Driving an automatic - do you use one foot or both?

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#1870857 22-Sep-2017 11:02

Batman:

eph:

Batman:

Why would you depress the clutch when emergency braking? That would increase the stopping distance.

Why is that? My (maybe naive) understanding is that if when you press clutch it would actually disengage the engine. If you don't the engine would still try to push the car forward (until stalled) even when you apply the brake.

Then engine will not push the car forward. It will hold the car back.

I accept the argument that with full brake power + ABS the car will slow down just as effectively as with full brake power + ABS + engine braking. Or does it? Who knows.

Why would you need the engine running after a crash?

If there is mental capacity left during emergency braking to depress the clutch I would recommend downshifting as you emergency brake. Not depress the clutch and let it free wheel.

It is not a very fun time when you have the vehicle in gear clutch engaged and the ABS kicks in.
P.S: Very effective way to destroy your driveline and engine.

Batman

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#1870861 22-Sep-2017 11:07

Coil:

It is not a very fun time when you have the vehicle in gear clutch engaged and the ABS kicks in.
P.S: Very effective way to destroy your driveline and engine.

I don't think you know what ABS does Tim!

In manual and auto 4WD cars, there is a feature called Hill Descent Control. How does it work?

You put it in first gear (or reverse) and point the car down a VERY steep hill, and the ABS takes your car down the hill.

Will it destroy anything? Nope.

ABS is ABS whether you're at 100mph or 1mph. It brakes and releases individual wheels. You don't damage the car when braking at any speed. Cars have differentials that allow wheels to spin at different speeds. I have not looked into locked differentials but you don't drive cars with locked diffs on tarmac, they are all open diffs, some with limited slip.

I maintain that you can depress the clutch before the car stalls but if you want to do that then best to downshift and engine brake all the way.

Coil

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#1870876 22-Sep-2017 11:31

Batman:

Coil:

It is not a very fun time when you have the vehicle in gear clutch engaged and the ABS kicks in.
P.S: Very effective way to destroy your driveline and engine.

I don't think you know what ABS does Tim!

In manual and auto 4WD cars, there is a feature called Hill Descent Control. How does it work?

You put it in first gear (or reverse) and point the car down a VERY steep hill, and the ABS takes your car down the hill.

Will it destroy anything? Nope.

ABS is ABS whether you're at 100mph or 1mph. It brakes and releases individual wheels. You don't damage the car when braking at any speed. Cars have differentials that allow wheels to spin at different speeds. I have not looked into locked differentials but you don't drive cars with locked diffs on tarmac, they are all open diffs, some with limited slip.

I maintain that you can depress the clutch before the car stalls but if you want to do that then best to downshift and engine brake all the way.

I have a very good understanding how ABS works :)
In my manual B5 S4 that I once owned I locked up in the dry while the car was in gear and clutch was not engaged. (I get confused between engaged and disengage what ever means it isnt being pressed!)
This car had a center LSD and rear LSD, When the abs kicked in it developed a massive driveline shudder until i pressed in the clutch as the engines centrifugal force was fighting the brakes locking up and slightly releasing then so fourth.

HDC uses the ABS/Traction control to brake each wheel as you said, Holds them at a constant speed.

The auto beema doesn't have issues when its locked up as its an auto, the trans takes the shock out of the driveline.

cadman

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#1870916 22-Sep-2017 12:33

geekIT:

I'm the guy who asked the question in the first place (and who drives with both feet ).

And I don't drive with my foot on the brake.

Or even awkwardly hovering over the pedal giving yourself cramp? Then why even bother? By the time you move your left foot all the way over to the brake you could have moved your right foot off the accelerator to there.

geekIT:

Gawd, gimme a break, willya, I've been driving for 61 years. And without ANY accidents or traffic tickets.

Ah, so you're one of THEM.

geekIT

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#1870961 22-Sep-2017 14:10

My left foot is poised over the brake pedal only in busy traffic. On the open road it's flat on the floor. And I don't get cramp.

Do you get cramp holding your right foot on the accelerator pedal? Or do you rest your foot on that pedal? If so, you must have a fairly stiff one. Accelerator pedal, that is.

And yes, I'm one of THEM. Perhaps you're not.

Trump crowned? No faux King way!

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#1870962 22-Sep-2017 14:10

I wonder if the drivers license limitation restricting driving students who sit their test in an Auto to Auto's only in future was (in part at least) in recognition of the fact that left foot braking is not a universally safe car braking method, but right foot braking is - ?

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Coil

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#1870978 22-Sep-2017 14:20

tripper1000:

I wonder if the drivers license limitation restricting driving students who sit their test in an Auto to Auto's only in future was (in part at least) in recognition of the fact that left foot braking is not a universally safe car braking method, but right foot braking is - ?

I was told it was to show they can operate a manual vehicle outside of supervision. Full licence suggests you can operate any vehicle in that class competently or have the responsibility to know what your limits are with vehicle operation and restrict yourself.
Plenty of people with a restricted fresh to manual have jumped in a manual and caused havok.

A way around this is by having an existing motorcycle licence then going for your restricted test in an Auto.

gzt

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#1871182 22-Sep-2017 19:26

Auto brake pedals were ginormous back in the day. The travel to any effective braking was similar. Auto gearboxes behaved different. There were maybe some reasons for using both at the same time long ago.

Not so today. Having said that, In careful gradient start situations one reason remains because many vehicles now lack a handbrake.

