Why sustained rev gearchanging works
Discussion
Hi All
This has previously been posted on the 'Old fashioned downshifting and braking' thread in Advanced Driving. What nobody yet seems to have explained anywhere on the internet (unless I have missed it) is why blipping the throttle helps with a single declutch gearchange. (sdc)
It seems that many people believe that if the clutch is disengaged then increasing engine revs will have no effect on the speeding up the internal components of the gearbox that would help with synchronising the gearchange.
This is logical as if the clutch is disengaged there is no drive from the engine to the gearbox, as pretty well every driving instructor (learner or advanced), car enthusiast or mechanical engineer will tell you. However experiential evidence shows otherwise. Although what follows may not be true in every car, I myself have witnessed it on various cars and have little reason to think that it isn't correct in the majority of cases.
As I could not find an explanation anywhere in any books that I read on the matter, and rather than believe 'experts' that told me it couldn't happen when the evidence of my own eyes told me otherwise, I decided to come up with a rational explanation that relied on the laws of physics rather than hearsay.
When my car was raised from the ground with the driven wheels free to rotate (no brake drag) they would do so when the engine was running, even when in neutral or with the clutch disengaged. (I must admit I never tried it with both)
The only way that I could explain it with is that power is unexpectedly transferred due to the small amount of friction in the bearing between the engine and the clutch shaft. This friction is normally ignored as bearings are regarded to all intents and purposes as frictionless when dealing with drive via the clutch. Consequently their effect is ignored in subsequent analyses with the clutch disengaged.
e.g. Where the shaft that supports the clutch plates enters the rear of the crankshaft it is held in a spigot bearing. In normal operation the friction drag is unnoticeable and its effects are, as stated before, therefore ignored. It is however friction, plus the effect of other factors , that will have an effect on slowing down as the clutch as it is disengaged and throttle released in a normal gearchange.
If the clutch is disengaged for long enough the clutch plates will slow down but not stop (As I discovered by observation of my raised car). Similarly it then seems reasonable they will speed up due to drive from friction in the crankshaft spigot bearing during a sustained revs gearchange. (I have no evidence to prove this but unless someone can offer another explanation of why sustained revs gearchanges work I will stick with it)
To continue, I needed to think of a reason why sustained rev gearchanges were not used as an alternative to double declutching originally. Historically, in the days before synchros, when ddc was necessary there were larger differences between gear ratios (3 speed boxes) and I would imagine that the components had a greater rotational inertia, hence they would speed up more slowly and had to speed up more due to the wider gear spacings.
With the paranoia about coasting from a control point of view (having the clutch down long enough for this to take effect) sustained revs would have been seen as unacceptable and inefficient. Not only that but it would probably have been more difficult to judge the speed matching and therefore double declutching was necessary.
This also explains why heel and toe can work without double declutching.
Obviously if someone can come up with a plausible alternative or see a flaw in my hypothesis I'm willing to change my view.
Edited to add that the also frequently ignored (including by me up till this point) effect of clutch disc 'skimming' will also have a similar and possibly greater effect. The point about 'negligible' effects still holding true.
Hope this helps.
Best regards
Martin A
This has previously been posted on the 'Old fashioned downshifting and braking' thread in Advanced Driving. What nobody yet seems to have explained anywhere on the internet (unless I have missed it) is why blipping the throttle helps with a single declutch gearchange. (sdc)
It seems that many people believe that if the clutch is disengaged then increasing engine revs will have no effect on the speeding up the internal components of the gearbox that would help with synchronising the gearchange.
This is logical as if the clutch is disengaged there is no drive from the engine to the gearbox, as pretty well every driving instructor (learner or advanced), car enthusiast or mechanical engineer will tell you. However experiential evidence shows otherwise. Although what follows may not be true in every car, I myself have witnessed it on various cars and have little reason to think that it isn't correct in the majority of cases.
As I could not find an explanation anywhere in any books that I read on the matter, and rather than believe 'experts' that told me it couldn't happen when the evidence of my own eyes told me otherwise, I decided to come up with a rational explanation that relied on the laws of physics rather than hearsay.
