Downshifting whilst Braking
Discussion
Adom said:
WilliBetz said:
RT106 said:
If this is an advanced driving forum, why isn't everyone heel-and-toeing
Two reasons.Firstly, most advanced training stresses the benefit of separating the activities of braking and gearchanging, so it's not necessary.
Secondly, even amongst advanced drivers, a decent heel and toe gearchange (perhaps employing double declutching for good measure) isn't normally a subconscious competence...
GreenV8S said:
Adom said:
With enough practice and use it becomes as much a subconcious competence as ordinary gearchanges.
And yet ... It is harder to do (so requiring more practice to achieve the same level of competence and implying that people who have not yet achieved this competence will have to apply more effort and do it less well).
It takes longer than an ordinary (single declutch) gear change, increasing the driver workload at a time where driver workload is typically already high.
It compromises the drivers ability to steer and brake, since the foot used for braking is also being used to operate another control, and the driver is obliged to steer with one hand for longer.
Under some circumstances the benefits can outweigh the costs. More usually they won't. To suggest that for a given person it is *always* sensible to do, is IMO mistaken thinking. To go further and suggest that *everyone* should always do it as a matter of course is fundamentally misguided IMO.
The difference in time for changing gear using DDC is miniscule - especially in the context of road driving.
I am not suggesting that it is 'always' sensible to DDC, just that for me, personally, it would now take more thought to not DDC than it does to do it. I'm pretty sure I'm not mistaken but maybe you know better.
I don't suggest that 'everyone' should do it, but I am of the opinion that if everyone thought about their driving to the degree where they did start to think about using such techniques, then it would perhaps be a sign that they were actually paying some attention to their driving and consequently, IMO the roads would be a better place.
Adom said:
I am not suggesting that it is 'always' sensible to DDC, just that for me, personally, it would now take more thought to not DDC than it does to do it.
I don't suggest that 'everyone' should do it, but I am of the opinion that if everyone thought about their driving to the degree where they did start to think about using such techniques, then it would perhaps be a sign that they were actually paying some attention to their driving and consequently, IMO the roads would be a better place.
As to your last paragraph, absolutely. The roads would be a better place if everybody thought about their driving. But this is not a thread about mental attitude. We are talking about overlapping brakes and gearchange, and now considering use of DDC with H & T. I know lots of drivers who have developed the skill to do each of DDC and H & T but choose not to use either regularly on the road .I don't suggest that 'everyone' should do it, but I am of the opinion that if everyone thought about their driving to the degree where they did start to think about using such techniques, then it would perhaps be a sign that they were actually paying some attention to their driving and consequently, IMO the roads would be a better place.
One of the reasons for teaching seperation of brakes and gearchange is to force drivers to brake earlier, leaving time for a gearchange after completion of braking before arriving at the hazard. This creates an extra margin of safety. Do you agree that other things being equal, some safety is given away by BGOL? What is gained?
waremark said:
Adom said:
I am not suggesting that it is 'always' sensible to DDC, just that for me, personally, it would now take more thought to not DDC than it does to do it.
I don't suggest that 'everyone' should do it, but I am of the opinion that if everyone thought about their driving to the degree where they did start to think about using such techniques, then it would perhaps be a sign that they were actually paying some attention to their driving and consequently, IMO the roads would be a better place.
As to your last paragraph, absolutely. The roads would be a better place if everybody thought about their driving. But this is not a thread about mental attitude. We are talking about overlapping brakes and gearchange, and now considering use of DDC with H & T. I know lots of drivers who have developed the skill to do each of DDC and H & T but choose not to use either regularly on the road .I don't suggest that 'everyone' should do it, but I am of the opinion that if everyone thought about their driving to the degree where they did start to think about using such techniques, then it would perhaps be a sign that they were actually paying some attention to their driving and consequently, IMO the roads would be a better place.
One of the reasons for teaching seperation of brakes and gearchange is to force drivers to brake earlier, leaving time for a gearchange after completion of braking before arriving at the hazard. This creates an extra margin of safety. Do you agree that other things being equal, some safety is given away by BGOL? What is gained?
Adom said:
I am somewhat confused by your first paragraph. Of course it will take more effort than for someone who is well-practised, but that is the same with anything, for example learning to drive a car at all. I would have thought that people taking an interest and practising something is actually something to be encouraged
I'm saying there is a cost to doing it, and there is a cost to learning how to do it. If you're saying it is something that people should be encouraged to do then the onus is on you to say what the benefits are that justify this cost. There are certain circumstances where this technique is appropriate, but outside of those circumstances it is not a sensible thing to do.waremark said:
One of the reasons for teaching seperation of brakes and gearchange is to force drivers to brake earlier, leaving time for a gearchange after completion of braking before arriving at the hazard. This creates an extra margin of safety. Do you agree that other things being equal, some safety is given away by BGOL? What is gained?
Some thoughts...The reasoning behind separating the activities of braking and gearchanging is sound. It would be sensible to learn to do this subconsciously before worrying about h&t.
However, that doesn't mean that h&t / bgol can't afford an extra margin of safety.
