Avoiding Downchanging and Braking. Why?
Discussion
In another thread some time ago Julian64 asked why avoid "engine braking". Turns out that "engine braking" is useful. But IAM/RoSPA/Roadcraft technique [i]does[/i] state to avoid changing down under braking.
Here is my explanation of why. More than happy to explore the subject if anyone has further questions.
[quote=Don]
[quote=Julian64]
And why rule out engine braking, when it confers an advantage that you cannot duplicate with the foot brake?
[/quote]
Proper use of engine braking is useful and a technique that is usually covered on IAM courses. People often confuse engine braking with "going down the box" under braking. On an IAM course Associates are taught to avoid "going down the box" NOT the use of engine braking - for example, selecting second prior to a steep downhill to use engine braking to prevent the car from speeding up...
"Going down the box" during deceleration has a number of disadvantages (IN A ROAD CAR WITH MANUAL TRANSMISSION)
a) You spend more time with the clutch depressed than actually in gear...coasting.. no engine braking during that!
b) You don't have both hands on the steering wheel at the very point when you are using up the grip of the tyres to brake and you may need to do something about it.
c) Unless you can heel'n'toe to match engine revs to road speed every time you engage the next lower gear and let the clutch up engine revs have to rise to meet road speed and the only thing smoothing this out is the clutch - which will wear away - and costs more to replace than brake pads.
d) When the engine revs are raised to match road speed via the clutch there is a "clutch braking" effect on the drive wheels. Under *extreme* conditions and espcially in RWD cars this can upset the brake balance of the car and induce a rear wheel skid - race driver's heel and toe to avoid this - the IAM method which seperates deceleration and gear change does the same - but doesn't require such fancy footwork...
That's the answer. Believe it or not.[/quote]
Here is my explanation of why. More than happy to explore the subject if anyone has further questions.
[quote=Don]
[quote=Julian64]
And why rule out engine braking, when it confers an advantage that you cannot duplicate with the foot brake?
[/quote]
Proper use of engine braking is useful and a technique that is usually covered on IAM courses. People often confuse engine braking with "going down the box" under braking. On an IAM course Associates are taught to avoid "going down the box" NOT the use of engine braking - for example, selecting second prior to a steep downhill to use engine braking to prevent the car from speeding up...
"Going down the box" during deceleration has a number of disadvantages (IN A ROAD CAR WITH MANUAL TRANSMISSION)
a) You spend more time with the clutch depressed than actually in gear...coasting.. no engine braking during that!
b) You don't have both hands on the steering wheel at the very point when you are using up the grip of the tyres to brake and you may need to do something about it.
c) Unless you can heel'n'toe to match engine revs to road speed every time you engage the next lower gear and let the clutch up engine revs have to rise to meet road speed and the only thing smoothing this out is the clutch - which will wear away - and costs more to replace than brake pads.
d) When the engine revs are raised to match road speed via the clutch there is a "clutch braking" effect on the drive wheels. Under *extreme* conditions and espcially in RWD cars this can upset the brake balance of the car and induce a rear wheel skid - race driver's heel and toe to avoid this - the IAM method which seperates deceleration and gear change does the same - but doesn't require such fancy footwork...
That's the answer. Believe it or not.[/quote]
mindgam3 said:
Can someone give the textbook instructions for IAM's method?
Sure. The textbook you need is "Roadcraft". It will detail the "System Of Car Control"...worth a read.
Here's a summary of how the System is used to take a corner.
1) Observe hazard (corner) ahead. Plan how to deal with it. Plan on what gear will be appropriate (for your car, for that corner). Plan on where to brake (in a straight a line as possible). Plan where the subsequent gearchange will take place.
2) Observe all around. Is there anyone who could benefit from a signal of some sort? (Could be a junction, say). If so: make a signal.
3) Now adjust the speed of the car to be correct for the entry to the hazard (corner/junction/etc). Going on the brakes smoothly, braking hard, then coming off the brakes smoothly.
4) Off the brakes now. Dip the clutch and blip the accelerator to bring engine revs up to that dictated by the road speed and the gear you wish to select. Simultaeneously select the gear you require. Let the clutch up. If you got it right you will hear the engine revs blip and change but you WILL NOT FEEL THE GEAR CHANGE AS THE CLUTCH IS RELEASED. You can tell if you get it wrong as the car will either pull forward a bit (too much revs) or retard a bit (too few). In either case "tut tut" to oneself and promise to do it better next time!
5) Both hands now back on the wheel. Turn smoothly into the corner/junction/hazard. Steer through it. Because you are ALREADY in the right gear smoothly accelerate away from the hazard. Change up. Change up.
Benefits:
1) Keeps both hands on the wheel during braking - the time when you are using up grip and may need to deal with a slide.
2) Does not waste time with intermediate gears - and loss of drive during the changes. Avoids "coasting".
