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  1. #176
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    Click here to enlarge Originally Posted by spdu4ea Click here to enlarge
    That said, there are still external reasons to wander (grooves/crowning in the pavement, uneven traction traction on one side of the lane vs the other) so it is important for the driver to know how to deal with it.
    When I bracket raced, I didn't get a good stable run until I switched to a spool. Even with skinny's it was a wobbly ride. Almost like riding in a boat. So I could imagine what 700+ HP on bias bly slicks would be like through an OEM diff..

    Bottom line though, the slick/radial combo was to blame.

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    I just watched the video for the first time.

    After looking closely it's really hard to tell what caused this. I will tell you what could have prevented it though.

    The driver took forever brake. He didn't let off when he should have, as soon as the car began to sway; you need to let off and regain control. I don't know why he stayed on the throttle as long as he did.

    Second, why the long ass burnout? Slicks only need a couple seconds to heat up. I think he was a little too riled up and just trying to show off... Which leads me to believe the "not letting off attitude" of my first point as to what really caused this accident.

    Most accidents are caused by people, not machines.

    I'm sure the tire combo didn't help; but I have seen a ton of people run strange tire combos on a variety of cars. That's not to say it's 100% tire combo, and 0% his fault. But somewhere in between.
    Some people live long, meaningful lives.

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  3. #178
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    Click here to enlarge Originally Posted by spdu4ea Click here to enlarge
    An OS Giken would not have saved him once he started to lose it, but there is a decent chance it would have prevented him from getting so squirrelly in the first place. And differentials do not all work the same:


    An open diff transfers torque to the path of least resistance. Once 1 tire starts spinning, more torque goes to that spinning tire. The car remains relatively stable -- aided in large part by 1 rear tire maintaining traction.

    The M3's "Variable M" diff is an odd duck -- but basically when 1 wheel starts spinning fluid pressure builds up, activating the opposing clutch packs to divert torque to the slower-spinning wheel. Whereas a typical gear-type torque sensing diff might be able to split 75% torque to 1 wheel, 25% to the other, the M variable is capable of delivering 100% torque to one side. That sounds great in theory, but in practice there is quite a bit of lag when pressure is building up. Combine that lag with 3x more power than was calibrated for the unit, and you've got a recipe for some instability: right rear starts spinning fast enough to activate 100% torque for the left rear, which, thanks to the shear pump's lag, then spins fast enough to activate 100% torque for the right rear. During this time, each wheel assembly is toeing-in under load and toeing-out when torque is diverted back away causing the back end to start wandering around. Add a novice driver combined with an unstable tire setup and you've got a recipe for disaster.

    A clutch-type diff locks based on the torque being passed through the differential -- regardless of whether one side is spinning faster than the other. Once you put the required amount of torque through the rear end, the axle locks. Since both wheels are rotating the same speed the toe-in under loading is equalized (provided both tires have roughly same available traction) -- so even when the back end loses complete traction the chassis isn't giving the back end a reason to wander.


    That said, there are still external reasons to wander (grooves/crowning in the pavement, uneven traction traction on one side of the lane vs the other) so it is important for the driver to know how to deal with it.
    Click here to enlarge

  4. #179
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    Click here to enlarge Originally Posted by spdu4ea Click here to enlarge
    An OS Giken would not have saved him once he started to lose it, but there is a decent chance it would have prevented him from getting so squirrelly in the first place. And differentials do not all work the same:


    An open diff transfers torque to the path of least resistance. Once 1 tire starts spinning, more torque goes to that spinning tire. The car remains relatively stable -- aided in large part by 1 rear tire maintaining traction.

    The M3's "Variable M" diff is an odd duck -- but basically when 1 wheel starts spinning fluid pressure builds up, activating the opposing clutch packs to divert torque to the slower-spinning wheel. Whereas a typical gear-type torque sensing diff might be able to split 75% torque to 1 wheel, 25% to the other, the M variable is capable of delivering 100% torque to one side. That sounds great in theory, but in practice there is quite a bit of lag when pressure is building up. Combine that lag with 3x more power than was calibrated for the unit, and you've got a recipe for some instability: right rear starts spinning fast enough to activate 100% torque for the left rear, which, thanks to the shear pump's lag, then spins fast enough to activate 100% torque for the right rear. During this time, each wheel assembly is toeing-in under load and toeing-out when torque is diverted back away causing the back end to start wandering around. Add a novice driver combined with an unstable tire setup and you've got a recipe for disaster.

