Engine Braking in Emergency Situations

[Prodigal Son]

I don't see how the hell using engine braking whilst braking will not improve braking distance. It has to.

I doesn't have to. The limit of braking is the limit of adhesion between the tires and the road. If the brakes alone cannot apply enough force to the wheels to bring them to that limit, then supplementary braking from another source may improve braking. But if the brakes can bring the wheels to that limit -- that is, if they can lock the wheels -- then there is not anything more than any other source of braking can add to that.

In almost any emergency situation, however, steering is more important than stopping. Unless the emergency is that someone has built a concave brick wall across the highway such that your car is an equal distance from that wall in all directions, your chances of avoiding a collisions depend more on steering than they do on braking. Taking your hands off the wheel to change down to possible marginally increase braking force, at the expense of giving up 50% of your steering control, is just a bad bargain. So is paying attention to anything other than steering.

Steering is more important to accident avoidance than braking. That is why ABS represents a good trade-off. Even in situations where it increases braking distance, it maintains steering control, allowing you to steer around the obstacle. (This is why I say that part of defensive driving is to be constantly planning your escape route. You are more likely to steer away from an obstacle if you have maintained 360 awareness and planned where you would steer if an emergency happened.)

[jomotopia]

I am more impressed by someone who can drive any kind of road. I have seen people who have driven all their lives in a city become completely unglued trying to drive a rural road with a bit of patchy snow cover on it.

haha, my girlfriend's mom has done all or most of her driving in Miami. it's totally flat there. she's afraid to drive in Atlanta b/c there are hills.

[JackBauer]

Well, if you have no ABS, engine braking during hard braking will do you no use, thats implied. However, in an ABS equipped vehicle, Engine braking WILL stop you faster, changing gears is a fraction of a second, you can steer with one hand while you do this. It's not even an argument, i challenge you to do an expirament.

[Shaolin]

I am more impressed by someone who can drive any kind of road. I have seen people who have driven all their lives in a city become completely unglued trying to drive a rural road with a bit of patchy snow cover on it.

haha, my girlfriend's mom has done all or most of her driving in Miami. it's totally flat there. she's afraid to drive in Atlanta b/c there are hills.

Hahah oh she'd love it in NewZealand

[SteveUK]

if your doing 40 in 4th and all of a sudden traffic appears infront of you, what do you do? brake in 4th? well according to the law, you brake as hard you can (ABS) and at the alst possible moment, disengage the clutch. how much can you slow down on 4th gear before you start to sputter? if a driver can keep a clear head and depress the clutch pedal at the last moment, that same driver can surely quickly drob it in second while flooring the brake.

No they can't.

In order to pass your test here you have to be able to do an emergency stop both correctly and safely. This means not stalling. If the person driving can't do this, they are not safe and do not pass.

If you are at an acceptable standard, you are able to dip the clutch at the last minute. If you can't do it you are still, in my eyes and driving examiners eyes, below the standard to be able to drive on your own.

I am now going to turn into an old man.

Youngsters think they know better. They get behind the wheel and think they are invincible. They're not. Some things you learn and can adapt eg hill starts. An emergency stop is not one of those things. This skill, is the most important one you can have. In fact, most of your first few driving lessons are focused on this.

Luckily I live here, where people for this follow the rules. In work I am considered a youngster and I know what it is like to be patronised. This though, is not that. This is me saying I do know better than you. I am a better driver than you. You have lots to learn about driving, I still have things to learn, but a damn sight less than you.

(Another busy night shift preceeded this post folks. )

[Shaolin]

Well, if you have no ABS, engine braking during hard braking will do you no use, thats implied. However, in an ABS equipped vehicle, Engine braking WILL stop you faster, changing gears is a fraction of a second, you can steer with one hand while you do this. It's not even an argument, i challenge you to do an expirament.

After driving manual for many years it becomes second nature to dip the clutch when the engine is about to stall, even in an emergency situation, a driver of decent experience will be able to do that.

Shifting down gears in order to attempt to improve stopping distance in an emergency is so unnatural its not funny.

When something happens that you are not expecting you are lucky if you perform the most basic of tasks to avoid a disaster.

Keep it simple, stupid!
It's theoretical advantage is not worth all the other cr4p that would go with it, imo.

Youngsters think they know better. They get behind the wheel and think they are invincible. They're not. Some things you learn and can adapt eg hill starts. An emergency stop is not one of those things. This skill, is the most important one you can have. In fact, most of your first few driving lessons are focused on this.

Luckily I live here, where people for this follow the rules. In work I am considered a youngster and I know what it is like to be patronised. This though, is not that. This is me saying I do know better than you. I am a better driver than you. You have lots to learn about driving, I still have things to learn, but a damn sight less than you.

