19 replies to this topic

[aisiai]

Hi all
I have a question regarding the clutch of a regular road car.
I have no driving experience (got my driving licence 2 months ago , and still have no car ), so forgive if I sound incompetent:

My impression is that while I'm able to press/release the brake or gas pedal(right foot) with my heel on the floor , the same is not true for the clutch pedal(left foot).
My instructor insisted that I should press/release the clutch with my heel on the floor, but I think it is not possible(too long travel, too hard to hold continuously). Till now I haven't noticed a driver(even my instructor ) which does it(press/release cluth) with heel on the floor through the whole travel of the clutch.

My Q: What is the right technique? How you do it?

Note: my impressions are based on Ford Escort, but most of(if not all ?)the cars I've seen have that long clutch travel (the Escort had also really late clutch bite..maybe worn out clutch )

My quess is that it is intentionally build that way so you are forced to press the clutch with
the whole leg, not only the foot and thus fully disengage it, and also not to be able to slip the clutch too much . Right?

Cheers and... Thanks

[McGuire]

I don't know why keeping one's heel on the floor should be considered only proper practice for operating the clutch. You will encounter many vehicles where that is just not possible. Trucks for example, and older cars where the pedals come through the floor rather than being suspended under the dash. And many vehicles simply require too much pedal effort to make this comfortable, especially if you are small in stature or have any disability.

Frankly, I've never heard of anyone teaching such a thing. If I had to guess, if there is any thinking behind this practice at all, it may be the instructor is trying to invent a way to keep students from riding the pedal. Just keep your foot off the pedal when you are not using the clutch and you will accomplish the same thing.

Has anyone else ever heard of this?

[MarkWRX]

Never heard of anything like that myself. I have been driving for more than 30 years in a variety of cars. It is not possible to keep your heel on the floor in many trucks and some competition cars, with heavy clutch springs almost require that you lift your foot and stab the pedal.

My last two cars have been more performance oriented but still very easy to engage and disengage the clutch with the heel of my left foot on the floor.

Just make sure you keep your foot off the clutch when you are not using it. Throwout bearing replacement can be expensive!

Mark

[aisiai]

Thanks guys

However it is weird(for me) why the cluch is made that way - due to expenses or some mechanical precaution

Edit: I see Mark assumes the second ...however I prefer a clutch without that precaution

If I press the gas and brake with my ankle, not the whole leg, it is reasonable to assume the clutch should be made the same way, which is not the case

cheers

[schumyfan]

I have driven 2-3 cars and could use the clutch with heel on the floor for 2 of them. My current car has almost half a foot of clutch travel and it is impossible to rest the heel on the floor.

There could be benefits from resting the heel. When you rest your heel, you are pivoting about your heel and hence can control your foot movement better (or train your leg better). When you are using the clutch with the heel lifted, there isn't much reference for your foot and so the movement can tend to be less precise. Imagine having to use the throttle with the heel lifted. Would you be able to maintain a steady pressure to keep your car rolling just at the speed limit??

Then again, you need to use the throttle continuously and need a foot-rest.

I think, the reason behind having the long travel on the clutch is that, most cars have the clutch pedal linked to the clutch mechanically via cable. Since the clutch requires considerable force to engage and disengage, the shorter the travel, the more force you will have to apply, even after the force reduction achieved through the lever action at the clutch.

Force to disengage clutch * Displacement clutch = Force on clutch pedal * displacement clutch pedal

(ignoring losses)

I think if the clutches were hydraulically operated, their travel could be reduced a lot, making their movement similar to brakes. Might just be too expensive and complicated for a clutch because of all the moving parts.

[Greg Locock]

On my horrible old Corona the clutch /is/ hydraulic. The clutch is very light compared with almost any other car. Even so I've never tried to keep my heel on the floor, I'll try it and see. I could see an advantage if you were 4wd ing off road, as your foot is less likely to get bumped off the pedal. It may help with feathering the clutch when you are learning, I suppose.

Anyway it is useless as a general principle for all the reasons given by the other posters.

[bobdar]

The ultimate "right technique" is to burn through all this, find a real race car with dog rings, shift without the clutch, brake with the left foot, throttle with the right. Life gets so much easier.

[Greg Locock]

and that helps the original poster how exactly, even if it is true, and even if you have ever done it?