    A clutch-type diff locks based on the torque being passed through the differential -- regardless of whether one side is spinning faster than the other. Once you put the required amount of torque through the rear end, the axle locks. Since both wheels are rotating the same speed the toe-in under loading is equalized (provided both tires have roughly same available traction) -- so even when the back end loses complete traction the chassis isn't giving the back end a reason to wander.


    That said, there are still external reasons to wander (grooves/crowning in the pavement, uneven traction traction on one side of the lane vs the other) so it is important for the driver to know how to deal with it.
    Sorry but part of this is incorrect, an open diff applies the same torque to both wheels at all times. Each wheel does not get different amounts.

    He is already running a limited slip. An OS Gilken is an LSD just with with different locking characteristics. I don't see this making any difference from him already running an M diff on the strip. On the roadcourse or in poor weather? Sure.
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  5. #180
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    Something you guys need to understand about a Limited Slip, which he was already running:

    This type of LSD has all of the same components as an open differential, but it adds a spring pack and a set of clutches. Some of these have a cone clutch that is just like the synchronizers in a manual transmission.

    The spring pack pushes the side gears against the clutches, which are attached to the cage. Both side gears spin with the cage when both wheels are moving at the same speed, and the clutches aren't really needed -- the only time the clutches step in is when something happens to make one wheel spin faster than the other, as in a turn.
    A different LSD would not have saved him from a poor setup and driver error, it is a moot point.
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  6. #181
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    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    Something you guys need to understand about a Limited Slip, which he was already running:



    A different LSD would not have saved him from a poor setup and driver error, it is a moot point.
    Some can't understand this fact, and thats the sad part.
    Click here to enlargeClick here to enlarge

  7. #182
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    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    Sorry but part of this is incorrect, an open diff applies the same torque to both wheels at all times. Each wheel does not get different amounts.
    Different ways of looking at it... Jack one wheel in the air like this wavetrac video:

    and you'll get ~0tq to both wheels despite the open diff's input shaft getting >0 power/torque from the engine. All of that energy is wasted through the lifted wheel. In this same scenerio, a spool will transfer power/torque equally to both axles, but only 1 will be able to use it.


    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    Something you guys need to understand about a Limited Slip, which he was already running:
    You got that quote from a how-stuff-works article (inaccurately) describing the operation of a conventional clutch-type LSD (http://auto.howstuffworks.com/differential4.htm). That description is inaccurate in this part:

    Click here to enlarge Originally Posted by how stuff doesn't work
    the only time the clutches step in is when something happens to make one wheel spin faster than the other, as in a turn. The clutches fight this behavior, wanting both wheels to go the same speed. If one wheel wants to spin faster than the other, it must first overpower the clutch
    Again, the clutches are activated based on a minimum input torque being met. If you're coasting in neutral with an LSD, no torque is activating the clutch packs so there is no resistance to wheel speed differentiation. Think of it like a manual transmission:

    No torque going through diff = clutch pedal pressed to the floor (clutch disk pulled away from mating surfaces and freewheeling)
    Some amount less than lock-up torque going through diff = clutch pedal held partway between floor and released (clutch disk slipping between mating surfaces)
    More than lock-up torque going through diff = clutch pedal released (clutch disck forced against mating surfaces preventing slip)


    The 01+ M3 uses a 100% different, speed-based LSD design: the GKN Visco-Lok. BMW calls it the M Variable, but it is not exclusive to BMW and is also found in the '08-10 Viper... Whereas under load a clutch type differential tries to lock the axle (both wheels turning same speed), the visco-lok is reactive -- it needs a wheelspeed difference before it applies torque to the other wheel. It never, ever, ever, ever tries to lock both axles together.

    The visco-Lok's functions essentially the same as a gerotor pump-type LSD, described here by wikipedia:

    Gerotor pump
    This works by hydraulically compressing a clutch pack. The gerotor pump uses the housing to drive the outer side of the pump and one axle shaft to drive the other. When there is differential wheel rotation, the pump pressurizes its working fluid into the clutch pack area. This provides a clamp load for frictional resistance to transfer torque to the higher traction wheel. The pump based systems have a lower and upper limits on applied pressure, and internal damping to avoid hysteresis. The newest gerotor pump based system has computer regulated output for more versatility and no oscillation.
    Hmm problems with oscillation sound familiar? There are no electronics in the E46 M3 LSD (not sure about E9x)... And the internal damping and pressure limits were calibrated for 262 ft-lbs -- not 640...