When my car was raised from the ground with the driven wheels free to rotate (no brake drag) they would do so when the engine was running, even when in neutral or with the clutch disengaged. (I must admit I never tried it with both)
The only way that I could explain it with is that power is unexpectedly transferred due to the small amount of friction in the bearing between the engine and the clutch shaft. This friction is normally ignored as bearings are regarded to all intents and purposes as frictionless when dealing with drive via the clutch. Consequently their effect is ignored in subsequent analyses with the clutch disengaged.
e.g. Where the shaft that supports the clutch plates enters the rear of the crankshaft it is held in a spigot bearing. In normal operation the friction drag is unnoticeable and its effects are, as stated before, therefore ignored. It is however friction, plus the effect of other factors , that will have an effect on slowing down as the clutch as it is disengaged and throttle released in a normal gearchange.
If the clutch is disengaged for long enough the clutch plates will slow down but not stop (As I discovered by observation of my raised car). Similarly it then seems reasonable they will speed up due to drive from friction in the crankshaft spigot bearing during a sustained revs gearchange. (I have no evidence to prove this but unless someone can offer another explanation of why sustained revs gearchanges work I will stick with it)
To continue, I needed to think of a reason why sustained rev gearchanges were not used as an alternative to double declutching originally. Historically, in the days before synchros, when ddc was necessary there were larger differences between gear ratios (3 speed boxes) and I would imagine that the components had a greater rotational inertia, hence they would speed up more slowly and had to speed up more due to the wider gear spacings.
With the paranoia about coasting from a control point of view (having the clutch down long enough for this to take effect) sustained revs would have been seen as unacceptable and inefficient. Not only that but it would probably have been more difficult to judge the speed matching and therefore double declutching was necessary.
This also explains why heel and toe can work without double declutching.
Obviously if someone can come up with a plausible alternative or see a flaw in my hypothesis I'm willing to change my view.
Edited to add that the also frequently ignored (including by me up till this point) effect of clutch disc 'skimming' will also have a similar and possibly greater effect. The point about 'negligible' effects still holding true.
Hope this helps.
Best regards
Martin A
Edited by Martin A on Tuesday 24th November 18:04
Not a bad summary I'd say. You can also feel it through the gearlever as it operates the down change - less force due to less work for the synchromesh to do. Anyone who's driven a non-synchromesh gearbox such as motorcycle or race car will also have found that there's no need to double de-clutch.
A friend of mine once spent some time teaching himself to ddc before we both attended racing school. I had ridden motorcycles and reckoned no need so was chuffed to be proved right (Hewland Mk9 on FF1600). I found that violent blips were not good because you couldn't easily match the revs at both the gear engagement point and the clutch release point which are separated by a small time. Therefore, a more progressive blip or sustaining the revs tends to work best.
The lesson from driving a non-synchro box also applies to a normal road gearbox for lighter quicker gear change with less wear combined with nice smooth drive.
Like you I reckon there's an effect with increasing vehicle size - certainly the old lorry drivers used to double de-clutch.
Snailpace
A friend of mine once spent some time teaching himself to ddc before we both attended racing school. I had ridden motorcycles and reckoned no need so was chuffed to be proved right (Hewland Mk9 on FF1600). I found that violent blips were not good because you couldn't easily match the revs at both the gear engagement point and the clutch release point which are separated by a small time. Therefore, a more progressive blip or sustaining the revs tends to work best.
The lesson from driving a non-synchro box also applies to a normal road gearbox for lighter quicker gear change with less wear combined with nice smooth drive.
Like you I reckon there's an effect with increasing vehicle size - certainly the old lorry drivers used to double de-clutch.
