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Originally Posted by graywolf624
Completely useless technique on a track or road despite what he says. The only reason to left foot brake is to unsettle the car for things like slides. Its not the best way to get around a corner. It might help you if you've already screwed up to correct understeer or oversteer, but its not what you should be doing.
Go karts.. good for keeping the revs up..
Rally cars, good for forcing the proper amount of rotation.
But other wise not worth it.
Hell my Iroc had a torsen differential. Left foot breaking does nothing for it. Hes essentially trying to argue that by braking while accelerating he keeps the cars weight from shifting rearward. The problem with that arguement is that you can do the same damn thing by moderating your gas correctly rather then hitting it hard.
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He is not trying to argue that braking whilst accelerating keeps the weight transfer forward at all, that is just stupid as it means that the car is not accelerating if you are increasing the weight transfer to the front of the car.
What he is saying, which is actually correct is all to do with the quaife ATB differential in the front of the focus RS, i know about this as we fitted one to the rear of our formula student car at university and spent quite a bit of time altering suspension set ups and driving techniques to get the best out of it traction wise.
The torsen or quaife ATB are essentially the same in function (not neccesarily design). Both are not limited slip, therefore they do not work at 100% slip, as chris harris stated. The reason for this is in the design, in a limited slip diff you have a series of clutch plates (or viscous plates, or cones etc depends on design) that try to equalise the speeds of the two outputs of the diff when there is a certain amount of speed differential between the two outputs. The ATB or torsen does not have these plates, it depends upon the friction force on the end of the planetary gears inside it which are thrown in a particular direction depending on the torque varience across the diff and its outputs. Its a bloody difficult thing to understand when you have the pieces in your hands let alone to explain!
Anyway, the only time the ATB doesnt bias the torque across the diff is when there is too much slip on the inside wheel (we found this as we were picking up the inside rear on the apex and exit of corners) when this happens, the only thing limiting the slip of the inside wheel are a few sprung washers in the middle of the diff, and they do very very little and are not going to hold the torque produced by the engine which is soley trying to spin the inside airborne wheel!! It just acts like an open diff.
So (i eventually get onto the left foot thing!) by left foot braking on the apex and exit of the corner, you are applying a braking torque to the inside wheel, this means that there is less slip on that inside wheel and therefore the diff is sending more torque to the outside front wheel (in the Rs's case) meaning better acceleration out of the corner. This is mostly the case on uphill exit, slippy, gravelly, tight corners, where your typical ope diff'd FWD car would be sat there spinning the inside front for half an hour before you get anywhere!!
You are effectively using the brakes to act as a clutch pack to lock the differential when the slip of the inside wheel becomes too much, and you keep the accelerator buried so that you are overcoming the braking torque you are applying with the extra engine torque.
Its all about transfering torque to the wheel that has the most weight on it, which the torsen differential fails to do beyond a certain slip point. Anyone remember the video of the audi quattro vs the bmw X drive trying to drive the car off of some rollers with the front wheels on the ground and the rears free to spin on the rollers. The audi which had a torsen centre differential failed to get off for the same reason, too much slip across the diff, if the driver applied the brakes to the rear wheels then it would send torque to the fronts and drag the car off the rollers (as they eventually did).
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