Left foot braking

[SSK]

In these days, 2 pedal is standard in the top categories(i.e. Formula1, GP2 LMP1,etc.). Most driver use their left foot on braking. They overlap the throttle and brake around the corner exit.They use the advantage in using left foot braking to control the body motion and vertical load.
I could roughly understand the advantage but I want to know more detail.
Could you tell me the advantage in detail and the point which the engineer should consider to set up the race car which is usually driven by right foot braking driver?

[adrianjordan]

In these days, 2 pedal is standard in the top categories(i.e. Formula1, GP2 LMP1,etc.). Most driver use their left foot on braking. They overlap the throttle and brake around the corner exit.They use the advantage in using left foot braking to control the body motion and vertical load.
I could roughly understand the advantage but I want to know more detail.
Could you tell me the advantage in detail and the point which the engineer should consider to set up the race car which is usually driven by right foot braking driver?

I don't understand in great detail, possibly no more than you do already, but I'll say it how I see it and maybe it will be of use...

Think about the physics of a car in motion. If you think that there is a finite amount of grip available at each tyre and that amount of grip has to deal with, at the front, braking and steering, and at the rear, braking and acceleration. Push any tyre too hard and it will lose grip and either lock up of slide - neither of which is desirable.

When you brake the weight distribution is moved forwards (simplifying the physics a lot, I'm sure someone else can chip in with more detail if needed) and so the front tyres have to do more work. When the accelerate the opposite happens, weight shifts rearwards and the rear tyres have to work harder.

When you're cornering you want to find a balance so that the front and rear tyres are both being worked as hard as you can without exceeding their finite amount of grip at the right points in the corner. By balancing brakes and throttle in a turn this is what you're attempting to do...balance the weight distribution shift at the right points. So you can have more grip at the front on turn in, more grip at the rear on traction and gradually shift between the two as you progress through the corner which will be inherently more stable (and faster) than switching from one to the other.

Doesn't that make sense??

[Tim.Wright]

I wouldn't agree that its controlling load transfer. That only depends on the resulting longitudinal acceleration. If you achieve say 0.5g longitudinal acceleration, it will correspond to a certain load transfer regardless of whether its done while combining throttle and brake or not.

I'd guess the simultaneous application of brake and throttle is done to preload the diff which stabilises the car mid corner which, I'd speculate, might allow you to accelerate out of the corner sooner without fear of loosing the rear.

[SSK]

When you're cornering you want to find a balance so that the front and rear tyres are both being worked as hard as you can without exceeding their finite amount of grip at the right points in the corner. By balancing brakes and throttle in a turn this is what you're attempting to do...balance the weight distribution shift at the right points. So you can have more grip at the front on turn in, more grip at the rear on traction and gradually shift between the two as you progress through the corner which will be inherently more stable (and faster) than switching from one to the other.

I agree with your opinion. Left foot braking take an advantage in transition of weight.
And the disadvantage is fuel comsumption, but the amount is small and negligible.

[Vary]

I think that another advantage is a faster transition from accelerator to brake, giving some fem tenths here the car is still accelerating...

[SSK]

I wouldn't agree that its controlling load transfer. That only depends on the resulting longitudinal acceleration. If you achieve say 0.5g longitudinal acceleration, it will correspond to a certain load transfer regardless of whether its done while combining throttle and brake or not.

I'd guess the simultaneous application of brake and throttle is done to preload the diff which stabilises the car mid corner which, I'd speculate, might allow you to accelerate out of the corner sooner without fear of loosing the rear.

I think load transfer is not caused by long. acceleration. As you know, the geometrical force (i.e. anti squat force and anti lift force etc.) affect to the wheel load. I know that the anti squat force is very small particually in formula car.

But your opinion about diff is very interesting. It maybe work to make the vehicle stable.

[giantfan10]

the major plus to left foot braking is time... less time off throttle= faster lap time... the time spent switching from gas pedal to brake pedal adds up over a lap
left foot braking also slows the car without losing revs for example on a long straight when u need to brake to avoid a slower car... keeping your throttle on and tapping the brakes slows your speed without losing as much revs as you would coming off the throttle. to brake the conventional way
left foot braking also helps to reduce turbo lag on corner exit ...
a smaller benefit is controlling load transfer on corner entry
biggest negative is drivetrain load is increased

[dmjunqueira]

There is some discussion about this subject here:
http://jalopnik.com/why-you-should-brak ... -434604934

[autogyro]

Tim is as usual right on it at least in regard to loading the diff.

Originally left foot braking was as a result of gearbox control under braking when the driver would use the heel and the toe of the left foot to brake and clutch at the same time.
Saving time and making gear shifts more efficient.
Some skilled drivers managed to speed up the process even more by using the left foot for this and the right foot for finer control over the throttle.
In rallying it was used on loose surfaces to drive the cars balancing the designed wide moment of inertia almost like a pendulum.
Pitch control was a secondary benefit for corner set up.