Snailpace
Isnt it the engine speed that you matching to the gearbox and not the other way round. with the clutch disengaged the gearbox is been driven by the wheels rather than the engine ( assuming it still in gear)
as the engine was in a higher gear the rpm will be lower, than is needed for the same speed in a lower gear. so if you shift without matching the revs, you need to speed up the engine or slow the gearbox. if you dont speed up the engine you run the risk of locking the wheels as the gearbox is slowed down to the engine rpm.. Try it with a dog box change down without matching revs!!!
or am i quite possibly missing the point :-)
as the engine was in a higher gear the rpm will be lower, than is needed for the same speed in a lower gear. so if you shift without matching the revs, you need to speed up the engine or slow the gearbox. if you dont speed up the engine you run the risk of locking the wheels as the gearbox is slowed down to the engine rpm.. Try it with a dog box change down without matching revs!!!
or am i quite possibly missing the point :-)
Hi Graham
The engine speed is changed to enable the temporarily 'undriven' components of the transmission to match speed with those being driven by the wheels, hence facilitating smoother gear engagement. By adjusting the engine revs there is then little or no differential in speeds of the clutch plates when they are brought together as the clutch is engaged, and hence no jolt. The less power an engine is producing prior to the change the easier this is.
Hope this helps
Best regards
Martin A
The engine speed is changed to enable the temporarily 'undriven' components of the transmission to match speed with those being driven by the wheels, hence facilitating smoother gear engagement. By adjusting the engine revs there is then little or no differential in speeds of the clutch plates when they are brought together as the clutch is engaged, and hence no jolt. The less power an engine is producing prior to the change the easier this is.
Hope this helps
Best regards
Martin A
Martin A said:
(I have no evidence to prove this but unless someone can offer another explanation of why sustained revs gearchanges work I will stick with it)
Surely it is because engine speed is matched to road speed in the new gear, leaving only the gearbox internals travelling at a different speed. These gearbox internals have relatively little intertia in relation to the forces involved, and the synchro mechanism does its job of adjusting the speed of the layshaft or input shaft as required to match the speed of the output shaft, which is connected to the road wheels.I am not arguing with your suggestion that there may be some friction through a disengaged clutch, meaning that rev matching even without DDC results in some increase in the layshaft speed. However, this if it happens at all is a very insignificant benefit of rev matching. The point of rev matching is to raise the engine speed to the level required for the new gear; by contrast, with non rev-matched downchanges the whole engine has to be speeded up against its compression to match the speed of the road wheels, causing the clutch to work hard. Even this use of the clutch however apparently causes relatively minor wear by comparison with starting off from rest.
waremark said:
I am not arguing with your suggestion that there may be some friction through a disengaged clutch, meaning that rev matching even without DDC results in some increase in the layshaft speed. However, this if it happens at all is a very insignificant benefit of rev matching. The point of rev matching is to raise the engine speed to the level required for the new gear; by contrast, with non rev-matched downchanges the whole engine has to be speeded up against its compression to match the speed of the road wheels, causing the clutch to work hard. Even this use of the clutch however apparently causes relatively minor wear by comparison with starting off from rest.
I think Martin's point re "clutch drag" in this respect is that with your foot on the clutch, when you rev, the gearbox input shaft gets spun up which helps the smooth meshing of gears by helping out the synchros. Not that it helps with rev-matching.Bert
waremark said:
Martin A said:
(I have no evidence to prove this but unless someone can offer another explanation of why sustained revs gearchanges work I will stick with it)
Surely it is because engine speed is matched to road speed in the new gear, leaving only the gearbox internals travelling at a different speed. These gearbox internals have relatively little intertia in relation to the forces involved, and the synchro mechanism does its job of adjusting the speed of the layshaft or input shaft as required to match the speed of the output shaft, which is connected to the road wheels.I am not arguing with your suggestion that there may be some friction through a disengaged clutch, meaning that rev matching even without DDC results in some increase in the layshaft speed. However, this if it happens at all is a very insignificant benefit of rev matching.
Hi All
Agreed, but they do have some inertia which I would argue that although small, is not completely insignificant.
My argument is that if the friction were very insignificant it would not turn the wheels of a car that has been raised with the clutch disengaged or in neutral. As it can provide enough energy to rotate a wheel, rotating a shaft will be easy. Therefore my contention is that it is of benefit. So by adjusting the revs it allows the synchros to synchronise better. This is why when done well the gears slip in so sweetly.