Fred99

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#1871184 22-Sep-2017 19:36

gzt: Auto gearboxes behaved different. There were maybe some reasons for using both at the same time long ago.

Yeah - to "line-lock" it so you could get the back wheels spinning and smoking, then you'd let go the brake when the traffic lights turned green and drift across the intersection, smoking the competition.

Tried this several times in my dad's Vauxhall (with Powerglide), but never succeeded.

Fred99

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#1871192 22-Sep-2017 20:09

tripper1000:

I wonder if the drivers license limitation restricting driving students who sit their test in an Auto to Auto's only in future was (in part at least) in recognition of the fact that left foot braking is not a universally safe car braking method, but right foot braking is - ?

That applies only for restricted license. Pass the full license test with an (auto only) endorsed restricted license - driving an auto car in the test - and the full license is not endorsed "auto only".

Geektastic

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#1871207 22-Sep-2017 20:42

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#1871217 22-Sep-2017 21:14

Using both feet as a habit is very dangerous.

My late grandmother nearly killed her passenger sister by backing under a bus when she mistakenly selected reverse, panicked, hit both pedals, shot under moving bus, selected drive still under panic mode and ploughed into power pole.

I do not recommend as a habit.

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#1871234 22-Sep-2017 21:51

sbiddle:

I'm a little bit late to this thread but am amazed that anybody would consider left foot breaking in an automatic. What possible benefit in the world is there?

I learned to drive in an automatic originally but for the last 18 or 19 years have driven manuals before moving back to an automatic quite simply because it's getting harder and harder to get manual cars due to the increased fuel efficiency figures of an automatic and customer preference being for them. I love driving a manual but certainly don't miss them in stop start traffic.

I was actually taught to drive by an ex MOT driving instructor and recall him saying to press the clutch and brake in an emergency and actually found myself doing that when I was in an accident a couple of years ago. I know I did that because the clutch had actually become stuck down from pushing it hard and I needed to wedge my foot under it to pull it back to move my car when I was hit.

I can totally understand left foot breaking if you're driving a track car - but other than that see absolutely no benefit or need.

@sbiddle I have no intention of changing to using 2 feet instead of 1 for the brake and accelerator. (How will I be able to keep driving manual cars if I did?) The reason I made that comment was that virtually everyone who said that they use 2 feet said they do so because they have done so for ages and don't see any need to change. But I wanted to find out if there was any advantage that I hadn't thought of. No one has been able to suggest anything (and I wasn't expecting to get any reasons). So that answers my question.

As for clutch engaged / disengaged under emergency braking - If you are cruising at 100Km/Hr the engine will probably be running at 2000-3000RPM. There will be alot of momentum in the moving parts of the engine. To emergency brake to a complete stop, the engine would also have to come to a complete stop if you don't disengage the clutch. Yet the kinetic energy in the moving parts of the engine also has to be handled by the braking system. And engine braking is more for stopping the brakes from overheating on long downhill stretches of road and for reducing fuel consumption. As the ECU stops injecting fuel into the engine if there is 0 accelerator but engine RPM is more than 1500 or so. And diesel engines have poor engine braking ability unless they are fitted with exhaust brakes as well.

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#1871275 22-Sep-2017 23:25

Batman:

Coil:

It is not a very fun time when you have the vehicle in gear clutch engaged and the ABS kicks in.
P.S: Very effective way to destroy your driveline and engine.

I don't think you know what ABS does Tim!

In manual and auto 4WD cars, there is a feature called Hill Descent Control. How does it work?

You put it in first gear (or reverse) and point the car down a VERY steep hill, and the ABS takes your car down the hill.

Will it destroy anything? Nope.

ABS is ABS whether you're at 100mph or 1mph. It brakes and releases individual wheels. You don't damage the car when braking at any speed. Cars have differentials that allow wheels to spin at different speeds. I have not looked into locked differentials but you don't drive cars with locked diffs on tarmac, they are all open diffs, some with limited slip.

I maintain that you can depress the clutch before the car stalls but if you want to do that then best to downshift and engine brake all the way.

To be pedantic, ABS usually won't work below a certain speed (5 or 10 mph I think) in a normal road scenario unless they have changed the systems a lot.

My Land Rover makes use of the ABS functionality to provide off road specific things, such as locking one wheel if it is not in contact with the ground when the other one on the same axle is, the aforementioned HDC, traction control to reduce wheel spin in slippery conditions like mud and so on. Those kinds of functionality are the reverse in that they usually won't work above a certain speed rather than below a certain speed.

Batman

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#1871283 23-Sep-2017 05:28

Geektastic:

To be pedantic, ABS usually won't work below a certain speed (5 or 10 mph I think) in a normal road scenario unless they have changed the systems a lot.

My Land Rover makes use of the ABS functionality to provide off road specific things, such as locking one wheel if it is not in contact with the ground when the other one on the same axle is, the aforementioned HDC, traction control to reduce wheel spin in slippery conditions like mud and so on. Those kinds of functionality are the reverse in that they usually won't work above a certain speed rather than below a certain speed.

Funny you mentioned this.

ABS works at any speed. I was driving at 4km/h on snow at the ski field on summer tyres and tested it by slamming the brakes and the car did not stop, just shuddered away (ABS, not drivetrain). And no, my drivetrain did not explode either.

AH now I know why Tim thought his drivetrain was exploding. My guess is Tim does not know that a working ABS causes shudder normally. And it is NOT his drivetrain exploding. The shudder and loud noises that scared him was a normal ABS working.

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