Left Foot Braking
Discussion
Before we begin, this is not a conversation about where LFB is/isn't to be used, it's purely a conversation to improve my understanding (and hopefully other peoples') of the effect it has on the car/driving. A dynamics kind of question.
I was on Youtube and I tripped over this ancient video by a certain Mr Harris and it got me thinking - what is happening at the driven wheels when the brake is applied while the engine is also providing drive? What's different about the reaction a car with a torsen diff has to one with an open diff? Is it still useful to LFB with an open diff? What other diff types are there where it has a positive/negative/neutral effect?
I was partly thinking of the old chestnut of a car stuck with one wheel on ice and another on tarmac - could LFB be used in a car to make it able to move?
I was on Youtube and I tripped over this ancient video by a certain Mr Harris and it got me thinking - what is happening at the driven wheels when the brake is applied while the engine is also providing drive? What's different about the reaction a car with a torsen diff has to one with an open diff? Is it still useful to LFB with an open diff? What other diff types are there where it has a positive/negative/neutral effect?
I was partly thinking of the old chestnut of a car stuck with one wheel on ice and another on tarmac - could LFB be used in a car to make it able to move?
wst said:
Before we begin, this is not a conversation about where LFB is/isn't to be used
Spoilsport!I'll have a go at answering your questions as best I can, but as I've stated before, I'm not a competition driving expert, so I'm happy to be corrected by someone who is.
There are several reasons why left-foot braking is considered by some people to have benefits over traditional, right-foot brakng.
Firstly, there is no delay in transitioning from accelerator to brake. This is particularly important in circuit racing where any time off the accelerator or brake could be considered wasted. Going immediately from full throttle to full brake application will result in a quicker lap time than lifting off the accelerator, moving your foot and then pressing the brake. It's a very small advantage, granted, but that's what makes the difference when it comes to lap times.
Whilst we're on the circuit, Braking can be carried right up to a corners apex, with a smoother transition back on to the throttle away from the apex, rather than, again, there being a silght delay whilst coming off the brake and on to the throttle.
Left-foot braking was developed by rally drivers in front-wheel drive cars as a way of controlling understeer, particularly in tighter corners, where there is a tendency for front-wheel (and many four-wheel) drive cars to push on under heavy throttle application on loose surfaces. Modern stability systems effectively do the same thing by quelling understeer through application of individual brakes.
Rally drivers also use left-foot braking as an additional - and instantly adjustable - method of changing a cars angle and attitude through a corner. So if they go into a corner a little too hot, the brakes can be applied to check the cars speed whilst balancing the weight transfer with an application of the throttle at the same time. The brakes can be used to reduce understeer and assist turn-in, or released to allow the car to exit quickly from the corner.
Where a front-wheel drive car has an open differential, it will have a tendency to spin up the unloaded wheel under heavy acceleration through tighter corners. Left-foot braking can counteract this tendency by bringing the spinning wheel under control and distributing the torque more evenly across the front axle.
All this makes me sound like a real advocate of left-foot braking. I am - but not on the road. But that would be breaking the first rule of your original post. So I won't go there!
R_U_LOCAL said:
Left-foot braking was developed by rally drivers in front-wheel drive cars as a way of controlling understeer, particularly in tighter corners, where there is a tendency for front-wheel (and many four-wheel) drive cars to push on under heavy throttle application on loose surfaces. Modern stability systems effectively do the same thing by quelling understeer through application of individual brakes.
All this makes me sound like a real advocate of left-foot braking. I am - but not on the road. But that would be breaking the first rule of your original post. So I won't go there!
I guess with the ability to control an open diff it'd have minor effectiveness on an open-diff'd RWD as well, if it didn't have systems to do that for you - never thought of those computerised systems as things doing the same job!All this makes me sound like a real advocate of left-foot braking. I am - but not on the road. But that would be breaking the first rule of your original post. So I won't go there!
And yeah, I was a spoilsport just to keep the thread concise really, no amount of arguing will change peoples' behaviour away from the forum (eg when driving) so let's not go there
I've seen LFB used to prevent a rear drive car from spinning. Power and brakes together mean that while the rear wheels keep turning, the fronts lock up, causing them to skid straight on, killing the incipient spin. Done right it was very effective.
