Why you need a LSD if you like cornering!

[CSG Mike]

Originally Posted by blackhawkdown

how does the cusco 1.5 compare to the OS Giken 1.5 compare?

The major differences:

Engagement - Cusco RS is positive engagement, while OS Giken is negative engagement. In other words, the Cusco is trying to engage all the time, while the OSG is trying to disengage all the time. Cusco RS engagement is controlled by springs in the center gear, while the Cusco MZ engagement is controlled by cone springs on the ends. OSG engagement is controlled by cone springs on the ends, and disengagement is controlled by springs in the center gear. This sounds complicated, but we'll be more than happy to show you in person what is going on.

Maintenance - Clutch packs all eventually wear out. How quickly they wear out depends on your setup, how you drive, and if you're using the proper fluid for your application. **USE THE RIGHT FLUID** Typically speaking, the OSG clutch disks should last longer than the Cusco RS clutch disks.

Maintenance cost - OSG diff fluid is more expensive than Cusco diff fluid. Our blanket recommendation is to use the fluids by the respective manufacturers, but they may vary on a case-by-case basis. Clutch disk cost is approximately the same, but the Cusco will require more frequent clutch disk changes. That being said, you will NOT be replacing the clutch disks frequently. Most Cusco LSD owners have never replaced their clutches, and I've yet to run into a single OSG owner who has replaced their clutch disks.

Initial cost - OSG costs ~200 more than Cusco. Custom configuration of the OSG also costs more than custom configuration of the Cusco.

Break in - Cusco requires a 30 minute break-in. OSG requires no break-in.


Both LSDs come in a 1/1.5 and 1.5/2.0 configuration. Meaning, if you buy a 1.5 way LSD, you can reconfigure it into a 1.0 or 2.0 way LSD later on, if you choose to do so, depending on the version you buy.

[blackhawkdown]

a few more months and ill be contacting u guys at csg

[CSG Mike]

Hmmmm a little birdie tells me that we got another LSD for testing...

[dp1]

Thanks again @CSG Mike and @CSG David, the OS Giken I got from you was installed by EFI Logics today, great shop. So far quieter than stock with Whiteline diff and other reinforcements. Can't wait to try it on track and AX. Last planned big mod on my car. Thumbs up

[Ubersuber]

Torsen work quite differently from other types of mechanical lsd. In reality they are not limited slip differentials at all as raising one wheel off the ground (or reducing traction torque close to zero as if on ice) will defeat them.

For normal spirited driving they are close to ideal unless you get the car hard over onto the bump stops, because they torque bias: i.e. the torque delivered to the pinion gets divided equally as long as equal tractive torque is available but as one wheel, usually the inside wheel, loses its grip on the road the torque available for transfer to the other wheel rises as a multiple of the torque utilized by the wheel starting to slip. This multiple is fixed by the internal bias ratio which differs from Torsen to Torsen.

Other types just brake the overspeeding wheel against the slower turning wheel and no torque biasing occurs. Eventually, the mechanical type will simply overspeed both wheels (locked) even though one of the wheels won't be delivering much drive due to inadequate grip, but the Torsen cannot do that, it reverts to a more equal torque split if both wheels begin to spin up.

The ideal is the new electronically modulated mechanical lsd which vary the degree of lock not by relative wheel speed but by computer map. Pioneered in racing this is now available for mundane cars. The latest clever awd systems use this technology to eliminate gearing altogether in the transfer case, replacing them with basically the guts of an electronic lsd, just the oil bathed plates and a solenoid pressure control. In theory a geared differential is no longer actually required, just a standard crown and pinion with the axles connected only through the lsd clutches but there are heat dissipation and wear issues still with using such systems full time. They work for awd because they are part time awd. BMW, Jaguar and others use gearless transfer cases. Torque vectoring can be achieved by these electronic lsd. Haldex is a major manufacturer of this type of transfer case. The new European Golf R awd looks very much like it is using these gearless clutchpacks between the front axles as well, for lsd effect without gears.

For hard track work, especially with high roll stiffness, the Torsen is much less useful because loss of traction on one wheel deprives the other of traction (torque drive) also. You can get a weird feeling of cycling going on as the Torsen reacts to incipient wheelspin by shuffling torque back and forth across the helical "spider gears". In fact, I think somewhere on this site somebody actually measured this happening by graphing the wheel speed sensor traces.

