# Brake faster in drive or neutral?



## Phallic Idolatry (Jul 25, 2004)

I dont know that much about cars, other than i love my altima, and that i keep it squeaky clean. My question is:

Do i come to a stop faster if i am in neutral or if i dont even bother shifting?

My theory is, if Im in drive, then there is something pushing the car forward, so if i shift into neutral, nothing is pushing it, therefore i stop faster. But im starting to have some doubts.

help!


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## James (Apr 29, 2002)

You stop faster in drive because even on the automatics there is a level of engine braking built into the automatic. Which helps your brakes slow you down.


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## bahearn (Jul 15, 2002)

*"I disagree, Alex"*

Car & Driver found shorter braking in neutral.

With an auto trans, you don't have much choice in the matter. With a manual, you'll have to train yourself so that hitting the clutch is automatic and fast. If you have to think about it, you'll take longer to brake than whatever is "hard-wired" from practice.


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## James (Apr 29, 2002)

got a link?

for my car, my brakes are so much better if I leave it in gear coming to a stop.


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## bahearn (Jul 15, 2002)

C&D mentioned the braking phenomenom during their supercar shoot-out a year or two ago. They recorded significantly better braking from 150 mph in neutral since modern brakes and tires can decelerate the car quicker than the engine can spool down due to rotational inertia.


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## Jasper (Apr 2, 2004)

bahearn said:


> C&D mentioned the braking phenomenom during their supercar shoot-out a year or two ago. They recorded significantly better braking from 150 mph in neutral since modern brakes and tires can decelerate the car quicker than the engine can spool down due to rotational inertia.


heh, from 150mph, noshit the engine cant slow the car down as fast.


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## James (Apr 29, 2002)

bahearn said:


> C&D mentioned the braking phenomenom during their supercar shoot-out a year or two ago. They recorded significantly better braking from 150 mph in neutral since modern brakes and tires can decelerate the car quicker than the engine can spool down due to rotational inertia.


actually that makes sense. so I guess if you get a lightend flywheel in a manual the result can differ too. but I think generally at sane speeds with stock cars 'in gear' would stop better.


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## AwaySooner (Jun 19, 2004)

Which is cheaper ? Your clutch/transmission or brake pads and rotors ?


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## vector03 (Nov 12, 2003)

^^^
Bingo


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## James (Apr 29, 2002)

Which is cheaper? Your clutch or smashing into the car ahead of you?


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## ReVerm (Jan 13, 2003)

James said:


> actually that makes sense. so I guess if you get a lightend flywheel in a manual the result can differ too. but I think generally at sane speeds with stock cars 'in gear' would stop better.


That depends on how fast you're braking. For emergency stops and hard stops, no. Even at 30mph in 1st or 2nd gear, it's pretty easy to "out-brake" the engine's rate of deceleration during a hard stop. I have a fair bit of experience with this from when I first started testing with my car (controlled testing of course. And no, I didn't hit anything : P).

You're being misled by what seems like an enrmous amount of internal friction generated within the engine when you let up on the pedal at low revs in low gears. It happened to me too when I first got my car. It seems really weird at first, but the numbers don't lie.


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## AwaySooner (Jun 19, 2004)

Why would I smash into the car in front of me ? My brake can stop much faster than my transmission, that's what they were designed to do. Why would you want to use your transmission to stop ? Ask me how I know, cause I used to do this all the time, and I had to change my stock clutch at 30k miles. After $600 parts and labors, I use my brakes now.  



James said:


> Which is cheaper? Your clutch or smashing into the car ahead of you?


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## Flying Vv (Apr 10, 2003)

i use a combination of both. no problems as of yet


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## James (Apr 29, 2002)

AwaySooner said:


> Why would I smash into the car in front of me ? My brake can stop much faster than my transmission, that's what they were designed to do. Why would you want to use your transmission to stop ? Ask me how I know, cause I used to do this all the time, and I had to change my stock clutch at 30k miles. After $600 parts and labors, I use my brakes now.


I have to use both at times because my brakes suck oem anyways, and couple that with the fact the pads are on their last leg... I'm doing a brake upgrade so I don't want to replace the pads.



