Originally Posted by CSG Mike
(Post 1756859)
I've been getting a lot of PMs about LSDs lately, so hopefully this will answer a lot of questions!
A torsen differential can apply as determined by the internal TBR (torque bias ratio). A 4:1 ratio means that one side can handle up to 80% of the torque from the engine.
The Torsen itself works by attempting to slow down the wheel spinning faster (outer wheel) and speed up the wheel spinning slower (inner wheel). It can do this up to the TBR described above. If the torque to the wheels exceeds the TBR, then you get inner wheel spin.
A locking, or clutch type limited slip differential works by literally locking the outer and inner wheels when there is a speed difference and a torque being applied, forcing the wheels to turn at the same speed. You can only spin both wheels, or neither wheel, with this type of diff, under normal use. The actual locking is done by a series of clutch disks.
Building on my other post, we can infer a few things.
- When a Torsen (the oem type) diff's capacity is exceeded, the inside wheel will still spin, like an open differential
- A Torsen is "locked" only when you stay within the capability of the differential, the TBR
- A Torsen's behavior can be demonstrated by jacking up the rear of the the car, and then spinning one of the rear tires; the other rear tire will spin in the opposite direction
Now, from that, you can see that there are a few problems:
- If you lift a rear wheel, you effectively have an open differential
- If you are cornering hard enough under acceleration, then you will spin the inner wheel, effectively having an open differential
- If you suddenly hit a patch of low traction (hydroplaning on one side of the car, ice, snow, etc.), you effectively have an open differential
Now, a clutch/locking type differential addresses the following:
- If the inside wheel is lifted, both tires will be spinning the same speed
- If one wheel wheel suffers a loss of traction, both tires will still be spinning the same speed.
- Under cornering and acceleration, you can only spin both tires, or neither tire. You cannot spin only one tire.
The end result:
- The car will rotate more readily, but also more progressively, giving you a much larger window of opportunity to correct/compensate for the rotation. Effectively, car is **more predictable** under cornering.
- **The limit of adhesion under cornering is substantially raised.** Previously, losing traction on one rear tire resulted in a loss of control. Now you have to overcome the grip of BOTH rear tires to lose control of the rear.
- Remember, the inner rear tire is the one that spins; the inner tire is the one that is unloaded! Now you have to spin both the unloaded AND loaded (outer) tire. All that weight transfer that happened to the outer tire, giving it extra grip, also has to be overcome to lose control of the rear!
- You will not suddenly spin if you suffer loss of traction on just one side of the vehicle
- You can much more easily "throttle steer" the car (a more advanced driving technique, where the car has minimal steering wheel input, but weight transfer is being sustained horizontally, so you can make the car turn more or less by modulating the throttle)
Bonus:
- VSC Sport activates when it detects a change in rate in wheel speed between the four wheels. Because the Clutch type LSD prevents the rear wheels from spinning at different rates, you're effectively increasing the limits of the car, **substantially**.
Side note:
- VSC works by activating the brakes. If you're doing hard driving, you really should not be using VSC; it puts a lot of strain on **all** types of differentials.
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