When there is no rev matching, as the gearbox doesn't 'know' which gear is to be selected until the instant it is done. Relying solely on the synchros there is a different, less satisfying, feel as the gear (not the clutch) is engaged. Some people may never have experienced or noticed this 'sweet' feeling or if they have, may not have been curious to wonder why sometimes it feels better than others.
Hope this helps
Best regards
Martin A
waremark said:
Martin A said:
(I have no evidence to prove this but unless someone can offer another explanation of why sustained revs gearchanges work I will stick with it)
Surely it is because engine speed is matched to road speed in the new gear, leaving only the gearbox internals travelling at a different speed. These gearbox internals have relatively little intertia in relation to the forces involved....waremark said:
...and the synchro mechanism does its job of adjusting the speed of the layshaft or input shaft as required to match the speed of the output shaft, which is connected to the road wheels.
Agreed but as far as I understand it this is only once the gear selection is made. First the synchros engage and only once the speeds are synchronised do the teeth engage. This happens after a slight delay which depends on the speed differential of the shafts.waremark said:
I am not arguing with your suggestion that there may be some friction through a disengaged clutch, meaning that rev matching even without DDC results in some increase in the layshaft speed.
Again in agreementwaremark said:
However, this if it happens at all is a very insignificant benefit of rev matching.
This appears to be the only point on which we really differ.My argument is that if the friction were very insignificant it would not turn the wheels of a car that has been raised with the clutch disengaged or in neutral. As it can provide enough energy to rotate a wheel, rotating a shaft will be easy. Therefore my contention is that it is of benefit. So by adjusting the revs it allows the synchros to synchronise better. This is why when done well the gears slip in so sweetly.
When there is no rev matching, as the gearbox doesn't 'know' which gear is to be selected until the instant it is done. Relying solely on the synchros there is a different, less satisfying, feel as the gear (not the clutch) is engaged. Some people may never have experienced or noticed this 'sweet' feeling or if they have, may not have been curious to wonder why sometimes it feels better than others.
waremark said:
The point of rev matching is to raise the engine speed to the level required for the new gear; by contrast, with non rev-matched downchanges the whole engine has to be speeded up against its compression to match the speed of the road wheels, causing the clutch to work hard. Even this use of the clutch however apparently causes relatively minor wear by comparison with starting off from rest.
Agreed in general but as this is a slightly different topic I won't stray.Hope this helps
Best regards
Martin A
Martin A said:
My argument is that if the friction were very insignificant it would not turn the wheels of a car that has been raised with the clutch disengaged or in neutral. As it can provide enough energy to rotate a wheel, rotating a shaft will be easy.
I have also seen this on a MINI Challenge car. When warming up the engine whilst on the axle stands, increasing the throttle did appear to slightly increase the speed at which the wheels/hubs were rotating.I'm not sure that I understand what's written above. If such an effect exists, it's minimal and probably inconsequential to a smooth downchange.
Bear with me on this one because I'm no mechanic, but here's the way I (and probably 99% of rev matching drivers!) see it:
Non rev-matched gear changes are bad because, as we know, they force the engine to speed up to the speed of the lower gear and the resistance from the engine (inertia and compression) causes an unecessary braking force to be applied to the driven wheels, shifting them closer to the limit momentarily (bad on the road sub-limit, and disastrous on the track when threshold braking). By blipping the throttle when the clutch is down (SDC) you're speeding the engine up in readiness so you avoid this engine braking surge. For sure, with a SDC the driven wheels still have to surge the gearbox internals up to speed when the clutch is re-engaged, but they carry such little intertia it's surely not a problem? 99% of the problem is the compression and rotational inertia of the engine, which is solved by a SDC gearchange blip.
The principle of a SDC H&T downchange is universally taught the world over at racing schools and on advanced driving courses (usually on the road drivers are encouraged to SDC rev match off the brakes). I've never seen or heard of a racing driver in a modern racing car using DDC. The only exceptions to this are the footage of Rohl in Group B that we discussed on the other thread, and someone also said on that thread that the Skip Barber school teaches DDC. For everywhere else, it's SDC H&T. I've seen the chief instructors of both Jim Russell in Canada (on the excellent video "Drive to Win") and Silverstone racing school (in person at an instructor training day) asked the question and the answer every time is that DDC is not necessary, but SDC H&T is essential. This applies to straight cut race boxes and synchro boxes.