The problem, however, is that ABS means you can't lock the wheels while many (most?) modern cars have systems that kill the power as soon as simultaneous power and braking is detected, which rather spoils whatever effect you're trying to achieve!
The problem, however, is that ABS means you can't lock the wheels while many (most?) modern cars have systems that kill the power as soon as simultaneous power and braking is detected, which rather spoils whatever effect you're trying to achieve!
I reminded of a well known historic racing driver that I know who offers advanced tuition for would be gentleman racers. One asked him whether he should try left foot braking to which his response was that it would help if he could master right foot braking first! Apologies to the OP as I could see his was a serious question.
Yes, with my current lack of driving talent I think any attempt at LFB on a road or track or wherever in snow, with my lack of ABS just helping things a bit, would result in me going in a perfectly straight trajectory, either with rotation (oversteer) or not (understeer), and the art would be in hitting the tree nice and straight.
I've never tried it and the question may seem odd, but is it more using some accelerator when braking rather than some brakes when under power? Im trying to work out in my head the forces involved and If you wanted to moderate power to the wheels, reduce the throttle for instance.
Brakes work on all 4 wheels and the balance is set up so all 4 wheels are doing as much stopping as possible locking up at the same point (with a slight forward bias so the rears are less likely to lock). Using some throttle will reduce the stopping force on the driven wheels changing the brake bias. I imagine the art of LFB is therefore just the ability to adjust the brake bias through power.
Modern brake systems do this for us now without applying power; they just modulate the brake force.
Brakes work on all 4 wheels and the balance is set up so all 4 wheels are doing as much stopping as possible locking up at the same point (with a slight forward bias so the rears are less likely to lock). Using some throttle will reduce the stopping force on the driven wheels changing the brake bias. I imagine the art of LFB is therefore just the ability to adjust the brake bias through power.
Modern brake systems do this for us now without applying power; they just modulate the brake force.
Jon1967x said:
I've never tried it and the question may seem odd, but is it more using some accelerator when braking rather than some brakes when under power? Im trying to work out in my head the forces involved and If you wanted to moderate power to the wheels, reduce the throttle for instance.
Brakes work on all 4 wheels and the balance is set up so all 4 wheels are doing as much stopping as possible locking up at the same point (with a slight forward bias so the rears are less likely to lock). Using some throttle will reduce the stopping force on the driven wheels changing the brake bias. I imagine the art of LFB is therefore just the ability to adjust the brake bias through power.
Modern brake systems do this for us now without applying power; they just modulate the brake force.
I'm no expert with left foot braking, but I do a little circuit driving.Brakes work on all 4 wheels and the balance is set up so all 4 wheels are doing as much stopping as possible locking up at the same point (with a slight forward bias so the rears are less likely to lock). Using some throttle will reduce the stopping force on the driven wheels changing the brake bias. I imagine the art of LFB is therefore just the ability to adjust the brake bias through power.
Modern brake systems do this for us now without applying power; they just modulate the brake force.
the best example I can give where I myself have used left foot braking is when I had a mk2 Focus ST with 400lbft of torque and an open differential.
On a lot of the slower 3rd gear corners (Bedford Autodrome) I found no matter how cautious I was with the throttle the inside wheel always wanted to spin up..cooking my tyres within a few laps and slowing me down. So I started to use my left foot on the brakes while exiting corners - This way I could get on the power earlier and apply full throttle faster, while maintaining a consistent speed and state of traction across the front axle by modulating my left foot. I did this by braking as normal into the corner, heel-and-toe, then as i moved my right foot off the brake onto the throttle I would move my left foot off the clutch and onto the brake.
It took some getting used to but after a few laps I could do it smoothly and it made me much faster...however I then started to cook the brakes quicker!
Cheers
Edited by JohnClem88 on Tuesday 31st March 11:31
What is the objection to LFB on the road? I really cannot see any reason not to LFB all the time in a 2 pedal car. It makes stop-start driving much easier, quite apart from being smoother and quicker in spirited driving.
If the objection is that people cannot use their left foot properly, how on Earth do they control a clutch in a 3 pedal car?! Clutch control is a lot more delicate than braking.
If the objection is that people cannot use their left foot properly, how on Earth do they control a clutch in a 3 pedal car?! Clutch control is a lot more delicate than braking.
