Downshifting whilst Braking
Discussion
probablychrisgilbert said:
You will also be aware that there is a NATURAL separation of brakes and gears running throughout the principles of Roadcraft and police driver training on the basis ' brakes are to slow and gears are to go'
So there we go again, and I know he doesn't mean it. But it's NOT on the basis of a purile couplet, or actually as he goes on to say, I suspect it is the only rationale!He then goes on to explain where it came from - an age long, long ago where cable brakes were very unequal and needed both hands on the wheel to maintain control of the car.
Further he goes on to explain that a BGOL is perfectly safe if well executed and planned.
Dunno who he is, but on what basis does that support the dogged adherence to not overlapping?
Bert
BertBert said:
probablychrisgilbert said:
You will also be aware that there is a NATURAL separation of brakes and gears running throughout the principles of Roadcraft and police driver training on the basis ' brakes are to slow and gears are to go'
So there we go again, and I know he doesn't mean it. But it's NOT on the basis of a purile couplet, or actually as he goes on to say, I suspect it is the only rationale!He then goes on to explain where it came from - an age long, long ago where cable brakes were very unequal and needed both hands on the wheel to maintain control of the car.
Further he goes on to explain that a BGOL is perfectly safe if well executed and planned.
Dunno who he is, but on what basis does that support the dogged adherence to not overlapping?
Bert
It's benefit in use is increasing safety margins for those who aren't highly skilled.
What Chris Gilbert refers to as overlapping most of us would perhaps call partial overlap - when the clutch is pressed shortly before releasing the brake, but the right foot is back on the accelerator to match engine revs to road speed before raising the clutch. This is quite different from full overlap as recommended by Chilli, which requires use of heel and toe if you are to match engine revs and so avoid clutch wear and poorly controlled deceleration of the driven wheels perhaps leading to lock up.
Chilli, would you explain why you prefer to go down through the box under braking, rather than block changing to the gear required for acceleration towards the end of the braking phase? Do you say that this helps you to slow faster, or is it down to reducing the load on the brakes, and making it less likely that you will make a mistake on the downchange?
BTW, Chris Gilbert is a former Police Sergeant at Metropolitan Police Driving School Hendon, who appears in the Roadcraft DVD and since retirement has recently produced his own driving DVD.
Chilli, would you explain why you prefer to go down through the box under braking, rather than block changing to the gear required for acceleration towards the end of the braking phase? Do you say that this helps you to slow faster, or is it down to reducing the load on the brakes, and making it less likely that you will make a mistake on the downchange?
BTW, Chris Gilbert is a former Police Sergeant at Metropolitan Police Driving School Hendon, who appears in the Roadcraft DVD and since retirement has recently produced his own driving DVD.
waremark said:
Chilli, would you explain why you prefer to go down through the box under braking, rather than block changing to the gear required for acceleration towards the end of the braking phase? Do you say that this helps you to slow faster, or is it down to reducing the load on the brakes, and making it less likely that you will make a mistake on the downchange?
I am not Chilli but...Heeling and toeing does not preclude block shifting...though it does "feel" nice to go down through the gears sometimes.
. I regularly H&T from 5th to 3rd, or even 5-2, (though I'll generally do 5-3-2 because it seems a bit easier to get a smooth change that way.)
I use H&T just because it is smoother and you don't get that "dead time" after braking, when you're coasting whilst changing gear which you do if you don't overlap.
RT106 said:
Can I ask how many of you have ever lost control under braking or because of destabilisation resulting from a bodged gear change? On the road, naturally.
Never - I'm careful to avoid it. I see it on every TVR track day I've ever been to though, and I guess that it accounts for a fair proportion of single vehicle TVR accidents. To get a true indication of the significance of this type of mistake you should also ask how many people have suffered from loss of control or destabilisation from other causes. I suspect you'll find that the number is extremely low there, too.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
BertBert said:
Gromit37 said:
Gromit's theory of ralativity at work here: I've read of people wearing clutches out in a 10-15K miles, whereas clutches should easily last 80K plus. I'd call that PDQ. Relatively speaking. 
Yes I agree that it's all relative. Interested to see how you showed that the early failures were down to "engine braking" though. How big was your sample, or did you post-mortem the faileed clutches to determine mode of failure, interview the drivers to classify their driving style and correlate the two?Sorry, couldn't resist
Bert
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.
I agree totally!Surely a poor downshift is just as likely to happen when not overlapping as it is when overlapping?
Changing down at poorly matched revs only suggests that the driver is lacking very basic driving skills.
Also, may I add that I think that it is complete nonsense that you need to match revs with heal and toe if overlapping. If you're in 4th gear at 55 mph and braking for a 25 mph corner, then you brake until the road speed is in the 2nd gear comfort zone (say 35 mph in my car, although it can get to 55+ in 2nd), let the clutch out, continue braking to 25mph and off you go.
No heal and toe required, no sudden engine braking, no mechanical stress...smooth as a Road Captain in his Rover 25.
Rather ironically I don't heel-and-toe in my rally car because it's a 106 with tiny, tiny pedals and I'm 6'7" and have size 13 feet. I overlap downchanges and braking because that's the only way I can drive the car. Put "Team Gimp EMCOS" into YouTube and watch the skilfully editted on-board video. From memory (because I'm at work and can't access it here) about a minute in there's a big moment under braking. Flat in fourth (~95ish), one hand on the wheel, hard on the brakes (with masses of rear brake bias), down a ramp, into a hairpin left. I'm sh*t and have poor car control (which you'll realise if you watch the remaining ~8 minutes), and yet that moment - which is hugely in excess of 99.999999% of situations you'll find yourself in on the road - isn't a problem.