> That depends on how fast you're braking. For emergency stops and hard stops, no. Even at 30mph in 1st or 2nd gear, it's pretty easy to "out-brake" the engine's rate of deceleration during a hard stop. I have a fair bit of experience with this from when I first started testing with my car (controlled testing of course. And no, I didn't hit anything : P).
> 
> You're being misled by what seems like an enrmous amount of internal friction generated within the engine when you let up on the pedal at low revs in low gears. It happened to me too when I first got my car. It seems really weird at first, but the numbers don't lie.



yeah I know but in an emergency I use both... normally I let the engine brake until I coast in and hit the brakes when it feels like the engine's compression isn't doing enough anymore. i know people don't like this method but I figure in an automatic, its being done all the time anyways and I check the vacum on the engine and its only like 24mmHG so not that much higher than vacum, I don't see how it can do any damage. the clutch is not slipping, the engine is not under any abnormal conditions...


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## ReVerm (Jan 13, 2003)

James said:


> normally I let the engine brake until I coast in and hit the brakes when it feels like the engine's compression isn't doing enough anymore. i know people don't like this method but I figure in an automatic, its being done all the time anyways and I check the vacum on the engine and its only like 24mmHG so not that much higher than vacum, I don't see how it can do any damage. the clutch is not slipping, the engine is not under any abnormal conditions...


Um... the "engine braking" feeling in our cars isn't caused by compression. The engines in our cars can't produce enough vaccum to slow the engine that quickly. The main factor that slows the engine down is friction.

But you're right about it not doing much damage. They're built to for it.


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## James (Apr 29, 2002)

ReVerm said:


> Um... the "engine braking" feeling in our cars isn't caused by compression. The engines in our cars can't produce enough vaccum to slow the engine that quickly. The main factor that slows the engine down is friction.
> 
> But you're right about it not doing much damage. They're built to for it.





> A gas engine has more engine braking than a comparable displacement diesel because at low throttle levels a gas engine is working against a closed throttle plate. A diesel has a wide open intake manifold without a throttle plate.
> 
> Think of a diesel piston and cylinder like an air cylinder. If you press the piston up to near TDC with the valves closed, it takes a lot of pressure, right? But guess what, after rotating beyond TDC all that compressed air now pushes down on the piston to accelerate it to BDC.
> 
> ...


Engine braking on diesels is done with a plate in the exhaust causing backpressure and limiting compression on the compression stroke. a gasoline engine, even with lower compression still has engine braking from its compression on the downstroke due to the throttle plate. Think about it this way... if there is enough friction to stop the car on deacceleration, there will be the same on acceleration. its not friction that stops the car its the compression.

http://www.humvee.net/hid/engine/engbrake.html


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## ReVerm (Jan 13, 2003)

James said:


> Engine braking on diesels is done with a plate in the exhaust causing backpressure and limiting compression on the compression stroke. a gasoline engine, even with lower compression still has engine braking from its compression on the downstroke.


That's the logic, but its effect on the engine and the car's rate of deceleration is minimal. People just started realizing that in the late 70's, and all of the modern engineering books I've read now regard the engine compression braking bit as a myth.

This is for small car petrol and diesel engines though. Jake brake equipped vehicles are an obvious exception, as they mechanically magnify that compression effect to help slow the vehicle.

BTW: That last bit you mentioned about the car having to overcome friction during the acceleration is true. The car does have to overcome the same amount of friction during acceleration. Why do you think gasoline engines have such low net output?


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## James (Apr 29, 2002)

why would internal friction stop a car? there is more friction from the wheels than from the engine! if there is enough friction to stop a car in the engine we should smash the fingers of the engineer that built that engine...



> This term describes the driving technique of slowing a vehicle by taking your foot off the throttle, particularly in a lower gear (such as first gear/Low Range). Engine braking uses the compression of the engine and the low gearing of the transmission/transfer gearbox to slow the vehicle.


