Zen and the art of changing gear.

[R_U_LOCAL]

Maybe, but surely, if the brakes are capable of reaching the point of lock-up, then this would be irrelevant.

[TripleS]

In an emergency braking situation I'm not sure that the part played by the engine is very significant anyhow.

If, assuming a non-ABS car, the driven wheels are locked the engine will also stop unless the clutch is disengaged.

If ABS is functioning the engine/transmission is going to be subjected to considerable shock treatment unless the clutch is disengaged.

Both feet down together seems best to me, although instinct will probably lead us to give priority to the braking.

Best wishes all,
Dave.

[GreenV8S]

In a high speed braking manoeuvre (thank God for spell chequers) I don't think you'd decelerate the engine quicker than it would naturally spin down in a typical road car. In lower gears it's distinctly possible but then the whole thing is over so quickly that the engine/wheels don't have time to accumulate much speed difference relative to the road (can't think of a better way to explain that but perhaps you can work out what I mean - plot vehicle speed vs time, wheel speed vs time, they drift apart but not far apart). With non-ABS the inertia of the engine provides a crude but very useful anti-lock effect on the driven wheels.

Edited by GreenV8S on Thursday 1st November 21:15

[TripleS]

GreenV8S said:

In a high speed braking manoeuvre (thank God for spell chequers) I don't think you'd decelerate the engine quicker than it would naturally spin down in a typical road car. In lower gears it's distinctly possible but then the whole thing is over so quickly that the engine/wheels don't have time to accumulate much speed difference relative to the road (can't think of a better way to explain that but perhaps you can work out what I mean - plot vehicle speed vs time, wheel speed vs time, they drift apart but not far apart). With non-ABS the inertia of the engine provides a crude but very useful anti-lock effect on the driven wheels.

Edited by GreenV8S on Thursday 1st November 21:15

<Thinks: I wonder if I should attempt a joke about things not always being black or white? Probably not. >

I wonder just how much of a contribution is made by engine momentum in terms of the anti-lock effect? Not much, I would suspect, but it seems likely that it will depend on the road speed, and what gear is engaged.

Best wishes all,
Dave.

[GreenV8S]

TripleS said:

I wonder just how much of a contribution is made by engine momentum in terms of the anti-lock effect? Not much, I would suspect, but it seems likely that it will depend on the road speed, and what gear is engaged.

Any effect would be least in the higher gears (where it's most likely to be needed). I can't put any numbers on it, and it may be a placebo effect, but wet finger in the air says it's enough to matter and subjectively it does feel as if it helps. Even in the higher gears the engine would be at 3:1 or so to the wheels so the inertial effects are amplified by a factor of 3 or so - and correspondingly more in the lower gears.

[whiteside67]

When changing down gear do you ease pressure on gas as clutch is depressed. Then once clutch is down you bring up the revs by pressing the accelerator

Or

Do you press accelerator down more to bring up the revs as you are pushing down the clutch and keep the revs there until youve completed the gear change?

[waremark]

whiteside67 said:

When changing down gear do you ease pressure on gas as clutch is depressed. Then once clutch is down you bring up the revs by pressing the accelerator

Or

Do you press accelerator down more to bring up the revs as you are pushing down the clutch and keep the revs there until youve completed the gear change?

Depends where the accelerator is to start with. You need higher revs. You may judge this by noise or by position of the accelerator - or even from the movement of the rev counter out of the corner of your eye. I most often change down when I have been slowing with my foot off the accelerator so I need to press the accelerator before releasing the clutch. If you were driving uphill under power when you started to change down revs would probably increase too far when you pressed the clutch if you kept the accelerator in the same position. You would have to raise your accelerator foot slightly to rev match.

[SK425]

whiteside67 said:

When changing down gear do you ease pressure on gas as clutch is depressed. Then once clutch is down you bring up the revs by pressing the accelerator

Or

Do you press accelerator down more to bring up the revs as you are pushing down the clutch and keep the revs there until youve completed the gear change?

As waremark says, what you actually do with the pedal depends where the pedal is to start with. But in terms of the revs, if they're at 2000 and they will need to be at 3000, why take them there via 1000? If they need to increase, why let them decrease?

[whiteside67]

waremark said:

Depends where the accelerator is to start with. You need higher revs. You may judge this by noise or by position of the accelerator - or even from the movement of the rev counter out of the corner of your eye. I most often change down when I have been slowing with my foot off the accelerator so I need to press the accelerator before releasing the clutch. If you were driving uphill under power when you started to change down revs would probably increase too far when you pressed the clutch if you kept the accelerator in the same position. You would have to raise your accelerator foot slightly to rev match.

Okay i understand your explanation. Does it not cause clutch wear though if you press clutch with your foot on the accelerator (clutch slip as plates seperate)?

