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Location:
Sydney
Registered:
January 2004
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whats a LSD?
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Sat, 06 March 2004 07:40
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can any one tell me whats a LSD is?
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Location:
Melbourne
Registered:
March 2003
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Re: whats a LSD?
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Sat, 06 March 2004 07:56
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A normal differential allows a car to have the driving wheels turning at different speeds while cornering due to the different radius' that the wheels follow. The problem with these "open" diffs is that when one wheel brakes traction, all the torque is fed to that wheel, hence the term single spinner.
A Limited Slip Differential locks both wheels so that they both recieve equal amounts of torque if traction is lost at one of the wheels.
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Location:
Sydney
Registered:
January 2004
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Re: whats a LSD?
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Sat, 06 March 2004 07:57
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ok thanks, do you know how much it will cost to get installed into an 86?
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I supported Toymods
Banned User
Location:
Brisbane
Registered:
May 2002
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Re: whats a LSD?
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Sat, 06 March 2004 09:38
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| crayz legz wrote on Sat, 06 March 2004 17:57 |
ok thanks, do you know how much it will cost to get installed into an 86?
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Lots. Just about impossible to find.
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Location:
Montrose, VIC
Registered:
May 2002
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Re: whats a LSD?
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Sat, 06 March 2004 10:20
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Why do I feel the urge to chuckle when someone has to ask what one is, then decides they must have one??
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Location:
Sydney
Registered:
January 2004
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Re: whats a LSD?
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Sat, 06 March 2004 11:08
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dont want it just wanna noe wat it is
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Location:
Sydney
Registered:
January 2004
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Re: whats a LSD?
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Sat, 06 March 2004 11:15
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yer har har  only intrested cause it talks about it on the drift bible
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Registered:
March 2004
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Re: whats a LSD?
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Sat, 06 March 2004 11:23
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You can get this lsd of a levin or if your very lucky a treuno gtv of sss automotive, but its around 1800 to 2 gran, plus you need to order your handbrake cables toyota penrith or get them custom made, also disk pads, shims anti rattle crape so it all hads up. i have done this convertion
http://www.geocities.com/toyae862003/1.htm
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Location:
Melbourne
Registered:
May 2002
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Re: whats a LSD?
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Sun, 07 March 2004 17:27
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Jee i cant honestly find any reason why you would go to such a expence for a lsd when it would probobly work out cheaper to put a lsd diff out of a hilux in it, providing you do all the fit up yourself, correct me if i am wrong
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Registered:
March 2004
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Re: whats a LSD?
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Sun, 07 March 2004 21:07
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would could but with those diff s you cant high rev, have i mention there crap, i had one before. drifting in the dry is twice has hard, also you dont get the disk brake for weight shifting when hanging sideways  , but if its for drags or normal street driving go for it, im installing a modified hilux lsd, but thats on the 20btt
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Location:
South Australia
Registered:
July 2002
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Location:
Brisbane
Registered:
May 2002
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Re: whats a LSD?
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Sun, 07 March 2004 23:20
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| FWDboy wrote on Mon, 08 March 2004 07:21 |
I'm not so sure if that is a technically correct description. A normal open differential splits the torque 50/50 at all times, that's it's problem - that when a wheel breaks traction it is still getting a 50% of torque - and without any resistance to that force, it spins up like all hell.
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No, he was correct; a single spinner transfers 100% of the torque to the wheel which has lost traction. If this wasn't the case, the car would still accelerate with one wheel spinning, and anyone who's done a one-wheel skid in the wet will tell you that isn't the case!
LSD's rule, but if you don't know what it is or what it does you definitely don't need one.
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Location:
South Australia
Registered:
July 2002
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Re: whats a LSD?
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Mon, 08 March 2004 04:22
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But a wheel spinning up really fast doesn't necessarily mean it's getting more torque than the other wheel.
I'm fairly sure that an open differential is a 'torque splitting' device. I'm not sure where I picked this up from, I'll go to my uni tomorrow to check this one out, because two against one means I should have my doubts!
