I thought this car came with an LSD?

[GhostShield]

Is it normal to feel the rear end at 1st gear speeds fight itself a little?

[Suberman]

Originally Posted by GhostShield

Is it normal to feel the rear end at 1st gear speeds fight itself a little?

Yes, definitely. Torsen tends to shuffle torque back and forth across the axles when traction is low.

[Suberman]

Originally Posted by rice_classic

Well the OP may be right. According to some purists or pedantics, the Torsen LSD isn't actually an LSD.

Actually it isn't. This can easily be proved if you put one drive wheel up in the air.

It's not an LSD because it doesn't limit slip. It is an ATB because it biases torque. The difference is fundamental and important.

For a lengthy period of time the Achilles heel of Audi's much vaunted Quattro drive was the Torsen center diff. Guess what, they don't use it anymore because of its limitations.

Torsen themselves make a hybrid ATB that is also an LSD, they fit a clutchpack as got a true LSD.

[Suberman]

Originally Posted by rice_classic

Don't quote me, I don't need the lesson.

I was simply commenting on the puritan or pedantic viewpoint of some.

Apparently you still do.

[Suberman]

Originally Posted by AZOOZ_95

I thought this car came with an LSD? But when i had the car jacked up and pushed one wheel clockwise the other went counter-clock wise.

I tried looking everywhere for an answer.... but couldnt find anything

A torque biasing differential(ATB) is an open differential. It uses internal friction forces acting on the gear faces and thrust washers to force torque across the differential. It does not limit slip, it transfers torque that would otherwise be wasted spinning a drive wheel. However, it only transfers unused torque. If the lower grip wheel has no grip,there's no torque to transfer. Its important to remember that torque is an unmoving force. Only if the lower grip wheel offers resistance to applied torque can that torque be transferred to the other drive wheel. The beauty of a Torsen is you don't get single wheel spin at all until the torque transferred to the other drive wheel exceeds the grip available to that wheel, divided by the bias ratio (or, if you prefer, the low grip wheel will also spin the higher grip wheel when the bias ratio is exceeded, in our cars by four times). In that sense it prevents wheel slip and does not "limit" wheel slip. It is not a reactive system like a clutchpack or viscous coupling is. The Torsen prevents slip before it can occur up to the bias ratio.

The ratio of torque transfer capability is the bias ratio of the ATB. The one fitted to the BRZ is a 4:1 bias ratio which is very high. 5:1 is about the maximum feasible for a road car. 4:1 means that up to four times the torque driving the lower grip wheel can be transferred to the other wheel. In winter or in the wet this rarely exists so the actual drive effects can be disconcerting. A lower bias ratio is usually fitted for a winter application. 4:1 works better in dry conditions and with an excess of torque such as on the Mustang GT.

It mimics a LSD only if each wheel has some grip otherwise it acts as the open differential it is.

A clutch type LSD absorbs engine torque that would otherwise spin the lower friction drive wheel. An LSD does not transfer any torque, it absorbs engine energy and creates a lot of heat until it locks up. A viscous coupling also wastes engine torque generating heat which increases the viscosity of silicone based fluid in the coupling (silicone increases viscosity with added heat). A viscous coupling works like a torque converter but with its operating fluid changing viscosity with the relative motion of the stator and impeller vanes. Subaru also uses this type in their other models. Both of these devices essentially brake the spinning wheel against the wheel with more grip. That's why these have largely been abandoned in favour of ABS based traction control which actually uses the wheel brake to perform the braking function of a clutchpack LSD of viscous coupling. Even awd systems generally only have a LSD transfer case (centre diff) and rely on the traction control to control wheelspin across the axle.

An ATB is not a LSD it is an open diff.

Now you don't need to google Torsen.

[1086]

Ha, what are you saying 'No' to? bad grammar is no bueno... :/

[humfrz]

Originally Posted by Suberman

A torque biasing differential(ATB) is an open differential. It uses .......

Ooooo ...... interesting, but, that made ma brain hurt .....

humfrz

[jonboy99]

What does the slip in lsd refer to? I presumed it meant the wheel with least grip. If so, the torsen is an lsd isn't it?