Yeah, hes definitely a cop.

[Hatchman]

Sorry for quoting you out of context, but just to cite one example: applying a bit of power to correct a skid. I'd put this skill down to experience and maybe even instinct. But I'm guessing you wouldn't put this in the advanced skill category.

Well, I hate to feed you your own porridge but I have never found it necessary to use that technique in all my years of winter driving. I can control a mild skid without resort to this technique, which I think has too many changes of going wrong.

What could go wrong? It'd be worse, I think, if the car continued to go out of control. Let me use an example that often comes to mind when I am considering applying power to correct a skid. I'm thinking of a road with deep snow (I can't use a dry road as my example because I can't remember the last time I skidded on a dry road. I also can't use a rainy road because I adjust my speed well enough in rain to avoid skidding to a stop or losing grip in a turn.) Ok, so the raod is in deep snow. You're travelling at what you judge to be a safe speed for a slow 90 degree right turn coming up. There is no stop sign or light, and you are free to just turn. But as you're turning, the deep snow has caused the car to skid to the left even though you've stayed off the brake and just "coasted" around the turn. So, during the skid, what can you do to get the car going straight down the road again? I say get on the gas. The drive wheels will pull the car forward. What could go wrong? And please don't say this hasn't happened to you LOL.

In any case, skid control skills are really not the skills you want to rely on: skid avoidance techniques are what you really want to focus on. I haven't had to do significant skid correction in years because I use good winter tires, moderate my speed, and pay attention to surface and traffic conditions. I don't control skids; I avoid them.

All excellent points. Winter tires make such a huge difference. You want to stay out of skid situations on all road surfaces. I had in mind sort of sideways slides in snow, not really braking-induced skids in a straight line. I'm saying that in deeper snow or icy roads you have to know what to do in case you do start to skid even though you've taken precautions. If it's necessary to stop the car, going to neutral and concentrating on steering and safe stopping are what you should do. But if it's necessary to resume in a straight line or after a turn, a slide has to be corrected by use of the gas pedal. I mean, unless you stop completely and then relaunch, how else can you right the car during a skid? Nothing else comes to mind at the moment.

I have not had to do a full emergency stop in years. I have not had to correct a major skid in years. Basic defensive driving techniques will virtually eliminate the need to perform either maneuver. While some situations genuinely cannot be foreseen they should be very rare if you drive defensively.

I definitely agree. I was referring to minor skids, or maybe slides is better word. I think a good driver knows how to stay out of distress and stay in control of the car, no matter what the situation.

* Pay attention to the road surface. Learn to recognize black ice. Remember that bridges freeze before the road. Remember that intersections tend to be icier than the surrounding streets. Know how to find the parts of a snow covered road where the most traction exists.

* Anticipate places where children, pedestrians, or bikes may suddenly dart out into the road. Slow down and be ready to stop.

* Maintain 360 awareness at all times. Never be surprised by drivers behind or beside you. If you see a speeding driver coming up behind you, don't make any sudden moves that they may not anticipate.

* Be considerate of others. Don't block lanes or intersections. Let faster driver get by, and don't bully or crowd slower drivers. Don't stand on your rights. Don't cut people off. Never allow yourself to get angry or rushed.

* Plan your escape. Always have a plan for what you would do if an emergency arose. Update it minute by minute as conditions change. It is too late to plan an escape after an emergency has already arisen.

In 99% of cases, if you have to make an emergency stop or control a skid it is because you have already made a serious driving error. You would be better served to improve your defensive driving skills to avoid getting into such situations, rather than trying to learn advanced car control skills to get you out of them.

Nice!

[JackBauer]

Steve, I sure hope you can back your talk with your performance on the track.
Downshifting to improve braking distance becomes second nature, even in an emergency. You always downshift to aid your braking at the track, not only so you exit in the proper gear, but to slow you down faster. I'm not saying the typical driver should be able to H&T DS, well really, if you H&T you'll probably end up hitting the car, but you should drop it into a pretty low gear, with a long range (2nd) and slam the brakes as you quickly dump the clutch, while controlling the vehicle.

And seriously, your not a cop are you?

[SteveUK]

No, I am not a police officer, however, we do train with the police. I am a Specialist Nurse in Intensive Care medicine and Emergency Care Practitioner. This means I work both in a hospital and with the NHS Ambulance Trust taking ITU to the patient in the field.

I can back up what I say on a track. I have a racing licence (taken in a manual) to go along with my standard driving licence( taken in a manual), my advanced driving licence (taken in a manual) and my persiut licence (guess what, taken in a manual too) plus the 12 years experince of driving manuals at this level.

Changing down whilst braking to go into a corner is completely different to performing a road emergency stop. If you could do either properly you would know this.