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Location:
South Australia
Registered:
July 2002
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Re: whats a LSD?
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Mon, 08 March 2004 04:55
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Okay - here's a quickie, I checked this in race car vehicle dynamics and it would seem that a open diff is a torque-splitting device.
Some quotes from race car vehicle dynamics
"The open differential cleverly allows the sum of the outside and inside wheel rotational velocities to equal a constant while allowing one wheel to speed up and the other to slow down. Of course, another result of the differential mechanism is that torque is split equally between the two sides and if one wheel loses traction the total drive force available will be just twice the force available from the tire with the least grip"
"In a real open differential there is stick-slip (Coulomb friction) in all the gear meshes and bearings and a small amount of hydraulic damping (proprotional to velocity or velocity squared) due to oil churning. This is shown in figure 20.3 which shows a small step in (delta)Torque with increase in (delta)RPM. The result of the friction is to slightly lock the two output shafts together. This gives a small offset to the theoritically even torque split. The wheel that gets the more torque is always the slower wheel".
I could scan in figure 20.3 but I'll just explain, (delta)Torque is the difference in output torque between the two shafts, and (delta)RPM is the difference between the rotational velocity of the two output shafts. (delta)Torque is shown to be zero at all times (theoritically).
So there you have it, open differential is a torque-splitting device.
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I supported Toymods
Location:
Perth
Registered:
May 2002
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Re: whats a LSD?
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Mon, 08 March 2004 05:58
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That only applies when both wheels have grip. Under a straight line, yes they will both get the same force applied to them. When you turn it allows slip so the outside wheel can turn faster as it has a larger arc.
What Norbie has said is true though, when one wheel loses traction, all force is applied to this wheel in an open diff until it gets grip in which case the situation reverts to the above.
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Location:
South Australia
Registered:
July 2002
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Re: whats a LSD?
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Mon, 08 March 2004 06:36
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Okay - maybe I should delve a little further...
Torque is a force - right? So let's say a wheel is being forced to spin - lets also say that the wheel has little interaction with the surface of the road - this means that the force of friction against the tire/wheel is minimal, such that if you apply torque to that wheel it will spin up faster than that of a wheel which has a frictive (?) force working *against* it.
Like I said, a wheel spinning doesn't mean that it has *more* force applied to it, it just means there is less force applied to counter the torque that the output shaft of a diff applies to a wheel.
I'm pretty sure, in regards to the 'torque' split between the wheels, that the ONLY way to change the *torque* that one output shaft receives would be to gear it at a different ratio to that of the other output shaft...a normal open differential's 'spider' gears apply the same gearing ratio to each side, hence the 50/50 torque split.
Because an open diff will only split torque evenly, then if one wheel is getting a bit of torque and is spinning up like all hell, then the other wheel is getting that same amount of torque (ie bugger all) and it's going nowhere.
Corollory : A locked diff does not split torque evenly! Surprised? Yeah I was too.
But imagine this, a car is turning around a corner, with a locked diff, one wheel will tend to 'lock/skip' a bit in order to travel the smaller turning arc...
Think about that -> that wheel is not applying force to the road of the same magnitude that the other wheel is, the other wheel is pushing the car forward, whereas the locking/skipping wheel is barely moving and is just being tugged along by the car's momentum - this diff is clearly NOT evenly splitting torque as the other wheel is getting torque to speed up!
Quote from Race Car Vehicle Dynamics in regards to locked diffs
"The torque split to the two wheels is determined by a variety of tire-related factors such as radius of turn (of whole vehicle), revs/mile (circumference of tires), load, and lateral force/friction circle effects. Tire traction characteristics are nonlinear (similar to the lateral force characteristics discussed in Chapter 2) and it is very difficult to determine the torque split at any given operating condition."
I hope I'm explaining this well enough...further more, I hope that I am right...
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Location:
brisbane
Registered:
March 2004
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Re: whats a LSD?
