Left foot braking vsCorner Brake Control

[Sands]

As a long time RWD manual driver, how does the progression of events happen entering the brake zone on a road course for LFB?

It would seam as though you need to start out with RFB to manage the heal toe down shifts, then move to LFB after turn in.

But do you do LFB for carousels only? Or is it a auto-x skill where you're in one gear the whole time and so heal-toe braking is not required?

On more transitional corners (which seam to be most of them), trail braking is enough get the rotation started, and by the time you're done trail braking you are setting up for apex and track out so it would seam to be more of throttle application problem on acceleration then a brake balance problem.

At least trail braking is how I manage to dial out understeer on medium to slower corners.

(be gentle, I'm a rwd driver....)

[nonsequitur]

Sands asks the right kind of questions. Why is any of this useful, and how specifically is it done?

I was focused on the CVT-equipped cars where throttle must be set and held to establish a stable Target Speed in the computer. That "uses up" one foot that's committed to the throttle pedal. I got to LFB simply trying to find "balance" in the corners without disrupting the whole engine management system; it worked. You can apply full throttle very early, balanced off with the brake, released near the apex to accelerate through the exit. We have two pedals, just like a kart. It's much easier than the same moves with three pedals requiring attention.

That Walter Rohrl video is in a manual AWD car, and he is moving both feet almost constantly to achieve the balance and reaction desired from the urQuattro. His procedures are far more skilled, and practiced, than anyone else I've ever seen.

Walter Rohrl/Audi Quattro

[Sands]

Hey thanks, but what about a manual car?

[nonsequitur]

I'd like someone with detailed experience in a rally car to explain the setup, braking, rotation, grip, balance, and exit technique we can see in that video.

There's no wasted effort, and he is not putting on a show for footwell camera. LFB is being used because his right foot is very busy managing weight transfer (fore/aft) and simply applying forward thrust to keep the car moving at those amazing speeds.

[L8Apex]

If I'm not mistaken, rally cars have more rear brake bias than any other race car category. So when they hit a corner and have the brakes and throttle working, the front wheels are accelerating the car while the rears are doing the rotating.

In rally, you have very little grip so rotation is absolutely needed.You have more grip on the road, so rotation isn't going to be as easy. If you ever see the rally cars going around paved corners they aren't sliding, or at least not nearly as much.

If they had it split-screened and synchronized so that you could see his foot movement before and during the corner you'd have a better understanding.

Now, an a road course I've never really been able to use LFB but on corners where I'm in the same gear at the apex as I was before the entrance.

[nonsequitur]

Agree; which is why I tried to point out the special situation I'm driving on the track, where the CVT-equipped car benefits from that technique to set up braking and turn in (the left foot is available so why not use it) and then establish a new Target Speed for the engine and gearbox for apex and exit. It works.

The situation is different in the wet or slalom where Steptronic (fixed ratio, "gears"), with more right foot-emphasis throttle steering is more fun on the track.

[Sands]

From how I think about this, LFB on a road course might look like this (remember, I have no experience with a FWD car on a track, so this is conjecture. I'm doing this to think through it and have others poke at it...)

Enter the brake zone in 4th for a 3rd gear corner..

Heal toe with the right foot on brake and gas. (I'd imagine that the right foot would need to only take up half the pedal to manage a foot switch)

At turn in, use a bit of trail braking to get the car to rotate a bit more aggressively (right foot for this). Compensated for the forward weight bias of a FWD car and the natural tendency to under steer. Does a limited slip diff impact this? Clutch packs and torsens will work differently on throttle overrun....

Should be off the brake and getting back on the gas prior to apex. Can transfer the left foot to the brake as the right foot is removed since your now in 3rd and don't need to work the clutch.

On the gas for track out at or prior to apex, working the LFB to balance the car and get the nose to tuck and hit apex.

A carousel corner will have a sustained, steady state car loading so LFB can be used for the entire middle part of the corner ( I think) to balance the car.

I would imagine that a clutch pack LSD with overrun lockup ability would need to be driven a little differently then a non-LSD car.

Is this right or am I all wet?

How can the car balance be changed with aggressive sway bar settings?