• A clutch type lsd also transfers torque surely? If it locks up, and 1 wheel has no grip and the other ample grip, then 100% of the torque goes to the gripping wheel - 50% of the torque which would have gone to the slipping wheel has been transferred, no?

Originally Posted by Suberman

A torque biasing differential(ATB) is an open differential. It uses internal friction forces acting on the gear faces and thrust washers to force torque across the differential. It does not limit slip, it transfers torque that would otherwise be wasted spinning a drive wheel. However, it only transfers unused torque. If the lower grip wheel has no grip,there's no torque to transfer. Its important to remember that torque is an unmoving force. Only if the lower grip wheel offers resistance to applied torque can that torque be transferred to the other drive wheel. The beauty of a Torsen is you don't get single wheel spin at all until the torque transferred to the other drive wheel exceeds the grip available to that wheel, divided by the bias ratio (or, if you prefer, the low grip wheel will also spin the higher grip wheel when the bias ratio is exceeded, in our cars by four times). In that sense it prevents wheel slip and does not "limit" wheel slip. It is not a reactive system like a clutchpack or viscous coupling is. The Torsen prevents slip before it can occur up to the bias ratio.

The ratio of torque transfer capability is the bias ratio of the ATB. The one fitted to the BRZ is a 4:1 bias ratio which is very high. 5:1 is about the maximum feasible for a road car. 4:1 means that up to four times the torque driving the lower grip wheel can be transferred to the other wheel. In winter or in the wet this rarely exists so the actual drive effects can be disconcerting. A lower bias ratio is usually fitted for a winter application. 4:1 works better in dry conditions and with an excess of torque such as on the Mustang GT.

It mimics a LSD only if each wheel has some grip otherwise it acts as the open differential it is.

A clutch type LSD absorbs engine torque that would otherwise spin the lower friction drive wheel. An LSD does not transfer any torque, it absorbs engine energy and creates a lot of heat until it locks up. A viscous coupling also wastes engine torque generating heat which increases the viscosity of silicone based fluid in the coupling (silicone increases viscosity with added heat). A viscous coupling works like a torque converter but with its operating fluid changing viscosity with the relative motion of the stator and impeller vanes. Subaru also uses this type in their other models. Both of these devices essentially brake the spinning wheel against the wheel with more grip. That's why these have largely been abandoned in favour of ABS based traction control which actually uses the wheel brake to perform the braking function of a clutchpack LSD of viscous coupling. Even awd systems generally only have a LSD transfer case (centre diff) and rely on the traction control to control wheelspin across the axle.

An ATB is not a LSD it is an open diff.

Now you don't need to google Torsen.

[mfbmike]

Originally Posted by Suberman

Actually it isn't. This can easily be proved if you put one drive wheel up in the air.

It's not an LSD because it doesn't limit slip. It is an ATB because it biases torque. The difference is fundamental and important.

For a lengthy period of time the Achilles heel of Audi's much vaunted Quattro drive was the Torsen center diff. Guess what, they don't use it anymore because of its limitations.

Torsen themselves make a hybrid ATB that is also an LSD, they fit a clutchpack as got a true LSD.

Sounds like the Haldex system used in some VAG cars.

[civicdrivr]

Originally Posted by cgrey

Try turning it counterclockwise.

This made me laugh in the middle of a meeting. Thanks, now everyone knows I'm not paying attention.

[ZDan]

Originally Posted by Suberman

A torque biasing differential(ATB) is an open differential.

It comes down to semantics, but for me, no, it is a limited slip differential.

It uses internal friction forces acting on the gear faces and thrust washers to force torque across the differential. It does not limit slip, it transfers torque that would otherwise be wasted spinning a drive wheel.

The ultimate effect of this being: limiting slip of the wheel that wants to spin.

However, it only transfers unused torque.

"ONLY"?! Reminds me of Homer Simpson bargaining with the nerdy science guy over a matter trasporting device: "Hmm, $3, and it only transports MATTER?"

If the lower grip wheel has no grip, there's no torque to transfer.