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Mon, 08 March 2004 06:44
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When a car is driving straight down the road, both drive wheels are spinning at the same speed. The input pinion is turning the ring gear and cage, and none of the pinions within the cage are rotating -- both side gears are effectively locked to the cage
When a car turns, the pinions in the cage start to spin as the car begins to turn, allowing the wheels to move at different speeds. The inside wheel spins slower than the cage, while the outside wheel spins faster
The open differential always applies the same amount of torque to each wheel. There are two factors that determine how much torque can be applied to the wheels: equipment and traction. In dry conditions, when there is plenty of traction, the amount of torque applied to the wheels is limited by the engine and gearing; in a low traction situation, such as when driving on ice, the amount of torque is limited to the greatest amount that will not cause a wheel to slip under those conditions. So, even though a car may be able to produce more torque, there needs to be enough traction to transmit that torque to the ground. If you give the car more gas after the wheels start to slip, the wheels will just spin faster.
Remember that the open differential always applies the same torque to both wheels, and the maximum amount of torque is limited to the greatest amount that will not make the wheels slip. It doesn't take much torque to make a tire slip on ice. And when the wheel with good traction is only getting the very small amount of torque that can be applied to the wheel with less traction, your car isn't going to move very much.
The solution to these problems is the limited slip differential (LSD), sometimes called positraction. Limited slip differentials use various mechanisms to allow normal differential action when going around turns. When a wheel slips, they allow more torque to be transferred to the non-slipping wheel.
In either case open diffs are for underpowered cars
IMHO any vehicle with at least 80rwhp needs a LSD
That's my 2 cents,
Gus
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Location:
South Australia
Registered:
July 2002
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Re: whats a LSD?
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Mon, 08 March 2004 06:50
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| "Hot Celica" |
in a low traction situation, such as when driving on ice, the amount of torque is limited to the greatest amount that will not cause a wheel to slip under those conditions.
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| "FWDBoy" |
Of course, another result of the differential mechanism is that torque is split equally between the two sides and if one wheel loses traction the total drive force available will be just twice the force available from the tire with the least grip
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Exactly the same thing...
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Location:
brisbane
Registered:
March 2004
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Re: whats a LSD?
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Mon, 08 March 2004 07:02
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I was a bit late with my post, but it is true that an open diff ALWAYS distributes torque evenly between two wheels, that is the problem with the open diff, and the LSD differs to torque between the two wheels to try and STOP the spinning of the wheels
thats why LSD is great for drag racing and also for drifting if your car has enough torque to keep both the wheels spinning
Gus
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: whats a LSD?
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Mon, 08 March 2004 07:48
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| FWDboy wrote on Mon, 08 March 2004 15:55 |
So there you have it, open differential is a torque-splitting device.
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so when i go around big roundabouts fast, the inside wheel lifts totally off the ground, and starts spinning at high speed, whilst the car stops going forward and loses all drive... i still have just as much forward drive cos of torque splitting????
you will get some reactionary force on the gripping tire, due to the rotational inertia that you are generating in the tire that is free spinning...
heres a trick  jack up one rear wheel.. put the car in 1st gear (remember to chock the front and sitting rear wheel well, and don't do it in front of a garage ) then let clutch out slowly..... see how far forard the car goes  heh heh
Cya, Stewart
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Location:
Lost in the K hole
Registered:
May 2002
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Location:
adelaide
Registered:
December 2003
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 Re: whats a LSD?
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Mon, 08 March 2004 12:18
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SNAP 
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Toymods Social Secretary
Location:
Sydney
Registered:
July 2002
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Re: whats a LSD?
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Mon, 08 March 2004 12:27
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its not funny dude. This is a pretty serious problem. Ed is trying to maintain a level of technical correctness and a clean forum so that more members are attracted to the forums and maybe even the club....
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Location:
South Australia
Registered:
July 2002
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Re: whats a LSD?
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Mon, 08 March 2004 12:45
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Well, the thing with lifting a wheel off is that it will cause the car to lose forward drive (with an open diff) which will have the result of putting the wheel back on the ground which means you'll have drive again.
Of course, as stated, there is resistance in the diff oil which will cause some level of drive to still be maintained (similar to the effect a viscous coupling has except completely different  ) and there's the fact that there is rotational inertia to overcome.