Modern F1 cars have KERS the reason for left foot braking at the same time as throttle control is an attempt to load the dif and control the variable braking that the KERS gives.
The auto and semi auto gearboxes developed from 1989 soon resulted in two primary peddles brake and throttle with a hand lever clutch so speed of foot action was already achieved.
Some top F1 drivers still have not mastered all these skills.

[Tim.Wright]

I wouldn't agree that its controlling load transfer. That only depends on the resulting longitudinal acceleration. If you achieve say 0.5g longitudinal acceleration, it will correspond to a certain load transfer regardless of whether its done while combining throttle and brake or not.

I'd guess the simultaneous application of brake and throttle is done to preload the diff which stabilises the car mid corner which, I'd speculate, might allow you to accelerate out of the corner sooner without fear of loosing the rear.

I think load transfer is not caused by long. acceleration. As you know, the geometrical force (i.e. anti squat force and anti lift force etc.) affect to the wheel load. I know that the anti squat force is very small particually in formula car.

But your opinion about diff is very interesting. It maybe work to make the vehicle stable.

The total longitudinal load transfer for a given car (i.e. fixed CG height and wheelbase) depends ONLY on longitudinal acceleration. To put it Mathematically: LT = Mass x LongAcc x CGheight / wheelbase.

Geometric effects like anti squat/lift/raise/dive change only the PORTION of that total load transfer which occurs more or less instantaneously through the links instead of through the springs.

The forces aren't insignificant if the anti-X is high. In this case they will typically be in the range of 10-20% of the braking load.

Every man and his dog have an opinion on how mucht anti-X geometry you should have but Ive never come across a valid justification in either direction. That means there are as many different anti-X setups as there are designers.

[lillschumi]

I would say most F1 drivers comes from rank of Karting thus leftfoot braking is natural thing.

In a GoKart (ICA and similar where you only have brakes on the rear axle) it is about keeping the momentum of the engine and not have to go off-throttle, you don´t need the brake for weight transfer it should be enough with a quick "flick" on steering wheel to induce oversteer/opposite lock and get that nice feeling of a controlled fourwheel G-slide through a fast short corner.

[MadMatt]

Tim is as usual right on it at least in regard to loading the diff.

Originally left foot braking was as a result of gearbox control under braking when the driver would use the heel and the toe of the left foot to brake and clutch at the same time.
Saving time and making gear shifts more efficient.
Some skilled drivers managed to speed up the process even more by using the left foot for this and the right foot for finer control over the throttle.
In rallying it was used on loose surfaces to drive the cars balancing the designed wide moment of inertia almost like a pendulum.
Pitch control was a secondary benefit for corner set up.

Modern F1 cars have KERS the reason for left foot braking at the same time as throttle control is an attempt to load the dif and control the variable braking that the KERS gives.
The auto and semi auto gearboxes developed from 1989 soon resulted in two primary peddles brake and throttle with a hand lever clutch so speed of foot action was already achieved.
Some top F1 drivers still have not mastered all these skills.

It is still used, and not only on loose surface, but also tarmac sometimes

[autogyro]

Modern F1 cars are two pedal cars, brake and clutch.
Some past F1 drivers never did fully adapt to left foot braking, Gerhart Berger being one I believe.

My developments in power trains helped me to adapt to many experimental pedal arrangements and I became fairly skilled in driving all the possible arrangements including vintage types that I see more of these days.
Because of this though I probably never managed to develop the ultimate skill on one type.

By comparison highly competitive drivers who have learnt and developed a skill with one particular layout sometimes have great difficulty in changing to new ideas.
This can be frustrating for the team engineers and designer.

Other cars by and large still retain three pedals.
If the manufacturers were to spend more money on power train development and stop wasting energy with twin clutch/shaft units we might see more two pedal cars on the roads.

Double de-cluching a dual clutch road car gearbox is pointless the electronics speed up the shift for you.
Unfortunately although the shift is fast there is less feed back.

Rally cars and many race cars use ratchet shift systems with electronic selector fork actuation.
Usually you have to go in sequence and cannot jump from say top to second.
This can be slower than an ordinary gated shift when setting up a corner.

[J.A.W.]

Coming from riding motorcycles where complex control coordination actions are regularly required..
..to driving automatic work cars, it seemed natural to left foot brake, even when criticised for it as a "bad habit"..

[autogyro]

Coming from riding motorcycles where complex control coordination actions are regularly required..
..to driving automatic work cars, it seemed natural to left foot brake, even when criticised for it as a "bad habit"..

Motorcycles retain a very inefficient control layout dictated by the historical demands of bike riders.

It is possible to build a motorcycle with a semi automatic gearbox with push button shifts and front and rear brakes on the left and right feet.

Control and performance would be much improved.