OK, even with the Corona's ridiculously straightforward clutch I start with my heel on the floor, but then transfer my weight to the ball of my foot as I press down, otherwise the top muscles of my foot have to over extend, and the centre of action of the pedal moves up to my toes, which is odd, to say the least.

[aisiai]

Originally posted by bobdar
The ultimate "right technique" is to burn through all this, find a real race car with dog rings, shift without the clutch, brake with the left foot, throttle with the right. Life gets so much easier.

you bring me a good memory - once, some time ago a friend gave me to try a Vectra(the new ones, the ugly ones), she was with automatic gearbox and only a brake and a gas pedal.
They were still made to be pressed with the right foot, both of them - i.e. too far on the right side
But at that time I was used only to a go kart and my MOMO Force wheel
So I was driving left foot braking...such a fun...and eeeeeeeeeasy...although i was very tilted to the right to be able to do that...my friend was not very happy about it

[aisiai]

Originally posted by Greg Locock

I could see an advantage if you were 4wd ing off road, as your foot is less likely to get bumped off the pedal

&&

and that helps the original poster how exactly, even if it is true, and even if you have ever done it?

OK, even with the Corona's ridiculously straightforward clutch I start with my heel on the floor, but then transfer my weight to the ball of my foot as I press down, otherwise the top muscles of my foot have to over extend, and the centre of action of the pedal moves up to my toes, which is odd, to say the least.

Thakns for taking the time to try
You brought up another problem I had - while driving in the dark with my instructor, I noticed it is hard to 'find' the clutch with my foot once I put my foot aside(The car has no illumination on the pedals...Are there cars with such?) But I suppose that is due to lack of experience
In that case it was useful to hold my foot ready on the clutch(not press it of course)...I know that is not right

[F1Champion]

My instructor said the exact same thing. Keep my heel on floor and control the clutch but the clutch just had too much travel and it was hard to continue finding the precise placement of my heel when my instructor kept insisting that my foot should be off the clutch and on the footrest when the clutch was not in use.
The instructor's reasoning was that I could better control the biting point in 1st gear than if my foot was hovering in the air. I preferred the 'hovering' method though.

[aisiai]

Originally posted by F1Champion
My instructor said the exact same thing. Keep my heel on floor and control the clutch but the clutch just had too much travel and it was hard to continue finding the precise placement of my heel when my instructor kept insisting that my foot should be off the clutch and on the footrest when the clutch was not in use.
The instructor's reasoning was that I could better control the biting point in 1st gear than if my foot was hovering in the air. I preferred the 'hovering' method though.

I'm somehow relieved to hear someone has the same...hm..dilemma
So either we suck, or our instructors do. :
That's why I like the answers from the guys here - it seems the problem is not in ourselves

[Dmitriy_Guller]

Originally posted by aisiai


Thakns for taking the time to try
You brought up another problem I had - while driving in the dark with my instructor, I noticed it is hard to 'find' the clutch with my foot once I put my foot aside(The car has no illumination on the pedals...Are there cars with such?) But I suppose that is due to lack of experience
In that case it was useful to hold my foot ready on the clutch(not press it of course)...I know that is not right

You really should not be looking at the pedals when you drive.

[Fat Boy]

Originally posted by schumyfan
Force to disengage clutch * Displacement clutch = Force on clutch pedal * displacement clutch pedal

(ignoring losses)

I think if the clutches were hydraulically operated, their travel could be reduced a lot, making their movement similar to brakes.

You might want to rethink that whole hydraulic theory. Not that a hydraulic clutch is bad, but it doesn't change mechanical advantages. They do tend to be smoother and easier to package.

You only have to move the clutch pedal (on a road car) enough to disengage the engine from the rest of the drivetrain. I think that a lot of people probably move the clutch a lot further that what is necessary. Possibly that is what the instructor was getting at. Whether or not you can do that while leaving your heel on the floor is going to be a matter of foot size and pedal placement more than anything else, IMO.

Some road cars will put up quite well with clutchless shifting. I had a Mazda 323 GTX years ago that was just fine going up or down with just throttle blips. Oddly enough, it seemed faster to dip the clutch on upshifts. The ECU was tuned to let the engine slow down slowly when not under load (i.e. not like a race engine where the revs just drop), so you would have to wait a second for the engine to drop enough revs to get it into the next highest gear. When using the clutch, that wouldn't matter. Downshifts weren't a problem, because you were always blipping the revs up.