ORD said:
If the objection is that people cannot use their left foot properly, how on Earth do they control a clutch in a 3 pedal car?! Clutch control is a lot more delicate than braking.
The opposite I think! When I push the clutch down it's a firm shove coming from my thigh and knee. Braking you have to press much softer otherwise you go through the windscreen.Maybe if I practiced I could do it, but having a manual RWD car that never goes rallying, I can't see the benefit...
ORD said:
What is the objection to LFB on the road? I really cannot see any reason not to LFB all the time in a 2 pedal car. It makes stop-start driving much easier, quite apart from being smoother and quicker in spirited driving.
If the objection is that people cannot use their left foot properly, how on Earth do they control a clutch in a 3 pedal car?! Clutch control is a lot more delicate than braking.
I think it's because it's not so much taking off pedal force..it's applying it as depressing the clutch requires no real though or consideration, once you've found the natural biting point of clutch anyway...but as you say releasing clutch is a delicate process.If the objection is that people cannot use their left foot properly, how on Earth do they control a clutch in a 3 pedal car?! Clutch control is a lot more delicate than braking.
Most people, including myself, when first trying left foot braking into corners will head butt the steering wheel
JohnClem88 said:
I think it's because it's not so much taking off pedal force..it's applying it as depressing the clutch requires no real though or consideration, once you've found the natural biting point of clutch anyway...but as you say releasing clutch is a delicate process.
Most people, including myself, when first trying left foot braking into corners will head butt the steering wheel
I suppose it depends in part on the brakes how long it takes to develop a feel for it. I wouldn't fancy doing it in an Audi, but its easy enough in car with progressive brakes with a bit of feel.Most people, including myself, when first trying left foot braking into corners will head butt the steering wheel
ORD said:
What is the objection to LFB on the road? I really cannot see any reason not to LFB all the time in a 2 pedal car. It makes stop-start driving much easier, quite apart from being smoother and quicker in spirited driving.
If the objection is that people cannot use their left foot properly, how on Earth do they control a clutch in a 3 pedal car?! Clutch control is a lot more delicate than braking.
Its nothing to do with whether people can adapt to left-foot braking - a skill which, given time, I'm sure most people could adapt to.If the objection is that people cannot use their left foot properly, how on Earth do they control a clutch in a 3 pedal car?! Clutch control is a lot more delicate than braking.
The reason is that, on the road, there are real advantages to seperating (as much as possible) the braking phase from the gearchange phase. Sticking to right-foot-braking-only for road driving takes away the likelyhood that the driver will be operating both pedals at the same time.
I'm not saying that left-foot braking is inherantly wrong. I'm sure there are many drivers of two-pedal cars who use the technique as a matter of course without incident. It's just that it doesn't sit well with traditional advanced road driving techniques.
R_U_LOCAL said:
The reason is that, on the road, there are real advantages to seperating (as much as possible) the braking phase from the gearchange phase. Sticking to right-foot-braking-only for road driving takes away the likelyhood that the driver will be operating both pedals at the same time....
....It's just that it doesn't sit well with traditional advanced road driving techniques.
Can of worms alert!!!....It's just that it doesn't sit well with traditional advanced road driving techniques.
Just wondering, other than mechanical sympathy, is operating both pedals at the same time occasionally such a terrible thing?
Ps. I Like overlapping my braking and gear changing (and double declutching!) having practiced a lot I don't want to lose the skills.
From the first post...
t!
Tales of driving a ridiculous Focus ST with an open diff, however, are! I'm supposing that it scales down to a puny shopping hatchback on a frozen ice lake. Do you reckon it can help with cornering traction when the car hasn't the ability to spin up the inside-front? (FWD/AWD)
wst said:
Before we begin, this is not a conversation about where LFB is/isn't to be used, it's purely a conversation to improve my understanding (and hopefully other peoples') of the effect it has on the car/driving. A dynamics kind of question.