3) Ensures the correct gear for accelerating smartly away from the hazard - so many get this wrong! You can see 'em failing to get away from the junction frantically stomping in the accelerator as sod all happens because they bleedin' well insist on leaving the damn car in too high a gear. Planning to yse the right gear means BEING in the right gear which means a smart getaway!
4) Is kind to the clutch as road speed and engine revs are matched.
5) Does not destabilise car under hard braking.
As I said before race drivers achieve (5) with heel and toe. During "track" instruction I have been told to "block" downchange from 4th to 2nd too (for example) the only difference being an overlap between the downchange and the braking - but this means being able to brake and "blip" the throttle whilst the clutch is depressed at the same time. You use your right foot for both things - takes a bit of practice I can tell you! I can do it because I love all that racing technique business - but the System avoids the need for such fancy footwork and achieves the same thing.
Lots of road cars have pedal arrangements which utterly preclude heel and toe (My Porsche being an obvious exception) in which case the "System" is the best option anyway.
mindgam3 said:
But as i said before, you are not going to be in the correct gear at all times during the braking. Say you're coming along a dual carriageway in 5th and want to change down to a 2nd gear roundabout, what happens if you want to accelerate when you're say doing 25 mph in 5th in you're braking process, how can you possibly accelerate?
Why would you ever need to? If my plan says 5th to 2nd then I'll do that. The System dictates that if something changes during the execution of a driving plan you just go back the beginning and do the whole thing again. So, if something DID require me to take third, that's what I'd do - but I'd do it once I'd adjusted my speed to what was suitable for third gear.
This is something that comes with practice. Most people start the IAM with absolutely NO ability to work out what gear they need for any particular hazard. After a while they get good at deciding what gear will be necessary and seldom get it wrong. Once one is good at that then wasting time with unnecessary gear changes actually becomes something you actively don't want to do. In short - the System becomes natural. Actually more efficient than the alternative.
mindgam3 said:
Going down the box also gives you a greater amount of reassurance because as you are engine braking; to acheive the same amount of overall braking force as you would with not going down the box, you don't have to apply the pedal brake as hard.
Motor manufacturers go to a lot of bother to create braking systems with the perfect distribution of braking force to the front and back wheels. Sure - on racing systems this can be driver adjustable! Actually they mean "computer" adjustable, really...
So when you plant your foot on the brake the perfect distribution of braking force slows the car. Going down the box produces "clutch drag" braking which increases braking force on the drive wheels. On a RWD car this can seriously destabilise the perfect distribution...and cause spins in extreme circumstances.
There is little engine braking advantage over the simply using the braking system. Clutch drag braking can destabilise the vehicle. Given the benefit of one why bother with the downside of the other?
mindgam3 said:
Surely to make the best of the IAM method you have to brake seriously harder than usual? and on Britains roads with Britains drivers, this surely isn't a wise move?
Nope. I've never needed to brake much harder than usual. Engine braking simply doesn't contribute that much. What you do need to do is brake a little earlier than usual - to make time for the matched revs downshift after the braking is completed and before the hazard.
Sounds difficult and unweildy, I know. But trust me - its not once you've practiced it. A bit like playing the guitar. At first its all thumbs and after some practice you've got Eddie Van Halen.
There are a host of sophisticated driving techniques that a tiny proportion of the driving population can make use of.
On here - we LOVE driving. Every aspect of it.
We love all that "what to do in RWD, rear engined car mid-corner" vs "what to do in a FWD, mid-engined car" vs vs vs.
I heel and toe for example - both on track and when I can use it to advantage whilst pressing on. My car is set up for it and I practice enough that I pretty much get it right most times.
I also consider that the truly "Advanced" driver should have a range of steering techniques at his disposal: Pull-push, Rotational, Fixed Position and so on.
The IAM concentrates on getting a core set of "Advanced" skills up to muster. Car control (whilst important) is also viewed as secondary to creating a thinking, observant driver. There are going to be techniques it does not cover. An excellent (in fact, a competition) driver, such as yourself, is going to have additional techniques at your disposal than someone who has passed the "basic" IAM Advanced Test.
I have undertaken loads of additional training in track and other driving techniques - some of which conflicts with Roadcraft - much of which does not.
The thing that IAM/RoSPA/Roadcraft does at its very best is develop a thinking road driver. Developing and enhancing anticipation and hazard identification and avoidance.
If, as an expert driver, you take away, at the end of the course, something of use - you've had your money's worth and can decide, from a firm standpoint of knowledge, what suits you and what doesn't - and build that which does into your driving style.
Many, many people who come on IAM/Rospa are not starting from your position though, Peter. Roadcraft is both an excellent way of managing the driving the process and also a thorough grounding in car control. Clearly it is quite possible to go well beyond what is covered in it in those terms.
