Re: Torsen

[Kennon Hines <kwh@bellsouth.net>]

> Torsen sends more power to the diff that spins slowest.


I keep seeing this in the anti-Torsen posts.  In fact, it seems to be
the crux of the "spider bite" argument.  Problem is, as best I can
determine, it is simply not correct.  This single fact negates the
entire argument as it relates to the Torsen.

The whole point of the Torsen is that it is torque sensitive, not
rotation sensitive.  A VC, by contrast, is rotation sensitive.  This is
one reason why Audi chose not to use a VC in production models.  The
Torsen is designed to function as a standard open diff as it relates to
rotation rates.  By definition it will send equal force (torque) to both
output shafts while allowing them to rotate at different speeds. 
However, the Torsen will also instantly distribute torque up to the bias
ratio based on the output shafts' ability to transmit the applied
torque.  Rotation rates have nothing to do with this.

The other missed detail is the flawed concept of an all or nothing
torque transfer.  The Torsen is much more fluid than this.  It can split
torque in any manner up to the bias ratio, not just from 50/50 directly
to 30/70 (or 25/75).  Also, as I understand it, max torque is limited by
the axle with the least traction.  It is not just a simple division of
applied torque.  It looks like this (an example):

200 lb/ft applied to Torsen input shaft
front axle will only accept 50 lb/ft due to low traction
max torque to rear axle is 115 lb/ft with 2.3:1 BR
35 lb/ft of torque is lost

An open center diff will only be able to transmit 50 lb/ft to the rear -
100 lb/ft is lost.  A 100% locked center will send 100 lb/ft to both
front and rear, but only 50 lb/ft reaches the ground in the front - 50
lb/ft is lost.  I'll take the Torsen, thank you very much.

IMO, the "spider bite" may be real, but it is not the result of the
Torsen diff.  Please feel free to correct me if I'm wrong on this one...

Regards,

Kennon Hines
1990 Coupe Quattro
Atlanta, GA