[Engineguy]

Originally posted by Fat Boy

You might want to rethink that whole hydraulic theory. Not that a hydraulic clutch is bad, but it doesn't change mechanical advantages. They do tend to be smoother and easier to package.

I assumed he meant active hydraulic assist, like the hydraulic assisted power brakes that are (were?) used (rather than vacuum diaphram assist) on some heavy duty pickup trucks. I've driven them, and the feel is not much different... so I think engagement finesse would be possible, while also allowing a shorter travel due to a mechanical advantage reduction you could get away with. Rubs me the wrong way though... goes the wrong direction on the simplicity scale.

[schumyfan]

Originally posted by Engineguy


I assumed he meant active hydraulic assist, like the hydraulic assisted power brakes

Thanks for the experiment Greg!

I didn't really put my logic down completely in my earlier post. So here goes.... When your heel is not resting on the floor, you effectively have a 3 bar mechanism with turning pairs between every consecutive pair of links. This 3 bar-mech. is trying to achieve a circular movement, which is relatively complex to achieve (lot of variables). With the heel resting, you effectively have a single bar mechanism with the link turning about the heel base. Much reduced complexity when compared to the 3 bar mech resulting into better precision in movement....advantage # 1. Any clutch pedal would need movement in an arc, since it is basically pivoted about a hinge. The 1-bar-mec. has this circular movement by design and so could be better used by proper design of the clutch pedal (pedal coming out of the floor with radius and heel-rest designed so that an average person could pivot his foot and achieve perfect movement of clutch pedal)....advantage # 2

Now what are the problems with this?
1) Pivoting movement of foot has limited range as Greg found out
2) Pivoting movement can apply only a limited amount of force due to the typical muscle structure

So to use this movement, we need a clutch pedal which requires a very light force and very small movement.

Coming to the main need of a clutch-pedal mechanism, the basic thing we are trying to achieve is to have a major reduction in force. Whether we do this by a mechanical lever action or hydraulic force multiplication, would give the same effect, viz., increase in clutch pedal travel. Since reducing force and movement have mutually conflicting effects, we would need an external agency assisting this. And as the engine guy pointed out, this would be some sort of an active hydraulic assist. I suggested hydraulic, because I couldn't think any other simpler system to achive this.

[bobdar]

and that helps the original poster how exactly, even if it is true, and even if you have ever done it?

You certainly have a point, Greg.

My advice to aisiai: after about fifty years of driving a variety of vehicles, I don't recall any where keeping the heel on the floor was required, and there are a number of situations where it would not be possible at all. It would be a mistake to develope a habit which cannot be applied accross the board. Pardons for not addressing your original question.

As far as "even if you have ever done it", I've raced something or other for 22 seasons, some karts but mostly formula cars. Clutchless shifting and left-foot braking is "true" for me, and I have done quite a bit of it. Somewhat irrelevant to aisiai's question, but not the first irrelevant post of 2004.

Happy New Year.

[DoS]

Originally posted by Greg Locock
and that helps the original poster how exactly, even if it is true, and even if you have ever done it?

OK, even with the Corona's ridiculously straightforward clutch I start with my heel on the floor, but then transfer my weight to the ball of my foot as I press down, otherwise the top muscles of my foot have to over extend, and the centre of action of the pedal moves up to my toes, which is odd, to say the least.

Good description ! At this point i would like to add that the above technique helps (me at least) to "play" with a soft clutch with more finesse than putting my whole foot on it would allow.

[Mark Beckman]

Originally posted by Fat Boy


You might want to rethink that whole hydraulic theory. Not that a hydraulic clutch is bad, but it doesn't change mechanical advantages.

Hydraulics do not have cable stiction (that increases with age).

Put a new cable on an older Corolla for instance and your foot pressure is often halved.

Mathematics doesnt always tell the story.

[desmo]

As a sometime shade tree mechanic, I appreciate the simplicity of cable clutch actuation with a simple threaded adjuster. It isn't always easy to thread a new clutch cable in, but it's still easier than troubleshooting a hydraulic linkage. Just remember to grease the cable before you install it.