It depends on your speed. At "legal" speeds, just declutch and brake for an emergency stop. At very high speeds, leaving the car in gear will help initially if you don't have enough braking force to fully utilize traction. At what speed that occurs with the S2K, I don't know.

UL

 

[QUOTE]Originally posted by ultimate lurker
[B]if you don't have enough braking force to fully utilize traction.

 

On a bike you want to use the rear brake a bit to stabilize the bike when breaking as well as get that whatever small extra percentage of breaking power that the rear actually contributes. If this is relevant for using the engine to slow down a car (with ABS, multi-circuit brake systems connecting the front and rear etc) i have no idea.

 

There is a theoretical and a practical question here.

Theoretically, it depends on the engine speed, but in most cases in an emergency you will come to a marginally quicker stop with the car in neutral. This is because with the car in gear the brakes have to stop BOTH the rotation of the wheels AND the inertial rotation of the engine. (Imagine revving the engine to 6000 RPM or so with the hood open, then reaching in, grabbing the flywheel and STOPPING it from turning--that's how much additional work the brakes have to do.)

With the car in neutral, the brakes only have to stop the wheels.

Actually the question is asking something slightly different. If you're going 150 with the engine at idle and you let out the clutch with the car in first gear AS you are braking, the engine's internal friction will add some braking and you will stop more quickly. This is a one time deal as you will BREAK your car the first time you try it...

Bottom line, don't think about it and, as BassMan says, "Stomp the brake AND clutch!"


[Edited by LATEOTT on 02-20-2001 at 02:20 PM]

 

What happens when you lift off the throttle? You DECELERATE!!! This is mainly because of internal friction within the engine. This will aid in braking (but only a very small amount). You can downshift and use the engine to aid in showing (don't let the engine rev drop with the clutch pedel down, then let the clutch up, that is BAD). Will it get you stopped faster? I wouldn't count on it. I use it to aid in slowing in every day driving, it requires less pedal force on the brakes to come to a stop. When I drive "spiritedly", and need to slow down in a hurry for a turn, I use ALL BRAKE PEDAL. I downshift, but so I have the revs up during the turn exit.

 

Everybody please remember, the limiting factor in how quickly you can brake is the limit of friction between your tires and the road surface. You cannot possibly stop any faster than having all 4 wheels at impending lock, no matter what method you use (engine, brakes, will power) to get them there.

That being said, and particularly with anti-lock brakes, the absolute fastest reliable way to make an emergency stop is to put in the clutch and stomp on the brakes (LATEOTT had a reasonable point that at high speed/rmp, you are having to slow down the engine/tranny's rotational inertia as well, though I think this is probably negligable).

Clark

 

Sounds good in theory but I dunno Clark. In my experience a number of my emergency stops have either been on wet roads, during turns or situations where I need to quickly accelerate again after braking. In all of these instances I find it is always better to be in gear (and change down gears) when braking. Staying in gear provides a level of stability) and just plain stops the car getting unbalanced and losing the back end. This is why I never feel comfortable driving an automatic to its limits, I feel a vehicle should always be subject to either engine power or braking to give it that surefootedness that it is otherwise missing.

Maybe some of this comes from being a long time motorcycle rider. A number of other posters have commented on this - once you have ridden a bike under extreme conditions you become acutely aware of just how tyres can let go unexpectedly and you become painfully aware of the consequences.

 

Is it crucial to always push in the clutch at all sudden stops? What if you're not downshifting? Is it that much of a load on the engine if you are breaking and do not push in the clutch (or downshift)?

 

...In my experience a number of my emergency stops have either been on wet roads, during turns or situations where I need to quickly accelerate again after braking. In all of these instances I find it is always better to be in gear (and change down gears) when braking...[/B][/QUOTE]

I'm another old biker, and I agree. Staying in gear doesn't stop you any faster. However, it makes the transition back to acceleration much smoother than if you had to press the clutch, find a gear, match revs, and then get on the gas.

But IMO this is important only for cornering, where you're going to accelerate out. If you're just stopping for a light it doesn't matter. I usually just coast up in neutral. For straight-line emergency stops, on the other hand, I just nail the brake and don't give the clutch a thought. I'll worry about that after it's clear that I'm not going to hit anything.

 

[QUOTE][B]Originally posted by Tox
But IMO this is important only for cornering, where you're going to accelerate out.