  8. #183
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    Click here to enlarge Originally Posted by spdu4ea Click here to enlarge
    and you'll get ~0tq to both wheels despite the open diff's input shaft getting >0 power/torque from the engine. All of that energy is wasted through the lifted wheel. In this same scenerio, a spool will transfer power/torque equally to both axles, but only 1 will be able to use it.
    Ok, and? Maybe different ways of looking at it but it is still a constant that an open diff provides the same torque to both wheels at all times. They must spin at the same speed, period.

    Click here to enlarge Originally Posted by spdu4ea Click here to enlarge
    Again, the clutches are activated based on a minimum input torque being met. If you're coasting in neutral with an LSD, no torque is activating the clutch packs so there is no resistance to wheel speed differentiation. Think of it like a manual transmission:

    No torque going through diff = clutch pedal pressed to the floor (clutch disk pulled away from mating surfaces and freewheeling)
    Some amount less than lock-up torque going through diff = clutch pedal held partway between floor and released (clutch disk slipping between mating surfaces)
    More than lock-up torque going through diff = clutch pedal released (clutch disck forced against mating surfaces preventing slip)


    The 01+ M3 uses a 100% different, speed-based LSD design: the GKN Visco-Lok. BMW calls it the M Variable, but it is not exclusive to BMW and is also found in the '08-10 Viper... Whereas under load a clutch type differential tries to lock the axle (both wheels turning same speed), the visco-lok is reactive -- it needs a wheelspeed difference before it applies torque to the other wheel. It never, ever, ever, ever tries to lock both axles together.

    The visco-Lok's functions essentially the same as a gerotor pump-type LSD, described here by wikipedia:
    I think we are getting away from the point here.

    The OS Gilken is a clutch type isn't it? How would that help exactly? It wouldn't.

    The M3's diff is a limited slip (speed sensing design) and it didn't save the car, so the differential discussion is really pointless.
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  9. #184
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    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    an open diff provides the same torque to both wheels at all times. They must spin at the same speed, period.




    I think we are getting away from the point here.
    thread split?

    The OS Gilken is a clutch type isn't it? How would that help exactly? It wouldn't.
    The OS Giken is a clutch type and it would lock on launch forcing both axles to turn the same speed. It would have helped prevent the rear end instability that caused the rear end to start veering to the right @ 1:10 -- which lead to the tankslapping overcorrections after the 2-3 shift (all of course still ultimately caused by driver staying in it beyond his skill)

    The M3's diff is a limited slip (speed sensing design) and it didn't save the car, so the differential discussion is really pointless.
    The M3's LSD doesn't react until after there is a wheelspeed difference.


    Listen closely during the 1st second, you'll hear the LR start squabbling for traction & spinning (and see the rear of the car hunkering down) before the right rear wheel even moves. This react-compensate speed-based design results in differing wheel speeds the entire time traction is low -- totally different from a clutch type...


    Don't get hung up on the term "LSD." It encompasses a wide range of different designs, features, and operation. Pump action, double-barrel, and semi-automatic are all shotgun types -- but they differ greatly.

  10. #185
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    Click here to enlarge Originally Posted by spdu4ea Click here to enlarge
    The OS Giken is a clutch type and it would lock on launch forcing both axles to turn the same speed. It would have helped prevent the rear end instability that caused the rear end to start veering to the right @ 1:10 -- which lead to the tankslapping overcorrections after the 2-3 shift (all of course still ultimately caused by driver staying in it beyond his skill)
    I see absolutely no reason why the clutch type LSD would make any difference. The Gilken LSD is not a 100% locking diff (like in offroad cars). Cars with clutch type LSD's go into the wall just as easily with a poor setup.

    Click here to enlarge Originally Posted by spdu4ea Click here to enlarge
    The M3's LSD doesn't react until after there is a wheelspeed difference.
    That is how an LSD works, when the wheels are going different speeds, like an outer or inner wheel in a turn. A clutch type LSD also senses different speeds it just goes about it slightly differently with the clutch, instead of the fluid friction. Still the same principle.

    Click here to enlarge Originally Posted by spdu4ea Click here to enlarge
    thread split?
    Maybe, not really necessary. Regardless, a peg leg (one wheel spinning) is the result of the power going to where the is the least amount of resistance. Since it has no traction, it will just keep spinning until it gets traction and then torque will be sent to both wheels. An open diff can't send different torque to different wheels, still a moot point.

