Lsd vs non LSD

TurboSubie · Post by **TurboSubie** » Sat Jun 04, 2005 8:56 pm

LSD vs non LSD whats the difference?

ej22t · Post by **ej22t** » Sat Jun 04, 2005 10:55 pm

With LSD, you could make donut on snow, without LSD you can't make donut on snow...
Simple explanation

Ben (^V^)..hheheee

IronMonkeyL255 · Post by **IronMonkeyL255** » Sat Jun 04, 2005 11:10 pm

In a regular (non-LSD) differential, when one wheel starts slipping, the torque from the engine goes to that wheel, as that becomes the path of least resistance.

In an LSD, when one wheels starts slipping, the the diff locks, so the same amt. of torque goes to both wheels, increasing traction.

Just imagine all the civics doing smoky 1-wheel burnouts. That is because they don't have an LSD, so all their (pitiful) power is going to that 1 wheel..

BAC5.2 · Post by **BAC5.2** » Sat Jun 04, 2005 11:31 pm

ej22t wrote:With LSD, you could make donut on snow, without LSD you can't make donut on snow...
Simple explanation

Ben (^V^)..hheheee

I can make donuts in the snow without an LSD....

Here's the break down.

There are a few types of LSD. Vicious Coupling (like what comes on the 91 Turbo Legacy's), Clutch Type, and gear type. There's a few others, like electronic, and brake distributed types, but those aren't entirely relevant.

First. Vicious Coupling Limited Slips. What there is, is fluid inside the differential that heats up works to spin both ouput axles at the same speed. There's a few problems with this type of limited slip. One being the simple fact that fluid can shear under load. That is, that when there is significant load (high power or high axle speed differences), you can spin the axles at different speeds, and the fluid is not thick enough to handle it. In a situation like that, the LSD will act as an open diff.

The advantages to a V-LSD, is that they are very progressive in their locking. When turning and on-power, they progressively become locked, which prevents severe unloading like with clutch type diffs. They are also mostly one-way diffs, in that the fluid generally cools to the point where it acts less like a limited slip upon deceleration. It's really only effective when turning on-throttle. These types of diffs rely on speed variations between the wheels to work. The center diff in a Manual transmission car is a vicious coupling type.

Second. A Clutch Type limited slip uses springs, plates, and friction material to lock the rear wheels together. This is good, because they can handle phenomenal amounts of power, and the amount of power transfer is just a rearangement of the plates away. There is a down side also, however. They CAN be horribly unpredictable to someone not used to them. Meaning, there is a very definite engagement point (set by the arangement of the plates). Get on it to much in a turn (trying to unload the inside tire), and the rears will lock and throw you into oversteer. Straight line acceleration is improved with this type of diff, as ANY speed differences in the rear axles are being fought by the clutches trying to keep things moving at the same speed.

Third. Gear type diffs. TORSEN and Quaife make these types of diff. They are super expensive (around $1200 for a front diff for a WRX by Quaife), but they are really nice. They work by using planetary gears and worm gears. What they do is the gears force themselves outwards as there are load differences between the sides. They only work if there is resistance on one side, however. So if one wheel is on ice, and the other is on pavement, the wheel on ice will spin and it will almost be like an open diff. These are the best handling types of diffs (arguably), as they work with the inputs, and don't have definite settings. It splits the power coming in, to both wheels evenly reguardless of the input speed or the loading from one wheel to the other (as long as there IS load). AUDI uses a TORSEN diff for the center diff of the Quattro setup. Quattro is super efficient.

What does this all mean compared to an open diff? A differential is like everything else in nature. Power wants to take the path of least resistance, and so the wheel that has the least amount of traction is the one that all power will be diverted to. You can't increase traction of one wheel, so the next best thing is to transfer the power that wants to escape to the easiest path, to the path of most resistance. You can't make traction, but you can distribute power, and that's what a limited slip differential does.

You can still spin the wheels, even if you have a limited slip though. That's the limits of traction, and the limited slip is doing everything in its design to control that.

There are other types of traction control to counter this, however. Thats another thread, however.

IronMonkeyL255 · Post by **IronMonkeyL255** » Sun Jun 05, 2005 12:53 am

I tried, but that is a FAR more thorough explaination.

scottzg · Post by **scottzg** » Sun Jun 05, 2005 1:08 am

I didn't think this topic would get any replies.

In the practical sense, lsd doesnt do all that much on a garden variety road driven subaru. It's unlikely you'll spin the tires on a takeoff, or that it will harm much (besides your driveline) if you do, and in a turn a lsd equipped scoob will be more inclined to understeer.

This isn't true as the power goes up and/or the traction goes down, but imho if you're not pushing 210hp, you're better off open diff.

I'm skipping a lot here, spdusa has some info iirc, and there's a wonderful piece aimed at DSM's running around the net.

dzx · Post by **dzx** » Wed Jun 08, 2005 8:30 pm

Do wrx's come with a lsd? And can they work on our cars with some modifying to get the right gear ratio's since i have a 4.11?

scottzg · Post by **scottzg** » Wed Jun 08, 2005 9:56 pm

They have a 3.9 lsd.

BAC5.2 · Post by **BAC5.2** » Thu Jun 09, 2005 7:28 am

No they don't Scott.

WRX's have a 1.1:1 center diff. The front is a 3.9:1 Open diff. The rear is a 3.54:1 open diff. The STi has 3 limited slips, but the WRX, at least my friends 02, has an open diff in the front and in the rear. The rear is DEFINATELY not 3.9:1.

scottzg · Post by **scottzg** » Thu Jun 09, 2005 7:48 am

we're both wrong.

as per subaru.com

viscous-type limited slip rear differential

BAC5.2 · Post by **BAC5.2** » Thu Jun 09, 2005 7:52 am

It's still not a 3.9 rear end.

My friends 02 doesn't have LSD stamped on the sticker like the 91 Turbo Legacy did. Maybe they stopped doing that?

professor · Post by **professor** » Fri Jun 10, 2005 6:47 pm

as BAC5.2 was alluding to, traction control can vastly change the characteristics of these systems, and make up for the glaring faults of some of them. In the most sophisticated systems, the traction control detects wheel spin and applies braking power to the spinning wheel only, thus transferring useful power to the other wheel at that end of the car.

simpler systems may simply cut engine power which does not change the result through the differential, and the wheel just spins slower or hopefully hooks back up

skid542 · Post by **skid542** » Sat Jun 11, 2005 12:55 am

I don't know a ton about LSD's but I will say this, if you've ever been stuck and had just one wheel sit there spinning keeping you from getting out ... I know I've had times I wished I had LSD.

snowjob · Post by **snowjob** » Sat Jun 11, 2005 1:14 am

If that does happen, Gently engage your E-Brake, it will confuse the diff and put some power to the other wheel. DO not do this and then floor it, you will cook your ebrake, but I've done this and it works

Frazer

skid542 · Post by **skid542** » Sat Jun 11, 2005 3:05 am

True and good tip, if only I weren't also FWD

.

THAWA · Post by **THAWA** » Sat Jun 11, 2005 3:11 am

BAC5.2 wrote:It's still not a 3.9 rear end.

My friends 02 doesn't have LSD stamped on the sticker like the 91 Turbo Legacy did. Maybe they stopped doing that?

They stopped that in like 96-97.

BAC5.2 · Post by **BAC5.2** » Sat Jun 11, 2005 8:34 am

Well there we go. Learned somethin new

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Lsd vs non LSD

Lsd vs non LSD