vendetta against LSDs. Did one cheat on you once? Maybe you don't have one. Your argument has evolved from "They decrease gas mileage and they only serve to compensate for inadequate traction to begin with." To you position now of "all the cars you listed have capabilities so far above the average driver that only people with the skill and experience necessary to actually push them to their limits" It seems you're jumping from point to point, and you're drifting slowly away from your initial position.
     
  17. deusexaethera

    deusexaethera OT Supporter

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    They do serve to compensate for inadequate traction, at least in most cases, and the cars you listed that actually make use of them because all other options are exhausted do have capabilities so far above the average driver that few people will ever actually need the extra 1-2% traction that the LSD adds to an already optimized system.

    Since you seem to be confused by the way I'm adding onto my original argument each time I post, I'll state the entire thing all in one shot for you and leave you to find the supporting evidence in your own prior responses:

    Limited-slip differentials transfer power from wheels that slip to wheels that grip, as most everybody knows. The reason why I recommend against getting one until you've got the best suspension and tires you can buy is threefold:

    1. They transfer power when they don't need to (i.e. whenever the differential's internals are rotating during a corner, whether there is wheelspin or not), meaning they consume energy when they don't need to, meaning they reduce gas mileage and wear out faster than an open differential. An open differential is nearly 100% efficient, introduces almost no drag into the system, and provided that the car is actually capable of sticking to the ground, will not result in wheelspin.

    2. In an off-road vehicle, being able to actively reduce wheelspin while climbing hills and even driving on flat yet slippery ground is a huge advantage since the available traction differs for every patch of dirt and rock the vehicle drives across. On a road car, however, an LSD will be most active in corners and will transfer extra torque away from the inside wheels to the outside wheels. This is almost always a bad thing, however irritating squealing tires may be, because the outside tires are already under enormous stress moving the car forward AND rotating it around a circle AND resisting shear forces that can be as strong or stronger than what the car would experience driving along the side of a 45-degree slope. (that would be 1g for you noobs.) If the tires are already at or near their traction limit, then the extra traction provided by the LSD will, instead of harmlessly spinning the inner wheels, break the outer wheels free from the road, at which point the car will go out of control almost instantly and with little hope of recovery since, unlike off-road where the wheels may slide onto a firmer patch of ground, the roadway that the tires are skidding onto is not going to provide any more traction than the roadway the tires just skidded away from.

    3. They are all-too-often installed as aftermarket parts by people who believe that they are the best means to improve traction on their car. They are not the best means to improve traction; the best means to improve traction on a car is to equip it with suspension that keeps it as balanced as possible at all times, so as to keep the forces on all four wheels as close to equal as possible, and to install tires that have enough grip to withstand the full accelerative forces of the engine and brakes if at all possible. The reason why this is better than installing an LSD is because improving the suspension and using better tires will improve ALL aspects of the car's performance, not just its ability to corner under power.

    Points 1 and 2 derive from physics and are not arguable. Point 3 is certainly arguable since some people may only care about being able to peel out at stoplights without their car being a one-wheel-wonder, but for almost everyone the better solution is proper suspension and sticky tires -- and the designs of many sportscars and even supercars support that assertion. It's very simple: you don't need to worry about balancing power across the driveaxle if the tires don't slip in the first place.
     
    Last edited: May 2, 2007
  18. 1. The increase in performance more than offsets the parasitic loss through the LSD. If it didn't, then people wouldn't use them.

    2. Your "instantly out of control" idea only works if the person driving has no idea what he's doing. Anyone who is competent can find that edge between traction and oversteer and stay on it. A little oversteer can be cured by modulating the throttle. Perhaps you can't control oversteer, but others can.

    3. Here you are arguing against LSDs when they are installed by people who have no idea what they're doing. That's fine. I don't care about them. I don't see your point.

    It seems that you, at first, made a statement about LSDs and their usefulness. Under pressure you started to qualify your position. Now you've placed so many qualifiers and provisions on your position that it's really quite another position.
     
  19. deusexaethera

    deusexaethera OT Supporter

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    No, it's the same position, just with a better-defined context than it started out with. And yes you do see my point, you're just choosing to dismiss it -- that's not the same as not seeing it at all.

    You can say you don't care about people who don't know what they're doing, but even in just two years of commuting I've seen way too many bad accidents -- mostly involving sports cars -- to be able to say I don't care about them either. Anything that gives Joe Idiot a false sense of security makes it that much easier for him to go sliding out of control and take out my car along the way. Since these world-class cars we're talking about get driven on public highways just like any beat-up old Honda Civic, it seemed reasonable to take the setting and the relevant portion of the driving population into consideration when posting my opinion.
     
  20. Now you're arguing that idiots who install LSDs in cars that didn't come with them are a hazard on the roads. That's a COMPLETELY different position than you started with. You're hopping from one lilly pad to another.
     
  21. deusexaethera

    deusexaethera OT Supporter

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    No I'm not. My basic assertion that LSDs are crutches is exactly the same as it has always been. My mistake has been in trying to account for the various reasons why your point-of-view might be the way it is. I'll try to remember to not do that next time.
     
  22. LSDs are a "crutch" as much as sway bars are a "crutch" They're all part of a system. Everything works together. You don't get that. You want to put all suspension parts in one group, and then put the LSD in another. That's not how it works. They're all designed to work together.
     
  23. deusexaethera

    deusexaethera OT Supporter

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    I like how you keep trying to lecture to an engineer about system design.

    The differential and the driveaxle are NOT part of the same system as the chassis and the suspension, because the suspension is specifically designed to isolate its movement and the movement of the chassis from the operation of the driveline.

    Not all suspension designs succeed brilliantly at fulfilling this requirement, and that is where the point I made about LSDs being a crutch comes in. When the suspension is insufficiently-capable of isolating the chassis from the driveline, undesirable events like wheel-hop can occur under conditions that don't exceed the vehicle's overall capabilities. Installing an LSD to compensate for the suspension's inability to keep all four wheels firmly planted on the ground is the very definition of a crutch; a crutch is a device that one system depends on to compensate for its own deficiencies, e.g. a human with a broken leg depends on a crutch to help him stand up, and a car with shitty suspension can just the same depend on an LSD to keep its tires from squealing every time it goes around a corner. However, just like the human would be better off if his leg were not broken, a vehicle with a properly-designed suspension will be better off compared to one that compromises its other systems to make up for the suspension's deficiencies.
     
    Last edited: May 3, 2007
  24. I don't think you get it. Maybe you should sue whatever college gave your engineeing degree, becuase they obviously didn't teach you much. All of the systems have to work together.

    As to your human with a broken leg argument, the "crutch" helps the human get around, but he's slowed by his injury. The LSD is PART OF THE WHOLE DESIGN. You don't understand that the suspension is designed WITH THE LSD IN MIND. It's part of a total package. These people don't design this stuff without talking to each other.

    I still have a real hard time coming to your conclusion because ALL OF THE REAL HIGH PERFORMANCE CARS IN THE WORLD USE LSDs. Why? Beacause THEY WORK.

    Jesus christ, you are thick headed.

    By your own "it's a crutch" argument, why don't you argue against sway bars? They just limit side to side weight transfer. Real stiff springs can do that. So are sway bars a crutch for inaqequate spring design? NO. They are PART OF A TOTAL PACKAGE.
     
  25. deusexaethera

    deusexaethera OT Supporter

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    At this point I think it's safe to say that you're never going to give my point of view an ounce of unbiased consideration, so I'm not going to bother arguing with you anymore. Go look at some photos of Lamborghinis and fantasize about driving one; you'll feel better in no time.
     

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