http://www.carlist.com/autoglossary/autoglossary_68.html



> "What is Engine Braking"
> 
> .Many racing transmission manufacturers make their competition valve bodies with one or more forward gears having NO ENGINE BRAKING ! What does this mean? If you wish to slow your car down, you put your foot on the brake pedal and apply enough pressure to slow the vehicle down. If you had an emergency stop necessary and you were driving a car with standard transmission, you might in addition to applying your brakes put your car into a lower gear and let out the clutch which would engage the transmission directly to the motor. At this point, the rear wheels begin to try to turn the engine, but due to the compression in the engine it resists the action of the rear wheels and would help to slow the car down. Thus you have Compression Engine Braking. If you were to push in the clutch, you would no longer have compression engine braking, instead you would have No Compression Engine Braking or in short you would have No Engine Braking. Automatic transmissions also can have engine braking or no engine braking in certain gears.
> 
> Many Turbo Action valve bodies have No Engine Braking in first gear. This in many cases improves E.T. and also prevents oil pan damage if you do dry hops after your burnouts. Note we do not recommend dry hop burnouts! We also make some Turbo Hydro 350 and 400's that have no engine braking in second gear in addition to first gear.


http://www.turboaction.com/technicaltips2.html


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## chimmike (Oct 17, 2002)

in an automatic transmission car, braking in DRIVE will be result in faster stops, as well as prolonged life of the brake system. this is the truth.

oh, and in my manual, I've downshifted for 40k miles, not one tranny problem. throwing into neutral is just a great way to kill brakes fast and not stop as fast either.


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## ReVerm (Jan 13, 2003)

James said:


> why would internal friction stop a car? there is more friction from the wheels than from the engine! if there is enough friction to stop a car in the engine we should smash the fingers of the engineer that built that engine...


Why? Have you ever checked the overall efficiency of gasoline engines? They're incredibly inefficient. The reason for it is friction. Didn't your high school/college physics texts talk about the topic at all?


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## James (Apr 29, 2002)

ReVerm said:


> Why? Have you ever checked the overall efficiency of gasoline engines? They're incredibly inefficient. The reason for it is friction. Didn't your high school/college physics texts talk about the topic at all?


Inefficient because of HEAT loss from combustion! Not from friction man.


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## chimmike (Oct 17, 2002)

if your combustion engine had that much friction in it............it would tear itself apart.

the inefficiency comes from heat loss. Hence why most stock exhaust manifolds are cast iron.....it holds heat much better. Why would people swain coat their internals? they retain heat better.

it's all about the heat loss. Thermal coated turbos retain the heat better allowing them to spool faster.


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## James (Apr 29, 2002)

In saying its internal friction stopping the car you're saying that the engine can normall overpower the brakes...

check here... 6 % of efficiency of an IC engine is lost to friction... that's probably average... on a good engine its probably much less... (ours is a good engine if it can hit 30 mpg!)

http://ffden-2.phys.uaf.edu/102spring2002_Web_projects/Z.Yates/Zach's%20Web%20Project%20Folder/EICE%20-%20power%20losses.htm


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## ReVerm (Jan 13, 2003)

James said:


> Inefficient because of HEAT loss from combustion! Not from friction man.


The losses from heat loss from combustion are significant, but so are the losses from friction. If I can find a working scanner I'll scan in a chart that breaks down the losses in terms of percentages.


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## James (Apr 29, 2002)

http://ffden-2.phys.uaf.edu/102spring2002_Web_projects/Z.Yates/Zach's%20Web%20Project%20Folder/EICE%20-%20power%20losses.htm

Did it for you. You're wrong.


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## ReVerm (Jan 13, 2003)

chimmike said:


> if your combustion engine had that much friction in it............it would tear itself apart.


Why? Have you even seen the numbers or are you just making assumptions from what you think is going on?


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## ReVerm (Jan 13, 2003)

James said:


> http://ffden-2.phys.uaf.edu/102spring2002_Web_projects/Z.Yates/Zach's%20Web%20Project%20Folder/EICE%20-%20power%20losses.htm
> 
> Did it for you. You're wrong.


How am I wrong? Considering the total amount of energy that is wasted in a petrol engine, you don't think 6% is significant?


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## James (Apr 29, 2002)

It is significant. And it does contribute to some stopping. But the engine braking you feel is the compression or rather fighting the decompression...


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## ReVerm (Jan 13, 2003)

James said:


> It is significant. And it does contribute to some stopping. But the engine braking you feel is the compression or rather fighting the decompression...


And we're back to square one.


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## chimmike (Oct 17, 2002)

ReVerm said:


> Why? Have you even seen the numbers or are you just making assumptions from what you think is going on?



I'm a commercial rated instrument pilot. In order to fly a plane, you have to know exactly how a combustion engine works, and in the case if an airplane, a horizontally opposed piston engine. That's technical for a boxer engine, if you didn't know.