It's been flogged to death and isn't relevant to the thread. You wouldn't push a button that says "do not push"... wait, you would? st!Tales of driving a ridiculous Focus ST with an open diff, however, are! I'm supposing that it scales down to a puny shopping hatchback on a frozen ice lake. Do you reckon it can help with cornering traction when the car hasn't the ability to spin up the inside-front? (FWD/AWD)
From a physics perspective I don't get why its a good method to stop the inside front from spinning up. I get that it negates power as the engine is working to overcome the brakes but surely less gas does the same? My cars traction control brakes spinning wheels but that's individual wheels not all if them. It's akin to saying I use the accelerator to stop my driven wheels locking under braking which really sounds odd to me.
I can also see arguments in the wet as it can dry the brakes and generate a little heat to prime them and so give more initial bite when you need them. I think carbon ceramics benefit quite a lot from the preheating.
I can also see arguments in the wet as it can dry the brakes and generate a little heat to prime them and so give more initial bite when you need them. I think carbon ceramics benefit quite a lot from the preheating.
MC Bodge said:
R_U_LOCAL said:
The reason is that, on the road, there are real advantages to seperating (as much as possible) the braking phase from the gearchange phase. Sticking to right-foot-braking-only for road driving takes away the likelyhood that the driver will be operating both pedals at the same time....
....It's just that it doesn't sit well with traditional advanced road driving techniques.
Can of worms alert!!!....It's just that it doesn't sit well with traditional advanced road driving techniques.
Just wondering, other than mechanical sympathy, is operating both pedals at the same time occasionally such a terrible thing?
For clarity:
Before being selectively edited Reg actually said:
I'm not saying that left-foot braking is inherantly wrong. I'm sure there are many drivers of two-pedal cars who use the technique as a matter of course without incident.
So no, operating both pedals at the same time isn't a "terrible thing" - it just goes against the police/Roadcraft/IAM (i.e. "traditional") advanced driving principles. MC Bodge said:
Ps. I Like overlapping my braking and gear changing (and double declutching!) having practiced a lot I don't want to lose the skills.
At the risk of sounding like Vonhosen, if it works for you, then fine - if you don't want or need to pass a course of instruction which requires you to use certain techniques, and you've found some techniques which work (safely) for you, then carry on to your hearts content. I did selectively edit the quote, fairly obviously. Hence the ".... ...." Which is an accepted method of doing so.
Pressing both pedals together is contrary to the Advanced Driving teachings, which is what I was highlighting.
I agree with most of your extensive and considered posts on the other topics, but on this subject there appears to be a slight hint of , "because the rules of Advanced Driving say so" -which was also my experience of Advanced Driving (but much less so of IAM biking).
Left foot braking isn't something I use often(although I have tried on a number of occasions), but I see no reason at all (other than tradition) why it shouldn't be done in a 2 pedal car. It is of course much trickier in a 3 pedal car, due to the need for switching both of the feet between the brake pedal and pressing the clutch with a very different "feel".
It would be very interesting to try left foot braking on a testing ground or track in a range of vehicles with different drivetrains to see what the outcomes/benefits might be.
Pressing both pedals together is contrary to the Advanced Driving teachings, which is what I was highlighting.
I agree with most of your extensive and considered posts on the other topics, but on this subject there appears to be a slight hint of , "because the rules of Advanced Driving say so" -which was also my experience of Advanced Driving (but much less so of IAM biking).
Left foot braking isn't something I use often(although I have tried on a number of occasions), but I see no reason at all (other than tradition) why it shouldn't be done in a 2 pedal car. It is of course much trickier in a 3 pedal car, due to the need for switching both of the feet between the brake pedal and pressing the clutch with a very different "feel".
It would be very interesting to try left foot braking on a testing ground or track in a range of vehicles with different drivetrains to see what the outcomes/benefits might be.
Edited by MC Bodge on Tuesday 31st March 23:44
Jonsv8 said:
From a physics perspective I don't get why its a good method to stop the inside front from spinning up. I get that it negates power as the engine is working to overcome the brakes but surely less gas does the same? My cars traction control brakes spinning wheels but that's individual wheels not all if them. It's akin to saying I use the accelerator to stop my driven wheels locking under braking which really sounds odd to me.
It might have some benefit where you have a Torsen/Quaife etc. ATB type diff, the the braking torque applied to the wheels should be applied as a multiple in drive torque to the wheel which is not slipping thus providing a net drive torque.Gassing Station | Advanced Driving | Top of Page | What's New | My Stuff