But the frictional resistance in the worm gears will still transfer drive torque to the non-spinning wheel. I have never had either of my Torsen-equipped cars give a 1-wheel spin on snow or even ice. There is effective rear lockup even with very very very low-traction/low-torque conditions, at least in my experience with them.

Its important to remember that torque is an unmoving force.

"Unmoving"? Of course applying torque can and usually does produce motion.

Only if the lower grip wheel offers resistance to applied torque can that torque be transferred to the other drive wheel. The beauty of a Torsen is you don't get single wheel spin at all until the torque transferred to the other drive wheel exceeds the grip available to that wheel, divided by the bias ratio (or, if you prefer, the low grip wheel will also spin the higher grip wheel when the bias ratio is exceeded, in our cars by four times). In that sense it prevents wheel slip and does not "limit" wheel slip.

Semantics. If it's preventing slip from happening at all, in my book that is LIMITING slip.

It is not a reactive system like a clutchpack or viscous coupling is.

It is reactive, providing more lockup with increased torque, unlike some clutchpack diffs, but similar to a Salisbury (with ramps to increase lockup with increased applied torque) clutch type with low breakaway torque.

It mimics a LSD only if each wheel has some grip otherwise it acts as the open differential it is.

In my experience with Torsen diffs, as long as both wheels are on the ground it will lock up enough to maximize drive even in snow and ice.

A clutch type LSD absorbs engine torque that would otherwise spin the lower friction drive wheel. An LSD does not transfer any torque,

WHAT?! A "mechanical" clutch type diff absolutely DOES transfer torque. It doesn't just "absorb" it. Torque that would act to spin the inside wheel in cornering is transferred through the clutch pack to the loaded outside wheel.

it absorbs engine energy and creates a lot of heat until it locks up.

SOME of the energy is converted into heat in the clutch pack, but a significant amount of it IS transferred as torque to the wheel with grip. Otherwise you'd just feel a big LUG and the car wouldnt' accelerate any more than it would with an open diff, if ALL was lost as heat. Plus you'd vaporize the differntial fluid and melt the diff in short order...

An ATB is not a LSD it is an open diff.

In my book, it absolutely is a limited slip, in theory and in practice. I've driven torsens and Salisbury clutch diffs, and their characteristics aren't too dissimilar. Both can provide adequate lockup without being too obtrusive at low-speed low-torque.

Now you don't need to google Torsen.

I *highly* recommend that people do their own research and not take mine or anybody else's word for it!

[Suberman]

How does it limit slip if it won't stop the wheel spinning on ice?

If it is an LSD how come Torsen built the T3 which incorporates a clutchpack to limit wheelspin?

It's not semantics. The difference is real and can be objectively described. Put simply, the Torsen accelerates the wheel with more grip. The LSD decelerates the spinning wheel. That's quite a difference. The two systems also produce very different driving feel as I'm learning rapidly in my current severe winter conditions.

I will concede that I am unsure about the one wheel spinning as I cannot observe that and drive at the same time. Also, I'm not sure the BRZ lets you switch off the traction control completely with the console buttons. In theory, the Torsen ought to spin only the one wheel if the torque bias is exceeded. Whether that actually occurs with both wheels on the ground in reality I don't know. Certainly at the limit it does, zero torque on one wheel. That alone demonstrates that the Torsen is an open differential.

The remainder of your post is just inaccurate and describes all the common misconceptions about the way a mechanical LSD operates. No torque is transferred by the clutchpack. Are you saying that the ABS type do absorb torque but the clutch do not?

That's rhetorical. Both the ABS and clutchpack "LSD" operate in exactly the same way, by braking the spinning wheel.

Clutchpack LSD wear out as do the brake pads on ABS types. Torsen retain full effectiveness for the life of the car. They do not wear out.

[Suberman]

Originally Posted by mfbmike

Sounds like the Haldex system used in some VAG cars.

Yes, the latest Haldex use the T3 Torsen.

[ZDan]

Originally Posted by Suberman

How does it limit slip if it won't stop the wheel spinning on ice?

Are you saying that you're getting 1-legged, single-wheel wheelspin in these conditions? Because in the other thread you were complaining that the FR-S/BRZ Torsen is *too tight*. Which is it?

