With Helical LSD's, although are pre-loaded, do not function the same way that pre-load does in a Plate type LSD, so there isn't the same sort of pre-load "force" generated.
In a Plate LSD, the pre-load is how much torque is generated to the axles from a standstill. Once torque goes about this amount, the pre-load is irrelevant
On a Helical LSD, the pre-load is only used to keep the side-gears pre-loaded to "simulate" a torque load on the axles (along with generating friction. A Helical LSD works on friction). Even without any pre-load, a Helical LSD will still function at standstill/low-torque unlike a Plate LSD (provided there is sufficient traction of course)
I defer to your experience, but that doesn’t sound quite right.
For a clutch type, your description is correct. With zero traction, the clutch is limited by the preload. Once one wheel has traction, the pressure angle then determines how much torque the clutch pack can transfer to either wheel, which is some function of the total torque/traction from both wheels (modified by the pressure angle)
As I understand from the helical, the helix angles create a bias/gear ratio which can deliver a multiple of the traction at the low traction wheel.
I think the specific question he’s trying to ask is, based on the coil spring choices, what range of simulated torque can the zero load system on your diff apply to the unloaded wheel. That torque would then by multiplied by the bias ratio to determine how much torque can be put to the wheel with traction.
However, I see where this is an apples to oranges comparison. To answer that question, you’d also need to know the other characteristics of both LSDs. Specifically:
- clutch pack preload, disc diameter, area and coefficient of friction of the clutch type. Also the pressure angle and some other parameters.
- Coil spring preload, mechanism diameter and area, plus the bias ratio of the differential
So you’d be correct in saying “I can’t give you a useful comparison to the question because it depends on other characteristics of both specific differential models in question”
I imagine you could probably answer how much simulated torque can the Ford Fiesta VTB apply to an unloaded wheel, and what is the bias ratio. If you were willing to and MFactory is willing to publicize those figures.
But that still can’t be compared directly without knowing all the workings of the Clutch-type as well, and even then the two diffs will act very differently