Edited to say: I've just read the comments on sustained revs changes. I can only assume this is an internet phenomenum?! Since I started driving I've been instructed by a variety of road and track instructors, as well as privately studying driving technique over that period. Other than once before on this forum I have never heard of such a technique. 99.9999% of the world just blips the throttle. It's easy - why not?
Bear with me on this one because I'm no mechanic, but here's the way I (and probably 99% of rev matching drivers!) see it:
Non rev-matched gear changes are bad because, as we know, they force the engine to speed up to the speed of the lower gear and the resistance from the engine (inertia and compression) causes an unecessary braking force to be applied to the driven wheels, shifting them closer to the limit momentarily (bad on the road sub-limit, and disastrous on the track when threshold braking). By blipping the throttle when the clutch is down (SDC) you're speeding the engine up in readiness so you avoid this engine braking surge. For sure, with a SDC the driven wheels still have to surge the gearbox internals up to speed when the clutch is re-engaged, but they carry such little intertia it's surely not a problem? 99% of the problem is the compression and rotational inertia of the engine, which is solved by a SDC gearchange blip.
The principle of a SDC H&T downchange is universally taught the world over at racing schools and on advanced driving courses (usually on the road drivers are encouraged to SDC rev match off the brakes). I've never seen or heard of a racing driver in a modern racing car using DDC. The only exceptions to this are the footage of Rohl in Group B that we discussed on the other thread, and someone also said on that thread that the Skip Barber school teaches DDC. For everywhere else, it's SDC H&T. I've seen the chief instructors of both Jim Russell in Canada (on the excellent video "Drive to Win") and Silverstone racing school (in person at an instructor training day) asked the question and the answer every time is that DDC is not necessary, but SDC H&T is essential. This applies to straight cut race boxes and synchro boxes.
Edited to say: I've just read the comments on sustained revs changes. I can only assume this is an internet phenomenum?! Since I started driving I've been instructed by a variety of road and track instructors, as well as privately studying driving technique over that period. Other than once before on this forum I have never heard of such a technique. 99.9999% of the world just blips the throttle. It's easy - why not?
Edited by RobM77 on Wednesday 25th November 10:45
Hi All
Then Rob said
My contention is that the gearbox internals are rev matched with the engine (by sustained revs or blipping) between coming out of one gear and going into the next which especially helps with non synchro boxes.
This is why, for maximum benefit, rev matching should be done before the new gear is selected rather than after gear selection but before clutch re-engagement. As I said in my original post, and Rob has agreed, many drivers don't realise that there is this small extra benefit and the reason it makes ddc unnecessary.
One way I have tried of testing my theory was to let the engine revs drop before changing gear and then blipping the throttle before raising the clutch. The change didn't feel as sweet to me (it certainly didn't feel any better) but that may be because I'm looking for evidence to support my understanding. Perhaps others could try and let me know their findings.
Hope this helps
Best regards
Martin A
RobM77 said:
I'm not sure that I understand what's written above. If such an effect exists, it's minimal and probably inconsequential to a smooth downchange.
I agree it is small, but not inconsequential, as I alluded to at the beginning of my post in the quote below. So I'll try to explain a bit better.Martin A said:
...This friction is normally ignored as bearings are regarded to all intents and purposes as frictionless when dealing with drive via the clutch. Consequently their effect is ignored in subsequent analyses....
Then Rob said
RobM77 said:
Bear with me on this one because I'm no mechanic, but here's the way I (and probably 99% of rev matching drivers!) see it:
Martin A said:
...as pretty well every driving instructor (learner or advanced), car enthusiast or mechanical engineer will tell you...
