Gears at Junctions
Discussion
I too use double de clutching to aid down-shifting into first whilst in the move. I've only become reasonably competent at it through using it for almost all down-shifting though.
Smoothly (well, aiming to) moving the gear-stick into gear with the minimum resistance is quite satisfying to some.
Smoothly (well, aiming to) moving the gear-stick into gear with the minimum resistance is quite satisfying to some.
1st gear is pretty much useless once moving in most cars, so the chap suggesting that you use it at 20mph is on crazy pills. You'll get about 10mph of acceleration and a lot of noise and mechanical wear, but almost nothing else. Unless your car is geared absolutely bizarrely, 2nd gear is almost certain to be more appropriate above about 12mph (i.e. anything above a crawl).
I am sure someone who learned to drive in 1960 will disagree, but cars have easily enough torque these days to cope admirably at low speed in 2nd. You could even, God forbid, dip the clutch, give it some revs and lift the clutch again in the same gear. But that is probably breaking about 2000 rules
I am sure someone who learned to drive in 1960 will disagree, but cars have easily enough torque these days to cope admirably at low speed in 2nd. You could even, God forbid, dip the clutch, give it some revs and lift the clutch again in the same gear. But that is probably breaking about 2000 rules
We used to teach DDC at Hendon, then stopped and now teach rev on the down change.omegac said:
MC Bodge said:
I too use double de clutching to aid down-shifting into first whilst in the move.
Why not just depress the clutch and blip the throttle if needed at all, no need to DDC.Rev-matching makes life easier for the clutch, a double de-clutch also does the job of the synchromesh.
On a new car, changing down into 2nd, 3rd or 4th will be absolutely fine with a simple rev-match.
In an older car with tired synchros, or in any car when changing into first above a few mph, DDC has real benefits (and not just the sound of it).
On a new car, changing down into 2nd, 3rd or 4th will be absolutely fine with a simple rev-match.
In an older car with tired synchros, or in any car when changing into first above a few mph, DDC has real benefits (and not just the sound of it).
omegac said:
SK425 said:
You asked that before. The two techniques do different things. One is not a replacement for the other.
Really? What do they do differently to smooth out a change down?That just illustrates the difference though. How often do any of us drive something without synchromesh? Personally, it's round about never. My point is that, whilst I could see why someone might say that with synchromesh there's no benefit to DDC (although I wouldn't entirely agree), you are saying that if you can rev match there's no benefit to DDC, and even if one assumes, as I'm sure we all are, that synchromesh is present, that statement is simply a non sequitur.
In my - and it would seem, others' - experience, there are two ways DDC can offer benefit even with synchromesh, bearing in mind that syncromesh is not magic, it's just mechanical gubbins that has to do work. Firstly, DDC can facilitate gear engagements that would otherwise be noticeably harder and take longer. That's more fundamental than smoothing out a down change as per your question - that can create options that otherwise might not even seem available (e.g. the OP's change into 1st gear). Secondly, see my erlier post:
SK425 said:
That said, DDC can also help with rev matching, as you get some confirmation (or not) of whether you've raised the revs to the right level as you move the gear lever into the new position hoping to feel little or no resistance.
That one clearly is about smoothing out a down change. The smoothness comes from the rev matching. The DDC helps get the rev matching right.I find these benefits more likely to be apparent when changing into lower gears at higher revs, when the torque due to the gear ratio and the delta in revs a) make the synchromesh's job harder and b) show up more obviously any mismatch in engine speed and road speed when the clutch is re-engaged.
I have to say this kind of thing isn't doing much to dispell the idea that 'Advanced Driving' is an old-fashioned pursuit from a time when 4-speed gearboxes were the norm and dodgy synchros were par for the course.
Who in their right mind would advocate downshifting into 1st at anything above walking pace? You're going to need an almighty blip in the middle of your double-declutch because 20mph in 1st is probably near 4000rpm, as a previous poster said you'll get a few moments of acceleration then you'll practically be in the limiter. Okay, if it's a one in five gradient maybe it's appropriate, but if visability is good enough to join the road without stopping then nine times out of ten it's doable in 2nd, and the rest of the time you're approaching at too shallow an angle and you need to stop to complete your observation anyway.
If this is what 'Advanced Driving' is about then aahm oot, I can't remember the last time I downshifted to 1st whilst moving in a road car.
Who in their right mind would advocate downshifting into 1st at anything above walking pace? You're going to need an almighty blip in the middle of your double-declutch because 20mph in 1st is probably near 4000rpm, as a previous poster said you'll get a few moments of acceleration then you'll practically be in the limiter. Okay, if it's a one in five gradient maybe it's appropriate, but if visability is good enough to join the road without stopping then nine times out of ten it's doable in 2nd, and the rest of the time you're approaching at too shallow an angle and you need to stop to complete your observation anyway.
