I read some article about limited slip differencial and so far understand, that certain amount of torque from one wheel is transfered to the other wheel when cornering.

What I dont understand is:

• Terminology. LFS uses power/coast (%), the article mentions "locking (%)". Does "coast" have the exact meaning as "locking"?
  
• What exactly is "locking"? What does it mean if a diff is set to 40% locking? (simple explanation plz)
  
• How does this effect the car behaviour?

I'm not interested in exact technical describtion found in advanced setup guides and articles on the net (which is why I ask in this thread, so please keep it simple :tilt. I'm interested in racing, so I need to know "What does it do? How does it effect the car? And how do I set it?". Thnx.

well, im not a car wizzard, so i will explain it in the terms that i understand.

If you have 60% (Power) and 50% (Coast) Clutch pack, Then when accelerating (power) out of a corner you differential will be 60% locked, meaning that 40% of the power could dissipated by the wheel with the least grip (inside). This is easiest to explain when you are close to an open diff, which allows all the power to travel through the path of least resistance, i.e. the unloaded tyre. This means that the loaded tyre is very unlikely to skid/slip as very little of the power will be tranismitted to it. So, increase that upto 60% lock, and 60% of the power should be transmitted into the loaded wheel, giving it more power and a greater chance of skidding/slip.

The difference between power/coast from what i understand is that power works under throttle, and coast locking comes into effect when coasting (no throttle). Try experimenting. Try a locked differential and you will see it is hard to turn in, but is stable, but when you give it gas there is a large chance you will spin up both wheels and drift.

Generally, more locking on Power (60-80%), this will allow the car to get more power down, with a greater chance of spinning both the rear wheels but also in LFS giving a little bit of slide and often helping turn-in. Less locking on power (0-30%) will allow you do drive like a hooligan out of the corners without much chance of sliding as the power will be dissipated through the least loaded (inside) wheel.

As for more locking on Coast (50-80%) this will make the car more stable into the turn, but harder to turn right in as the car is having to twist(?) more. If you have a very low locking on coast, then the car will often step out alot easier under braking and will turn in easily.

Hope thats clear, that is how i understand it.

I think I understand now, so power(%) in LFS means how much power will be ,,locked" when accelering out of corner and coast(%) how much power will be ,,locked" when the car doesnt accelerate (i.e. is entering a corner).

Yes, that is basically correct.

Do you know the principle of a differential and why cars have one?

Quote from AndroidXP :

Yes, that is basically correct.

Do you know the principle of a differential and why cars have one?

I think I know the basics of "what does it do" and "why cars have it".

One more thing comes into my mind. When GTRs use clutch pack, the revs drop drastically under heavy braking and then just jump up when you apply anough throttle. Why does this happen? Both wheels should have the same load when braking.

The driven wheels lock and thus the engine revs drop (up to the point where the magic auto-clutch kicks in to prevent stalling)?

Simple explanation of an LSD? Not really possible if you want it accurate.

Quote :

Then when accelerating (power) out of a corner you differential will be 60% locked, meaning that 40% of the power could dissipated by the wheel with the least grip (inside).

Not so easy I'm afraid. You need to be thinking torque, not power. And the amount of torque transferred does not equate linearly to the locking factor. See attached graph. The TBR value means how many times more one wheel can have than another. An open diff provides equal torque to each wheel. A 50% locked diff will send wheel up to 3 times more torque to one wheel than another.

The basic affects on handling have been explained reasonably accurately, although I prefer lower locking values myself: 20-50% power side and 33-60% coast (usually only one number will be high). I would consider a high locking factor to be over 40%. I tune diffs for handling and tyre heating rather than ultimate speed.

Also, to complicate matters, the clutch pack diffs in LFS are progressive, so the amount of locking depends on the amount of torque going through the diff. So with no torque, there is no locking (since we don't appear to have any preload), which is why when at very low throttle (controlled engine braking) the car will understeer, when enough throttle is applied to neutral torque going through the diff the car will turn in best, and when more throttle is applied, turn in decreases again (unless the rear breaks loose).

you might also want to add that the locked diffs in LFS are also a bit iffy, as in they shouldnt really be easy to use. i think?

i drove the FZ5 with locked diff the other day, and didnt realise what i had been missing, it makes it so much easier to drive, without any mojor handling issues tbh. IRL surely it would be a pig and cook tyres?

thanks for the clarification bob. could you clarify whats wrong with the diffs in LFS atm? especially being able to use the locked diff? is it basically just because the tyres dont have enough grip (or too much slip) that the inside can easily turn at the same rate as the outside wheel?

I guess the locked diff is so good at the moment because the tyres are able to deform enough to make up for the deformation posed on them by the diff without heating up too much.
That's the feeling I get from driving LFS. At some points the deformation of the tyres is rather extreme, judging from the FF.

Vain

I can only guess, but locked diffs don't seem to give enough understeer (comparing to locked diffs in RBR anyway), but otherwise seem ok. They should make the car very stable. Don't really know about tyre heating, but I on the FXR Madman and myself noticed how switching his set from locked diffs to clutch pack (with sensible locking) dropped the tyre temps a lot. So that would make sense?

Clutch pack suffers from a lack of preload (although again I assume, the lack of adjustment makes me think it isn't there).