Once again we're in agreement about most people's understanding, which is why I want to improve that understanding. I'm not saying you need to do anything differently just explaining why ddc is not necessary in a modern car and sustained rev sdc makes things smoother. Rob's point about not being a mechanic is the crux of the matter. Most people's understanding of what goes on inside a modern gearbox and how it works is somewhat vague.RobM77 said:
Non rev-matched gear changes are bad because, as we know, they force the engine to speed up to the speed of the lower gear and the resistance from the engine (inertia and compression) causes an unecessary braking force to be applied to the driven wheels, shifting them closer to the limit momentarily (bad on the road sub-limit, and disastrous on the track when threshold braking).
The crucial detail difference here is that it is not the gearchange that forces the engine to speed up (and, I agree, cause problems), it is the re-engagement of the clutch. Once again I suspect many people including Rob know this and are considering the gearchange as a whole from clutch going down to being back op again. I'm just explaining the detail of what goes on when the clutch is down. I have no problem with the general understanding.RobM77 said:
By blipping the throttle when the clutch is down (SDC) you're speeding the engine up in readiness so you avoid this engine braking surge.
Agreed, but an added benefit is, as I said, that this also helps the synchros engage more easily, making the actual gear engagement quicker and causing less wearRobM77 said:
For sure, with a SDC the driven wheels still have to surge the gearbox internals up to speed when the clutch is re-engaged,...
Only if the engine revs are not sustained or the throttle blipped which is what Rob understands.RobM77 said:
...but they carry such little intertia it's surely not a problem? 99% of the problem is the compression and rotational inertia of the engine, which is solved by a SDC gearchange blip.
Agreed, it is not a problem as such, but is caused by re-engaging the clutch ,what I'm explaining is the actual little understood benefit before the clutch is re-engaged.My contention is that the gearbox internals are rev matched with the engine (by sustained revs or blipping) between coming out of one gear and going into the next which especially helps with non synchro boxes.
RobM77 said:
The principle of a SDC H&T downchange is universally taught the world over at racing schools and on advanced driving courses (usually on the road drivers are encouraged to SDC rev match off the brakes). I've never seen or heard of a racing driver in a modern racing car using DDC. The only exceptions to this are the footage of Rohl in Group B that we discussed on the other thread, and someone also said on that thread that the Skip Barber school teaches DDC. For everywhere else, it's SDC H&T. I've seen the chief instructors of both Jim Russell in Canada (on the excellent video "Drive to Win") and Silverstone racing school (in person at an instructor training day) asked the question and the answer every time is that DDC is not necessary, but SDC H&T is essential. This applies to straight cut race boxes and synchro boxes.
Agreed once again. All I am trying to do is to help people, with less specific gearbox knowledge than me, understand that ddc is unnecessary in a modern car, and why sustained revs or blipping helps more than just preventing jerkiness (as many on this forum will already know) it actually helps gear engagement too(a benefit that few are aware of). This is why, for maximum benefit, rev matching should be done before the new gear is selected rather than after gear selection but before clutch re-engagement. As I said in my original post, and Rob has agreed, many drivers don't realise that there is this small extra benefit and the reason it makes ddc unnecessary.
One way I have tried of testing my theory was to let the engine revs drop before changing gear and then blipping the throttle before raising the clutch. The change didn't feel as sweet to me (it certainly didn't feel any better) but that may be because I'm looking for evidence to support my understanding. Perhaps others could try and let me know their findings.
Hope this helps
Best regards
Martin A
Martin A said:
This is why, for maximum benefit, rev matching should be done before the new gear is selected rather than after gear selection but before clutch re-engagement. As I said in my original post, and Rob has agreed, many drivers don't realise that there is this small extra benefit and the reason it makes ddc unnecessary.
One way I have tried of testing my theory was to let the engine revs drop before changing gear and then blipping the throttle before raising the clutch. The change didn't feel as sweet to me (it certainly didn't feel any better) but that may be because I'm looking for evidence to support my understanding. Perhaps others could try and let me know their findings.