If this is what 'Advanced Driving' is about then aahm oot, I can't remember the last time I downshifted to 1st whilst moving in a road car.
It can be useful to be able to shift smoothly into first on the move at times. It's not necessarily used frequently, but why not learn the skill/ability?
As for the original post, it sounds like unnecessary rule-making.
I disagree with much of the dogma and don't have blind faith in "the commandments as handed down to Hendon"
As for the original post, it sounds like unnecessary rule-making.
I disagree with much of the dogma and don't have blind faith in "the commandments as handed down to Hendon"
SK425 said:
Firstly, DDC can facilitate gear engagements that would otherwise be noticeably harder and take longer. That's more fundamental than smoothing out a down change as per your question - that can create options that otherwise might not even seem available (e.g. the OP's change into 1st gear).
This is where I disagree, having done many hours instruction of pursuit training I and other instructors have never felt that gear changes took longer (remember the order of the four S's), were any less smooth or led to lost opportunities. So while I think it might be nice for looking the part, in reality, when a car is being driven in anger, it has no practical purpose unless you're driving something with a man with a red flag walking in front of you.BritishRacinGrin said:
If this is what 'Advanced Driving' is about then aahm oot, I can't remember the last time I downshifted to 1st whilst moving in a road car.
I mentioned DDC first so I guess I kicked this off. I mentioned it simply because the OP seemed to be finding something he wanted to do difficult and I thought DDC might help him. Nothing more to it than that. Since we talking Advanced Driving, I hope it's taken as read that a) if the OP chose to try it out he would review what difference it made (which can obviously involve asking the person sat next to him their view too) and b) the only person who can ultimately decide whether or not it works for the OP is the OP.If you took something more dictatorial than that from this thread then you're reading into it something I certainly never intended to say and something I don't think anyone in this thread has said. The fact that you don't downshift into 1st while moving doesn't make the OP's desire to do so wrong. And the fact that the OP feels he wants to does not make the fact that you don't want to wrong either. Neither of you should feel you need to be oot of Advanced Driving over something so trivial as a different choice of style. That would be silly.
omegac said:
SK425 said:
Firstly, DDC can facilitate gear engagements that would otherwise be noticeably harder and take longer. That's more fundamental than smoothing out a down change as per your question - that can create options that otherwise might not even seem available (e.g. the OP's change into 1st gear).
This is where I disagree, having done many hours instruction of pursuit training I and other instructors have never felt that gear changes took longer (remember the order of the four S's), were any less smooth or led to lost opportunities. So while I think it might be nice for looking the part, in reality, when a car is being driven in anger, it has no practical purpose unless you're driving something with a man with a red flag walking in front of you.Look at a single clutched upshift. A competent driver will depress the clutch and time the shift so that the revs have fallen away to a reasonable match for the next gear. However, during the shift the gear assembly (which is spinning in oil) loses speed quite quickly once the stick is shifted out of gear.
By double clutching, the gearbox is disconnected from drive for the shortest time possible, meaning that the clutch and the synchros have less work to do to get everything back into mesh again.
The advantage when upshifting is that the gearbox assembly is connected to the engine for much more of the shift. Because the gearbox assembly is spinning in oil it creates drag on the engine, which reduces the revs faster on a trailing throttle. Reducing the revs faster means that the engine synchronises with the road speed faster.
That means that, providing you can perform the footwork quickly enough, a DDC upshift can be performed quicker than a single clutch one on the majority of road cars when pushing on, and smoother when just pottering around.
davepoth said:
omegac said:
SK425 said:
Firstly, DDC can facilitate gear engagements that would otherwise be noticeably harder and take longer. That's more fundamental than smoothing out a down change as per your question - that can create options that otherwise might not even seem available (e.g. the OP's change into 1st gear).
This is where I disagree, having done many hours instruction of pursuit training I and other instructors have never felt that gear changes took longer (remember the order of the four S's), were any less smooth or led to lost opportunities. So while I think it might be nice for looking the part, in reality, when a car is being driven in anger, it has no practical purpose unless you're driving something with a man with a red flag walking in front of you.Look at a single clutched upshift. A competent driver will depress the clutch and time the shift so that the revs have fallen away to a reasonable match for the next gear. However, during the shift the gear assembly (which is spinning in oil) loses speed quite quickly once the stick is shifted out of gear.
By double clutching, the gearbox is disconnected from drive for the shortest time possible, meaning that the clutch and the synchros have less work to do to get everything back into mesh again.
The advantage when upshifting is that the gearbox assembly is connected to the engine for much more of the shift. Because the gearbox assembly is spinning in oil it creates drag on the engine, which reduces the revs faster on a trailing throttle. Reducing the revs faster means that the engine synchronises with the road speed faster.
That means that, providing you can perform the footwork quickly enough, a DDC upshift can be performed quicker than a single clutch one on the majority of road cars when pushing on, and smoother when just pottering around.
(In seriousness, this does sound right to me.)
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