    Click here to enlarge Originally Posted by spdu4ea Click here to enlarge
    on't get hung up on the term "LSD." It encompasses a wide range of different designs, features, and operation. Pump action, double-barrel, and semi-automatic are all shotgun types -- but they differ greatly.
    Not really, they are all designed to do a similar thing in a similar application. RWD limited slips aren't going to differ all that much on the strip, even vs. an open diff. A C63 with an open diff puts down great launches, same with 335's and 135's.

    The LSD's benefit comes mostly on the roadcourse, not in a straight line.

    Click here to enlarge Originally Posted by spdu4ea Click here to enlarge
    This react-compensate speed-based design results in differing wheel speeds the entire time traction is low -- totally different from a clutch type...
    How is it any different from a clutch type that is designed to do the same thing? React based on the speed of one wheel vs. the other, it just does it with a different design.
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    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    I see absolutely no reason why the clutch type LSD would make any difference. The Gilken LSD is not a 100% locking diff (like in offroad cars).
    OS Giken (no L). No it isn't a rigid spool, and no it isn't an offroad-style locker... But it is next closest thing and it can still lock 100% which makes it very different from other LSDs. Try one and you'll understand

  12. #187
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    All these posts trying to blame it on the diff...... Click here to enlarge
    Click here to enlargeClick here to enlarge

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    I've said many times that driver skill was the underlying cause. I was just responding to those who said a diff upgrade would make no difference.

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    I will say it again, in my 7+ years of owning this car and abusing the hell out of it Ive never ever had one of my rear tires spinning without the other. Ive never had diff problems.... I did run bias plys once (never went to the track) I drove it on the street and they were very unstable.
    Click here to enlarge

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    Click here to enlarge Originally Posted by spdu4ea Click here to enlarge
    OS Giken (no L). No it isn't a rigid spool, and no it isn't an offroad-style locker... But it is next closest thing and it can still lock 100% which makes it very different from other LSDs. Try one and you'll understand
    Actually, I switched to a different diff in my E92 M3. I went with a higher locking clutch type diff from dan@diffsonline, I went with a 30-90% variable lock differential which should offer the same characteristics as the OS Gilken. I tried it, didn't like it, went back (more for the gear ratios) but I did not feel an advantage on the strip vs. the LSD I already had. I did feel it in the corners though, especially tight and low speed ones.
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    Click here to enlarge Originally Posted by TaZaM3 Click here to enlarge
    I will say it again, in my 7+ years of owning this car and abusing the hell out of it Ive never ever had one of my rear tires spinning without the other. Ive never had diff problems.... I did run bias plys once (never went to the track) I drove it on the street and they were very unstable.

    BAMMMMMM. Good info, and we have all seen many of your video's raping the streets. The person who went to the track in the video lacked understanding of what mixing true slicks with radials can do on the track. Everyone seems to want to blame it on the diff instead of thinking.
    Click here to enlargeClick here to enlarge

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    Click here to enlarge Originally Posted by GG///M3 Click here to enlarge
    Everyone seems to want to blame it on the diff instead of thinking.
    I think more info on the diff isn't a bad thing but let's be honest here, a different diff won't make up for driver error and won't make bias-ply more compatible with radials.

    The problem was the driver stayed in it once it started swaying. A diff needs to put the power down to make use so even with a different diff you would have to stay in it to get benefit. Staying in it is what caused the accident because once the moving started then he got on the brakes way too late only exacerbating the rotation.
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    Sorry if this has been covered already of if it's a stupid question but... On the topic of mixing the two types of tires being a bad idea. That would not apply to say a drag radial like the NT05r, R888 or BFG would it? For instance if You were running a high performance summer radial up front such as a NT05 and then some NT05rs on the rear. That would be ok right since they are both "Radial"? Thanks in advance guys.

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    Click here to enlarge Originally Posted by ogshooter Click here to enlarge
    That would not apply to say a drag radial like the NT05r, R888 or BFG would it? For instance if You were running a high performance summer radial up front such as a NT05 and then some NT05rs on the rear.
    Nope, they are both radials, no issue.
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    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    Nope, they are both radials, no issue.
    Thanks Sticky! Just wanted to make sure before ordering tires.

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    Click here to enlarge Originally Posted by ogshooter Click here to enlarge
    Thanks Sticky! Just wanted to make sure before ordering tires.
    No worries, definitely better safe than sorry.
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