Left Foot Breaking, can someone explain?

[salmo]

by applying the accelerator and the brake simultaniously you can lock the LSD and the rear of the car will become even looser than is usually achieved simply by braking and weight transfer.

Good point.

With a FWD car I believe what you are doing is effectively adjusting the brake balance.. by applying both accelerator and brake simultaniously you are effectively adjusting that brake balance to the rear at that instant

Hmm, I'm having trouble seeing how the brake bias could be directed toward the rear with LFB; could you please explain?

I think LFB is especially useful with FWD cars because the front wheels are often overworked as it is, and more likely to let go. This is why most FWD cars are inherently understeery, and why LFB is a good tool for getting more weight transferred over the front wheels.

I forgot to mentioned another great use of LFB, which is for turbocharged cars (like WRC cars). By keeping your right foot on the accelerator, you can keep the turbo spooled during even slow turns, offering a huge advantage when accelerating out of the turn.

[salmo]

Hmm, I'm having trouble seeing how the brake bias could be directed toward the rear with LFB; could you please explain?

Never mind, I just watched that video clip that explains it pretty well. That's a great clip; thanks for the link.

BTW, I can't believe that bit at the end where he demonstrates LFB with heel-and-toe downshifting! He says "not many people can do this." Yeah, no kidding! I've never even heard of such a thing before. It looks pretty wild, and I believe him when he says that it's probably not worth it. I'll continue to right-foot brake with heel-toe when I'm downshifting while entering corner.

[Zico]

Good point.

Hmm, I'm having trouble seeing how the brake bias could be directed toward the rear with LFB; could you please explain?

Only with Fwd.. Think of brake distribution ie F65 R35 as an optimum set-up, If you apply the throttle while braking the power to the front wheels cancels out a percentage of the braking force while the rear remains constant.

[Zico]

I forgot to mentioned another great use of LFB, which is for turbocharged cars (like WRC cars). By keeping your right foot on the accelerator, you can keep the turbo spooled during even slow turns, offering a huge advantage when accelerating out of the turn.

With the modern WRC cars having such effective ALS, this use for LFB now offers limited effectiveness compared with the early Group A cars when it was a far more critical skill to learn.

Most people who try it for the 1st time in their roadcar usually hit their head on the windscreen , and think they will never develop a feeling for it, but practice helps no end and its worth noting that its actually far, far easier to modulate in a rally/race car due to the brakes lack of servo assistance.

[Nenukknak]

Ok I understand somewhat. But what I don't understand is why the same can't be accomplished, with either just the throttle or just the break. Do you use the throttle to push the drivenwheels through the breaks, and to lock/break harder on the non-driven wheels. But if the car doesn't decelerate under braking, because you're still holding down the throttle, how can the weight still transfer?

[Zico]

Weight transfer will occur with either the throttle and the brake, and to a lesser degree simply by letting off. By accelerating while still on the brake you add the adjustment of the brake balance rearwards to the equation, making the rear able to swing round even more easily, reducing the need to use the pendulem effect, ie scandinavian flick.
If the car doesnt de-accelerate while you do this you either have a very powerful engine/weedy brakes combination or you simply are not being aggresive enough. Naturally rallycars usually have decent anchors..

[pentti]

How come Pentti isnt around on the forum these days?

I am still here and I read WRC forum.It's just I have been very,very busy to write. But this subject is some thing which I want to help and correct.
In fwd you use brakes and throttle same time to help steering.Harder you brake and 60% throttle more the car turn into corners.95% teason lfb in 4wdr and rwd is just a lot quicker(at least 0.5 seconds)as reaction time.

[pentti]

Also found some videos on the subject..

Fairly basic explanation for FR, FF and RR.. http://uk.youtube.com/watch?v=XVDfDTp0Y7g

Colin in the Focus WRC.. http://uk.youtube.com/watch?v=BMEqOG...eature=related He doesnt mention the mapping of the centre diff in the Focus but I think this is only what Subaru had to use to deal with the inherrant problem of poor PMI in the Impreza.

That first clip is 95% nonsense.Colin was quite good.

[Nenukknak]

I am still here and I read WRC forum.It's just I have been very,very busy to write. But this subject is some thing which I want to help and correct.
In fwd you use brakes and throttle same time to help steering.Harder you brake and 60% throttle more the car turn into corners.95% teason lfb in 4wdr and rwd is just a lot quicker(at least 0.5 seconds)as reaction time.

But you do also use LFB to steer in 4wd (and RWD) as well, not just because reactiontime is quicker?

And how do you use the brake and throttle then? Do you keep the pressure constant on either one or the other, or do you alternate pressure on both brake and throttle as is needed?

[Steve Boyd]

Most people who try it for the 1st time in their roadcar usually hit their head on the windscreen , and think they will never develop a feeling for it, but practice helps no end and its worth noting that its actually far, far easier to modulate in a rally/race car due to the brakes lack of servo assistance.

Another problem with modern road cars is the emergency braking assistance part of the anti lock brake system. This assumes normal right foot braking an measures the time taken between lifting the throttle and applying the brakes. If the time is less than a set value it assumes you're making an emergency stop and applies maximum brakes whatever the pedal pressure. Left foot braking with these cars can make the brake computer think you want to make an emergency stop - hence face on windscreen!