Hope this helps
Best regards
Martin A
First off, I completely agree with what you're saying re: SDC vs DDC. DDC is unecessary, even with a racing dog box. However, I'm not convinced by these mysterious "sustained revs" gearchanges. Answering your conundrum above (para 2 in my quotes) is the best way to explain what I mean: With a blip change you don't wait till the revs have falled completely, you complete the whole gearchange in a fraction of a second, and this ensures that the gearbox internals are still spinning, you're just boosting things a bit. This is especially relevant with a dog box, as this article by Hewland explains: http://www.hewland.com/svga/help.htmOne way I have tried of testing my theory was to let the engine revs drop before changing gear and then blipping the throttle before raising the clutch. The change didn't feel as sweet to me (it certainly didn't feel any better) but that may be because I'm looking for evidence to support my understanding. Perhaps others could try and let me know their findings.
Hope this helps
Best regards
Martin A
BertBert may also like to see the note at the base of the page in that article regarding where to change gear in the braking zone. The instructor that taught you was clearly mistaken. Bear in mind that G Hill and A Senna both used block changing (though I realise this isn't possible in your Radical Bert). I've sat with plenty of instructors and chatted to them in the paddock and you see it a lot - people who want to be around racing cars and earn a bit of money, or are simply "know it alls" who want to impart advice to others. I know plenty of people like this. You get the same thing with diving according to a diving instructor friend of mine. However, there are good instructors out there if you look though
Sadly they're often the quietly spoken ones, for obvious reasons.RobM77 said:
BertBert may also like to see the note at the base of the page in that article regarding where to change gear in the braking zone. The instructor that taught you was clearly mistaken. Bear in mind that G Hill and A Senna both used block changing (though I realise this isn't possible in your Radical Bert). I've sat with plenty of instructors and chatted to them in the paddock and you see it a lot - people who want to be around racing cars and earn a bit of money, or are simply "know it alls" who want to impart advice to others. I know plenty of people like this. You get the same thing with diving according to a diving instructor friend of mine. However, there are good instructors out there if you look though Sadly they're often the quietly spoken ones, for obvious reasons.
I'm not going to disagree with Mr Hewland am I? However, I think it's wrong to consign a good driver and coach to the bin on this basis. To give more detail and get way off topic... Sadly they're often the quietly spoken ones, for obvious reasons.we were trying to achieve a specific aim in my driving. I was using Hewland's "method". However we found using data logging that my coach's cornering speeds were all a little higher than mine which is entirely where he got his better lap times than mine (in my car). We concluded that he always entered a corner with the car more settled and balanced than I did. And got better cornering speeds than me (specifically higher exit speeds). One of the differences on the corners with multiple down-changes was that he went down through the gears more slowly, more smoothly and starting earlier in the braking (and finishing earlier). I got to the end of the braking zone, banged down three gears (touring car stylee), turned in and took my foot off the brake. All in all, a bit of an unsettled mess. I moved the gear change back in the process, made it smoother, took it more slowly, rolled off the brake and got higher exit speeds in the process. All facilitated by a change to the down change timing!
Bert (driving deity)
Martin A said:
This is why, for maximum benefit, rev matching should be done before the new gear is selected rather than after gear selection but before clutch re-engagement. As I said in my original post, and Rob has agreed, many drivers don't realise that there is this small extra benefit and the reason it makes ddc unnecessary.
One way I have tried of testing my theory was to let the engine revs drop before changing gear and then blipping the throttle before raising the clutch. The change didn't feel as sweet to me (it certainly didn't feel any better) but that may be because I'm looking for evidence to support my understanding. Perhaps others could try and let me know their findings.
So I'm with Martin here. It might be a marginal effect, but either blipping or raising the revs with the clutch down before (or actually as) you push the gear lever through the gate makes it go through the gate more easily. I have experienced it in many cars and it feels nice!One way I have tried of testing my theory was to let the engine revs drop before changing gear and then blipping the throttle before raising the clutch. The change didn't feel as sweet to me (it certainly didn't feel any better) but that may be because I'm looking for evidence to support my understanding. Perhaps others could try and let me know their findings.
When I was teaching U17 yr olds to start to rev match, I searched for a way to help with the timing. I found that if I said "clutch down, change gear, raise revs, engage clutch" it was quite hard to grasp. Each gear change took a long time and tended to be messy. When I suggested that they should change gear as usual but imagine that you needed to raise the revs to get the gear lever through the gate, so time a blip to coincide with pushing through the gate, it all worked much better! It's always fun to find a way to tell someone how to do something as well as what to do!