Know something else? On break in, piston aircraft use something called mineral oil for the first 50 hours. They use it because from the factory, the cylinder walls of the engine have pits and protrusions. They instruct you to run the engine as hard as you can for the first 30-50 hours. The mineral oil, unlike regular oil, does not suspend dirt and particles, so any metal shavings from the cylinder walls fill holes in the cylinder walls. Once break in is done, there is as little friction in there as possible by the laws of physics. 

The highest percentage of lost power from engines is heat loss. I'm sure Kojima has mentioned this somewhere on sentra.net or se-r.net in the archives, not like it should matter.

If an engine was 100% thermally efficient, the amount of power it could make would be phenomenol. 

If friction were a factor in engines such as ours, the type of friction you're talking about, engines would last no longer than 20,000 miles.


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## James (Apr 29, 2002)

Not my fault. I've provided many links with many sources stating on a gasoline engine its compression that does the engine braking. You have provided none except tell me that its so. In fact look at the first link I provided. It seems to me you're the one thinking about a diesel engine.


> .>On another thread on engine braking. Yes, gas engines can produce a higher braking hp than a diesel. However, like "normal" hp, it is a function of rpm. You need to get up in the rpms to get the maximal braking. However, under wheeling conditions, you usually don't need maximum braking like if you were towing. Instead, you want more braking hp at a lower speed which a diesel does provide. The "braking torque" curve is flatter.
> 
> 
> Gerald, the only thing that's braking the diesel truck is the drive train friction. As you well know, when you are driving off road in low lock, low gear, descending a steep hill, the engine and drivetrain is forced to turn at a higher RPM than when driving in say high gear. Because the engine and drivetrain are turning at a high RPM they produce a lot more friction, thus more stopping, than in the high gear. This stopping power is due to drivetrain and engine friction, not engine braking in the sense of a gas motor.
> ...


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## ReVerm (Jan 13, 2003)

chimmike said:


> in an automatic transmission car, braking in DRIVE will be result in faster stops, as well as prolonged life of the brake system. this is the truth.


Can you demonstrate using (at minimum) back to back testing that demonstrates that what you say is true?



chimmike said:


> throwing into neutral is just a great way to kill brakes fast and not stop as fast either.


Can you demonstrate that this is true as well? Bahearn has referenced a test which suggests the contrary. Former F1 driver Alain Prost admitted shortly after his retirement that it was his team engineers that instructed him to skip gears (shift into neutral immediately after letting up on the accelerator, then engage the target gear immediately before finishing braking) to shorten his braking distances. I'm not asking you to debunk what they've done. I'm asking you to provide evidence to back what you're saying.


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## chimmike (Oct 17, 2002)

dude, I'm still waiting for you to provide facts to back up your statements. 

I've given you 10 posts waiting for links, proof, any shred of evidence that you're not just talking out your ass.

want proof? Take a manual transmission car. Go out. Drive to 60mph. throw it in neutral and hit the brakes, hard. Oh, and try not to lock them up.

now go to 60 again, and brake while downshifting. For one thing, the wheels won't lock as easily, and you'll stop faster. I do it all the time. I don't need to prove it to you.........i'm the one that does it every day on the interstate highway.


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## James (Apr 29, 2002)

ReVerm said:


> Can you demonstrate using (at minimum) back to back testing that demonstrates that what you say is true?
> 
> 
> 
> Can you demonstrate that this is true as well? Bahearn has referenced a test which suggests the contrary. Former F1 driver Alain Prost admitted shortly after his retirement that it was his team engineers that instructed him to skip gears (shift into neutral immediately after letting up on the accelerator, then engage the target gear immediately before finishing braking) to shorten his braking distances. I'm not asking you to debunk what they've done. I'm asking you to provide evidence to back what you're saying.


By what you just said its proof that leaving it in gear is better anyways. You're arguing friction is braking the car anyways so chimmike has to offer no proof.

Bruce was talking about stopping from triple digit speeds down to zero. From that speed the compression of the motor does not contribute as much to the braking because the car is usually in a very high gear anyways and the rotational inertia of the rotating engine contributes very little. Plus on the cars that have capability to go to that kind of speeds have brakes that are developed to stop from that speed.


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## chimmike (Oct 17, 2002)

until you come back with proof, this thread is locked. You've been proven wrong....................so, that's the end.


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