I can't drive with locked diffs myself, it's just so horrible unless you bugger up the rest of the setup. That's more of the problem - you can get all the bad sides of the locked diff to disappear with weird sets. Clutch pack is perfectly driveable but requires a finely balanced set.

In a jeep wrangler with locked diffs on painted cement (with water on the ground) you can hear the inside tire "scrubbing" < DOn't know what else to call it.

Quote from wheel4hummer :

In a jeep wrangler with locked diffs on painted cement (with water on the ground) you can hear the inside tire "scrubbing" < DOn't know what else to call it.

yeah thats right. and i would expect locked diffs to make the cars 'skip' more under power.

And again, the physics update might even cure that. Currently, tyres on the edge of grip arent 100% realistic. A locked diff means, that unless you go in a straight line, the tyres are always on the edge of grip, scrubbing around. A "fixed" on-edge-of-grip behaviour might completely change the usefullness of the current locked diff.

Pretty good of you guys to explain all this more in detail. I have a rough idea, but this helps more, as i have problems with the lx4 sliding a lot around fe club. A dsrc server i believe. Anyway, i have been fiddling around with the diff for ages an cant seem to get a decent enough setup going. But now i have read this though a couple of times i hopefully can improve on my set Cya on track!

I never had a problem, 40 or 50% locked is enough for me, but then I don't trail brake.

Quote from skylineadam :

Pretty good of you guys to explain all this more in detail. I have a rough idea, but this helps more, as i have problems with the lx4 sliding a lot around fe club. A dsrc server i believe. Anyway, i have been fiddling around with the diff for ages an cant seem to get a decent enough setup going. But now i have read this though a couple of times i hopefully can improve on my set Cya on track!

just recently i tried a viscous diff on the LX4, it was pretty sweet tbh. i thought it felt best between 16-20Nm on most tracks. maybe give that a try? imo it handles really well like that. pretty stable into turns, but having really smooth modulation while in the turn as well as being able to take hairpins well by allowing some rear slides. no problems under power either as long as you are smooth.

id like to hear what some of you setup gurus think of the viscous differential as nobody seems to use it, but i think it was pretty sweet on the LX4 at least. i know its not as customisable, but imo it was pretty flexible anyway to give good control.

For the MRT season in the OWRL, I had downloaded a WR set that used a viscous diff. I just couldn't get the hang of it at all. As soon as I switched to a clutch pack, it was much better, much more predictable. I ended up winning the sprint at AS Cadet Reverse and came in second in the main race due to a spin (you know where...).

i suppose it maybe suits some cars/tracks better than others?

tbh, i used viscous @ BL1R and found it alot better, then i found clutch pack to be better at FE.

Jaakko from n1 team has made an LX4 set with viscous diff for South City. He was doing great times, just few tenths of second from WR. I couldn't handle the set, was strugling with the car in fast corners and it seemed very nervous on bumps. Had to switch back to clutch-pack, I like the handling much better with this diff. I think it comes down to personal preference. Viscous can be very fast on LX4, but don't force yourself to use it, if you don't like it (at least that's my experience).

I have one question to the clutch diff....especially the coast lock...it is known that a high coast lock gives you better stability when entering a corner and low coast lock makes you stepping out very easy....but I cannot get the point why? could someone pls explain this for me non-mechanic-noob?

Diff locking creates a resistance to turning by not letting the outside and inside wheels turn at different speeds (they take different (and therefore different length) lines through the corners), so increasing coast locking reduces agileness or in otherwords increases stability.
Use too much though and you'll just get unnecessary understeer.

Hi Bob,

thanks for yr answer....but I still dont understand why the car is going to understeer while having low coast lock ....is it because due to easier turning ability which is creating more weight-transfer...and loosing grip?

thanks,

It isn't, it will understeer with high coast lock. Low coast lock means that the inner wheel is allowed to rotate at a lower rate than the outer, creating less turning resistance, hence:

High coast lock -> understeer
Low coast lock -> less understeer / lift-off oversteer

@Pudel: What?
More coast lock = more understeer, not the other way round.


Lets roll this up from the beginning:

POWER lock engages when the engine is under power, accellerating the wheels
- happens usually right after the corner/apex ("corner exit")

COAST lock comes into play when the engine "idles" and is braking the wheels
- happens most of the time when braking into a corner ("corner entry")

Now, what does a locked diff mean? A fully locked diff is basically like a solid fixed axle, thus both wheels will always turn at the same speed, while a fully open diff will allow free rotation for each wheel. Gradually locked diffs are somewhere inbetween, still allowing some free rotation but also forcing the wheels to rotate togehter, depending on how much locking is applied.

If you want to know why a locked diff resists turning, then imagine there's a miniature axle with two wheels attached infront of you. Now you try to rotate the axle, holding one wheel and pushing the other away from you (or you grab the axle and try to steer it like it was a bike handle). You will notice there's a conflict between the wheels, with the pushed wheel trying to revolve while the wheel you hold wants to remain still. The same conflict also happens on the car, resisting any turning, because the only state where there's no conflict when using a diff is when driving in a straight line (or standing still).

Okay ...sorry I mixed up something....when I said I want to know why my car is stepping out of a corner with LOW coast lock....of course my car is massively OVERSTEERING....(not understeering...sorry)....and I want to know why the car is doing that.