In my experience with the Torsen diffs in my S2000 and RX-7, they do all that they possibly can to limit wheelspin by ensuring that both wheels get maximum possible torque before both spin together.

No differential can do more than this. There is only so much total tractive force available, if you need more than that to move the car, it doesn't matter what you have for a diff, you're spinning.

If it is an LSD how come Torsen built the T3 which incorporates a clutchpack to limit wheelspin?

I'm not familiar with the T3, but the Torsen in my RX-7 is a T2R which has preload in it. Behaves similarly to the T2 in my S2000 on snow/ice.

It's not semantics. The difference is real and can be objectively described. Put simply, the Torsen accelerates the wheel with more grip. The LSD decelerates the spinning wheel. That's quite a difference.

You're wrong on both counts. They fundamentally do the same thing, transferring torque from the slipping wheel to the gripping wheel. If the clutch-type *only* decelerated the slipping wheel, it would suck balls at the track and GREATLY limit acceleration drive out of corners. But no, it does allow more torque to the loaded outside wheel and killer drive out of corners. Just like the Torsen does.

The two systems also produce very different driving feel as I'm learning rapidly in my current severe winter conditions.

In my experience with the Salisbury clutch-type in my 240Z, they produce very similar responses. They both have lighter lockup under low-torque conditions and lock up more under heavier torque application. Non-Salisbury clutch types do behave a little differently, and require a lot more breakaway torque to perform well in performance applications. Undesirable for a street car.

I will concede that I am unsure about the one wheel spinning as I cannot observe that and drive. In theory, the Torsen ought to spin only the one wheel if the torque bias is exceeded. Whether that actually occurs with both wheels on the ground in reality I dint know. Certainly at the limit it does, zero torque on one wheel. That alone demonstrates that the Torsen is an open differential.

I haven't tried one wheel on ice and one wheel on dry pavement, but even if that allows wheelspin, it is *still* a limited slip.

If there is ONE case where it doesn't limit slip, it still DOES limit slip for its primary design mission: performance driving on the street/autoX/track.

Still a limited slip, just like a Salisbury ramp-type clutch diff is *still* a limited slip with zero breakaway torque (which would cause it to behave the same way with one wheel on a no-grip surface and one on a grippy surface, would spin one wheel).

The remainder of your post is just inaccurate and describes all the common misconceptions about the way a mechanical LSD operates. No torque is transferred by the clutchpack.

OF COURSE torque is transmitted by the clutchpack, that's precisely what it is there to do!

Are you saying that the ABS type do absorb torque but the clutch do not?

NO. Both the biasing and clutch diffs lose some to heat. Both do primarily effectively transmit torque to the side with more grip under most conditions.
[edit]Somehow misread "ABStype" as "torque-biasing"... Revised answer: YES. ABS antilock brake virtual "limited slips" DO "absorb" the torque into the braking system, whereas clutch-type LSD transfers that torque back to the other drive wheel.

That's rhetorical. Both the ABS and clutchpack "LSD" operate in exactly the same way, by braking the spinning wheel.

No no no. The clutch pack connects the two output shafts, providing a torque path via the carrier. When one wheel has less grip, the torque that *would* be acting to spin that wheel goes to the opposite wheel with more grip.
Same with the Torsen, only the torque path isn't a clutchpack but the helical gears connecting the side gears. It is still ultimately frictional and also generates heat, but BOTH are still transmitting torque from the no-grip side to the side with grip.

Clutchpack LSD wear out as do the brake pads on ABS types. Torsen retain full effectiveness for the life of the car. They do not wear out.

The clutchpack in my 240Z's Salisbury clutchpack lsd has lasted for two decades and ~100 track days and still works great. Probably because I kept the breakaway torque very low (~18 lb-ft) and let the ramps provide the lockup instead of shimming the bejeezus out of it up to 50-100 lb-ft like a lot of guys do.

Torsen will have wear, as there is a TON of friction on the helical gears. In fact, Torsens create more heat than most clutch types. There was a batch of T2Rs that wore out prematurely, but they seem to have that issue fixed now. But with proper metallurgy, most seem to last a very long time, effectively forever (afaik).