One thing though as a Royal Naval Reserve Officer, I do have the same powers of a Special Constable whilst in the Untied Kingdom and the Colonies. I am not a Special, but I am afforded the same rights and responsabilities as one but across the whole UK and colonies, not just in the limited areas mentioned in the article below. So, watch out.

http://en.wikipedia.org/wiki/Special_constable

[JackBauer]

(yaawn) yadi yadi yada, next time your in the states, we'll have a little high speed get together at a twisty road someplace I also never said braking for a crner is the same as braking for an emergency, i don't know what part of this you don't understand, but i am saying that you will stop faster when you use engine braking together with caliper to rotor braking. but in all seriousness, it's always the people with the 'i'm better than you' additude i end up smoking. I guess it's just something i can do that some others can't (braking while using compression at the same time) I am a very quick thinker, infact, after racing courses, defensive driving courses, etc. I have never ran into a situation where i hit something because i couldn't think clearly. How old are you? i think coordination starts to drop after 26 right?

[Prodigal Son]

i am saying that you will stop faster when you use engine braking together with caliper to rotor braking.

We may be talking at cross purposes here. The issue of which braking technique produces superior results could, as you suggest, be settled on a track, assuming two equally prepared cars and equally skilled drivers (neither of whom would be me).

But the issue of what you should do in an emergency is not as cut and dried as that. The issue of what you should recommend to another driver as correct emergency procedure is even less so. The point is, the best theoretical behavior is not necessarilly the one that produces the best real world results. The issue isn't what whould Michael Schumacher do in an emergency; the issue is what should John Q. Public do in an emergency. And for John Q. Public, as basic maneuver executed correctly beats an advance maneuver that is botched.

Stomp and steer may not be the theoretical best maneuver; but it is simple and reliable. I differ with SteveUK on one point. He says put the clutch down at the last minute; I say put it down immediately. His approach may be theoretically superior (though I do not know on what grounds), but my reasoning is this:

1. If I wait too long to put down the clutch the engine may stall and then I will loose power assist on steering and braking, as well as ABS.

2. The worst mistake you can make in an emergency, and one of the most common, is to forget to steer. Since you tend to steer towards what you look at, you have to actually look away from the thing you are trying to avoid so as to steer away from it. That is an act of will that will require every synapse in the brain focussed on that one task. I don't want to divide those precious moments of attention trying to time the clutch. In the split seconds that make the difference in an emergency, most mortals will have time to process one thought at best. My thought will (I hope) be: STEER!

SteveUK can probably stop quicker in an emergency than I can. You probably can too. I really don't care which of you can do it faster. But my emergency procedure -- which I hope and intend never to use again in my life -- is to stomp on the brake and clutch as hard as I can and try to remember to steer. And I will recommend to other people to do the same. No one with the skill and training to do more than that reliably under extreme stress is going to be asking for my advice anyway.

The simple maneuver you can do correctly beats the sophisticated maneuver that you screw up. In an emergency, keep it simple. Stomp and steer. But practice defensive driving and you will rarely, if ever, have to perform an emergency maneuver of any kind. Emergencies that never happen have the best survival rate.

[JackBauer]

Steves whole purpose of clutching in at the last point is to take advantage of that last bit of compression, and to maintain traction as long as possible. Am i right steve? in that case, you (to some extent) agree with me.

[Prodigal Son]

BTW, I clutched in AFTER I had stopped moving completely, and saved the engine from stalling. So, the engine won't stall instantly... just a FYI. I'd say I probably had 2-3 seconds more before the engine would've given out (I was in second).

I'm inclined to believe that either your memory is defective, or your clutch. If the car is stopped and the clutch is engaged (and not slipping) then the engine is not turning over.

[Prodigal Son]

Steves whole purpose of clutching in at the last point is to take advantage of that last bit of compression, and to maintain traction as long as possible. Am i right steve? in that case, you (to some extent) agree with me.

You may be right. I would rather steer around the obstacle going 21 km/h than plow into it doing 20 km/h. I therefore choose a strategy that I believe will optimize my chance or steering over one that might slightly optimize my braking distance. If I though I could further optimize the braking without compromising the steering, I would try to do that. But I estimate my chances of optimizing two elements of a maneuver that I perform once every decade or so to be very low.

I'll agree with Paul to this extent though. The clutch is less important than the brake or the steering wheel. Even if you left clutch too late, the drama would probably be over by the time you stalled.

I am a simple man, but I have learned this. 98% of the time, simplicity kicks perfection's ass.

[screenname]

If you stall during an emergency braking maneuver and you're still moving, the car will start right back up if you dump the clutch.

Paul, I think it's the tC's electronic throttle that saved the engine. It's happened to me a few times too - I could've sworn I stalled my car, but when I put the clutch in the engine came back on.