The mystery surrounding the use of the Quafie ATB LSD with the stock TVC is no longer a mystery. I had the opportunity to ask an authority about the interaction of the Quaife and TVC. This is coming from an ST owner installing a Quaife ATB differential in a few months, who is an automotive engineer since 2000 and is currently the Technical Project Manager at Robert Bosch LLC for Chassis Control Active Safety - North America : What is it that has you wanting the Quaife ATB diff and do you have concerns about the interaction of the TVC and the Quaife? No, I’ve no concerns. The Quaife (or other ATB) and the TVC (e-diff) are complimentary. The Quaife active wheel (driveshaft) torque biasing is “faster” and offers better granularity, in that it is not dependent on active brake pressure increases/decreases at the wheelends. Unfortunately, brake applications generate heat, so with (particularly) track use (frequent TVC activations), heat is being put into the brakes, both on vehicle deceleration (under braking) AND acceleration. Not ideal. And, as the brake temperature changes and the rotor/brake pad clearance (retraction/knockback) changes, TVB performance varies. Actually, the combination of an ATB and TVC is beneficial, as the ATB cannot bias torque in the case where one wheel has low/zero normal force (axle torque), as is the case with weight transfer causing a lifted or near-lifted wheel (or riding curbs / dropping a wheel). In this case, TVB brakes the unloaded wheel, permitting again torque transfer via the ATB. The Wavetrac ATB also functions in this way, by generating internal friction to “brake” the unloaded driveshaft. For that reason, the Wavetrac is a great choice, but (so far) no FST application and the potential added maintenance/complication of changing bias ratio friction material. Ford SVT chose the Quaife for the ST-R. It was a well-thought choice and reason enough to trust the application. Is the Quaife worth it for a street car? Is it worth it? That is, of course, for each individual to determine. It is certainly my primary interest in tracking the car, that makes it quite easy to rationalize. Is it beneficial for a street car? In my opinion, yes. The vehicle is more driveable/ more “predictable”, due to better torque biasing response and lack of brake temperature, caliper piston retraction/knockback influence. Is it a “must have” for solely street-driven vehicle? Honestly, my answer would be no. If I only drove on public roads, it would be hard to justify. It’s just too difficult (and typically illegal) to use the vehicle hard enough on the street to substantially benefit. ________________________________________________________________________________________ Straight from the horses mouth. I found the discussion on TVB, Torque Vectoring by Braking, to be the most in depth information on this topic I have read. It has been clear from the start this upgrade is not for everyone and a very select few actually do this upgrade, which historically has always been the case. Now, at least we know what the benefits of the Quaife are and the performance issue of TVB. PCA is a Quaife dealer as well as a Wavetrac dealer. There is a Wavetrac Focus ST unit expected out in a few months. No exact ETA as there has not been reported vehicle testing.