Specifications
Limited slip units that can generate dynamic lock prior to torque reaching
the rear wheels behave in an anticipatory way, since the dynamic lock is generated BEFORE
there is a need for it. With this kind of anticipatory engineering, wheel slip should (theoretically) not occur. However, that assumes that either:
1)both rear wheels are getting the same relative amount of traction, or
2) this type unit also has sustainable, static lock capabilities.
In the anticipatory category of limited slip units are the helical gear type (e.g.,Quaife, Torsen) and all the friction disc type units. The lesser of these two types - helical gear - have only dynamic lock capabilities (at a pre-determined, unmodifiable rate).
Without static lock, if both rear wheels are not getting comparable traction, the instant one wheel slips, the differential will behave like an open (non-limited slip) unit . All torque will be diverted
to the slipping wheel. But even among the various friction disc type units, any without an internal mechanism to maintain stock lock over time will act just like a helical gear type if one wheel is registering significantly less traction than the other. The more aggressive your driving, the less effective units with no static lock will be.
The Performance Gearing Limited Slip is the only comprehensive, anticipatory
differential that can:
1) provide on-demand lock (static/dynamic) in all driving situations and
2) either statically or dynamically generate more lock for any given driving situation to prevent any wheel slippage before it can even occur.
Overview
Because of an across-the-board change in differential design, BMW has eliminated the interchangeability of differential components that was common in models from 1971 to 1994. With the exception of models with Motorsport ("M")engines, limited slip has also disappeared as an option. Because of the ring-and-pinion offset and smaller confines of the main housing itself, no existing stock limited slip unit will fit any of the '95 and later models (except E36,Z3).
Since Traction Control is a safety feature and not a performance enhancement, the challenge was to design a limited slip unit that used the proper sized internal components - bevel gears, cross shafts, ramp housings, friction discs, etc. - that could withstand the torque/horsepower outputs of the 6 cylinder, V8 and V12 engines, respectively.
drawingside view of product
Schematic and actual machined limited slip unit.
Internal components include:
- five 90mm, ceramic coated friction discs (6 cylinder models),
four 106mm friction discs (twin-turbo, V8/V12 models)
- ramp housings machined for three dynamic lock generation options: 30/50,
40/60, 45/45
- opposing Bellville washers for maintaining static lock
Lock options with the limited slip differential
The comprehensive Performance Gearing Limited Slip Differential is the most flexible
with regard to configuration of any of *those available in the BMW aftermarket*. Both *static lock* and *dynamic lock* are configured independently for optimum performance in ALL driving situations,
depending upon how the car is intended to be driven.
Typical configurations would include:
street : 30% static lock , 45/45 angle ramp housings for a modest amount of
wheel slip control during cornering, with options for dynamic lock in both
acceleration and deceleration mode (from 30% to 70%)
aggressive street/driver's schools : 40% static lock (for maximum inside
wheel spin control, without generating understeer) and 30/50 ramp angles for
the most aggressive dynamic lock during acceleration (40% to 100%), yet
modest dynamic lock during deceleration (40% to 60%)
dedicated track: 25%-30% static lock , 40/60 ramp angles for more dynamic
lock governing during full-throttle acceleration (30% to 100%) and hard
deceleration (30% to 40%) to prevent rear wheel lockup.
With the Performance Gearing Limited Slip Differential, there are a multitude of
configurations to suit individual driver's needs.