LSD in layman's terms?

TriedandTested · 13 Sep 2009 at 13:04

What is it and what does it do/benefit? Might be a newbie question but I'm going to ask it anyway!

From Wiki:

"
The main advantage of a limited slip differential is shown by considering the case of a standard (or "open") differential where one wheel has no contact with the ground at all. In such a case, the contacting wheel will remain stationary, and the non-contacting wheel will rotate freely—the torque transmitted will be equal at both wheels, but will not exceed the threshold of torque needed to move the vehicle, and thus the vehicle will remain stationary. In everyday use on typical roads, such a situation is very unlikely, and so a normal differential suffices. For more demanding use, such as driving in mud, off-road, or for high performance vehicles, such a state of affairs is undesirable, and the LSD can be employed to deal with it. By limiting the angular velocity difference between a pair of driven wheels, useful torque can be transmitted as long as there is some traction available on at least one of the wheels."

I'm still none the wiser.

Help.

Phate · 13 Sep 2009 at 13:07

Best way I can think of it.

No LSD - Wet roundabout, foot down, understeer crash and die
LSD - Wet roundabout, foot down, grip and go

Prophet · 13 Sep 2009 at 13:10

When one wheel starts to spin power is shifted to the other wheel.

With a standard diff, when one wheel spins it just keeps on spinning until it grips.

paradigm · 13 Sep 2009 at 13:30

Phate said:
Best way I can think of it.

No LSD - Wet roundabout, foot down, understeer crash and die
LSD - Wet roundabout, foot down, grip and go

Well that sums it up about as badly as possible.

Fuzz · 13 Sep 2009 at 13:41

Indeed, Phate hasn't got a clue.

But we knew that anyway

Wet roundabout, inside wheel has decreased traction and power will go to this wheel with an open diff. ergo wheel spin on that wheel.

With a Limited Slip Diff it "limits the slip" to the wheel with decreased traction. hence the name.
There is a whole load more to it than that as you get get 1 way, 1.5 way and 2 way LSD's but that about sums it up

Dogbreath · 13 Sep 2009 at 13:43

Phate said:
Best way I can think of it.

No LSD - Wet roundabout, foot down, understeer crash and die
LSD - Wet roundabout, foot down, grip and go

An LSD does not prevent understeer, it's purpose is to improve traction where it would otherwise be limited by one wheel losing grip.

Locky · 13 Sep 2009 at 13:53

LSD = more controllable steer from the rear?

Fuzz · 13 Sep 2009 at 13:57

LSD = controllable DRIFT.

Biohazard · 13 Sep 2009 at 14:02

LSD - one trippy ride!

Lashout_UK · 13 Sep 2009 at 14:06

A differential that helps prevent the wheels from spinning or losing traction by diverting torque from the wheel that is slipping, to the other that is not.

The LSD will allow for some difference in wheel speeds, to allow for smooth cornering and general driving - but once the difference in speed between the wheels reaches a certain point (i.e one is spinning on a loose surface, the other is not), it will start to work to reduce the difference in output by transferring the torque between the wheels, maintaining traction.

There are numerous ways an LSD can be designed to do this - some use gears, some use clutches, others use viscous fluid-based mechanisms.

Nick1881 · 13 Sep 2009 at 14:32

Dogbreath said:
An LSD does not prevent understeer, it's purpose is to improve traction where it would otherwise be limited by one wheel losing grip.

On a fwd car by improving traction you get less under steer.

Disco Boy · 13 Sep 2009 at 14:34

mr_x_plosion said:
On a fwd car by improving traction you get less under steer.

Number of FWD cards with an LSD <<< number of RWD cars with an LSD. So when explaining it "in layman's terms" it's best to assume that the car in question is RWD.

Nick1881 · 13 Sep 2009 at 14:36

Do that many cars on the road have an LSD?

I have had Integra's and Civic's and I think my Saab has LSD too, all fwd.

Disco Boy · 13 Sep 2009 at 14:42

mr_x_plosion said:
Do that many cars on the road have an LSD?

I have had Integra's and Civic's and I think my Saab has LSD too, all fwd.

I can't think of many other than lots of BMWs.

I have to admit that I forgot that civics have LSDs, I thought that only the 'teg had it, don't ask me why.

Which saabs have an LSD?

Prophet · 13 Sep 2009 at 15:02

Disco Boy said:
Number of FWD cards with an LSD <<< number of RWD cars with an LSD. So when explaining it "in layman's terms" it's best to assume that the car in question is RWD.

Why? An LSD works the same front or rear wheel drive.

rypt · 13 Sep 2009 at 15:09

Orange Peel said:
Why? An LSD works the same front or rear wheel drive.

You are not putting that much power through most FWD cars to require an LSD, equally with RWD the back end of the car is lighter so an LSD is more beneficial even at lower power levels.

Clarkey · 13 Sep 2009 at 15:09

Only the JDM Civics have LSDs (apart from the 1 special edition) and then only Type-R have them standard fit. There are tonnes of cars with LSDs on, pretty much anything JDM and sporty has one in there.

Lashout_UK · 13 Sep 2009 at 15:15

A fair bit of stuff on the road has an LSD - virtually any performance car, many off-roaders, small sports cars like MX5s, turbocharged Nissans, various BMWs, Mercs, a fair few trucks, so on and so forth.

Lots of classic cars have LSDs too, again, virtually anything 'performance' or with a rallying/racing heritage. Some factory fitted, some not (or a factory/aftermarket option).

Lopéz · 13 Sep 2009 at 15:16

In RWD applications, an LSD allows me to hold the tail out when I want to - with no LSD you have to rely a lot on momentum and weight transfer to hold the tail out, after a while one wheel will just spin to obilivion and you stop drifting.

Prophet · 13 Sep 2009 at 15:18

rypt said:
You are not putting that much power through most FWD cars to require an LSD, equally with RWD the back end of the car is lighter so an LSD is more beneficial even at lower power levels.

That's a very generalised statement.

Less power doesn't mean more grip, especially with FWD.