Nobody is saying that you have to brake later, or more firmly, or to enter a corner or hazard more quickly, just because you make a conscious decision to use h&t / bgol as part of your considered plan.
But let's consider two 911 SC drivers entering a slippery, off camber, left hand bend. The limit point isn't running at the point that they enter the corner. In fact, the severity of the bend can't be assessed yet...
Our first driver - IAM trained - of the 911 SC will have braked in good time to a speed that they consider appropriate. They'll then have selected, say, second gear and started to accelerate gently to pull the car through the bend. The entry speed is a guess, because the bend isn't opening when the driver enters the bend, but it's a pretty good guess because the driver is pretty well trained.
Compare this to our other advanced driver - the one that embraces appropriate use of other techniques. While braking, on approach to the corner, they realise it isn't going to be assessable before they start to turn. As they don't like guessing, they use bgol and h&t to change smoothly into second gear while braking, and enter the bend by gradually building up the steering angle as they gradually ease off the brake. All the time matching road speed to vision, as defined by the limit point.
Unfortunately, on this bend and on this occasion, a few sheep have strayed onto the road just after the sharpest part of the bend and both our drivers have to stop quickly...
When the IAM driver sees the sheep, they are accelerating. Let's hope they've been practicing their cadence braking skills, and are comfortable with the handling characteristics of their car, because stopping an accelerating 911 SC on a slippery off camber bend is one of those situations where you wish you'ld stayed in bed.
The other driver has, I would suggest, an easier time. They were still braking when they saw the sheep, albeit gently. With the weight still over the front wheels, they are better placed to stop and to steer.
As I say, just a thought...
Edited by WilliBetz on Saturday 23 February 13:35
WilliBetz said:
But let's consider two 911 SC drivers entering a slippery, off camber, left hand bend. The limit point isn't running at the point that they enter the corner. In fact, the severity of the bend can't be assessed yet...
A useful example, Willi, in which BGOL offers a clear benefit to progress.The IAM trained driver will enter the bend as you say with just enough gas applied to maintain his speed round the bend. His speed will be selected to enable him to stop in the distance he can see to be clear, that is, the distance before the limit point, and the distance before the sheep. His assessment of stopping distance will take into account the particular handling characteristics of the car he is driving (have you met an IAM trained 911 SC driver? - send him off promptly to Bernard Aubry, Hugh Noblett, Mike Franey or the like!) as well as the slippery surface and camber. So he will be able to stop safely before the sheep.
But the extremely valid point you are making is that in this particular vehicle he will not be able to make as much progress as a driver who trail brakes into the bend, who will have the ability to stop from a higher speed in the same distance.
You remind me why I chose a C4 in earlier 911 days! Does a modern GT3 behave in a similar way to the 911 SC of old?
GreenV8S said:
Adom said:
I am somewhat confused by your first paragraph. Of course it will take more effort than for someone who is well-practised, but that is the same with anything, for example learning to drive a car at all. I would have thought that people taking an interest and practising something is actually something to be encouraged
I'm saying there is a cost to doing it, and there is a cost to learning how to do it. If you're saying it is something that people should be encouraged to do then the onus is on you to say what the benefits are that justify this cost. There are certain circumstances where this technique is appropriate, but outside of those circumstances it is not a sensible thing to do.The benefit IMO is a smooth gearchange which doesn't unsettle the car under braking (appreciate that H&T in isolation would achieve this). For me, I find it satisfying when i get it spot on, and when driving my old cars it makes downchanges easier (as the synchro is 18 years old). This seems pretty sensible to me rather than simply forcing it into gear.
Out of interest, under what circumstances do you consider the technique appropriate?
stefan1 said:
RT106 said:
Avoiding braking/gearshift over-lap seems to me to be akin to using a large sledge-hammer to crack a practically non-existent nut.
Hardly. As StressedDave and GreenV8S have said, in a powerful car a poor downshift without matching revs can easily overcome the tyres' grip, even on a dry road.Powerful motorbikes often have a system to avoid rear wheel lock up when shifting down through the 'box, in case revs are not matched (eg, my old Aprillia RSV Mille).
On less powerful cars, in slippery conditions, shifting down at high revs can still be an issue.
(NB. This is not about BGOL per se. Matching revs can still be achieved through H&T whilst braking. The key is matching revs, whether with or without BGOL.)
Kind regards
Steve
"Engine drag torque control (MSR)
Within the TC function there exists also engine drag torque control. This may be required for instance after changing down to a lower gear on slippery ground. On changing down to a lower gear the resulting engine braking effect can be so severe as to fracture the rear axle. MSR prevents this by calling for power (giving gas) through the engine management system. There is always the possibility that the Carrera GT driver may switch off the traction control functions by pressing the button labelled “TC”. He is then reminded of this by the display “TC off” in the multi-function instrument.
It is however inadvisable to switch off the TC functions. Doing so will in any case not lead to better lap times on the race track."
Extract, Porsche Carrera GT workshop manual
I have marked in bold the sentence which makes the point quite well!
(I also rather like the last sentence.)
Kind regards
Steve
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