Finally, an lsd isn't the be all and end all. Lotus refused to fit one, and still does so for at least the Elise and Exige, (not sure about the Evora (edit, sure enough the Evora uses only an electronic lsd)), as did Jaguar for a long time until very recently. So did Porsche for its excellent Cayman, again until demand from the racing set "required" Porsche to offer one. A road car is still nicer to drive without one and all the traction control a driver actually needs nowadays can be supplied by the ABS system and software. Purely mechanical lsd are of decreasing interest to most drivers even if they drive aggressively.

A lsd will push for the same reason that stability control works by braking a wheel. Torsen or mechanical will drive the inside rear wheel (mechanical will drag the outside wheel) which induces understeer, i.e. counter rotation forces, making turn in more difficult (which is where the electronics work some magic by backing off the locking) and then on exit the locking effect will tend to straighten the car which is when the electronics usually maximize locking, but if you have high rear roll stiffness relative to the front axle this is when the Torsen will wimp out but the clutch type will shine. Mechanical lsd do rob power though and you benefit less from them if you have a low powered car, such as an Elise or a BRZ. Torsen do not rob power. Mechanical lsd work well only if you have enough drive torque to easily and consistently overspeed one of the rear wheels. The Torsen is completely adequate for our cars most of the time.

[CSG Mike]

Originally Posted by Ubersuber

Finally, an lsd isn't the be all and end all. Lotus refused to fit one, and still does so for at least the Elise and Exige, not sure about the Evora, as did Jaguar for a long time until very recently. So did Porsche for its excellent Cayman, again until demand from the racing set "required" Porsche to offer one. A road car is still nicer to drive without one and all the traction control a driver actually needs nowadays can be supplied by the ABS system and software. Purely mechanical lsd are of decreasing interest to most drivers even if they drive aggressively.

A reactive system will *never* be as good as a proactive system.

If a driver chooses to drive with electronic aids, that is their choice, and in all reality, the majority of drivers out there will be faster with the aids on, whether they want to admit it or not.

For those that want to truly be in control of their cars actions, instead of letting a computer decide what it thinks the driver wants, a mechanical LSD cannot be overlooked.

Originally Posted by Ubersuber

A lsd will push for the same reason that stability control works by braking a wheel. Torsen or mechanical will drive the inside rear wheel which induces understeer, i.e. counter rotation forces, making turn in more difficult (which is where the electronics work some magic by backing off the locking) and then on exit the locking effect will tend to straighten the car which is when the electronics usually maximize locking, but if you have high rear roll stiffness relative to the front axle this is when the Torsen will wimp out but the clutch type will shine. Mechanical lsd do rob power though and you benefit less from them if you have a low powered car, such as an Elise or a BRZ. Torsen do not rob power. Mechanical lsd work well only if you have enough drive torque to easily and consistently overspeed one of the rear wheels. The Torsen is completely adequate for our cars most of the time.

Miatas are faster with a LSD, and this is 100% substantiated by evidence. They don't have very much power. I'm talking NA and NB, not the current NC, which has more power.

[Ubersuber]

The Miata will be faster with more power though, lol. All I am saying is that a mechanical lsd absorbs power (which shows up as heat in the diff oil).

I'd be interested to know if a Miata is faster with a locker or a Torsen. I'd be surprised if a locker worked better but it is of course possible. I'd also be interested to know if this is a Miata with modified suspension or stock suspension because roll stiffness front to rear makes a big difference to traction out of corners with and without a locker versus open or Torsen.

A Torsen is actually a special type of open diff, not a locker. It never locks and is unable to resist differentiation unless both wheels have some traction. A Torsen reveals the diff(erence) between traction and torque delivery which needs to be understood when selecting the type of lsd or differentiation limiting device you need.

A locker works no differently to a brake based system until you want both wheels to overspeed available traction because a locker doesn't transfer torque (which of course a Torsen does) it merely brakes the overspeeding wheel against the other wheel (whereas the brake based systems brake the overspeeding wheel against the chassis). To benefit, the engine must be able to deliver enough torque to at least be capable of spinning up the inside wheel.

These are all reasons why Torsen works better for the front axle than the rear and for the centre diff in awd systems. The new Haldex type systems work even better as lsd than lockers or Torsens.

[ZDan]

A clutch-type LSD is not a "locker". A locker is something else entirely, and not really appropriate for road course work.

Also, a Torsen is most definitely a limited slip.

[CSG Mike]

A locker is either locked or open; it can't dynamically change.

An open diff is open. A limited slip diff can limit the amount of wheel slip based on how it is adjusted/set, and can range all the way from open to fully locked, although not all diffs use the full range. A locker in locked position is 100% locked whether you want it to be or not.

