What's the difference between a locked diff and a LSD with preload set to a sky-high value?

One's fully locked all the time, the other is up to 80% locked and has adjustable coast locking.

Quote from S14 DRIFT :

One's fully locked all the time, the other is up to 80% locked and has adjustable coast locking.

if the preload is high enough, the locking factors are irrelevant, and it will act just like a locked diff.

You avoid the wrath of the anti-locked diff brigade.

Quote from NightShift :

What's the difference between a locked diff and a LSD with preload set to a sky-high value?

None, although there is the possibility to overpower the preload... I'm just not sure how helpful an opening diff is when you're already spinning (quite wildly at that)...

So the LSD is 100% locked as long as the torque difference is less than the preload?

And how do you calculate the 'critical' preload value that turns the diff into a locked one? in LFS?

Quote from Bob Smith :

You avoid the wrath of the anti-locked diff brigade.

Our torches and pitchforks can't be misled so easily

Quote from NightShift :

So the LSD is 100% locked as long as the torque difference is less than the preload?

And how do you calculate the 'critical' preload value that turns the diff into a locked one? in LFS?



Our torches and pitchforks can't be misled so easily

the threshold will depend on the size of the tires and the amount of grip they are getting, among other things, but it's felt easily enough in a test drive to find by trial and error. set your locking factors low and work your way up from a low initial preload setting. when the preload crosses the threshold the inside tire will not be able to exert enough force on the diff to cause it to slip, so it will slip against the road instead, causing an obvious change in handling.

That's understood, I was thinking something analytical (ala VHPA) or .raf files analysis, maybe looking at slip ratio or torque at the wheels? I'm not on windows now and can't remember exactly what data is available.

Quote from NightShift :

That's understood, I was thinking something analytical (ala VHPA) or .raf files analysis, maybe looking at slip ratio or torque at the wheels? I'm not on windows now and can't remember exactly what data is available.

ya, well it should be possible to calc out, based on the tractive force of the tires and the leverage they apply to the axle (which depends on the diameter of the wheels) but is the data really that useful? somebody who wants a "psuedo locked" diff doesn't need to hit the threshold exactly, they can just go way past it and get the same effect.

are you trying to create a rule for your league or something? (ie, no locked diffs, and no lsd's with too much preload)

No sir I don't manage any league the pitchforks line was an attempt at autoirony since I guess my words often sound like those of a realism nazi to some ears.

I'm just interested in learning as much as possible on setting up a car. Having a good feel is certainly a great thing, but there are so many subjective factors outside our control.

There's always a certain degree of guessing, how much of what you feel is really there and how much is a cognitive/perception bias, or just your driving subtly changing without you noticing.

That I take is a problem even for car manufacturers, if it's true they made self-driving prototypes to minimize the human error/variance due to test drivers, and I'm sure they are better and more consistent at it than me!

Am I mistaken if I believe the following method should yield the maximum senseful preload?
1. Define maximum engine torque T.
2. Multiply by smallest gear ratio r1.
3. Multiplay by differential ratio r2.
4. Multiply by differential power-locking factor F
(Assumed definition of F: F = Difference in torque between the two tyres devided by aligning input torque. Example: With F = 20% and T*r1*r2 = 20 Nm the torque split may be up to 4 Nm before slipping at the LSD clutch plates appears.)
5. If preload P is larger than T*r1*r2*F the engine will not be able to make the clutch of the LSD slip in any gear. The differential behaves as a locked diff in all power situations.
6. Define braking torque B.
7. Define braking torque split K.
[Assumed definition of K: K = (Front braking torque)/(Front braking torque + rear braking torque) as I believe it is defined in LFS ]
8. If B * (1 - K) (for RWD) respectively B * K (for FWD) are larger than preload P the brakes wouldn't be able to make the differential clutch plates slip even if one tyre was in the air and the other perfectly sticking to the ground.

I'm not quite sure how the coast locking factor works, so please feel free to comment on my ideas.

Vain

Quote from Vain :

I'm not quite sure how the coast locking factor works, so please feel free to comment on my ideas.

afaik exactly the same as the power lock but with the engine brake torque instead of the power torque