MFactory Mechanical Clutch Plate Diff soon available for E89 DCT

[techathy]

This also means that a helical lsd finds traction faster when one wheel comes on a decent piece of road.

Yes, and by chasing traction the diff introduces larger thrust vectors into the situation…. not a very good idea to do when you’ve got almost zero warning going from grip to total loss of directional control.

This is a common misconception. A helical LSD also has a bias under braking.
Look at it this way (very simple representation of the inner workings of a helical LSD): basically a helical LSD is a bunch of wormgears. If you have a wormgear driving a spur, you can drive the spur by turning the wormgear. But you cant drive the wormgear by turning the spur. That goes for driving the spur clockwise (driving) and anticlockwise (braking).
The same goes for the helical LSD albeit that the braking bias is in practice always less than drive bias. (something like 4:1 or so)
(this is set by the relative angle of teeth both gears have and on what curve they are grinded, which makes it very complicated to calculate)

No it’s not because there’s no speed differential between the wheels to allow for torque biasing. On a 1.5 or 2 way LSD then the act of braking is trying to bind the axel together. By the time there’s something for the helical diff to work with the fan is already liberally redistributing the brown stuff.

On a fwd car the characteristic of a locking LSD means that the front wheels are more likely to lock than the helical lsd, not less likely.
That induces understeer (as steering requires a different rpm on left and right front wheel ). A clutch locking diff would lock here (with power applied) regardless of the road conditions whereas the helical LSD regulates the torque by what the requirements (dictated by tyre road surface) really are. That's why only a smart (computer controlled) torque vectoring LSD can compete with a helical lsd in terms of functioning.

On a RWD car its just the other way around: more likely to lock on the rear (where the diff is) induces now oversteer.
That's why bmw develloped the M diff. that only locks when there is loss of grip from one wheel. If your diff always locks on power, you always have a problem in corners as one wheel wants to turn faster than the other one (both on fwd and rwd). (more oversteer when you passed the apex)

You're assuming you're cornering when under braking. I'm assuming you're driving properly by trying to keep the car in a straight line on the brakes/keeping a neutral throttle input when cornering are not being a total idiot by asking a car which has virtually no grip doing 2 things at once.

 

[GuidoK]

This also means that a helical lsd finds traction faster when one wheel comes on a decent piece of road.

Yes, and by chasing traction the diff introduces larger thrust vectors into the situation…. not a very good idea to do when you’ve got almost zero warning going from grip to total loss of directional control.

I dont think that's generally a problem?
A lot of cars that do well on varying terrain with difficult and alternating grip situations use a torsen diff. Like audi's have for the last 3 decades. It's a very commonly used diff in both ralley and ralleycross. Those guys generally know what they're doing.

No it’s not because there’s no speed differential between the wheels to allow for torque biasing. On a 1.5 or 2 way LSD then the act of braking is trying to bind the axel together. By the time there’s something for the helical diff to work with the fan is already liberally redistributing the brown stuff.

No that's not true. A helical LSD works instantly. It's a force balance. As soon as there's a force (either drive or brake) it works.
So there is no 'by the time' of any sorts. Like with my example of the wormwheel: when you rotate one gear there is no pause on the other wheel.

You're assuming you're cornering when under braking.

No, I'm assuming giving throttle in the corner after passing the apex, exactly like I wrote.
The big difference between a locking LSD and a helical LSD is that a locking LSD always locks when throttle is applied and a helical LSD only when one wheel cant put that torque on the road. That means when in a corner and giving throttle (like you do roughly after passing the apex pulling the car through the corner), the locking diff will always lock/bind up, resisting both wheels spinning at different rpm (which per definition is needed in a corner because of the outside wheel has to travel a longer distance) and a helical LSD does not. Thats why the locking LSD doesnt work in a FWD car because that induces massive understeer. For a rwd it would induce oversteer but you can compensate for that with your steering wheel so it can work in a rwd car. That is one if the biggest differences between a locking diff and a helical diff.
The M diff can also allow different RPM between both wheels on throttle and acts more or less like the helical diff except it has to have loss of traction before locking action and the helical LSD doesnt.