Oh - I'm really curious because I'm looking to replace an e39 540 with a more fuel efficient car, but I still want to do several track days and auto-x a year.

[L8Apex]

First off, if you're worried about understeer in the MINI, just get a big rear sway bar. Seriously, that took ALL the understeer out of mine and even added a little oversteer. (mainly drop-throttle oversteer)

Second, you're idea about LFB is about right. I've done it so that the heel of my right foot is on the brake while the ball of my foot and my toes are on the gas. A little uncomfortable but you're only contorted like that for a few seconds while shifting. Then you bring the left foot back over to the brake.

An LSD is a better but I've heard that if you have a light foot then it's only a little faster. But it surely doesn't hurt.

[Sands]

Hey thanks for the tips.

I figured that understeer could be dialed out with sways.

I was thinking of an LSD for autocross where the speeds are generally under 45 and wheel spin is an issue in lower gears and higher corner loads then what is available on the track.

$500 or so is a pretty good price for an LSD as well.

Anybody know if they have a finite life and need to be re-built?

[robfenn]

I'm not really sold on the idea of getting just one sway bar, there is a tendency for the characteristics to me moved further away rather than disappear..i.e it will grip better up to a point, and then just understeer/oversteer more. Thats just an opinion though.

When i started racing the difference between me and the best was trail braking, it really is a must if you take your driving seriously on track i feel. Especially for a FWD as we can't be having understeer!

I used an instructor to learn how to do it effectively, he drove road and showed me at which points he started-eased-let off. Needless to say the first time i tried it (in a mid engined car) i span it and just missed a tyre wall

-Rob

[Sands]

For strut type front suspensions, a front sway will actually work to minimize understeer. A bit counter intuitive, but it controls camber gain and will keep the front tires in better contact with the road. (Or at least that's the case with 3 and 5 series BMWs...)

Normally, the stiffer end grips less on a car, but camber control is also important. Since the front end gains camber and the rear end looses camber on corner loads, the car is natually biased to understeer, front sways or massive reductions in front camber will do the trick.

True for the mini?

[L8Apex]

Quote: Originally Posted by Sands

For strut type front suspensions, a front sway will actually work to minimize understeer. A bit counter intuitive, but it controls camber gain and will keep the front tires in better contact with the road. (Or at least that's the case with 3 and 5 series BMWs...)

Normally, the stiffer end grips less on a car, but camber control is also important. Since the front end gains camber and the rear end looses camber on corner loads, the car is natually biased to understeer, front sways or massive reductions in front camber will do the trick.

True for the mini?

Ummmm...yes and no.

A front sway bar will help keep the front end straight and stiff. A stiff rear will lose grip.

In RWD cars you need a stiffer front so that weight will stay on the rear tires as much as possible, which is where your rotation will originate. You also need that stiffer front to help keep the steering straight and lite.

In a FWD car, you don't have that power coming from the rear so you need it to be stiffer so it will lose grip and (as we mentioned before) help to rotate the car around the corner. You'll need a relatively soft front so it will flex around the corner, thus making the outer contact patch larger. A front sway bar actually hinders this.

I can't find the pictures a want to use to explain this, so I'll try it with words:

Say you're coming upon a hard right corner. In all cases, your contact patch will be at the left front tire under braking and turning in and it will move to your left rear tire under acceleration.

In order to come out of it well in a FWD car you need your rear stiff so that weight will transfer more to the left front than to any other tire. You'll need a relatively soft front so it will flex and allow more weight to transfer to the left front tire (this is one reason most FWD race cars don't even have a front swaybar). Upon acceleration, you want the weight at your left front to stay there, so you have a stiff rear so that it's harder for it to transfer to the back. If you have it set up properly, the right rear tire will pick up off the ground under braking. This will ultimately put the best contact patch on the front left tire.

In order to come out of it well in a RWD you'll need your contact patch to transfer more easily to the rear tires. You do this by having a stiff front and a slightly softer rear. If you do this properly, you'll pick up the right front tire under acceleration.

[Sands]

Hey thanks, I was wondering what the dynamic differences where for FWD and RWD cars. Helps quite a bit.