However, I think the general gist of what's going on has been explained
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Location:
Brisbane
Registered:
May 2002
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Re: whats a LSD?
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Mon, 08 March 2004 13:30
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I can't believe there's even an argument here... haven't you guys ever driven a car with a single-spinner diff in low grip conditions? If the diff always send 50% of the torque to each wheel, that's effectively a locker and you'd have plenty of traction. I know from my extensive experience driving horrendously overpowered shit-tins that this isn't the case!
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Location:
South Australia
Registered:
July 2002
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Re: whats a LSD?
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Mon, 08 March 2004 13:48
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Okay, maybe we'll call this a difference in opinion, but you can either believe this figure or not...it's taken from Race Car Vehicle Dynamics (considered to be quite a reference text I understand)
As stated before, the (delta)RPM is the difference between left and right RPM (ie when a wheel is spinning at a different speed to the other), and the (delta)Torque is the difference in torque applied to one wheel from the other.
If you want, go out and buy Race Car Vehicle Dynamics (mega exy), or go to a library and read it. This is a *serious* text book and has been used as a basis for the understanding of vehicle motion and if you want to know how good it is go play any Papyrus from Grand Prix Legends onwards (wicked games btw!)
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Location:
Brisbane
Registered:
May 2002
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Re: whats a LSD?
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Mon, 08 March 2004 13:52
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I don't need a text book to tell me how my car drives FFS!
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Location:
South Australia
Registered:
July 2002
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Re: whats a LSD?
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Mon, 08 March 2004 14:20
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I actually just thought of another thing as my bro was asking a bunch of questions.
Lets say you lift a wheel off the ground with a locked diff in the middle of a corner, the wheel that is lifted off the ground (lets call it the inside wheel) is going to move at exactly the same rotational velocity as the wheel at the other end (the outside wheel). Now rotationally accelerating (applying torque to) a wheel that is up in the air is a piece of piss, you would need 1 Nm of torque to accelerate it at the rate that it will.
If torque was split 50/50 between the inside and outside wheel, then the outside wheel would also be getting 1Nm of torque regardless of how paw-to-the-floor you are, which means that as soon as you lift a wheel in a locker, you will lose all acceleration.
This is clearly...bullshit...the majority of the torque would be applied to the outside wheel which would get 90%ish or so depending on a million and one factors. There is simply no way to argue against this unless you completely disregard physics.
Anyway, I know what you are saying in regards to the behaviour of a locker compared to an open diff...I was just hoping to point out the physical pedantics of the issue - it's simply a different nomenclature that I'm sure maybe one other person may be interested in knowing
I'll drop the issue now! Back to frivolity - yipee!!!
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Location:
Melbourne
Registered:
October 2003
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Re: whats a LSD?
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Mon, 08 March 2004 14:33
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I have no exp with locked diffs, but is it safe to say that a locked diff will behave the same as a single axel? ie: one axel with one (crown) gear at one side of the drivetrain's final gear, which simply transfers the force 90deg to the axel?
now, regardless of anything if this were the case: the torque will be delivered to the crown wheel (fixed to the axel) at a certain figure. Now excluding twisting of the rear axel - Torque will be evenly spread across the rear axel, thus both wheels all the time.
Can this be said of a locked diff?
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Location:
Melbourne
Registered:
October 2003
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Re: whats a LSD?
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Mon, 08 March 2004 14:38
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| Norbie wrote on Tue, 09 March 2004 00:30 |
I can't believe there's even an argument here... haven't you guys ever driven a car with a single-spinner diff in low grip conditions? If the diff always send 50% of the torque to each wheel, that's effectively a locker and you'd have plenty of traction. I know from my extensive experience driving horrendously overpowered shit-tins that this isn't the case!
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this is true norbie, it is always sending equal torque to each wheel - its the difference in the friction between tyre and ground that effects the rotation of the wheels.
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I supported Toymods
Location:
Perth, WA
Registered:
May 2003
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Re: whats a LSD?