Bert
RobM77 said:
For sure, with a SDC the driven wheels still have to surge the gearbox internals up to speed when the clutch is re-engaged, but they carry such little intertia it's surely not a problem?
Rob, to be pedantic I think there is a slight error here. It is moving the gear lever into the new (lower) gear which, with help from the synchro, causes the layshaft to spin up to the higher speed required to match the road speed (neutral disconnects the layshaft from the driven wheels, the clutch disconnects the layshaft from the engine).This is why Martin suggests the revs should be raised before moving the lever into gear, so that you benefit from the suggested clutch drag (or whatever you call it) before putting the synchro to work.
RobM77 said:
Edited to say: I've just read the comments on sustained revs changes. I can only assume this is an internet phenomenum?! Since I started driving I've been instructed by a variety of road and track instructors, as well as privately studying driving technique over that period. Other than once before on this forum I have never heard of such a technique. 99.9999% of the world just blips the throttle. It's easy - why not?
Rob, in my experience sustained rev changes are far more common than blipped changes among the Roadcraft trained community. As I tried to explain a few weeks ago, I think sustained rev changes go better than blipped changes with the Roadcraft driving style where you make a block downchange only when you are ready to pick up the drive. A good illustration of the style I am talking about was linked - a vid of Reg RU Local showing his hairy legs in an MX5, if that helps you remember!I am sure you only find your style easiest because of the practice you have had with it. I have many times been driven by drivers who DDC using sustained revs so instinctively and accurately that you have to watch their feet to see what they are doing. John Lyon formerly of the High Performance Course is an example. He always used DDC both up and down the box.
Hi All
I fear I should have entitled the subject 'Why ddc is unnecessary in a modern car'. To clear up any ambiguity I would like to emphasise that I regard sustained revs and blipping as having the same benefit. I am not saying blipping is incorrect. From how I read it we are all agreed that revs should be matched, all I was explaining was why in detail.
Hope this helps
Best regards
Martin A
I fear I should have entitled the subject 'Why ddc is unnecessary in a modern car'. To clear up any ambiguity I would like to emphasise that I regard sustained revs and blipping as having the same benefit. I am not saying blipping is incorrect. From how I read it we are all agreed that revs should be matched, all I was explaining was why in detail.
Hope this helps
Best regards
Martin A
BertBert said:
RobM77 said:
BertBert may also like to see the note at the base of the page in that article regarding where to change gear in the braking zone. The instructor that taught you was clearly mistaken. Bear in mind that G Hill and A Senna both used block changing (though I realise this isn't possible in your Radical Bert). I've sat with plenty of instructors and chatted to them in the paddock and you see it a lot - people who want to be around racing cars and earn a bit of money, or are simply "know it alls" who want to impart advice to others. I know plenty of people like this. You get the same thing with diving according to a diving instructor friend of mine. However, there are good instructors out there if you look though Sadly they're often the quietly spoken ones, for obvious reasons.
I'm not going to disagree with Mr Hewland am I? However, I think it's wrong to consign a good driver and coach to the bin on this basis. To give more detail and get way off topic... Sadly they're often the quietly spoken ones, for obvious reasons.we were trying to achieve a specific aim in my driving. I was using Hewland's "method". However we found using data logging that my coach's cornering speeds were all a little higher than mine which is entirely where he got his better lap times than mine (in my car). We concluded that he always entered a corner with the car more settled and balanced than I did. And got better cornering speeds than me (specifically higher exit speeds). One of the differences on the corners with multiple down-changes was that he went down through the gears more slowly, more smoothly and starting earlier in the braking (and finishing earlier). I got to the end of the braking zone, banged down three gears (touring car stylee), turned in and took my foot off the brake. All in all, a bit of an unsettled mess. I moved the gear change back in the process, made it smoother, took it more slowly, rolled off the brake and got higher exit speeds in the process. All facilitated by a change to the down change timing!
Bert (driving deity)
Now I understand that I can see exactly what he was doing. Sorry for the confusion Interesting article though isn't it?
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