[Ubersuber]

Originally Posted by ZDan

A clutch-type LSD is not a "locker". A locker is something else entirely, and not really appropriate for road course work.

Also, a Torsen is most definitely a limited slip.

Any diff that locks to 100%, no slip, is technically a locker. The fact that some lock immediately with a pawl (rare now) or lock progressively using clutch packs makes no difference. It still locks.

A Torsen is by definition an open differential. It never locks and cannot limit slip. It only transfers torque from a wheel with grip turning faster to a wheel with more grip turning slower. It always differentiates the wheels and never limits slip.

Tor Sen stands for Torque sensing, by which is meant "sensing" (technically "reacting to") the torque the driven wheel can deliver to the ground. The Torsen can then deliver that torque multiplied by the bias ratio to the other wheel if that wheel is turning more slowly and has the capability to use the torque (i.e. enough grip on the road).Failure to understand this essential difference to an lsd creates a mystery where there is none.

[Ubersuber]

Originally Posted by CSG Mike

A locker is either locked or open; it can't dynamically change.

An open diff is open. A limited slip diff can limit the amount of wheel slip based on how it is adjusted/set, and can range all the way from open to fully locked, although not all diffs use the full range. A locker in locked position is 100% locked whether you want it to be or not.

OK, if you prefer that difference. It is true that there are lsd that lock essentially immediately and those that do so progressively, though a clutch type usually locks up pretty dramatically. If you want to call one type of lsd a locker and the other just an lsd that is fine with me. A Torsen isn't either type and never locks nor even limits slip. A Torsen is an open differential as you can easily test by raising one driven wheel off the ground. It limits the rate at which differentiation progresses but it doesn't limit slip between the drive wheels or drive shafts nor can it.

[CSG Mike]

Originally Posted by Ubersuber

Any diff that locks to 100%, no slip, is technically a locker. The fact that some lock immediately with a pawl (rare now) or lock progressively using clutch packs makes no difference. It still locks.

A Torsen is by definition an open differential. It never locks and cannot limit slip. It only transfers torque from a wheel with grip turning faster to a wheel with more grip turning slower. It always differentiates the wheels and never limits slip.

Tor Sen stands for Torque sensing, by which is meant "sensing" (technically "reacting to") the torque the driven wheel can deliver to the ground. The Torsen can then deliver that torque multiplied by the bias ratio to the other wheel if that wheel is turning more slowly and has the capability to use the torque (i.e. enough grip on the road).Failure to understand this essential difference to an lsd creates a mystery where there is none.

Precisely what it is doing, is limiting slip by forcing torque to go to the other wheel.

[CSG Mike]

Originally Posted by Ubersuber

OK, if you prefer that difference. It is true that there are lsd that lock essentially immediately and those that do so progressively, though a clutch type usually locks up pretty dramatically. If you want to call one type of lsd a locker and the other just an lsd that is fine with me. A Torsen isn't either type and never locks nor even limits slip. A Torsen is an open differential as you can easily test by raising one driven wheel off the ground. It limits the rate at which differentiation progresses but it doesn't limit slip between the drive wheels or drive shafts nor can it.

You can do the same test with a clutch type LSD, and get the same result, provided it is tuned to do that.

However, the very example you bring up, is why a clutch type LSD is such a substantial upgrade over a torsen unit for those that are cornering hard.

[SomeoneWhoIsntMe]

@Ubersuber, I don't understand why you're trying to redefine this discussion in semantics which only you recognize. it's only going to confuse readers.

A welded differential or spool is locked 100% of the time.

A "locker" is a differential gear with a mechanism to change between 100% lock and 100% open. They may lock automatically or by cable or pneumatic shifter, but they cannot lock any less than fully.

A "limited slip differential" is "a type of automotive differential gear arrangement that allows for some difference in angular velocity of the output shafts, but imposes a mechanical bound on the disparity." (Wikipedia)

An open differential is a differential gear which is fully open all of the time. Four spiders in a carrier with no extra mechanisms. We all know what this looks like.

Inside the category of limited slip differential there are various types. Due to design limitations, relatively aggressive clutch-type differentials are the only differentials which can deliver power to a wheel which is lifted off the ground or on ice. Viscous and helical differentials will generally still allow you to get stuck in the extreme case of zero traction on one wheel. However, this does not mean that clutch types are "lockers" and other types of LSD are "open", it's just a finer point of the characteristics of each diff. Under normal conditions, all types of LSD bias torque, by definition.