LSDs....

[KSaiyu]

OK, I've read from these sources:

https://www.gtplanet.net/forum/showthread.php?t=31998
https://www.gtplanet.net/forum/showthread.php?t=11591
https://www.gtplanet.net/forum/showthread.php?t=49658
http://www.intothered.dk/simracing/differential.html

and a few other web pages, but I'm still confused as to a) what an LSD does and b) how to tune it. I know the first link gives a general guideline to what to do to dial out under/oversteer, but I want to know exactly what I'm tuning and why. It's the only part of tuning in GT that I have never completly understood

I'll start with what I think is right....

Cars in GT start out with an open differential, which allows the different wheels to spin at different rates (in a corner the outside wheel spins faster since it has more distance to cover). Open differential's always applies the same amount of torque to each of the wheels, but this torque is limited to whichever wheel has the least traction since it sends power through the path of least resistance (usually the inside tyre).

Taken from http://www.granturismobynumbers.com/ubb/Forum31/HTML/000572-2.html:

If one of your drive wheels sparks-out (exceeds its grip potential) and blows a little smoke the other drive wheel which still has grip receives no power so you are coasting receiving only the faint push provided by the friction of your spinning smoking drive wheel. This will continue until both drive wheels establish a proper interlock with the road. A limited-slip differential doesn't limit the amount that your wheels slip or spin directly, that would be a traction control system. It limits the amount of slip between the drive wheels being allowed by the differential. Back in the slick surface example we had two wheels both of which could be described as slipping. The one that is slipping against the ground and not slipping in relation to the drivetrain is undergoing what might be called powered slip. And the one that is holding still in relation to the ground and slipping in relation to the rest of the drivetrain is undergoing differential slip. Differential slip is the kind of slip that a limited-slip differential limits.

Now the settings:

Taken from http://www.intothered.dk/simracing/differential.html

By limiting the slippage between the rear wheels, the differential can have a profound impact on the car's handling. The rule of thumb is: the more the diff limits slippage, the more the car will tend to go straight or understeer up to a point. On the power side, if enough torque is applied to spin both wheels, the car will snap into oversteer.

Initial Torque - I have no idea, this is one thing I'm confused about

Acceleration - Controls how much locking there is between the wheels during acceleration. Higher setting means the inside wheel will be less likely to spin, and there can be more consistent transfer of torque to the wheels, even when one has lost traction, although cornering will be hampered. However, having it too high could lead to snap oversteer as the tyres can eventually break traction during the exit phase of a corner with little warning.

Deceleration - Controls how much locking there is between the wheels during deceleration. A high setting makes the car more stable under braking, even when braking during cornering, and also if you lift off during cornering.

"Set" LSD's (One's that aren't Fully customizable) -

Taken from http://www.club4ag.com/faq and tech_pages/limited_slips_differential_101.htm

This designation reflects the design of the cam groove which enables the LSD to function differently under different loads. A 1 way differential means that the cam is shaped in such way as to have positive lock only when accelerating. The 2 way is constructed in a way to have positive lock motion in either acceleration or deceleration. The 1.5 way is a new term used to describe the 2 way cam which enables different lock up rates during the two directional forces. The 1.5 distribute positive lock stronger under acceleration than when decelerating. The 1.5 way can provide more forgiving balance when braking than a full 2 way setup, although it is less effective for true racing applications, it provides easier operation for beginners in throttle off conditions. It is also effective for front drive cars which need extra stability during braking.

However, while this gives a good description, I don't understand the explanation on why a 1.5 way would be less effective for racing than a 2 way - surely the 2 way would prove least effective since it is locking up more under braking. I also think the 1 way would be a good LSD to use on FWD cars, as backed up by the GT2 manual, although this link from Suzuki http://www.suzukisport.com/english/sales/ignissport/product/lsd/ shows how a 1.5 way is also productive.

hmmmmm, so after all that I guess the only question I have is on initial torque - I have many different sites but I can't find one that fully explains what it adjusts - does it provide strength, or measure the response of something? For example I have:

http://www.unofficialbmw.com/all/drivetrain/all_limited_slip_explained.html
http://members.aol.com/agspeed/LSD-lock.htm
and the various explanations from posts I posted links to above.

Damn this post turned out messy....

 

[sukerkin]

Not to worry Ksai - your post may have been long but you quote your sources and state what you want to know clearly enough. Vastly superior to the spate of "text'ese" posts spawned by the Mobile Phone generation (throw 'em all in the Loch, that's what I say ).

As to what the Initial setting does on the LSD, it's supposed to be measure of how quickly the limited slip activates. The lower the Initial then the longer it takes for the 'locking' action to take place. So if you turn it all the way down (as many do) then you might as well not have bothered fitting it in the first place .

Despite the spread of possible settings, the Initial has a limited (no pun intended ) range of operating values that actually do anything within the game - at least that's what I've read elsewhere. Anything over 15 makes little difference and lowering it to 5 effectively turns it off.

Hope that's what you were looking for. Now all we need to re-confuse matters is someone to chime in with the "Initial value acts as a multiplier to the Accel and Decel" school of thought .

 

[KaiZen]

Thanks for that one Sukerkin.. didn't know that that's what the initial did..

So 20+ initial has little to no effect?.. have you experimented with that? (probably a dumb question)

Another one of your tips, hints, guides, that I must add to my list and experiment with..

 

[sukerkin]

Just to clarify a little.

When I said that cranking up the Initial above 15 has no noticeable effect, what I meant was additional effect i.e. the changes it invokes are not obvious compared to what happens as you turn it up to 15.

 

[KSaiyu]

Thanks for the explanation.

So I assume in this paragraph from http://members.aol.com/agspeed/LSD-lock.htm

The limited slip percentage (S) is also called the locking factor. It
describes the maximum applied torque
difference between rear wheels compared with total applied torque.
Passenger car LSDs are usually in the
25-40% locking factor range. Most BMW LSDs are 25%

is really the initial torque value in GT?

 

[sukerkin]

Ah, not quite (it has been discussed a few times that the LSD effect simulated in the game doesn't work very much like one of the more sophisticated diffs out there on the real roads).

In GT3 it is generally thought that the 'locking factor' is what you are changing when you set the Accel and Decel values. The Initial can be thought of as the 'initiator' of the lock - how much rotational difference is allowed before the LSD begins to work. That's why turning the Initial up makes the car harder to turn - it's quickly activating the 'lock' making the wheels rotate at a more similar rate.

 

[KSaiyu]

ahhhh I wondered why web pages didn't seem to relate to the explanations on GT initial torque, thankyou so much for explaining!

Time to test it out on the muscle cars in GT4

 

[Sctn2labor]

Seems like another way to put it is, if you crank the Initial up too high, it activates when your wheels are simply moving at different rates. IOW it creates a "false positive" when they're simply both gripping (or both gripping ENOUGH).

That sound right? 'Cause I'm Juuuuust now starting to understand what an LSD does.

 

[Vision GT]

Take a stock Subaru Impreza WRX STi Version VI, buy a fully customizeable LSD but don't install it yet. Then go to a track with a wide open area, like the first track(can't think of the name). Turn off the stability control and the traction control. Then do donuts and observe the rear tires, front tires, observe the inside and outside tires. Then install the full customizeable LSD and set all the front to lowest, and the rear to highest. Then observe from there.

If you really want to see how LSD work, take it to a track with a WIDE half circle like turn. Keep the Impreza stock, then just drive through it and when it starts to understeer or so, let off the throttle, the rear will kick out.

My friend posted up how LSD work and such but can't find it.