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Mon, 08 March 2004 17:29
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What i dont understand is the difference between a normal lsd and a mechanical lsd? or are they the same?
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Location:
Sunshine Coast
Registered:
February 2004
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Re: whats a LSD?
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Mon, 08 March 2004 22:02
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| FWDboy wrote on Tue, 09 March 2004 00:20 |
I actually just thought of another thing as my bro was asking a bunch of questions.
Lets say you lift a wheel off the ground with a locked diff in the middle of a corner, the wheel that is lifted off the ground (lets call it the inside wheel) is going to move at exactly the same rotational velocity as the wheel at the other end (the outside wheel). Now rotationally accelerating (applying torque to) a wheel that is up in the air is a piece of piss, you would need 1 Nm of torque to accelerate it at the rate that it will.
If torque was split 50/50 between the inside and outside wheel, then the outside wheel would also be getting 1Nm of torque regardless of how paw-to-the-floor you are, which means that as soon as you lift a wheel in a locker, you will lose all acceleration.
This is clearly...bullshit...the majority of the torque would be applied to the outside wheel which would get 90%ish or so depending on a million and one factors. There is simply no way to argue against this unless you completely disregard physics.
Anyway, I know what you are saying in regards to the behaviour of a locker compared to an open diff...I was just hoping to point out the physical pedantics of the issue - it's simply a different nomenclature that I'm sure maybe one other person may be interested in knowing
I'll drop the issue now! Back to frivolity - yipee!!!
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why would the outside wheel get most of the torque? a locked diff isnt a diff. its basically an axel with a drive gear, hence you cant have any deviation in torque delivery since there isnt any difference between the 2 wheels. if there was, then you've probably got an LSD
does your text state what happens when traction is lost in an open diff, or is it just assuming it isnt?
what does it say about LSDs or locked diffs?
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Registered:
March 2004
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Re: whats a LSD?
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Mon, 08 March 2004 22:24
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Limited Slip Diff. What this thing does is create a link between the rear wheels (or front wheels, in a FWD car, and often between the front and rear wheels as well in a 4WD) so that instead of letting them spin freely with respect to each other, they have a certain amount of friction. I'll be talking about three types, but only two in any detail. The cheapest and certainly the nastiest to drive is what we call in Australia as the 'CIG Locker'. What this means is that the centre of the diff has been welded up (By using an oxy welder, almost invariably powered by CIG gasses, gettit??) so that the rear wheels are solidly locked together. This makes the car very hard to turn around slow speed corners, as the inside tyre wants to rotate at the same speed as the more heavily loaded outside, and so tends to push the car in a straight line - big time understeer! If you have enough power, then you can get both rears spinning nicely, and so create and control the oversteer that will then develop. You really have to drive the car on the throttle a lot more than a 'normal' car, and so they can be a quite tricky unless you get used to it quickly.
What's far more common - and pleasant to drive - is the Salisbury (pro: Sawls-bree) LSD. All they are is a conventional open diff, but with a clutch pack on the axle diff gears so that there is friction created between the rear wheels when they rotate at different speeds.
There are a couple of different ways of getting the LSD to work - There are the options (from Toyota, at least) of a '1 way, 1.5 way, or 2 way'. What this means is that with a '1 way', you only get the LSD action when under power. A '1.5 way' has a little LSD action when on trailing throttle. (good for controlling the car when cornering) And finally the '2 way', which is the sideways driver's dream, as the car will want to slide everywhere.
Possibly the best LSD of all is the Torsen 'torque sensing' type. They are a very good thing, as they always spread the torque evenly between both wheels at all times, so even if you have one tyre on ice and the other on sandpaper, both wheels will spin evenly. There are two types of Torsen
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Location:
South Australia
Registered:
July 2002
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Re: whats a LSD?
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Tue, 09 March 2004 01:40
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| Quote: |
does your text state what happens when traction is lost in an open diff, or is it just assuming it isnt?
what does it say about LSDs or locked diffs?