The topic's about road driving. Over-lapping gearchanges is a ridiculous thing to worry about.
The topic's about road driving. Over-lapping gearchanges is a ridiculous thing to worry about.
Edited by RT106 on Wednesday 20th February 17:23
Get Karter said:
Also, may I add that I think that it is complete nonsense that you need to match revs with heal and toe if overlapping. If you're in 4th gear at 55 mph and braking for a 25 mph corner, then you brake until the road speed is in the 2nd gear comfort zone (say 35 mph in my car, although it can get to 55+ in 2nd), let the clutch out, continue braking to 25mph and off you go.
It actually hurts even to read that.Do I really understand you correctly? You really let the clutch and the synchros do all the work, at speeds over a crawl, with no attempt to bring the revs up using the throttle?
GetKarter said:
Also, may I add that I think that it is complete nonsense that you need to match revs with heal and toe if overlapping. If you're in 4th gear at 55 mph and braking for a 25 mph corner, then you brake until the road speed is in the 2nd gear comfort zone (say 35 mph in my car, although it can get to 55+ in 2nd), let the clutch out, continue braking to 25mph and off you go.
No heal and toe required, no sudden engine braking, no mechanical stress...smooth as a Road Captain in his Rover 25.
So, as you pick up the clutch in second the revs will have fallen to idle. At 25mph revs in second will be anything from 2,500 to 3,500 depending on gearing and the car's rev range.No heal and toe required, no sudden engine braking, no mechanical stress...smooth as a Road Captain in his Rover 25.
In any car, but particularly a powerful car, you will put a torque through the drivetrain as the engine revs have to rise to the 2,500 to 3,500 level. Definitively not as smooth as matching revs. And definitively not as sympathetic to the clutch - your way there is slip, matching revs there is no slip. Clutch longevity is entirely a function of how much slip you make it endure each and every drive. Just read Flemke's posts on his F1; or I could refer to my friend, who is a master at gear changing, with his MkIII Golf VR6 on its original clutch after 225,000 miles!
And, as I said above, BGOL is a red herring. If you BGOL you must H&T to match revs. If you avoid BGOL, no need to H&T. The important thing is to match revs if you want to be sympathetic. And in a mega powerful car it might just avoid an accident (StressedDave's Lambo example was a shift 3rd to 2nd at relatively slow speed IIRC).
Kind regards
Steve
Are there any police riders who could comment?
On the bike, I don't use the brakes as much, because downchanging through the intermediate gears can be enough to slow. (It's safer to avoid block changing on two wheels.)
Yet in similar road circumstances I'd brake then block change down whilst driving the car.
Have any other advanced drivers and riders noticed this different approach between two and four wheels?
When I was taking my advanced bike course, I found my car driving was affected. (E.g. I was taking intermediate gears on the approach to a hazard, instead of braking then block changing.) Has anyone else had similar experience?
Come to mention it, has anyone done their blue badge (i.e. an advanced commercial/goods vehicle)? Any interesting differences?
On the bike, I don't use the brakes as much, because downchanging through the intermediate gears can be enough to slow. (It's safer to avoid block changing on two wheels.)
Yet in similar road circumstances I'd brake then block change down whilst driving the car.
Have any other advanced drivers and riders noticed this different approach between two and four wheels?
When I was taking my advanced bike course, I found my car driving was affected. (E.g. I was taking intermediate gears on the approach to a hazard, instead of braking then block changing.) Has anyone else had similar experience?
Come to mention it, has anyone done their blue badge (i.e. an advanced commercial/goods vehicle)? Any interesting differences?
stefan1 said:
So, as you pick up the clutch in second the revs will have fallen to idle.
No, surely you can change into 2nd when the revs are matched. Just don't wait for them to fall to idle. Simple.I never get road speed driving my engine speed through this method. It's always smooth and unnoticeable.
Maybe you take too long making your actual gear change.
That is why you will have experienced the revs falling to idle.
It should be a quick clutch in, block change, clutch out, at the correct road speed so that you catch the falling revs at the correct road speed for the gear.
Edited by Get Karter on Thursday 21st February 08:54
SVS said:
Are there any police riders who could comment?
On the bike, I don't use the brakes as much, because downchanging through the intermediate gears can be enough to slow. (It's safer to avoid block changing on two wheels.)
Yet in similar road circumstances I'd brake then block change down whilst driving the car.
Have any other advanced drivers and riders noticed this different approach between two and four wheels?
When I was taking my advanced bike course, I found my car driving was affected. (E.g. I was taking intermediate gears on the approach to a hazard, instead of braking then block changing.) Has anyone else had similar experience?
Come to mention it, has anyone done their blue badge (i.e. an advanced commercial/goods vehicle)? Any interesting differences?
The difference with a bike is that you have a sequential gearbox and will have to engage a gear even if you don't use it. I have switched to block changing in the car on the road but wouldn't do it on a bike where it feels far safer to blip and downchange all in one smooth movement. I find that if you have good clutch control and mechanical sympathy it's quite common to end up not using the back brake at all.On the bike, I don't use the brakes as much, because downchanging through the intermediate gears can be enough to slow. (It's safer to avoid block changing on two wheels.)
Yet in similar road circumstances I'd brake then block change down whilst driving the car.
Have any other advanced drivers and riders noticed this different approach between two and four wheels?
When I was taking my advanced bike course, I found my car driving was affected. (E.g. I was taking intermediate gears on the approach to a hazard, instead of braking then block changing.) Has anyone else had similar experience?
Come to mention it, has anyone done their blue badge (i.e. an advanced commercial/goods vehicle)? Any interesting differences?
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