Don't let the car control bits put you off. You'd have no trouble "doing them for the test" and ignoring what you really didn't find worked for you after. Get the other benefits.
On here - we LOVE driving. Every aspect of it.
We love all that "what to do in RWD, rear engined car mid-corner" vs "what to do in a FWD, mid-engined car" vs vs vs.
I heel and toe for example - both on track and when I can use it to advantage whilst pressing on. My car is set up for it and I practice enough that I pretty much get it right most times.
I also consider that the truly "Advanced" driver should have a range of steering techniques at his disposal: Pull-push, Rotational, Fixed Position and so on.
The IAM concentrates on getting a core set of "Advanced" skills up to muster. Car control (whilst important) is also viewed as secondary to creating a thinking, observant driver. There are going to be techniques it does not cover. An excellent (in fact, a competition) driver, such as yourself, is going to have additional techniques at your disposal than someone who has passed the "basic" IAM Advanced Test.
I have undertaken loads of additional training in track and other driving techniques - some of which conflicts with Roadcraft - much of which does not.
The thing that IAM/RoSPA/Roadcraft does at its very best is develop a thinking road driver. Developing and enhancing anticipation and hazard identification and avoidance.
If, as an expert driver, you take away, at the end of the course, something of use - you've had your money's worth and can decide, from a firm standpoint of knowledge, what suits you and what doesn't - and build that which does into your driving style.
Many, many people who come on IAM/Rospa are not starting from your position though, Peter. Roadcraft is both an excellent way of managing the driving the process and also a thorough grounding in car control. Clearly it is quite possible to go well beyond what is covered in it in those terms.
Don't let the car control bits put you off. You'd have no trouble "doing them for the test" and ignoring what you really didn't find worked for you after. Get the other benefits.
GreenV8S said:
As far as I'm concerned shuffle steering is only good for getting my arms in the right position to avoid running out of lock at the apex.
That is a useful on road benefit where corners can be tight: you never run out of the ability to add lock.
There is always the old "airbag" reason too - if one has one.
There again. I would never consider using push-pull on track or to control a slide...as you say. Generally when adding opposite lock I can keep at least one hand in a fixed position on the wheel - good for knowing where straight ahead is.
Personally I use push-pull whilst doing ordinary road driving. In manouvers I'm quite happy to use rotational steering to get plenty of lock on and off quickly (Roadcraft even talks about this...its wrong to think it doesn't!) - but I don't need it when travelling along. In a slide or on track I'd use as Fixed position steering. If I run out of opposite lock doing that I'd go to rotational but, Blimey!, I'd be in deep s**t by then!
mindgam3 said:
People forget that a tyre has a finite amount of grip. It uses that grip to help you to accelerate, to stop and to steer. And what holds those tyres down on the road to give them all that grip? Yes, weight! If you are braking, then the weight of the car is biased towards the front wheels so the rear wheels carry less weight, ergo less grip. Chuck in a gearchange (especially a cack-handed one) and you stand a good chance of breaking whatever grip they have.
You want a greater load on the front wheels as they are what make you turn in. More load on the front wheels and the less likely you are to understeer. You are highly unlikely to lose the back end from turning in too quickly, if you do, you are going far to fast for the corner. The only thing that will break the rear ends grip is too much throttle, which is a completely seperate issue.
A car is much more stable in a corner if the front wheels have just been loaded from braking.
I've tried (and read) about it numerous times. Try going into a corner without loading the front tyres and then with and you (should) notice a considerable difference in the way the car corners.
By having the gearchange after your braking, the front tyres are not loaded and you are far more likely to understeer.
Ahhh yes. To "trailbrake" or not to "trailbrake". To actually keep the weight of the car forward onto the front wheels requires you to still be braking quite hard during turn-in. Feck this up and it will be rather nasty. I was experimenting with this at Brands last week and (the wise) clubsport said to me: "Trailbraking is your friend until it isn't and then it goes wrong very, very quickly."
On balance I wouldn't use it. Why? Well - you might get weight over the front of the car, but you lose it at the back. So the car turns-in...but now the back-end has to follow and it's "light". Sudden oversteer. In general understeer is a lot easier to cope with than oversteer...all though that can be a hoot in the right place and at the right time - NOT on the road!
Again: on track if you come off the brakes too sharply you get weight transfer to the back of the car. If you turn-in during this you will certainly get understeer. The answer is to come off 'em smoothly and then turn in.
How I've been taught to corner (on track) is to get smoothly off the brakes, get the car flat and then turn in using all the grip of the car for steering rather than for steering and braking at the same time. If it understeers you deal with that then. I've had this from some very fast guys and I believe them.
Now. Having said all this. If you are experiencing understeer during road driving you are trying waaaay too hard and it will all end in tears soon. The track is where to try edge of grip techniques.
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