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Okay okay...I was going to drop this, but yes the book does state stuff about locked diffs and limited slip (quaife/torsen/viscous you name it) if you read up in this thread bit you'll see that I've already quoted it as saying locked diff's torque distribution varies according to numerous factors.
Now, I think people are forgetting (or maybe never learnt, I dunno) Newtonian physics...well at least I think it was Sir Isaac Newton who came up with this, but the statement pretty much says 'Any action will have an equal and opposite reaction' this could be worded that 'Any force will have an equal and opposite reacting force'. In this case we are talking about the FORCE at the wheel (yep - torque is a FORCE, well pretty much anyway).
Locked diff example :
So, you are punting around a corner and lets say one wheel is up in the air, or even just spinning up due to loss of traction - call it "wheel A". 'Wheel B' is still on the ground gripping perfectly.
Sometimes the easiest way to measure how much force something is receiving is to plot it's reaction using Newton's laws.
What is Wheel A doing? Answer : Pushing a car.
What is Wheel B doing? Answer : Spinning a little bit in the air, pushing nearly nothing at all.
A little more indepth :
Firstly, rotational acceleration occurs with the application of a force (ie torque), that is when a wheel is spinning up faster and faster, it must be receiving torque.
Now wheel A and B will always rotationally accelerate at the same rate due to the fact that they are locked togetherm this means that they always travel the same distance as each other.
Wheel B is having to push the car forwards using the friction between the road and the tire...it is doing alot of 'work' -> work has dimensionality of mass, length^2 and time^-2. Wheel B is pushing the mass of the entire car, over the same length (due to the locked rotational velocity of the two wheels) and over the same period of time as Wheel A...meaning that Wheel B is CLEARLY doing alot more work because Wheel A only has to rotate itself and isn't pushing anything but air (alot less *mass* than Wheel B has to push forward).
Work is also equal to Force * Length = so if the length is the same (due once again to the locked rotational velocity) then if Wheel B is doing more work than Wheel A, it must be receiving much more FORCE than wheel A to balance out the equation.
Torque (a 'twisting' moment/force) is that force.
It is entirely true to say that wheel B is getting far more TORQUE than wheel A -> so this is the argument that a locked diff does not distribute torque evenly....especially when a wheel is off the ground or slipping (when it is slipping, it simply means that the tractive effort of wheel A is less due to the lower co-efficient of friction between road and tire, meaning that wheel A is still doing less pushing - ie less work - ie less force - ie less torque).
As for open diffs distributing torque evenly? Okay that's a complex thing to argue...it theoritically does, but here's another quickie. When you start spinning up 'one' wheel does the engine suddenly start to rev up? Yeah it does. Force and torque don't disappear, it's impossible...the amount of torque that the diff applies to the wheels will *definitely* diminish when one of them loses grip, but it is still evenly balanced between the two! What happens to the rest of the torque you ask? Well it just so happens that it acts on the crankshaft/propshaft/everything (edit) ***That is wrong*** the energy actually is being used to work against gas compression and expansion etc etc, but the effect is the same, the engine starts speeding up! (/edit) else causing the engine revs to rise. The torque stops acting on the diff, and starts acting more on the engine.
Here's a couple of links to some physics tutorials that may or may not help clear things up.
A very math's like torque tutorial
A slightly clearer explanation of torque
A list of physics tutorials that the second link is from
The final link has some links to explanations of rotational motion etc etc.
When you have read and understood these principals and what torque is and how newtonian physics works, then you can continue this 'argument'.
[Updated on: Tue, 09 March 2004 01:48]
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Location:
Newcastle
Registered:
May 2002
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Re: whats a LSD?
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Tue, 09 March 2004 04:35
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Go get em FWDboy. There's far to much "I reckon that..." and arguments based on "common sense". From my experience the remarkable thing about common sense, is how uncommon it is. Wow and to think that at the start of this thread I thought that LSD was lysergic acid diethylamide....
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Location:
Newcastle
Registered:
May 2002
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Re: whats a LSD?
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Tue, 09 March 2004 04:56
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Oh I forgot to mention.....make sure some of you aren't comitting the age old sin of confusing torque and power.
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