Say I am going up a hill in 5th gear and need to change down to 4th for acceleration e.g. to overtake. My foot is already half way down on the accelator pedal. When i press clutch to change down does this not cause clutch wear beacause my foot is a good bit down on the accelerator (quite high revs going through clutch)

[otolith]

Where did R_U_Local go?

[25NAD90TUL]

Of course the main thing is to avoid brake gear overlap in these circumstances.

[davepoth]

25NAD90TUL said:

Of course the main thing is to avoid brake gear overlap in these circumstances.

Because we don't have enough threads about that yet.

[SK425]

whiteside67 said:

waremark said:

Depends where the accelerator is to start with. You need higher revs. You may judge this by noise or by position of the accelerator - or even from the movement of the rev counter out of the corner of your eye. I most often change down when I have been slowing with my foot off the accelerator so I need to press the accelerator before releasing the clutch. If you were driving uphill under power when you started to change down revs would probably increase too far when you pressed the clutch if you kept the accelerator in the same position. You would have to raise your accelerator foot slightly to rev match.

Okay i understand your explanation. Does it not cause clutch wear though if you press clutch with your foot on the accelerator (clutch slip as plates seperate)?

Say I am going up a hill in 5th gear and need to change down to 4th for acceleration e.g. to overtake. My foot is already half way down on the accelator pedal. When i press clutch to change down does this not cause clutch wear beacause my foot is a good bit down on the accelerator (quite high revs going through clutch)

As waremark says, you would probably need to lift off a bit to rev match in that situation. I think I would be lifting off before/as I put the clutch down, not afterwards. If I waited until afterwards (i.e. when I pressed the clutch, my accelerator was still a good bit down like you say) I expect the revs would shoot up to the red line very quickly - not what I'd be trying to achieve.

Also, you disengage the clutch very quickly so I imagine there's very little time for any wear to take place. It's not like when you have to take ages slipping the clutch against the accelerator when you re-engage it with the revs massively mismatched.

[waremark]

otolith said:

Where did R_U_Local go?

He was a loss to us. He probably got fed up with the sometimes hostile reaction to his generally excellent videos (do you remember the knees in the MX5?). I searched for his videos some time back and could not find them, have they been taken down?

[otolith]

I wondered if his attitude to speed was a little too old-school for somebody upstairs.

[p1esk]

waremark said:

otolith said:

Where did R_U_Local go?

He was a loss to us. He probably got fed up with the sometimes hostile reaction to his generally excellent videos (do you remember the knees in the MX5?). I searched for his videos some time back and could not find them, have they been taken down?

I've just spoken to R U Local and he's fine. He doesn't get involved with forums much these days, so I've tried to persuade him to renew contact with us when he feels ready to do so.

He says the videos haven't been taken down, so they should all still be there on YouTube.

Best wishes all,
Dave.

Edie: http://www.pistonheads.com/gassing/topic.asp?h=0&a...

Edited by p1esk on Monday 13th January 19:26

[25NAD90TUL]

p1esk said:

He doesn't get involved with forums much these days,

Can't imagine why that would be.

[p1esk]

25NAD90TUL said:

p1esk said:

He doesn't get involved with forums much these days,

Can't imagine why that would be.

Maybe he has sufficient hassle in his normal line of work and doesn't feel the need for any more of it. Anyhow, I hope he will be back here occasionally; he was very helpful previously.

[25NAD90TUL]

p1esk said:

Maybe he has sufficient hassle in his normal line of work and doesn't feel the need for any more of it. Anyhow, I hope he will be back here occasionally; he was very helpful previously.

I watched his video, I thought it was good, some well executed overtaking imo.

I see from this thread that you used the TripleS nomdeplume at one time, why did you change? It's a good name. Just been reading some of your input at the other place, all good stuff, I see they changed the error in that captcha script.

[p1esk]

25NAD90TUL said:

p1esk said:

Maybe he has sufficient hassle in his normal line of work and doesn't feel the need for any more of it. Anyhow, I hope he will be back here occasionally; he was very helpful previously.

I watched his video, I thought it was good, some well executed overtaking imo.

I see from this thread that you used the TripleS nomdeplume at one time, why did you change? It's a good name. Just been reading some of your input at the other place, all good stuff, I see they changed the error in that captcha script.

I started off as TripleS when I joined PH in 2004, but after a year or two something went wrong within the PH system and it ceased to work, so I had to start again with a new name, hence the appearance of p1esk. This happened to quite a few other PH members, so they too had to operate under new names; e.g. Soren became Soren2. He doesn't seem to have posted anything here for quite a while, but he did used to contribute some good stuff a few years back. I think he is a Police Traffic Officer in Cumbria.

It would have been nice if the PH management had explained what went wrong, and why I had to lose the TripleS label, but despite me asking a time or two, there has never been any explanation. That's a pretty poor show, PH.

I expect I'll now get banned or somehow excluded again; it's happened before!

Best wishes all,
Dave.