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LSD

jasonchiu

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heard of it alot and i know its in cars to do something but donno hwo it works and what it does

please explain
 
It's Limited Slip Differential.
What differential does: allows rear wheels(I'm talking about RWD) to spin individually, redirecting the power to the wheel which has less resistance. Without it, you couldn't turn, because outer wheel needs to travel bigger distance than inner wheel. But when you're stuck in mud or something, one wheel will probably get all the power, while other will stay still, that's why offroaders usually have diff-lock, which as it's name suggests locks both wheels to turn simltaneusly.
But with diff-lock you basicly can't turn (well, you shouldn't), so there's a compromise - LSD. It allows wheels to spin individually to some degree, not locking them complitely (so you can turn), but not allowing to spin complitely independent either.

It's absolutely necessary for good drift-setup for example. Or very powerful vehichle in general. So you don't end up burning rubber on one wheel only, which has little less traction, but use both wheels to accelerate.
 
I presume that your talking about limited slip diff and not about lysergic acid diethylamide (the drug).

First: try some googling
Second: read this: http://auto.howstuffworks.com/differential.htm
howstuffworks is very nice. About everything can be found there and it'll be explained in a way most people will understand it.
And what MXM wrote is correct (although you can say a lot more about it), so I'm not going to repeat what he said.

Greetz Johan
 
limited slip basically means that if 1 wheel loses traction and starts spinning, it will route power to the other wheel as well. and yes very, very good for drifters. :D

p.s. i have a viscous lsd. :D
 
MXM said:
It's Limited Slip Differential.
What differential does: allows rear wheels(I'm talking about RWD) to spin individually, redirecting the power to the wheel which has less resistance. Without it, you couldn't turn, because outer wheel needs to travel bigger distance than inner wheel. But when you're stuck in mud or something, one wheel will probably get all the power, while other will stay still, that's why offroaders usually have diff-lock, which as it's name suggests locks both wheels to turn simltaneusly.
But with diff-lock you basicly can't turn (well, you shouldn't), so there's a compromise - LSD. It allows wheels to spin individually to some degree, not locking them complitely (so you can turn), but not allowing to spin complitely independent either.

It's absolutely necessary for good drift-setup for example. Or very powerful vehichle in general. So you don't end up burning rubber on one wheel only, which has little less traction, but use both wheels to accelerate.

Not entirely true. V8 Supercars use spool diffs and they get around the track fine.

A mate had one in his car. Hilarious when he backed out of parking space and the inner wheel starts bouncing up and down.
 
Leppy said:
A mate had one in his car. Hilarious when he backed out of parking space and the inner wheel starts bouncing up and down.

that happens alot in rear-LSD equipted cars as well.. but not to the extent of bouncing up and down though :lol:

btw, since we're on the topic about LSD, I was in a car workshop the other day and I saw this Evo8 with a LSD in the front diff... is there any advantage to this?.. usually I see it in the back diffs which is normal, but at the front?
 
Don't you just have them on driven wheels? So RWD cars only have them on the back, but an evo being 4wd will need one on the front and one on the back.

And doesn't the evo have diffs that can theoretically send 100% of the power to one wheel? They'll need it in rallying I guess...
 
na... you don't need a LSD on every driven wheels... RWD doesn't have to have a LSD in the back... I don't think the EVO can send 100% of the power to 1 wheel... I think the best it could do is send 20 to the front and 80 to the rear... sending all the power to 1 wheel would depend on the Diff and the LSD ;)
 
I know you don't need a limited slip diff, but you do need some kind of diff on driven wheels.... So as a LSD can do fancier things with the power, why not have one on the front wheels aswell?

They must be able to send more than 20 to the front otherwise they wouldn't be so good at rallying!
 
the Evo is like the Subaru... it can vary its center diff manually adjust shifting between 20% to 50% to the front wheels.... default is at 40% front ;)
 
an EVO has 3 diffs

1 inbetween the rear wheels
1 inbetween the front wheels
1 inbetween the 2 other diffs

but the third one isn't a real diff, you can more compare it to torque convertor on an automatic gearbox, also works with the fluid
 
bone said:
an EVO has 3 diffs

all 4wd cars have to have 3diffs... front, mid and rear diffs... btw, why do LSD differentials require different synthetic oil compared to normal differentials?...
 
Lol.

A V8 supercar has a very special setup to handle a spool diff, and they have to run neutral throttle for most of the corner, which isn't brill for trackspeed.

But boy do they accelerate!! :D

In the real world, a torsen diff rules in a fwd. You get a "skid steer" effect as torque directs to the outer wheel, which can improve corner speeds to the point of hilarity. The only downer is some nasty torque steer over uneven surfaces (case and point: the Focus RS on topgear!).

On a rear driver i'm a fan of the ZF plate style. Smooth, adjustable delivery, different for accleration and coast (nice and open on the coast side). Gives you nice turn in and stable exits. Downer is in the details. If you set the rear too tight you'll get power understeer followed by snap oversteer, so it's generally good to set it a little loose.
 
adrianpike said:
Wrong. 4WD cars have a transfer case, AWD cars have a center diff.
Well....that really is a question of definition. A true 'fulltime' 4wd car like the Landrover Defender has a transfer case with a built-in differential to distribute drive torque between the front and rear axle. 3 differentials in total.
A so-called 'parttime' 4wd drivetrain like the Toyota Hilux, Nissan Patrol and most other cheap terrain vehicles have, features a simple transfer-case without a diff. Here 4wd mode (either high or low gearing) means that the front and rear axles are rigidly connected, making cornering on normal surfaces as good as impossible, so the 4wd can only be engaged in true offroad conditions. In 2wd mode only the rear axle is driven.

Then there's all sorts of variations on this theme. My own Volkswagen syncro bus use a viscous coupling to engage the front wheels. Volkswagen's 4motion and some of Audi's quattro models (Golf 4 platform) feature an electronically controlled Haldex coupling to distribute power to the rear axle if necessary. AWD Porsche Carrera also have clutch-type center 'differentials'. Jeep Quadrasomething employs oil pumps to engage 4wd etc etc.

There's lots of ways to drive all 4 wheels :mrgreen:
 
snars said:
adrianpike said:
Wrong. 4WD cars have a transfer case, AWD cars have a center diff.
Well....that really is a question of definition. A true 'fulltime' 4wd car like the Landrover Defender has a transfer case with a built-in differential to distribute drive torque between the front and rear axle. 3 differentials in total.
A so-called 'parttime' 4wd drivetrain like the Toyota Hilux, Nissan Patrol and most other cheap terrain vehicles have, features a simple transfer-case without a diff. Here 4wd mode (either high or low gearing) means that the front and rear axles are rigidly connected, making cornering on normal surfaces as good as impossible, so the 4wd can only be engaged in true offroad conditions. In 2wd mode only the rear axle is driven.

Then there's all sorts of variations on this theme. My own Volkswagen syncro bus use a viscous coupling to engage the front wheels. Volkswagen's 4motion and some of Audi's quattro models (Golf 4 platform) feature an electronically controlled Haldex coupling to distribute power to the rear axle if necessary. AWD Porsche Carrera also have clutch-type center 'differentials'. Jeep Quadrasomething employs oil pumps to engage 4wd etc etc.

There's lots of ways to drive all 4 wheels :mrgreen:

That's why he wrote AWD and 4WD. There's a difference between them.

Greetz Johan
 
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